AS1.17 | Tropical Meteorology and Tropical Cyclones
EDI
Tropical Meteorology and Tropical Cyclones
Convener: Enrico Scoccimarro | Co-conveners: Allison Wing, Alyssa Stansfield, Leone Cavicchia, Eric Maloney
Orals
| Mon, 15 Apr, 08:30–12:30 (CEST)
 
Room 0.14
Posters on site
| Attendance Mon, 15 Apr, 16:15–18:00 (CEST) | Display Mon, 15 Apr, 14:00–18:00
 
Hall X5
Posters virtual
| Attendance Mon, 15 Apr, 14:00–15:45 (CEST) | Display Mon, 15 Apr, 08:30–18:00
 
vHall X5
Orals |
Mon, 08:30
Mon, 16:15
Mon, 14:00
The understanding of tropical phenomena and their representation in numerical models still raise important scientific and technical questions, particularly in the coupling between the dynamics and diabatic processes. Among these phenomena, tropical cyclones (TC) are of critical interest because of their societal impacts and because of uncertainties in how their characteristics (cyclogenesis processes, occurrence, intensity, latitudinal extension, translation speed) will change in the framework of global climate change. The monitoring of TCs, their forecasts at short to medium ranges, and the prediction of TC activity at extended range (15-30 days) and seasonal range are also of great societal interest.
The aim of the session is to promote discussions between scientists focusing on the physics and dynamics of tropical phenomena. This session is thus open to contributions on all aspects of tropical meteorology between the convective and planetary scale, such as:

- Tropical cyclones,
- Convective organisation,
- Diurnal variations,
- Local circulations (i.e. island, see-breeze, etc.),
- Monsoon depressions,
- Equatorial waves and other synoptic waves (African easterly waves, etc.),
- The Madden-Julian oscillation,
- etc.

We especially encourage contributions of observational analyses and modelling studies of tropical cyclones and other synoptic-scale tropical disturbances including the physics and dynamics of their formation, structure, and intensity, and mechanisms of variability of these disturbances on intraseasonal to interannual and climate time scales.

Findings from recent field campaigns are also encouraged.

Orals: Mon, 15 Apr | Room 0.14

Chairpersons: Enrico Scoccimarro, Eric Maloney
08:30–08:35
Tropical meteorology
08:35–08:45
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EGU24-12620
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Virtual presentation
Peter Haynes and Matthew Davison

A simple model is used to analyse the relation between the phenomenon of convective aggregation at small scales and  larger scale variability, including MJO-like behaviour, that results from coupling between dynamics and moisture in the tropical atmosphere. The model is based on the  single-layer dynamical equations coupled to a moisture equation to represent the dynamical effects of latent heating and radiative heating. The moisture variable q evolves through the effect of horizontal convergence, nonlinear horizontal advection and diffusion. Following previous work, the coupling between moisture and dynamics is included in such a way that a horizontally homogenous state may be unstable to inhomogeneous disturbances and, as a result, localised regions evolve towards either dry or moist states, with respectively divergence or convergence in the horizontal flow. The behaviour of the model system is investigated using a combination of theory and numerical simulation. The spatial organisation of the moist and dry regions demonstrates a spatial coarsening that, if moist regions and dry regions are interpreted respectively as convecting and non-convecting, represents a form of convective aggregation. When the weak temperature gradient (WTG) approximation (i.e. a local balance between heating and convergence) applies and horizontal advection is neglected the system reduces to a nonlinear reaction-diffusion equation for q and the coarsening is a well-know aspect of such systems. When nonlinear advection of moisture is included the large-scale flow that arises from the spatial pattern of divergence and convergence leads to a distinctly different coarsening process. When  thermal and frictional damping and f-plane rotation are included in the dynamics, there is dynamical length scale Ldyn that sets an upper limit for the spatial coarsening of the moist and dry regions. The f-plane results provide a basis for interpreting the behaviour of the system on an equatorial β-plane, where the dynamics implies a displacement in the zonal direction of the divergence relative to q and hence to coherent equatorially confined zonally propagating disturbances, comprising separate moist and dry regions. In many cases the propagation speed and direction depend on the equatorial wave response to the moist heating, with the relative strength of the Rossby wave response to the Kelvin wave response determining whether the propagation is eastward or westward. The key overall properties of the propagating disturbances, the spatial scale and the phase speed, depend on nonlinearity in the coupling between moisture and dynamics and any linear theory for such disturbances therefore has limited usefulness. The model described here, in which the moisture and dynamical fields vary in two spatial dimensions and important aspects of nonlinearity are captured, provides an intermediate model between theoretical models based on linearisation and one spatial dimension and three-dimensional GCMs or convection-resolving models.

How to cite: Haynes, P. and Davison, M.: A simple dynamical model linking radiative-convective instability, convective aggregation and large-scale dynamics, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12620, https://doi.org/10.5194/egusphere-egu24-12620, 2024.

08:45–08:55
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EGU24-7675
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On-site presentation
Remy Roca, Thomas Fiolleau, and Gregory Elsaesser

Deep convection gives rise to large upper level clouds that strongly interact with radiation and are important to the climate energy budget. From an object-oriented perspective, these individual deep cloud systems are characterized by a well depicted cloud shield life cycle, starting with small cloud extents that grow at varying rates before decaying and vanishing. A simple formulation of the growth rate of the cloud shield has been proposed that links together the growth rate on the convective part of the cloud, the mass flux of both the convective and stratiform parts of the cluster and a simple removal sink term (Elsaesser et al., 2022). In this presentation we first show using a suite of satellite observations (infrared from geostationary satellites, GPM radar, etc.) that the functional form of the proposed equation is well suited to quantify the shield growth rate. We then focus on RCE simulations, with deep cloud system objects post processed, to explore the relative role of each term of the growth rate budget. Three different models are used in the same RCEMIP-like configurations. The results show that the budget equation works very well for each model, although the time constants require model-dependent adjustments. We will further show in Vienna the commonalities and the specificities of each model.

How to cite: Roca, R., Fiolleau, T., and Elsaesser, G.: Growth rate of deep convective system cloud shields: satellite observations and km-scale radiative convective equilibrium simulations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7675, https://doi.org/10.5194/egusphere-egu24-7675, 2024.

08:55–09:05
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EGU24-10815
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ECS
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On-site presentation
Luca Schmidt and Cathy Hohenegger

The highly nonlinear moisture-precipitation relationship P(r) is a simple statistical model for tropical precipitation P that takes column relative humidity r as its only input variable. Its simplicity and robustness make the relationship useful for conceptual models and as a tool for model diagnostics. We use 10 years of daily ERA5 Reanalysis data to test if P(r) can reproduce the tropical land-ocean contrast of precipitation which we quantify by the tropical precipitation ratio χ(t), defined as the ratio between the spatiotemporal mean rain rate over land and ocean. We find that P(r) can adequately reproduce both magnitude and phase of the average seasonal cycle of χ(t) as long as we take into account that P(r) gets modified by the presence of land and that the relationship varies seasonally over both land and ocean. Since the values of χ(t) indicate that precipitation is enhanced over tropical land, we investigate in a second step whether this enhancement is explained by the distinct P(r) relationships over land and ocean, i.e. whether it rains more over land than over ocean for a given value of r, or by distinct land and ocean humidity distributions, or both. Our results show that the influence of the land surface on P(r) has the effect of disfavoring precipitation over land rather than enhancing it. Precipitation enhancement over land, thus, stems from the distinct humidity distributions over land and ocean with the land distribution exhibiting a more pronounced tail towards high r values compared to the ocean distribution.

How to cite: Schmidt, L. and Hohenegger, C.: Tropical land-to-ocean precipitation differences explained in the framework of the moisture-precipitation relationship, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10815, https://doi.org/10.5194/egusphere-egu24-10815, 2024.

09:05–09:15
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EGU24-4564
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ECS
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On-site presentation
Divya Sri Praturi and Bjorn Stevens

We investigate the small scale dynamical controls on the Intertropical convergence zone (ITCZ) in the Atlantic and East Pacific basins using 5 year, global km-scale coupled atmosphere-ocean-land simulations. To this end, using an ITCZ-based coordinate system, we develop a composited view of the zonal mean statistics of potential vorticity (PV) during Boreal Summer (JJA) at geopotential heights of 0.3, 1.5 and 4 km. The ITCZ-based coordinate system is defined locally at each longitude, such that the ITCZ latitude — identified as the latitude where the column water vapor is a maximum — constitutes the origin. The zonal, 5-year JJA mean latitudes of the Atlantic and East Pacific ITCZ determined based on this definition are 7.8°N and 10.8°N, respectively. The thus obtained composited PV profiles are robust with low inter-annual variability. The PV profiles exhibit a similar structure in both the basins of interest: a gradual increase in the PV values with latitude, followed by a sharp increase in the PV values in the ITCZ due to latent heating. The necessary conditions for the instability of the zonal flow are met, as the sign of the meridional gradient of PV is reversed at the ITCZ. The magnitudes of PV statistics in and around the Atlantic ITCZ are slightly smaller than those of the East Pacific ITCZ. The differences in PV values in the basins can be explained using one of the processes governing the vertical vorticity in the ITCZ, i.e., vortex stretching due to convergence. The vortex stretching term is proportional to the Coriolis parameter, i.e., for a given convergence rate in the ITCZ, more northern ITCZ latitudes could experience greater jumps in vertical vorticities. We also find that at geopotential heights of 0.3 and 1.5 km, the monthly mean relative vertical vorticity in the ITCZ increases as the ITCZ moves to the North. 

How to cite: Praturi, D. S. and Stevens, B.: On the vorticity statistics in the Atlantic and East Pacific ITCZ, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4564, https://doi.org/10.5194/egusphere-egu24-4564, 2024.

09:15–09:25
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EGU24-8141
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ECS
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On-site presentation
Hannah Croad, Jonathan Shonk, Amulya Chevuturi, Andrew Turner, and Kevin Hodges

We identify for the first time an Indian Easterly Jet (IEJ) in the mid-troposphere during the pre-monsoon season, using ERA5 reanalysis data.  The IEJ is weaker and smaller in zonal extent than the African Easterly Jet over West Africa, with a climatological location of 10°N, 60–90°E, 700 hPa, and strength 6–7 m s−1 during March–May. The IEJ is a thermal wind associated with low-level meridional gradients in temperature (positive) and moisture (negative), resulting from equatorward moist convection in the ITCZ and poleward dry convection arising due to surface heating of northern India and surrounding inland desert regions. The IEJ is associated with a negative meridional potential vorticity gradient, therefore satisfying the Charney-Stern necessary condition for instability.  However, no wave activity is detected in various metrics, suggesting that the potential for combined barotropic-baroclinic instability is not often realized. This is likely related to the small zonal extent of the jet, with insufficient time for wave growth, or the lack of upstream orography. The IEJ is found to be linked with the meteorology of pre-monsoon India. IEJ strong years feature increased near-surface temperatures and drier conditions over India, while the opposite is found in IEJ weak years. Initial investigations did not indicate strong relationships between the IEJ state and the El Nino-Southern Oscillation or the Madden Julian Oscillation, although more detailed investigations are needed to clarify this.  This study provides an introduction to the IEJ’s role in pre-monsoon dynamics, and a platform for further research. This includes identifying any links with pre-monsoon meteorological hazards (heatwaves and thunderstorms) and potential impacts on the subsequent monsoon, and understanding large-scale conditions that drive changes in the IEJ.

How to cite: Croad, H., Shonk, J., Chevuturi, A., Turner, A., and Hodges, K.: The Indian Easterly Jet During the Pre-Monsoon Season in India, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8141, https://doi.org/10.5194/egusphere-egu24-8141, 2024.

09:25–09:35
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EGU24-15819
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ECS
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Virtual presentation
Hagar Bartana, Chaim Garfinkel, Chen Schwartz, Ofer Shamir, and Jian Rao
Projected changes of tropical Convectively Coupled Equatorial Waves (CCEWs)  due to increased greenhouse gases, and the dynamical mechanism that forces those changes, are investigated in 13 state-of-the-art models from phase 6 of the Coupled Model Intercomparison Project (CMIP6).   The equatorial wave spectrum in the historical simulation from most of these models quantitatively (and even quantitatively) resembles that observed, a remarkable improvement from CMIP5. Most models project a future increase in power spectra for the Madden-Julian Oscillation  (MJO), while nearly all project a robust increase for Kelvin Waves (KW). In contrast, the power spectrum weakens for most other wavenumber-frequency combinations, including higher wavenumber Equatorial Rossby waves (ER). In addition to strengthening, KW also shift toward higher phase speeds (or equivalent depths). These changes are even more pronounced in models with smaller biases in their historical simulations.

The qualitatively different projected response of the different CCEWs (e.g., KW strengthening vs. ER weakening) suggest that dynamical forcings have an important role in the physical mechanism of the changes. This hypothesis is tested using targeted simulations of the Model of an Idealised Moist Atmosphere (MiMA) in which we impose perturbations in upper-troposphere zonal winds mimicking projected end-of-century changes in wind. These simulations demonstrate that future changes in KW and the MJO strongly depend on changes in the South Pacific subtropical jet. A similar dependence is also evident in the CMIP6 models. However, the winds in the south Pacific subtropical jets in the historical simulation of these CMIP6  models  are highly biased, and models with a stronger change in the jet tend to project a stronger intensification of both the MJO and KW. It is therefore necessary to account for this bias in the subtropical winds in order to provide more reliable projections of the KW and the MJO.

How to cite: Bartana, H., Garfinkel, C., Schwartz, C., Shamir, O., and Rao, J.: Influence of Subtropical Jets on the Equatorial Spectrum: implications for future changes in Kelvin waves and MJO variance, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15819, https://doi.org/10.5194/egusphere-egu24-15819, 2024.

09:35–09:45
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EGU24-12050
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ECS
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On-site presentation
Jack Mustafa, Adrian Matthews, Rob Hall, and Karen Heywood

The manifestation of the diurnal cycle (DC) over the Maritime Continent is influenced by the large-scale environment, including the state of the Madden–Julian Oscillation (MJO). It is widely recognised in existing literature that the amplitude of the DC of precipitation is greatest at around the same time as, or perhaps slightly ahead of, greatest mean precipitation. However, there is weaker consensus on the impact of the MJO (if any) on the phase of the DC.

Here, the boreal winter (DJF) composite DC of precipitation is calculated for each of the 8 MJO phases (P1–8) defined by Wheeler and Hendon (2004), using 20 years of IMERG — the state-of-the-art gridded satellite-derived precipitation data product with 30-minute resolution. With such high temporal resolution, subtle changes in the phase of the DC can be, and are, identified. The western sides of Sumatra, Borneo and Java typically experience an earlier than usual diurnal precipitation maximum around P5–6, while the eastern sides of these islands experience an earlier than usual diurnal precipitation maximum around P2–3. An analogous west–east divide in DC phase regime is also observed over certain water bodies, such as the Makassar Strait. The magnitude of this phase fluctuation is greatest across eastern Sumatra, parts of eastern Borneo, the western Java Sea and the eastern Makassar Strait, where a range of DC phase of over four hours is frequently observed. The opposing nature of the western and eastern local regimes is a consequence of changes to the direction of phase propagation; westward phase propagation is favoured over the Makassar Strait and the eastern sides of Sumatra and Borneo during P2–3, while eastward phase propagation dominates across entire islands and water bodies during P5–6.

If, by extension, the DC of cloud cover shows strong regional fluctuations in timing, these results will have significant implications for the influence of the MJO on regional radiation budgets.

How to cite: Mustafa, J., Matthews, A., Hall, R., and Heywood, K.: Modulation of the Maritime Continent diurnal cycle of precipitation by the Madden-Julian Oscillation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12050, https://doi.org/10.5194/egusphere-egu24-12050, 2024.

09:45–09:55
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EGU24-14122
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ECS
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On-site presentation
Daisuke Takasuka

The Madden–Julian oscillation (MJO) is the most predominant tropical intraseasonal variability and is a source of modulating global weather patterns. An accurate simulation of the MJO still remains a challenge for general circulation models (GCMs), and in fact, climate simulations with GCMs often struggle with the mean state-variability tradeoff. For this issue, a global storm-resolving climate simulation, which a recent increase in computing power makes possible, is expected to be a useful way because of its merit of direct coupling between moist processes and dynamics.

The present study examines the MJO representation in an AMIP-type ~10-year simulation with the Nonhydrostatic Icosahedral Atmospheric Model (NICAM) at 3.5-km horizontal resolution, in comparison with that in one of conventional GCMs (MIROC6). This NICAM simulation successfully reproduces the realistic initiation frequency, propagation, and hierarchical structure of MJO convection, as well as realistic mean states (e.g., mean tropical precipitation), whereas MIROC6 overly underestimates the number of robust MJO events, and the activity of westward-propagating synoptic-scale waves embedded within MJO convective envelopes. As specific processes, the enhanced mixed Rossby-gravity wave-like systems seem to be a precursor and building blocks of the MJO simulated with NICAM at least over the Indian Ocean, consistent with several observational studies. In addition, NICAM-MJO propagation into the western Pacific is helped by high-frequency intermittent advective moistening that can be triggered by the upper-tropospheric PV intrusion from the extratropics. This feature is also found in some of observed MJO events.

Our results suggest that good MJO simulations can attribute to representing the feedback from a complex of synoptic-scale waves onto MJO convective envelopes appropriately, and that the extratropics sometimes plays an active role in MJO dynamics. A success in simulating and scrutinizing these cross-scale interactions about the MJO is one of clear merits of kilometer-scale climate simulations without the assumption of a priori scale separation and quasi-equilibrium characteristics.

How to cite: Takasuka, D.: MJO initiation and propagation simulated with a global kilometer-scale climate simulation: Implication for the cross-scale interaction, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14122, https://doi.org/10.5194/egusphere-egu24-14122, 2024.

09:55–10:05
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EGU24-13921
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On-site presentation
Da Yang, Walter Hannah, and Lin Yao

We simulate the Madden-Julian oscillation (MJO) over an aquaplanet with uniform surface temperature using the multiscale modeling framework (MMF) configuration of the Energy Exascale Earth System Model (E3SM-MMF). The simulated MJOs have similar spatial structures and propagation behavior to observations. To explore the processes involved in the propagation and maintenance of the MJO, we perform a vertically resolved moist static energy (MSE) analysis for the MJO (Yao, Yang, and Tan 2022; Yao and Yang 2023). Unlike the column-integrated MSE analysis, our method quantifies how individual physical processes amplify and propagate the MJO’s characteristic vertical structure. We find that radiation, convection, and boundary layer processes all contribute to maintaining the MJO, balanced by the large-scale MSE transport. Furthermore, large-scale dynamics, convection, and boundary layer processes all contribute to the eastward propagation of the MJO, while radiation slows the propagation. We further show that the MJO can still self-emerge when radiative heating rate is horizontally homogenized, highlighting that convective and boundary-layer MSE transports are sufficient to sustain the MJO. These transport processes might be overlooked in the column-integrated MSE analysis.

How to cite: Yang, D., Hannah, W., and Yao, L.: Vertically resolved analysis of the Madden-Julian Oscillation highlights the role of convective transport of moist static energy, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13921, https://doi.org/10.5194/egusphere-egu24-13921, 2024.

10:05–10:15
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EGU24-14608
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ECS
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Virtual presentation
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Shreya Keshri and Suhas Ettammal

MRG wave belongs to one of the major synoptic scale modes of tropical atmospheric variability and they exhibit the properties of both slowly evolving Rossby and quickly evolving gravity type wave disturbances. Since the MRG waves bridges the gap between the low-frequency and high frequency modes of variability, it is crucial to understand the underlying dynamics of the MRG waves to improve the tropical weather and extended range forecasts. Many previous studies reported the observation of Doppler shifting of MRG waves in the western Hemisphere (e.g. Yang et al. 2003, 2007, Yang and Hoskins 2016 etc). Nevertheless, a comprehensive study of eastward propagating Doppler shifted MRG (E-MRG) waves and their frequency of occurrence relative to the westward propagating MRG waves is missing. In this study, we investigate the E-MRG wave events at 200 hPa pressure level using the wave fitting and Empirical Mode Decomposition (EMD) based wave event identification methodology. We have found 743 E-MRG wave events for the period 1979-2022 and a large fraction of them occur in the westerly duct during boreal winter seasons. It is noteworthy that E-MRG wave events account 33% of the total MRG wave events in the western Hemisphere during boreal winter seasons. As expected from the linear wave theory, 75% of the E-MRG wave events occur when the background winds are westerly. On the contrary, a notable fraction of the E-MRG events occur when the background winds are easterly. Detailed analysis reveals that westerly phase of the large-scale Kelvin waves setup the conducive environment for MRG wave events to be Doppler shifted and explain more than 75% of the E-MRG wave events that occur when the background winds are easterly. In addition to that the observation of strong link between the intrusion of eastward propagating extratropical disturbances and the E-MRG wave events support the extratropical-tropical interaction theory of Hoskins and Yang, 2016. The study underscores the importance of multiscale interactions and its realistic representation in the climate and numerical weather prediction models.

How to cite: Keshri, S. and Ettammal, S.: Does the tropical atmosphere support Doppler shifted MRG waves?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14608, https://doi.org/10.5194/egusphere-egu24-14608, 2024.

Coffee break
Chairpersons: Enrico Scoccimarro, Leone Cavicchia
10:45–10:50
Tropical cyclones
10:50–11:00
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EGU24-3598
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On-site presentation
Adrian Tompkins, Alejandro Casallas, and Michie Vianca De Vera

Idealized simulations of radiative-convective equilibrium (RCE) with cloud resolving models have been used as a numerical laboratory to understand how diabatic processes can drive convective clustering, which in turn leads to significant drying of the free troposphere and increase in spatial humidity variability.  These processes, such as feedbacks between radiation, clouds and water vapor have been found to have relevance for numerous large-scale modes of convective organization, such as the width of the upward branch of the Hadley cell, ENSO and the Madden Julian Oscillation.  However, the controls of water vapor associated with convective variability on the sub-1000km mesoscale are less well known.  We adopt a simple multivariate analysis technique previously used to assess convective organization in RCE, and apply it to analyze convective organization and its impact on column integrated humidity (precipitable water, PW) variability for order 106 km2 mesoscale-size boxes in the tropical western Pacific warm pool region lying on or to the north of the equator.  We find that during the boreal summer/autumn periods, when sea surface temperature (SST) gradients are very limited in the target regions, convection remains mostly random and the horizontal PW gradients are small on these scales, this despite the action of diabatic feedbacks such as LW-cloud feedbacks and surface latent heat fluxes that are acting to  force clustering of convection. In stark contrast, during the other months of the year, when the zones are subject to a weak meridional SST gradient of SST (> 10-3 K km-1), convection is mostly aggregated over the warmer SSTs, with much larger PW gradients associated with an increase of clear sky OLR exceeding 10 W m-2. However, this situation is regularly disturbed by intermittent, multi-day episodes of more homogeneous convection distribution and limited spatial PW gradients. During these periods the SST-PW relationship flips, and the convecting regions are found over the coldest SSTs.  By using an index based on the SST-PW covariance, we construct a composite of 44 such events over a 4 year period which shows that they are associated with a westward-propagating, convectively-coupled Rossby wave like mode that is symmetric about the equator.  An independent multivariate (SST-PW) rotated EOF analysis confirms this, indicating the robustness of the result. We hypothesize that the longer-term variations in an convective organization index which was directly related to the tropics-wide energy budget (Bony et al. 2020) may be driven by the frequency of occurrence of these westward propagating modes, that seem to act as a primary control on mesoscale water vapor variability in the warm pool region in the boreal winter and spring months.

How to cite: Tompkins, A., Casallas, A., and Vianca De Vera, M.: Dynamical controls of mesoscale water vapor variability in the tropical western Pacific, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3598, https://doi.org/10.5194/egusphere-egu24-3598, 2024.

11:00–11:10
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EGU24-6417
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Highlight
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On-site presentation
Gregory Foltz, Chidong Zhang, Andy Chiodi, Dongxiao Zhang, Edoardo Mazza, Edward Cokelet, Lev Looney, Hauke Schulz, Nan-Hsun Chi, Jun Zhang, Ajda Savarin, Hyun-Sook Kim, Eugene Burger, Francis Bringas, and Catherine Edwards

During the 2021-2023 Atlantic hurricane seasons, 24 Saildrone uncrewed surface vehicles (USVs) were deployed in the western Atlantic Ocean, Caribbean Sea, and Gulf of Mexico to collect ocean-atmosphere data within hurricane eyewalls. Sixteen different USVs intercepted tropical storms and hurricanes a total of 26 times, all with sustained wind measurements of at least tropical storm force (34 kt). Four USVs measured sustained hurricane-force winds (64+ kt) in the eyewalls of Hurricanes Sam (2021), Fiona (2022), Idalia (2023), and Lee (2023). An important advantage of the USVs compared to other observing platforms is that they can be actively steered into the paths of hurricanes and record data continuously during eyewall transects, enabling new insights into air-sea interaction processes in extreme conditions. This presentation gives an overview of the key observations and scientific results from the 2021-2023 missions. Direct measurements of the air-sea momentum flux and drag coefficient (Cd) from the USVs’ 20-Hz wind data show a distinct peak in Cd at wind speeds of around 40-50 kt and then a decrease and leveling off as winds approach 80 kt. These results extend findings from previous studies with direct covariance flux measurements, which were limited to winds of less than 50 kt. Measurements from the USVs also show diminished surface ocean cooling under the cores of Hurricanes Sam and Idalia due to strong upper-ocean salinity stratification, emphasizing the importance of salinity observations in the western Atlantic and Gulf of Mexico for potential improvements in hurricane intensity prediction.

How to cite: Foltz, G., Zhang, C., Chiodi, A., Zhang, D., Mazza, E., Cokelet, E., Looney, L., Schulz, H., Chi, N.-H., Zhang, J., Savarin, A., Kim, H.-S., Burger, E., Bringas, F., and Edwards, C.: Ocean-Atmosphere Observations and Key Results from the 2021-2023 Atlantic Hurricane Saildrone Missions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6417, https://doi.org/10.5194/egusphere-egu24-6417, 2024.

11:10–11:20
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EGU24-2780
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On-site presentation
Lina Bai, Yinglong Xu, Jie Tang, and Rong Guo

    This study investigates interagency discrepancies among best-track estimates of tropical cyclone (TC) intensity in the western North Pacific, provided by the Joint Typhoon Warning Center (JTWC), the China Meteorological Administration (CMA), and the Regional Specialized Meteorological Center (RSMC) Tokyo during 2013–2019. The results reveal evident differences in maximum wind speed (MSW) estimates, where linear systematic differences are significant. However, the Dvorak parameter (CI) numbers derived from the MSWs reported by the three agencies are internally consistent. Further analysis suggests that the remained CI discrepancies are related to differences in the estimation of intensity trends, initial intensities, and TC positions among these datasets. In addition, the CI estimates provided by the JTWC for TCs over the open ocean are generally higher than those reported by the CMA and RSMC. However, the CMA (RSMC) tends to estimate stronger intensity for TCs in the China (Japan) mainland and coastal zone than those in the open ocean with the same intensity in JTWC dataset. This pattern potentially reflects the extensive use of surface observations by these two agencies for landfalling and offshore TCs. These results may help the research community to get more accurate details about the TCs in WNP from the best track datasets of different agencies.

How to cite: Bai, L., Xu, Y., Tang, J., and Guo, R.: Interagency discrepancies in tropical cyclone intensity estimates over the western North Pacific in recent years, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2780, https://doi.org/10.5194/egusphere-egu24-2780, 2024.

11:20–11:30
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EGU24-4089
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Highlight
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Virtual presentation
Andra Garner

Quickly intensifying tropical cyclones (TCs) are exceptionally hazardous for Atlantic coastlines.  An analysis of observed maximum changes in wind speed for Atlantic TCs from 1971-2020 indicates that TC intensification rates have already changed as anthropogenic greenhouse gas emissions have warmed the planet and oceans.  Mean maximum TC intensification rates are up to 28.7% greater in a modern era (2001-2020) compared to a historical era (1971-1990).  In the modern era, it is about as likely for TCs to intensify by at least 50 kts in 24 hours, and more likely for TCs to intensify by at least 20 kts within 24 hours than it was for TCs to intensify by these amounts in 36 hours in the historical era.  Finally, the number of TCs that intensify from a Category 1 hurricane (or weaker) into a major hurricane within 36 hours has more than doubled in the modern era relative to the historical era.  Significance tests suggest that it would have been statistically impossible to observe the number of TCs that intensified in this way during the modern era if rates of intensification had not changed from the historical era.    

How to cite: Garner, A.: Observed Increases in North Atlantic Tropical Cyclone Peak Intensification Rates, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4089, https://doi.org/10.5194/egusphere-egu24-4089, 2024.

11:30–11:40
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EGU24-13617
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ECS
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On-site presentation
Hyeyoon Jung, Il-Ju Moon, and Dong-Hoon Kim

Tropical cyclones (TCs) are among the most severe and destructive natural events, and they have a major detrimental impact on both the economy and society. This study used Geo-KOMPSAT-2A (GK2A) satellite data to estimate TC intensity in the western North Pacific based on a convolutional neural network (CNN) model. Given that the GK2A data cover only the period since 2019, we applied transfer learning to the model using information learned from previous Communication, Ocean, and Meteorological Satellite (COMS) data, which cover a considerably longer period (2011–2019). Transfer learning is a powerful technique that can improve the performance of a model even if the target task is based on a small amount of data. Experiments with various transfer learning methods using the GK2A and COMS data showed that the frozen–fine-tuning method had the best performance due to the high similarity between the two datasets. The test results for 2021 showed that employing transfer learning led to a 20% reduction in the root mean square error (RMSE) compared to models using only GK2A data. For the operational model, which additionally used TC images and intensities from six hours earlier, transfer learning reduced the RMSE by 5.5%. Because continuous long-term data are not always available for TC intensity estimation based on geostationary satellite images, these results imply that transfer learning may constitute a new advance in this area.

Acknowledgement. This research was supported by Korea Institute of Marine Science & Technology Promotion (KIMST) funded by the Korea Coast Guard (RS-2023-00238652, Integrated Satellite-based Applications Development for Korea Coast Guard).

 

How to cite: Jung, H., Moon, I.-J., and Kim, D.-H.: Tropical cyclone intensity estimation using two geostationary satellite data and deep learning, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13617, https://doi.org/10.5194/egusphere-egu24-13617, 2024.

11:40–11:50
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EGU24-7240
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Virtual presentation
Xiaodong Tang, Huilin Li, and Juan Fang

Challenges persist in accurately predicting sharp changes in tropical cyclone (TC) motion over a short period of time, even with the employment of state-of-art forecasting technologies. The precise connection between these sudden changes and specific TC structure remains unclear. Here, we delve into the relationship between TC asymmetry (TCA) of outer-core size and anomalous motion, using best-track data spanning the period from 2001 to 2022. Results indicate that TCs characterized by lower TCA tend to display more pronounced deflections than their normal motion. Furthermore, fast-moving TCs exhibit heightened asymmetry and a propensity to accelerate, whereas slow-moving ones lean towards greater symmetry. In addition, TCs demonstrating substantial angular deviations are more prevalent at lower speeds, while fast-moving ones rarely generate anomalous deflections. These findings provide valuable insights into the potential impact of TCA on anomalous TC motion, which can ultimately be used to enhance the accuracy of TC track forecasting.

How to cite: Tang, X., Li, H., and Fang, J.: Relationship between Tropical Cyclone Size Asymmetry and Anomalous Motion, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7240, https://doi.org/10.5194/egusphere-egu24-7240, 2024.

11:50–12:00
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EGU24-13227
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ECS
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On-site presentation
Giuseppe Ciardullo, Yi-Ling Hwong, Leonardo Primavera, and Caroline Muller
Current studies about the role of rain evaporation in the development of deep clouds and storms, show that reduced rain evaporation leads to a significant aggregation of clouds in space. This aggregation process has been called “moisture-memory aggregation”. Rain evaporation removal in the boundary layer seems to be the major contributor to triggering the spatial clustering of clouds
The absence of cold pools, which are cold regions below clouds created by rain evaporation and known to hinder aggregation, has been suggested as the leading cause, but the precise physical mechanisms underlying this type of aggregation remains unclear. Our study aims to fill this gap. Cloud-resolving simulations in idealized, doubly-periodic geometry, are conducted, comparing results with and without rain evaporation in the boundary layer. We focus on the clustering of clouds into a large-scale tropical cyclone. 
The goal is to assess the sensitivity of clouds to rain evaporation during the processes preceding the formation of the tropical cyclone. The role of cold pools in the upscale growth of cloud clusters, hypothesized in earlier studies, is also exploited by Proper Orthogonal Decomposition (POD) technique. Energy associated spectra of both the spatial and temporal components are studied separately on three different ranges of scales.
The impact on atmospheric circulations is also investigated by a thermodynamical characterization, through the distributions of temperature, water vapor content and relative humidity. 

How to cite: Ciardullo, G., Hwong, Y.-L., Primavera, L., and Muller, C.: Understanding the role of rain evaporation during tropical cyclogenesis, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13227, https://doi.org/10.5194/egusphere-egu24-13227, 2024.

12:00–12:10
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EGU24-8728
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ECS
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Highlight
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On-site presentation
Beata Latos, Il-Ju Moon, and Dong-Hoon Kim

In recent decades, the Atlantic region has seen more frequent and intense hurricanes, with the 2023 season ranking as the fourth-most active on record. Despite progress in understanding hurricane dynamics and identifying precursors, challenges persist in seasonal predictions.

Conventional correlation measures often fall short in capturing causal relationships. Therefore, in this study, we employed the causal AI discovery tool PCMCI+ — a combination of the PC (Peter and Clark) algorithm and the Momentary Conditional test. PCMCI+ excels at uncovering causal relationships in time series data by addressing issues like autocorrelation, indirect links and common drivers.

PCMCI+ was applied to nearly 150 lagged atmospheric and oceanic monthly ERA-5 time series from January to May between 1980 and 2022. Precursor regions, identified based on their causal links to hurricane numbers, were determined. Linear regression models and random forests were then used to predict hurricane numbers for each season.

Results indicate that adopting PCMCI+ to select causal precursor regions significantly improved the accuracy of seasonal hurricane predictions, achieving a correlation of over 0.9 between observed and predicted numbers. While this study contributes to improved forecast precision, its primary focus is on exploring and discussing identified causes. The selected precursor regions are explained in the context of atmosphere-ocean interactions, providing valuable insights into their role in hurricane formation.

This work was funded by the Korea Meteorological Administration Research and Development Program under Grant (RS-2023-00237121).

How to cite: Latos, B., Moon, I.-J., and Kim, D.-H.: Advancing seasonal hurricane predictions using causal AI, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8728, https://doi.org/10.5194/egusphere-egu24-8728, 2024.

12:10–12:20
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EGU24-4324
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ECS
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Virtual presentation
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Ziqing Wang and Guanghua Chen

This study classifies 407 developing disturbances (DEV) and 2309 nondeveloping disturbances (NONDEV) over the western North Pacific into five large-scale circulation patterns, namely the pre-existing cyclone (PC), easterly wave (EW), zonal wind convergence (CON), zonal wind shear line (SL), and mixed zonal wind convergence and shear line (CON-SL) patterns. The SL pattern has the highest TC yield percentage, followed by the CON-SL, while the EW is the least favorable pattern. The composite analysis shows that upper-level divergence, midlevel relative humidity, and surface heat flux (SHF) growth are crucial to the disturbance development in all the five patterns. Besides, large lower-level barotropic kinetic energy conversion and a well-developed primary circulation are good indicators for disturbance development in the PC, EW, and CON rather than in the SL and CON-SL patterns. Furthermore, for the PC, EW and CON patterns, the DEV features strong and rapidly growing SHF and mesoscale convective systems (MCS) closer to the disturbance center, which allows deep-layer warming and moistening, and drives a deep secondary circulation. Interestingly, due to an environment with high lower-level vorticity, the SL and CON-SL patterns typically foster a relatively mature primary circulation with strong SHF and MCS concentrated close to the center, especially for the NONDEV at the pre-genesis stage. However, a drier mid-to-upper-level environment for the NONDEV inhibits deep convection and causes insufficient upper-level suction, which may explain its shallow secondary circulation and therefore poor potential to develop further.

How to cite: Wang, Z. and Chen, G.: Comparison between Developing and Nondeveloping Disturbances for Tropical Cyclogenesis in Different Large-Scale Flow Patterns over the Western North Pacific, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4324, https://doi.org/10.5194/egusphere-egu24-4324, 2024.

12:20–12:30
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EGU24-15011
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ECS
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Highlight
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On-site presentation
Dario Treppiedi, Gabriele Villarini, Leonardo V. Noto, Enrico Scoccimarro, Wenchang Yang, and Gabriel A. Vecchi

The North Atlantic hurricane season is officially recognized to start on June 1st and end on November 30th. The awareness of this time window is crucial both for federal, state and local agencies as well as the general public to put in place preparation and mitigation efforts to mitigate the impacts of this natural hazard. However, there is an underlying assumption of stationarity in the seasonality of these storms, implying a lack of narrowing or expanding of the hurricane season over the years. Here, we consider the days when tropical cyclones happen (TCdays) to model their seasonality using circular statistics, which is the appropriate modeling framework due to the nature of this quantity. By using mixtures of distributions to model the inter-annual variability of the TCdays, we find an expansion of the tails of the distributions over the period 1966 – 2020 for the North Atlantic basin, leading to a more prolonged hurricane season over the recent decades. These results will be explained in terms of physical drivers, providing insights into the mechanisms that could be responsible for the observed lengthening of the hurricane season.

How to cite: Treppiedi, D., Villarini, G., Noto, L. V., Scoccimarro, E., Yang, W., and Vecchi, G. A.: Changes in the Seasonality of North Atlantic Tropical Cyclones, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15011, https://doi.org/10.5194/egusphere-egu24-15011, 2024.

Posters on site: Mon, 15 Apr, 16:15–18:00 | Hall X5

Display time: Mon, 15 Apr 14:00–Mon, 15 Apr 18:00
Chairpersons: Allison Wing, Alyssa Stansfield
X5.51
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EGU24-145
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ECS
Influence of convectively coupled MRG waves on the north-east monsoon rainfall characteristics over south India.
(withdrawn after no-show)
Kartheek Mamidi, Nithya Narayanan, Vincent Mathew, and Siji Kumar S
X5.52
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EGU24-187
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ECS
Keerthi Sasikumar, Debashis Nath, Xu Wang, Wen Chen, and Song Yang

The Madden–Julian oscillation (MJO) is one of the leading modes of tropical intra-seasonal variability, which exerts significant impacts on the weather and climate across the globe, particularly in the tropics. MJO affects the Asian monsoon by producing enhanced and suppressed convection during the active and break periods, respectively. In the recent decades, the heat content of Indo-western Pacific Ocean has increased significantly, which strengthened the MJO activity. Previous studies also have shown that the expansion of Indo-western Pacific warm pool led to the warping of MJO life cycle, which decreases its residence time over the Indian Ocean (IO) and increases over the Pacific Ocean. Here we show that in the boreal summer months, MJO amplitude has strengthened during the global warming hiatus or rapid IO warming period (1999–2015) compared to the previous period (1982–1998). In the later period, MJO exhibits a faster regeneration over the western IO, and its residence time has increased in the western hemisphere and western IO but decreased in the eastern IO and eastern Pacific Ocean. The strengthening of MJO and the readjustment in its residence time are due to the local MJO feedback on the IO and the La Nina like sea surface temperature pattern in the Pacific Ocean. The prolonged MJO activity leads to bursts of rainfall over the Indian subcontinent in Phase 3 and Phase 4, influencing the active spells of the Indian summer monsoon and causing heavy rainfall over central India and East Asia.

How to cite: Sasikumar, K., Nath, D., Wang, X., Chen, W., and Yang, S.: Recent enhancement and prolonged occurrence of MJO over the Indian Ocean and their impact on Indian summer monsoon rainfall, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-187, https://doi.org/10.5194/egusphere-egu24-187, 2024.

X5.53
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EGU24-994
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ECS
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Joao B. Cruz, José M. Castanheira, and Carlos C. daCamara

Equatorial waves (EWs) are synoptic to planetary-scale disturbances in the tropical atmosphere and are associated to a variety of tropical atmospheric phenomena. For instance, EWs can couple with convection, modulating a substantial fraction of cloud and rainfall variability in the tropics. Space-time filtering techniques that rely on the projection of data onto the structures of EWs are widely used in the literature. Such projection methods are employed with multiple purposes, including the unravelling of physical mechanisms underlying tropical atmospheric phenomena and the evaluation of numerical weather predictions in the tropics. However, most projection techniques rely on the global structures of these waves and, to our knowledge, there have not been efforts toward developing methodologies that identify EWs locally, i.e. over regions covering specific longitude ranges. This type of approach would highly decrease both the amount of data required and the computational power needed to identify EWs. Furthermore, it could potentially reduce the artificial effects local forcings may have on global projections.

This work makes use of the meridional and zonal structures of the solutions to the free Laplace tidal equations, known as Hough vector harmonics. By exploiting the properties of these solutions, we propose a methodology that allows for the identification of EWs over specific longitude ranges and perform a local analysis of fundamental wave properties.

 

This work was supported by IDL (UIDB/50019/2020) and CESAM (UIDP/50017/2020+UIDB/50017/2020+LA/P/0094/2020) through national funds by Fundação para Ciência e Tecnologia I.P./MCTES (FCT), Portugal.

How to cite: B. Cruz, J., Castanheira, J. M., and C. daCamara, C.: Toward the Local Identification of Equatorial Waves , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-994, https://doi.org/10.5194/egusphere-egu24-994, 2024.

X5.54
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EGU24-1431
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ECS
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Erandani Lakshani Widana Arachchige, Wen Zhou, Johnny C. L. Chan, and Xuan Wang

This study investigates the diverse influence of the Indian Ocean Basin Mode (IOBM) on tropical cyclone (TC) genesis in the north Indian Ocean (NIO) and western North Pacific (WNP) Ocean. Three types of warm (W1-W3) and cold IOBM (C1-C3) years are identified based on their persistence and connectivity with the Indian Ocean Dipole (IOD) mode. Type 1 is when the IOBM is decayed without conversion to the IOD, and type 2 is the conversion of the IOBM to the IOD with a phase change as a W event converts to a cold IOD or vice versa. Type 3 is a W event transforming into a positive IOD or a C event transforming into a negative IOD. During W1, in the WNP, TC genesis locations shift northward. They are less intense, whereas W3 TCs shift toward the southern WNP, far away from land, and significantly intensify from July to September (JAS). On the other hand, NIO TCs from October to December (OND) during W2 events are more concentrated in the Bay of Bengal (BoB). The W1–associated Genesis Potential Index (GPI) shows enhancement over the southern NIO from April to June (AMJ), extending into the WNP from JAS to OND. Most importantly, there is an increase in TCs south of 10°N in the WNP due to W3 and C2 events modulating vertical wind shear, mid-tropospheric relative humidity, relative vorticity at 850 hPa, and other related physical mechanisms. In contrast, a decrease in TCs south of 10°N in the WNP is caused by mechanisms associated with W2 and C3 events.Overall, changes in the large-scale environmental factors provide the background for the observed TC variation in both ocean basins during three types of IOBMs. This study, therefore, presents a detailed picture of the impact of IOBM events on TC activity over the NIO and WNP.

Key Words: Indian Ocean Basin Mode, north Indian Ocean, western North Pacific, warm and cold IOBM, Genesis Potential Index

How to cite: Widana Arachchige, E. L., Zhou, W., C. L. Chan, J., and Wang, X.: Impact of the Indian Ocean Basin Mode on Tropical Cyclone Genesis in the North Indian and Western North Pacific Oceans, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1431, https://doi.org/10.5194/egusphere-egu24-1431, 2024.

X5.55
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EGU24-1602
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ECS
An Observational Analysis of Environmental Effects on Tropical Cyclones Size Expansion
(withdrawn after no-show)
Kexin Chen
X5.56
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EGU24-1354
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ECS
Chi Zhang and Xiaofan Li

This study investigated radiative effects on kinetic and potential energy budgets associated with rapid intensification of Typhoon Mujigae in 2015 by conducting sensitivity experiments with Weather Research and Forecasting (WRF) model simulation. We found that the inclusion of radiative effects mainly increases the symmetric rotational kinetic energy, while the radiative effects are from infrared longwave radiative effects. The comparison in symmetric potential energy and symmetric rotational kinetic energy budget between the sensitivity experiments excluding the radiative effects and solar shortwave radiative effects only reveals that the inclusion of infrared longwave radiative effects destabilizes the moist atmosphere and increases the conversion from symmetric potential energy to symmetric divergent kinetic energy , which reduces symmetric potential energy and enhances symmetric rotational kinetic energy through the strengthened conversion from symmetric divergent kinetic energy to symmetric rotational kinetic energy.

How to cite: Zhang, C. and Li, X.: Radiative Effects on Kinetic and Potential Energy Budgets Associated with Rapid Intensification of Typhoon Mujigae in 2015, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1354, https://doi.org/10.5194/egusphere-egu24-1354, 2024.

X5.57
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EGU24-1355
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ECS
Yishe Shi and Xiaofan Li

Tropical cyclone (TC) Khanun in 2017 was simulated in this study by the Weather Research and Forecasting (WRF) model. The observation-validated simulation data were used to examine dominant dynamic processes resulting in the contraction of the radius of maximum kinetic energy of symmetric rotational flow. The contraction rate was quantified by calculating the radial derivatives of symmetric rotational kinetic energy budget. The radius of maximum symmetric rotational energy was contracted rapidly before rapid intensification (RI) and moved inward slowly, then barely moved, and moved inward slowly again during RI.

The conversion from kinetic energy of asymmetric rotational flow to symmetric rotational flow induced by advection of asymmetric rotational tangential wind by asymmetric divergent radial wind at dominant azimuthal wavenumber-1 asymmetry and convergence of inward flux of symmetric rotational flow led to the rapid contraction before RI. During RI, symmetric rotational energy grew in the lower troposphere significantly, and upward flux convergence was equally important as inward flux convergence of symmetric rotational flow, which caused the first slow contraction. The conversion from kinetic energy of symmetric divergent wind to symmetric rotational flow associated with co-locations of maximum symmetric rotational energy and maximum symmetric inward radial flow produced stationary maximum symmetric rotational energy. Finally, horizontal and vertical flux convergence of symmetric rotational flow, and the conversion from environmental kinetic energy to symmetric rotational kinetic energy through the interaction between symmetric rotational flow and symmetric radial environmental flow generated the second slow contraction.

How to cite: Shi, Y. and Li, X.: Contraction of the radius of maximum symmetric rotational kinetic energy during the intensification of Tropical Cyclone Khanun (2017), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1355, https://doi.org/10.5194/egusphere-egu24-1355, 2024.

X5.58
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EGU24-2914
Eric Maloney and Wei-Ting Hsaio

The maintenance mechanisms for the Madden-Julian oscillation (MJO) remain an area of active research, and may include a combination of radiative feedbacks, wind-evaporation feedbacks, and moistening produced by lower tropospheric convective heating. This presentation will revisit the importance of radiative feedbacks for supporting MJO convection with a new GPCP precipitation dataset and NASA CERES radiative heating profiles. Prior work by Adames and Kim with the GPCP v1.3 precipitation product and NOAA OLR indicated that radiative feedbacks are strongly supportive of MJO convection as viewed through the vertically integrated moist static energy budget, and provide a strong scale selection mechanism. This presentation uses the newer GPCP v3.2 product to show that while radiative feedbacks still provide a strong scale selection mechanism, the overall strength of radiative feedbacks are weaker than with GPCP1.3. This suggests that the relative role of other feedbacks such as wind-evaporation feedbacks for supporting MJO convection may be more important than once thought.

 

This presentation also uses NASA CERES radiation profiles in a vertically-resolved moisture budget framework that employs the tropical weak temperature gradient assumption to determine the impact of radiative feedbacks on the MJO moisture budget. It is shown that longwave cloud radiative feedbacks onto MJO moisture anomalies are enhanced in the Indian Ocean and southern Maritime Continent region compared to other parts of the tropics, suggesting stronger support for MJO convection there. This finding is consistent with prior work by Mayta and Adames suggesting that the MJO most closely resembles a moisture mode in that region. It is hypothesized that enhanced vertical shear in the Indian Ocean and southern Maritime Continent supports convective organization that fosters greater cloud-radiative feedbacks.

How to cite: Maloney, E. and Hsaio, W.-T.: Maintenance of MJO Convection by Radiative Feedbacks  , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2914, https://doi.org/10.5194/egusphere-egu24-2914, 2024.

X5.59
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EGU24-5312
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ECS
Giousef Alexandros Charinti

Existing theoretical models for tropical cyclones have been instrumental in understanding the mechanisms under which their intensification occurs. The potential intensity (PI) which was first introduced by Emanuel 1986, provides an upper bound for the intensity a tropical cyclone can achieve based on the environmental conditions. However, this model and others naturally assume idealized settings which do not necessarily occur in the real world. Using simulations from the high resolution cloud resolving model SAM in rotating radiative-convective equilibrium settings, we assess the validity of these idealizations in the simulations. We find that some idealizations, such as assuming convection on a moist adiabat in the eyewall, are only partially valid. In order to understand why these deviations from the theory occur, we look at different possible mechanisms missing in simple models, such as upper level processes and entrainment.

How to cite: Charinti, G. A.: Assessing the validity of simple models for tropical cyclones in high resolution simulations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5312, https://doi.org/10.5194/egusphere-egu24-5312, 2024.

X5.60
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EGU24-5958
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Highlight
Enrico Scoccimarro, Paolo Lanteri, and Leone Cavicchia

Depending on the location on the Earth planet, the amount of precipitation associated with Tropical Cyclones (TCs) can reach 20% of the total yearly precipitation over land and up to 40% over some ocean regions. TC induced freshwater flooding has been suggested as the largest threat to human lives due to TCs. Therefore, a reliable quantification of the precipitation amount associated with each past TC is important for a better definition of the TC fingerprint on the climate. The temporal and horizontal resolution of state-of-the-art observational datasets and atmospheric reanalysis give the possibility to quantify the TC-associated precipitation over the Earth planet following the observed TC tracks. In this work we compare results from different observational and reanalysis datasets in terms of TC-associated precipitation, to verify the consistency between them. A particular focus is given to the record-breaking TC Freddy (Southern Indian Ocean, 2023).  Here we show that the time-varying bias in TC associated precipitation, due to the positive trend in assimilated observations, makes it difficult to assess long-term trend investigation based on reanalysis: to this aim we need to build on state-of-the-art General Circulation Models, free to evolve under historical radiative forcing. This work is part of CLINT EU project activity (grant agreement ID: 101003876; DOI: 10.3030/101003876).

How to cite: Scoccimarro, E., Lanteri, P., and Cavicchia, L.: Freddy: breaking record for Tropical Cyclone precipitation?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5958, https://doi.org/10.5194/egusphere-egu24-5958, 2024.

X5.61
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EGU24-6300
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ECS
Miriam Saraceni, Lorenzo Silvestri, and Paolina Bongioannini Cerlini

In the literature, Mediterranean hurricanes, i.e., mesoscale cyclones exhibiting tropical characteristics for at least a brief portion of their lifespan, are often labeled as "medicanes". However, the debate on how to classify such cyclones remains open. Initially, a Mediterranean cyclone was designated as a "medicane" if it displayed a central "eye" and spiral cloud bands around the core. Due to their low rate of occurrence,  the mechanisms contributing to the formation of medicanes have been investigated in a relatively restricted set of case studies. Generally, the initiation phases of "medicane" life cycles exhibit similarities, with all systems displaying growth through the interaction of an upper-tropospheric potential vorticity (PV) streamer and a low-level baroclinic region, as commonly observed in extratropical cyclones. However, during the mature stages, baroclinic forcing, air–sea interactions, and convection may significantly influence cyclone development. Recently, a general classification has been proposed, based on a limited number of cases, dividing "medicanes" into three groups: Group 1, where baroclinic instability plays a significant role throughout the cyclones' lifetime; Group 2, where baroclinicity is relevant only in the initial stage, and, akin to tropical cyclones, the theory of wind-induced surface heat exchange can explain their intensification; and Group 3, encompassing cyclones developing through a synergy between baroclinic and diabatic processes. The lack of a clear physical definition for medicanes has led to diverse climatologies, necessitating the identification or establishment of criteria for effectively determining which cyclones within this broad category resemble their tropical counterpart. In this study, the investigation of genesis and intensification processes is carried out by analysing the vertically integrated moist static energy (h', with h = cp T + Lv q  + gt) budget for a subset of twenty-three among the most studied Mediterranean cyclones labeled as "medicanes" from 1969 to 2023.  To cover all chosen cyclones and use a consistent dataset the cyclone tracking, analysis, and budget computation are done employing the ERA5 reanalysis. After tracking the cyclones, the budget is computed within a radius around the cyclone center (from 300 km to 800 km), at least three times the radius of the cyclone, according to each cyclone's size. Within the budget, the increase of h' variance connects radiative, convective, and moisture feedback with the increase in the vertically integrated humidity, temperature, and geopotential variance. The budget, previously employed in studies of convective organization in the context of the Radiative Convective Equilibrium (RCE) in the tropics has been successfully applied also to tropical cyclones. Here, it is utilized firstly to capture the nature of the former subset of cyclones, understanding objectively through the budget, and specifically with the variance increase of each moist static energy term, which of these cyclones can be assimilated into the tropical-like framework. Additionally, this approach has given insights into the radiative, convective, and moisture feedback mechanisms driving cyclone intensification for these cases. Preliminary findings suggest that the established groups in the literature can be reconciled through the budget, enabling the identification of genuinely tropical-like cyclones using this method.

How to cite: Saraceni, M., Silvestri, L., and Bongioannini Cerlini, P.: Investigating the complexity of Mediterranean Tropical-like cyclones through the use of the vertically integrated Moist Static Energy Budget, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6300, https://doi.org/10.5194/egusphere-egu24-6300, 2024.

X5.62
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EGU24-9275
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ECS
Guiling Ye, Jeremy Cheuk-Hin Leung, Wenjie Dong, Jianjun Xu, Weijing Li, Weihong Qian, and Banglin Zhang

Given the large impacts of tropical cyclones (TCs) on human society, the response of TC activity to climate change has widely drawn attention from both society and scientists. However, assessing how historical TC activity, especially intensity, evolved with climate change has proven challenging due to incomplete TC records in the early years. Here, we introduce the Reanalysis-Based Global Tropical Cyclone Tracks Dataset for the Twentieth Century (RGTracks-20C), which is reconstructed from the National Oceanic and Atmospheric Administration (NOAA) Twentieth Century Reanalysis (20CRv3) using two tropical cyclone tracking algorithms. Validations based on observations in the modern satellite era verify the ability of the RGTracks-20C to capture the climatology and long-term variability of TC numbers, tracks, duration, and intensity across various ocean basins. Furthermore, the RGTracks-20C fills the gaps of the incomplete TC track information, including position and intensity, in the early observational data. The RGTracks-20C is the first publicly available reanalysis-based century-long global TC track dataset, providing an alternative data reference for future research about climate change and TC-related disasters.

How to cite: Ye, G., Leung, J. C.-H., Dong, W., Xu, J., Li, W., Qian, W., and Zhang, B.: A Reanalysis-Based Global Tropical Cyclone Tracks Dataset for the Twentieth Century (RGTrack-20C), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9275, https://doi.org/10.5194/egusphere-egu24-9275, 2024.

X5.63
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EGU24-21575
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ECS
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Yegor Hudozhnik and Andreas Windisch

Tropical cyclones (TCs) are hazardous and destructive events that pose a threat to human life every year. Since the beginning of the meteorological observation era, predicting the behavior of cyclones has always been an issue. It has been proven that with climate change due to global warming, the proportion of stronger TCs increases, increasing the danger and potential harm of TCs.
Numerous techniques have been developed over the years and are used in ensembles to detect, predict, and classify TCs. Nevertheless, the tasks in the field of TC prediction are considered challenging because the development of TC systems exhibits nonlinear behavior and depends on many environmental factors.
Conventional TC forecasting methods are computationally intensive and require a relatively large amount of energy and time. Due to ongoing global warming, the behavior of TCs may constantly change and therefore requires the use of modern, environmentally friendly and more flexible learning methods for estimating and predicting the future behavior of TCs.
In recent years, the study of the application of Deep Learning (DL) in this area proved to be highly effective. These methods are designed to facilitate the prediction process, as well as automatically detect possible trends that may occur over time. DL methods provide the most modern statistical analysis and can thus exert their influence on research.
In our research, we have applied a novel approach of incorporating two-dimensional meteorological data to forecast the track and intensity of TCs together with scalar data of location, intensity, and temporal information. We have built and tested numerous sequence-to-sequence forecasting models based on ConvLSTM2D neural network layers and tested two-dimensional data compression using autoencoders as a data preparation technique. Our experiments have shown that the multivariate forecast yields perspective results. We have also succeeded in detecting the influence of recent trends in changes of TC behaviour in recent years and proved the ability of neural networks to fit themselves to those trends.

How to cite: Hudozhnik, Y. and Windisch, A.: Multivariate forecasting of tropical cyclones using combined neural networks, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21575, https://doi.org/10.5194/egusphere-egu24-21575, 2024.

X5.64
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EGU24-15249
Fabian Senf and Roxana Cremer

Tropical cyclones are impressive phenomena of tropical meteorology and form spatially highly organised structures. To shed more light on microphysical sensitivities of hurricanes, we present the initial outcomes of a sensitivity analysis of hurricane Paulette simulated with the German weather and climate model ICON. Paulette occurred in the North-Atlantic basin in September 2020 and was simulated with variable settings for model parameterisations and horizontal grid spacings down to hectometre. The study especially explores the microphysical details of the simulated hurricane case. In our examination, we find interesting sensitivities to Cloud Condensation Nuclei (CCN) type and concentration and to vertical resolution. Changes in the top-of-the-atmosphere radiation fluxes are presented in detail. Insights gained from this analysis contribute to the broader understanding of model performance in simulating microphysical processes such as the formation of cloud ice and precipitation.

How to cite: Senf, F. and Cremer, R.: Sensitivity analysis of hurricane Paulette with convection-permitting ICON simulations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15249, https://doi.org/10.5194/egusphere-egu24-15249, 2024.

X5.65
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EGU24-471
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ECS
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Maria Juliana Valencia Betancur, Johanna Yepes, John F. Mejia, Alejandro Builes-Jaramillo, and Hernan D. Salas

Tropical easterly waves (TEWs) are quasi-periodic wave disturbances found within the easterly trade winds during boreal summer and autumn. They influence the synoptic-scale circulation dynamics in tropical America and contribute up to 50% of the seasonal precipitation (June to November) over northern South America. This study evaluates the sensitivity of different spectral bands in classifying TEWs based on daily vorticity at 700 hPa during the Organization of Tropical East Pacific Convection (OTREC) campaign. TEWs were identified in real-time using data from NOAA's Marine Tropical Surface Analysis. Complementarily, we refined TEWs identification by correlating it with 700 hPa filtered relative cyclonic vorticity from ERA5. To consider the uncertainties associated with the TEWs chronology selection, we employed two filtering methodologies: the Fast Fourier Transform (FFT) with periodicity bands of 3–10 days, 2.5–12 days, and 2.5–15 days, as well as the Ensemble Empirical Mode Decomposition (EEMD) with periodicity bands of 3–6 days, 4-12 days, and 3–15 days. Thirteen TEWs were initially reported by NOAA as crossing the Caribbean at 80°W. In our study, we further analyzed these waves by correlating areas characterized by westward-moving features of filtered relative cyclonic vorticity at the same longitude. Through this analysis, distinct classifications emerged using different filters, revealing the presence of 5 to 9 TEWs. The results show that TEWs classification is sensible to the filtering methods and periodicity band windows.

How to cite: Valencia Betancur, M. J., Yepes, J., Mejia, J. F., Builes-Jaramillo, A., and Salas, H. D.: Sensitivity Analysis of Filtering Methods for Tropical Easterly Waves Classification, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-471, https://doi.org/10.5194/egusphere-egu24-471, 2024.

X5.66
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EGU24-2215
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ECS
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Thi Lan Dao, Claire L. Vincent, Yi Huang, Joshua S. Soderholm, and Dale S. Roberts

This study investigates the interaction of the Madden Julian Oscillation (MJO) with local scale forcings in regulating precipitation and its diurnal variation over coastal areas in Northeast (NE) Australia. Radar results show that the variation of rainfall with MJO phases exhibits both large-scale and local-scale influences. During the enhanced convection phases of the MJO, widespread increased rainfall signals are generated by large-scale forcings associated with the MJO convection, but the environmental factors controlling the type and amount of precipitation during each phase is different. By contrast, the locally enhanced rainfall probability during suppressed convection phases of the MJO possibly results from mesoscale convective systems such as sea breezes and the interaction of easterly trade-winds and topography. The amplitude of the rainfall diurnal cycle in suppressed convection phases is generally larger than in enhanced convection phases of the MJO. However, the impact of the MJO on diurnal rainfall characteristics (e.g., diurnal timing and amplitude) varies from phase to phase suggesting that each MJO phase needs to be considered separately. Simulations from the UK Met-Office Unified Model with grid-spacing of 2.2 km have been used to understand the processes driving this observed interaction of large-scale and mesoscale variability. The simulations show that coastal rainfall during suppressed convection phases of the MJO is sensitive to the trade-wind inversion height as well as moisture distribution. The findings are important for assessing numerical model skills at small scales and highlight the importance of process-based understanding at these scales.

How to cite: Dao, T. L., L. Vincent, C., Huang, Y., S. Soderholm, J., and S. Roberts, D.: Modulations of local rainfall in Northeast Australia associated with the Madden Julian Oscillation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2215, https://doi.org/10.5194/egusphere-egu24-2215, 2024.

X5.67
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EGU24-2239
Qinlu Gu, Renguang Wu, and Sang-Wook Yeh

Synoptic-scale disturbances prevail over the tropical western North Pacific during boreal summer. Those disturbances are generated over the equatorial western-central Pacific and propagate northwestward to the tropical western North Pacific. They may cause extremely heavy rainfall events and serve as initial disturbances for tropical cyclone genesis. The intensity of the synoptic-scale disturbance over the tropical western North Pacific is closely related to the El Niño–Southern Oscillation (ENSO) that modulates the seasonal atmospheric fields over the source regions, along the propagation paths, and over the impact regions of the synoptic-scale disturbances. ENSO displays a diverse range of amplitude, spatial pattern and temporal evolution. In view of the increasing frequency of extreme ENSO events under global warming and their substantial consequences, it is essential to investigate the relationship between the intensity of the synoptic-scale disturbances over the tropical western North Pacific and ENSO of varying amplitudes. In this talk, we will present evidences for the nonlinear response of the synoptic-scale disturbance intensity over the tropical western North Pacific during boreal summer to the amplitude of ENSO. A distinct difference is revealed between the nonlinear response of the synoptic-scale disturbance intensity over the tropical western North Pacific to the amplitude of El Niño and La Niña events. Physical explanation will be provided for the above feature based on observational analysis and numerical model experiments.

How to cite: Gu, Q., Wu, R., and Yeh, S.-W.: Nonlinear response of summertime synoptic-scale disturbance intensity over the tropical western North Pacific to ENSO amplitude, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2239, https://doi.org/10.5194/egusphere-egu24-2239, 2024.

X5.68
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EGU24-4620
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ECS
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Shiqi Xiao, Aoqi Zhang, Yilun Chen, and Weibiao Li

There is increasing attention to torrential rainfall remote from tropical cyclones (TCs). However, the relationship between precipitation and TC induced remote moisture transport over decades is still unknown. To find the relationship above, we used objective identification of TC induced remote moisture transport to obtain spatiotemporal evolution of clusters and rainfall characteristics inside the clusters. The contribution of TC induced remote moisture transport to annual mean rainfall over North China and surroundings are 5–15 % higher than that over South China and surroundings. TC cases that induced remote heavy rainfall over two regions are listed. The tracks of TC induced remote moisture transport are generated using spatiotemporal digraphs. We used double Gaussian function to fit the relationship heavy rainfall frequency and moisture transport height, and used sigmoid function for the relationship between heavy rainfall frequency and moisture transport intensity derived from thousands of clusters over decades. The moisture transport height of peak heavy rainfall frequency over TC induced remote moisture transport are significantly higher than the transport without TC effect. The moisture transport intensity threshold for heavy rainfall frequency over 20 % is smaller over South China and surroundings than that over North China and surroundings. Those results above have quantified the relationship between heavy rainfall and moisture transport inside clusters, which is beneficial to forecast of torrential rainfall remote from TCs.

How to cite: Xiao, S., Zhang, A., Chen, Y., and Li, W.: Association between torrential rainfall and tropical cyclone induced remote moisture transport over East Asia, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4620, https://doi.org/10.5194/egusphere-egu24-4620, 2024.

X5.69
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EGU24-5466
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ECS
Natasha Senior, Adrian Matthews, Ben Webber, Jaka Paski, Danang Nuriyanto, Donaldi Permana, and Richard Jones

Convectively coupled equatorial Kelvin waves (CCKWs) are eastward propagating weather systems that locally organise convection and have been linked to precipitation extremes across the Maritime Continent (MC). They are often embedded in convectively active phases of the Madden-Julian Oscillation (MJO) which too propagates eastwards but influences convection in the MC over longer timescales and larger areas. Previous high impact weather case studies have linked CCKWs to local precipitation extremes. In this study, we examine a case study during July 2021 of multiple CCKWs embedded within an active MJO. The final CCKW traversed the western MC causing precipitation extremes across equatorial Indonesia that lead to numerous reports of flooding and landslides, with the West Kalimantan region the worst affected. The MJO event itself was abruptly terminated following the passage of this CCKW. Through analysis of the moisture budget we find that the rainfall exceeded the convergence of moisture to produce the pronounced drying. Prior to the local MJO termination, we find there was enhanced westward propagating diurnal activity across the equatorial MC coinciding with a steady increase of total column water. We also examine observations of the extreme rainfall event in the West Kalimantan province. Comparing different deterministic model configurations, we find that the convection permitting models generally perform better when there are not multiple CCKWs present within the initial conditions. This research highlights how CCKWs should not simply be viewed as convective systems that locally affect weather but have the potential to have devastating impacts over the entire equatorial MC especially when involved in multiscale interactions both with the diurnal cycle and with the MJO.

How to cite: Senior, N., Matthews, A., Webber, B., Paski, J., Nuriyanto, D., Permana, D., and Jones, R.: Abrupt ending of MJO by CCKW precipitation leaves swath of flooding across Indonesia, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5466, https://doi.org/10.5194/egusphere-egu24-5466, 2024.

X5.70
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EGU24-5605
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ECS
Spatial variation of tropical cyclone rainfall trends in Mainland Southeast Asia
(withdrawn)
Aifang Chen and Haiyan Lu
X5.71
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EGU24-7283
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ECS
Samira El Gdachi, Pierre Tulet, Anne Rechou, Frederic Burnet, and Maud Leriche

 

Located at 21°07'S, 55°32'E, Reunion Island, a mountainous island in the Indian Ocean, is an extraordinary site for studying the formation and life cycle of slope clouds. The island is influenced by southeast trade winds, reaching peak intensity in winter (June-August) and moderating during summer (December to February). These winds create pronounced conditions along the southwest and northeast edges, accompanied by a leeward circulation in the northwest, notably in the Maïdo area. Sea and valley breezes converge on the slopes of Maïdo, facilitating the advection of oceanic air masses and initiating convection on the mountainous terrain. Duflot et al. (2019) have substantiated that this convective process leads to the daily formation of clouds, typically exhibiting shallow vertical development and containing minimal water content.

An intensive measurement campaign, BIOMAÏDO (Bio-physicochemistry of Tropical Clouds at Maïdo), took place from March 11 to April 7, 2019, at Reunion Island, in order to study the chemical and biological composition of the air mass, the formation processes of secondary organic matter in heterogeneous environments, the dynamics and evolution of the boundary layer, and the macro- and micro-physical properties of clouds.

In this study, cloud microphysical properties are examined and analyzed using observations from the campaign, followed by a comparison with a high-resolution (100m horizontal resolution) numerical simulation with the Meso-NH model. Among the two microphysical schemes (ICE3 and LIMA; Liquid Ice Multiple Aerosol), the model is initialized with the two-moment microphysical scheme LIMA, which is parameterized using aerosol CCN properties initialization derived from ground aerosol measurements (3 modes) and vertical balloon profile aerosol concentrations.

Firstly, a sensitivity study on the microphysical scheme will be presented. It demonstrates that clouds form simultaneously in both schemes. However, clouds exhibit greater vertical development in the ICE3 scheme. Additionally, cloud dissipation occurs an hour earlier in the LIMA scheme.

Subsequently, an analysis through a microphysical variable balance will be conducted to identify the primary thermodynamic processes characterizing the formation and dissipation of slope clouds.

How to cite: El Gdachi, S., Tulet, P., Rechou, A., Burnet, F., and Leriche, M.: Investigating Cloud Microphysical Properties: A Comprehensive Study Using High-Resolution Numerical Simulations and Observations in the Indian Ocean Region, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7283, https://doi.org/10.5194/egusphere-egu24-7283, 2024.

X5.72
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EGU24-7615
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ECS
Hiroaki Yoshioka, Hironori Fudeyasu, Ryuji Yoshida, Junshi Ito, Takeshi Horinouchi, and Kosuke Ito

A project ”Moonshot Goal 8” was established to study the possible weakening of typhoon intensity due to artificial interventions supported by Japan Science and Technology Agency. One of our measures is to increase the sea surface drag near typhoons by using obstacles such as large ships.

The maximum potential intensity theory suggests that the equilibrium intensity decreases as the surface drag coefficient increases.

Still, few numerical studies tested it for real tropical cyclones (TCs). Some studies used fine-resolution simulations (e.g., with a sub-kilometer grid) to agree with the theoretical indication, but the number of cases is limited by calculation resources. Also, no studies have been conducted to elucidate the effect of surface drag coefficient change in a limited oceanic region.

Therefore, we aim to conduct a comprehensive study on how TC would react to surface drag change over limited regions that can be set in various ways. Now, we focused on the intensification of Typhoon Faxai in 2019 and conducted sensitivity experiments by changing the drag coefficient (CD) over the circle area around it. In this study, we ran the Scalable Computing for Advanced Library and Environment (SCALE) at a coarse horizontal resolution of 5 km. The resultant central pressure and maximum 10m wind speed were sensitive to CD, especially for the value. These were reduced almost linearly and weakened by about 60% of the control run (CTL) when CD was set to 3.0 times that in CTL. Additionally, the results of the sensitivity to a radius of changing CD area showed that maximum wind speed during the mature stage has remained unchanged when over 100 km radius area changed.

We will conduct further studies until the meeting.

How to cite: Yoshioka, H., Fudeyasu, H., Yoshida, R., Ito, J., Horinouchi, T., and Ito, K.: Influence of Drag Coefficient for Tropical Cyclone Intensification by Numerical Simulations. , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7615, https://doi.org/10.5194/egusphere-egu24-7615, 2024.

X5.73
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EGU24-13792
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ECS
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Xuan Wang and Zhe-Min Tan

The selection of physical parameterization schemes for tropical cyclone (TC) forecasts has required a substantial amount of effort. In general, the evaluation of physical parameterization schemes and their combined performance was based solely on the deterministic forecast, which had inherent limitations in representing the overall performance of physical parameterization schemes due to the model uncertainty. This study introduces an uncertainty-informed framework of evaluating and selecting the combination of physical parameterization schemes for TC forecasts, based on the ensemble forecast that could include the model uncertainty roles. The performance ranking of the scheme combination based on the ensemble mean error is found to be distinct from that based on the deterministic forecast error. Moreover, differences in both ensemble mean errors and ensemble spreads for various scheme combinations highlight the importance of considering two metrics concurrently, i.e., via the quality of the forecast distribution as a whole, to assess the forecast performance. Consequently, the ensemble Continuous Ranked Probability Score (eCRPS) is used to quantify the performance of the scheme combinations, and it is demonstrated that the performance is more comprehensive than that in the deterministic context. Finally, the well-performed scheme combination for the forecasts of six intense TCs is chosen from the evaluated schemes in the context of model uncertainty, based on the overall quality of TC track and intensity forecast distributions.

How to cite: Wang, X. and Tan, Z.-M.: On the Combination of Physical Parameterization Schemes for Tropical Cyclone Track and Intensity Forecasts in the Context of Uncertainty, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13792, https://doi.org/10.5194/egusphere-egu24-13792, 2024.

X5.74
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EGU24-15547
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ECS
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Katharina Meike Holube, Frank Lunkeit, Sergiy Vasylkevych, and Nedjeljka Žagar

Kelvin waves are an important component of the tropical wave circulation. While the excitation of Kelvin waves by tropical convection is well understood, the influence of subtropical Rossby wave dynamics on the Kelvin waves has received relatively little attention. Our research investigates a Kelvin wave excitation mechanism through interactions of Rossby waves and the zonal subtropical jet. The investigation is carried out with a spherical rotating shallow-water model, using a quasi-geostrophic zonal jet as initial condition. The basis functions of the model are the eigensolutions of the linearized equations, which are identified with atmospheric waves. The model formulation thus includes the Rossby and Kelvin waves as prognostic variables. With an external forcing that impacts only the Rossby waves, Kelvin waves can be excited in the model through the wave-mean flow interactions and wave-wave interactions. The main finding is that Kelvin waves are resonantly excited by interactions of the Rossby waves and the mean flow, provided the Doppler-shifted frequencies of the Rossby waves and the Kelvin waves match. The wave-mean flow interactions are found to be stronger than the wave-wave interactions. The resonant Kelvin wave excitation is one of the possible mechanisms for the influence of the extratropical circulation on tropical waves.

How to cite: Holube, K. M., Lunkeit, F., Vasylkevych, S., and Žagar, N.: Resonant excitation of Kelvin waves by interactions of subtropical Rossby waves and the zonal mean flow, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15547, https://doi.org/10.5194/egusphere-egu24-15547, 2024.

Posters virtual: Mon, 15 Apr, 14:00–15:45 | vHall X5

Display time: Mon, 15 Apr 08:30–Mon, 15 Apr 18:00
Chairpersons: Enrico Scoccimarro, Alyssa Stansfield, Leone Cavicchia
vX5.2
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EGU24-8189
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ECS
Characteristics of the pre-monsoon cyclone over the Bay of Bengal in the last six decades
(withdrawn after no-show)
Biswajit Jena and Sandeep Pattnaik
vX5.3
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EGU24-9256
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ECS
Major drivers of summer extreme precipitation over the Yangtze River Basin
(withdrawn)
Yucong Lin, Silvio Gualdi, and Enrico Scoccimarro
vX5.4
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EGU24-12646
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ECS
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Paolo Besana, Marco Gaetani, Christoph Fischer, Cyrille Flamant, Tanguy Jonville, Andreas Fink, and Peter Knippertz

Studying Major Tropical Cyclones (MaTCs) is vital due to their significant impact on natural resource management, infrastructure resilience, and disaster preparedness, especially in vulnerable regions.

However there exists a gap in our understanding of the MaTC development and occurrence processes, particularly in the Eastern Tropical Atlantic (ETA) and on the Atlantic coast of West Africa where the interaction with African Easterly Waves (AEWs) appears to be a crucial aspect. In fact, although some AEWs evolve into MaTCs, a clear causal relationship between the two phenomena has not been established yet. In particular, the reason why only some AEWs evolve into MaTCs and other MaTCs evolve without an AEW's contribution has not been elucidated yet. 

The primary focus of this study is the characterization of the MaTCs in terms of “Weather Types” (WTs), which represent distinct atmospheric states showing persistence over days.

The aim of this research is to answer the following scientific questions:

1)Without explicitly describing the dynamic system or solving it analytically, how can WTs be utilized to characterize the patterns of atmospheric circulation in the ETA?

2)Which specific WTs exert a more significant influence on the frequency or occurrence of MaTCs in the region, assuming such a dependency exists?

3)How do MaTCs and AEWs interact with respect to the atmospheric circulation expressed through WTs?

To answer these questions we employed Self-Organizing Maps and Hierarchical Agglomerative Clustering to analyze atmospheric variables extracted from the ECMWF Reanalysis v5 (ERA5) and ECMWF Atmospheric Composition Reanalysis 4 (EAC4) reanalyses. Moreover, detailed information on the location, maximum winds, central pressure, and size of cyclones is extracted from the National Hurricane Centre database (HURDAT), while AEWs are identified and tracked by an algorithm developed at the Karlsruhe Institute of Technology (AEWDAT). 

This approach enables the identification of eight distinct WTs characterizing the atmospheric circulation in a region including ETA and the Atlantic coast of West Africa, making it possible to observe how the occurrence of a specific WT is suppressive or favorable for the occurrence of a MaTC. 

The analysis shows specific atmospheric conditions under which AEWs and MaTCs co-occur: in this sense we have identified WTs that are associated with the occurrence of a MaTC together with an AEW or with a MaTC alone. 

These results improve our knowledge on the relationship between AEWs and MaTCs as they provide the atmospheric circulation context in which they interact. 

The insights gained from this study may contribute to the field by offering a refined methodological framework, employing a WT-centric approach, and providing a comprehensive analysis of MaTC dynamics in the context of atmospheric circulation. 

How to cite: Besana, P., Gaetani, M., Fischer, C., Flamant, C., Jonville, T., Fink, A., and Knippertz, P.: Exploring the dynamics of Tropical Cyclones in the Eastern Tropical Atlantic: a Weather Types perspective, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12646, https://doi.org/10.5194/egusphere-egu24-12646, 2024.