The Amazon rainforest holds more than 40% of all remaining tropical rainforest and is a key component of the climate system. The scale of deforestation in the Amazon significantly impacts both local and global climates. Under a business-as-usual scenario as much as 40% of the Brazilian Amazon rainforest will be lost by 2050. Despite the magnitude of these changes and its importance, the overall effects of deforestation on rainfall remain uncertain. Land-use change influences rainfall through a variety of mechanisms acting at local to continental scales. As such, previous research indicates conflicting responses to rainfall depending on the scales studied. In reality, rainfall processes interact across these scales, but until recently have been impossible to capture within a single model due to computational expense. Consequently we are unable to rely on these simulations as future estimations of rainfall for such a sensitive and anthropogenically impacted region as the Amazon.

In this study, we overcome these limitations by running convection permitting simulations (horizontal resolution 4.5km) over a large domain (6000km covering the majority of South America) using a Tropical configuration of the UK Met Office Unified Model. The high-resolution and continental-scale of these simulations present an opportunity to reduce the uncertainty in Amazonian rainfall estimates within a single model and ensures rainfall processes and interactions across scales are captured. To investigate the impacts of deforestation we will include a series of land-use sensitivity runs making use of a range of socioeconomic scenarios to 2050. Here we present initial results from our simulations, indicating how localised storms, mesoscale convective systems and large-scale circulations respond to land-use change.

How to cite: Bassett, R., Garcia-Carreras, L., Lowe, D., Alves, L., Fisch, G., Halladay, K., Kahana, R., and Veiga, J.: Deforestation and changes in rainfall across the Amazon – reducing uncertainty using a continental scale convection permitting domain, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6107, https://doi.org/10.5194/egusphere-egu23-6107, 2023.

Weather models which allow explicit convection can add value to weather forecasting by improving the intensity and timing of precipitating systems and their dynamics, which is particularly valuable in the tropics where moist diurnal convection dominates. In West Africa, convection can become organised to form mesoscale convective systems which are crucial for supplying water but may have devastating impacts, and while convection-permitting models improve forecasts, issues remain in the implementation of operational convection-permitting models. A major problem is initialising weather models in the tropics, where measurements are sparse and weather systems are dominated by nonlinear diabatic processes, which makes data assimilation challenging. Currently, the UK Met Office runs a regional operational convection-permitting model in Africa, the Tropical Africa Model, which is initialised using lower-resolution global models. However, the global models have extremely limited convective-scale structures and as a result, there is a spin-up time of around 12-18 hours before the model begins to accurately reflect precipitation.

To counteract this problem, a “warm-starting” method has been trialled. The warm-starting technique blends large-scale features from the global model and fine-scale fields below a certain length scale from previous runs of the high-resolution model to use as an initial state in a new model run. It combines the more realistic convective structures of the regional model and the more accurate synoptic conditions in the global model. Not only is the approach cheaper and quicker than traditional data assimilation, both in terms of development and computational cost, but it also shows demonstrable improvements in the representation of precipitation for the first 12 hours of the model and beyond relative to simulations where the model has simply been initialised with the global model (a “cold-start”). The cold-start simulations appear to consistently predict rainfall that is too intense even beyond the first 12 hours.

We investigate why warm-starting models produces more realistic rainfall distributions by examining the dynamical structures: producing statistics of rainfall objects as forecasts evolve and examining their connection to the dynamics. We examine the energetics of convection in the convection-permitting models, aiming to provide a justification for the scale length at which we include structure from previous model runs using this technique.

How to cite: Morris, F., Warner, J., Bain, C., Schwendike, J., Parker, D., and Petch, J.: Dynamical Impacts of Warm-Starting Operational Weather Models over Africa, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5208, https://doi.org/10.5194/egusphere-egu23-5208, 2023.

How to cite: Klein, C., Barton, E., and Taylor, C.: Changes in land surface effects on organised convection in a convection-permitting climate projection, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14475, https://doi.org/10.5194/egusphere-egu23-14475, 2023.

Floods related to heavy precipitation are common over Europe during both the warm and the cold seasons. In a way to better understand these heavy precipitation systems and their potential evolution in a warming climate, several studies investigated the dependency of precipitation extremes to temperature over Europe (e.g. Lenderink et al., 2008; Berg et al., 2013). It was found that the scaling of precipitation extremes can exceed the scaling expected from the Clausius-Clapeyron (CC) relationship, relating temperature to the water holding capacity of the atmosphere. While several potential explanations were proposed, a recent study (Lochbihler et al., 2017) noted the important role of large systems in determining this “super-CC” scaling over the Netherlands.

Building on this study, we further investigate the role of Mesoscale Convective Systems (MCS) in determining the temperature precipitation relationship over Europe. The detection and tracking of MCSs is based on the recent Integrated Multi-satellitE Retrievals for Global Precipitation Measurement (IMERG; Huffman et al., 2019) satellite precipitation climatology. We use the EUropean Cooperation for LIghtning Detection (EUCLID) lightning dataset to distinguish between stratiform (or shallow convective) and deep convective rain patches without introducing bias in precipitation intensity. We select the temperature upstream of the MCS tracks, as a proxy of the moisture source involved in the formation of MCS precipitation.

MCS can display strong dynamical features such as the rear inflow jet or cold pools, of which the effects on precipitation as well as their changes with temperature are still unclear. It suggests that MCS precipitation may deviate significantly from the CC scaling. Additionally, the processes involved in MCS precipitation may differ depending on the stage of the MCS life cycle. We thus characterize the temperature dependency of MCS precipitation and their 2-D structure at different stages of their life cycle. This work contributes to better understanding the drivers of MCS precipitation and how these may evolve in a warming climate.

References

Berg, P., Moseley, C., & Haerter, J. O. (2013). Strong increase in convective precipitation in response to higher temperatures. Nature Geoscience, 6(3), 181-185.

Huffman GJ, Stocker EF, Bolvin DT, Nelkin EJ, Tan J. 2019. GPM IMERG final precipitation L3 half hourly 0.1 degree x 0.1 degree V06, Greenbelt, MD, Goddard Earth Sciences Data and Information Services Center. doi: 10.5067/GPM/IMERG/3B-HH/06

Lenderink, G., & Van Meijgaard, E. (2008). Increase in hourly precipitation extremes beyond expectations from temperature changes. Nature Geoscience, 1(8), 511-514.

Lochbihler, K., Lenderink, G., & Siebesma, A. P. (2017). The spatial extent of rainfall events and its relation to precipitation scaling. Geophysical Research Letters, 44(16), 8629-8636.

How to cite: Da Silva, N. and Haerter, J.: Do Mesoscale Convective Systems precipitation follows the Clausius-Clapeyron relationship?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15734, https://doi.org/10.5194/egusphere-egu23-15734, 2023.

In this study we investigate the impact of several selected sources of uncertainty on convective precipitation prediction. For this purpose, we conduct numerical simulations with the ICOsahedral Non-hydrostatic (ICON) model for two consecutive days in June, 2021, on which deep moist convection triggered by different synoptic forcing occurred over southwestern Germany. We use single- and double-moment microphysics schemes and vary the initial soil moisture, grid spacing, and cloud condensation nuclei (CCN) concentration. We compare the results with measurements conducted on the same two days during the Swabian MOSES (Modular Observation Solutions for Earth Systems) field campaign. We find that the applied dry bias (initial soil moisture in the model reduced by 25%) much better represents the actual soil moisture conditions and leads to an improved quantitative precipitation forecast when compared to radar-derived precipitation amounts. Furthermore, the model resolution impacts the precipitation amount, intensity, and the timing of convection initiation: while 1-km runs show the least root mean square error for 24-hour precipitation sums, the onset of convective precipitation in 2-km resolution runs matches better the observations. However, the overall impact of this factor is not always systematic. The comparison of several radiosounding-derived convective indices (e.g. lifted index, convective available potential energy, convective inhibition) with model data yield many non-systematic results. For instance, CCN concentrations do not seem to have any significant impact on any of the calculated indices. At the same time, runs with coarser resolution (2-km) often better depict the temporal development of CAPE but overestimate its amount.

How to cite: Czajka, B., Barthlott, C., Kohler, M., Wieser, A., and Hoose, C.: Analysis of the impact of selected sources of uncertainty on precipitation simultaions of summer convection over Central Europe, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14661, https://doi.org/10.5194/egusphere-egu23-14661, 2023.

The predictability of deep moist convection is subject to large uncertainties, mainly due to inaccurate initial and boundary data, incomplete description of physical processes, or uncertainties in microphysical parameterizations. In this study, we present hindcasts of a supercell storm that occurred during the Swabian MOSES field campaign in southwestern Germany in summer 2021. The supercell storm of 23 June 2021 passed directly over the main observation site equipped with various instruments, allowing a detailed comparison of simulations and observations. The preconvective radiosonde observations revealed suitable conditions for supercell development, i.e., low convective inhibition, moderate convective available potential energy, sufficient deep-layer shear, and a Bulk Richardson number of 22. Numerical simulations were performed with the ICOsahedral Non-hydrostatic (ICON) model using two horizontal grid spacings (i.e., 2 km/1 km) with a single-moment and a double-moment microphysics scheme. The double-moment scheme allows us to study aerosol effects on clouds and precipitation with cloud condensation nuclei (CCN) concentrations ranging from low to very high. Numerical results show that all 2-km model realizations do not simulate convective precipitation at the correct location and time. For the 1-km grid spacing, changes in aerosol concentration resulted in large changes in convective precipitation, causing the supercell to disappear completely in some simulations. Only the 1-km model run, which assumes a clean environment, is able to realistically capture the supercell storm. During the Swabian MOSES field campaign, aerosol particle concentrations and size distributions were continuously measured with an optical particle counter from June to August 2021. The day of the supercell storm was characterized by the lowest potential CCN values of the month, suggesting that the low aerosol concentration in the successful model run is a reasonable assumption for this case study. Possible reasons for the discrepant model results, i.e., effects of grid spacing on convection initiation and detailed analyses of microphysical process rates, are discussed. These results demonstrate the benefits of using an aerosol-aware double-moment microphysics scheme at high model resolution for convection initiation and cloud evolution, and that the use of different CCN concentrations can determine whether a supercell is successfully simulated or not.

How to cite: Barthlott, C., Czajka, B., Kohler, M., Hoose, C., Kunz, M., Saathoff, H., and Zhang, H.: Grid spacing effects on convection initiation and aerosol-cloud interactions: A case study of a supercell storm from the Swabian MOSES 2021 field campaign, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6994, https://doi.org/10.5194/egusphere-egu23-6994, 2023.

 On the western coastal region of the Korean Peninsula in the winter, heavy snowfall occurs due to air mass modification which is called the western coast snowfall. The western coast snowfall occurs through a mechanism similar to the lake effect snowfall that is formed over the Great Lakes in the North America. In the winter season, cold and dry northwesterly wind blowing from the south-eastern flank of the Siberian High is formed over the Yellow Sea. The cold and dry air mass from the continent gets heat and moisture from the ocean when it passes over the relatively warm sea surface, , which invigorate snow clouds. The snow clouds generated over the ocean flow into the western coastal region by the westerly winds, hence predicting when the snow clouds flow into the land is important for snowfall forecast. Although the western coast snowfall can persist for several days when the synoptic environment is maintained, diurnal fluctuations in snowfall inflow appears during the snowfall cases. In this study, the diurnal variation of snowfall inflow on the western coastal region was investigated by analyzing of the dynamic/thermodynamic factors affecting the diurnal variation. The western coast snowfall shows snowfall inflow into the land in the evening, then inflow decreases after sunrise, with the snowfall becoming concentrated over the ocean, and the snowfall inflow increases after sunset. The diurnal variation of the snowfall inflow structure appears with the diurnal variation of the dynamic/thermodynamic structure according to the solar radiation diurnal cycle. During the evening, as the temperature of the lower troposphere over the land decreases due to radiative cooling, the lower troposphere thermal stability increases. After sunrise, the planetary boundary layer (PBL) height grows due to radiative heating, and the wind in the lower troposphere weakens, limiting the snowfall inflow to 9 LST, where both factors affect simultaneously. In addition, as the lower troposphere temperature over the land decreases, the land-sea horizontal temperature contrast increases, and the density wall of the colder land blocks the inflow of the snowfall. On the other hand, during the daytime, the lower troposphere temperature of the land rises due to radiative heating and the thermal stability decreases. As the horizontal temperature contrast decreases and the PBL height decreases after sunset, the lower troposphere wind becomes stronger, which allows the snowfall penetrates into the land. According to the time lag in heating/cooling by radiation of the lower troposphere, it is analyzed that the time point of snowfall inflow interruption (increasing) appears after sunrise (sunset).

Acknowledgement

This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government(MSIT) (No. 2021R1A4A1032646).

How to cite: Yoo, S., Chang, E.-C., and Lee, G.: A study on the diurnal variation of the snowfall structure in the western coastal region of the Korean Peninsula., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11509, https://doi.org/10.5194/egusphere-egu23-11509, 2023.