Displays

This presentation reports the findings of a multi-model pre-mission study in preparation for an airborne field campaign to investigate the upper troposphere and lower stratosphere (UTLS) composition under the influence of the Asian summer monsoon (ASM). The NSF/NASA supported airborne study is planned for the western Pacific atmosphere during July-August 2020 using a base in Okinawa, Japan. The pre-mission study uses three chemistry-transport models (i.e., NASA GSFC GEOS5, NCAR WACCM, and ECMWF CAMS) to investigate transport patterns and gas and aerosol chemical composition in the campaign region UTLS during the 2019 ASM period. In addition, artificial surface tracers from the WRF model helped identify the locations and evolution of rapid convective uplifting from regional sources. The impact of one typhoon occurrence during this 2019 ASM period will be discussed. Together, the multi-model results support the hypotheses of the ACCLIP campaign which identifies the western Pacific as a significant pathway for reactive chemical pollutants and climate relevant emissions from the ASM to enter the global UTLS.

How to cite: Kinnison, D., Liang, Q., Pan, L., Newman, P., Atlas, E., Toon, B., Randel, W., Bresch, J., Chin, M., Tilmes, S., Hodzic, A., Honomichl, S., Lait, L., Smith, R., Case, P., Saiz-Lopez, A., Jones, L., Barre, J., and Flemming, J.: Asian summer monsoon Chemical and Climate Impact Project (ACCLIP): Highlights of multi-model pre-mission study, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2778, https://doi.org/10.5194/egusphere-egu2020-2778, 2020.

During the StratoClim 2017 measurement campaign in Nepal, within the Asian Monsoon Anticyclone (AMA), measurements of the aerosols’ microphysical properties up to UT/LS altitudes were successfully completed with a modified version of the commercially available (Droplet Measurement Technologies Inc.) aerosol spectrometer UHSAS-A. Technical rearrangements of parts of the UHSAS-A were developed and implemented, which improve the instrument’s measuring performance and extend its airborne application range from around 12 km altitude to the extreme ambient conditions in the stratosphere at heights of 20 km. The measurement techniques used for this purpose were characterized by laboratory experiments.

Within the AMA region, extreme values of the particle mixing ratio (PMR) ranging between 6 mg^-1 and about 10000 mg^-1 were found with the UHSAS-A (particle diameter range: 65 nm to 1000 nm). The median of the PMR for all research flights was about 1300 mg^-1 close to the ground. Within tropospheric altitudes, the PMR was highly variable and median values between 70 mg^-1 and 400 mg^-1 were observed.  At levels of 370 K potential temperature, the median PMR maximally reaches about 700 mg^-1 while the 1 Hz resolved measurements show values up to about 10000 mg^-1. Between 450 K and 475 K, median PMR between 40 mg^-1 and 50 mg^-1 were observed. The aerosol size distributions (measured by the UHSAS-A) were extended by an additional diameter size bin obtained from the 4-channel Condensation Particle counting System (COPAS), i.e. for aerosol diameter between 10 nm and 65 nm.

The UHSAS-A measured aerosol particle size distributions were compared with balloon-borne measurements (by T. Deshler et al., Dep. of Atmospheric Science, University of Wyoming, USA) at altitudes of up to 20 km. These show that the size distributions measured during the StratoClim 2017 campaign fit well within the range of the balloon-borne measurements during the Asian Monsoon season over India (Hyderabad) in 2015 and the USA (Laramie) in 2013. Further analyses of measured particle size distributions by means of backscatter ratio show remarkable consistency with CALIOP satellite observations of the ATAL during the StratoClim mission period.

How to cite: Mahnke, C., Borrmann, S., Weigel, R., Cairo, F., Afchine, A., Krämer, M., Vernier, J.-P., and Deshler, T.: The ATAL and its aerosol microphysical properties in the Asian Monsoon Anticyclone, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6759, https://doi.org/10.5194/egusphere-egu2020-6759, 2020.

Strong convection within the Asian monsoon system quickly transports polluted air masses from the boundary layer into the upper troposphere where secondary aerosol formation can take place. Here we present remote sensing observations by infrared limb sounding systems providing vertical and horizontal distributions of ammonia (NH₃) and solid ammonium nitrate (AN) aerosol particles. Besides the identification of trace gases, characteristic signatures in the mid-infrared spectral region are used to infer information about composition and phase of the aerosol particles. We will show an analysis of AN and NH₃ in the Asian monsoon upper troposphere from a combination of two satellite limb sounders, CRISTA on SPAS in August 1997 and MIPAS on Envisat, from 2002-2011.

In addition, limb-imaging measurements obtained with the GLORIA instrument on board the Geophysica high-altitude aircraft provided the opportunity to obtain vertical cross sections along the flight path of AN aerosol mass and NH₃ volume mixing ratios during the Asian monsoon field campaign of the StratoClim project in summer 2017. We analysed the airborne dataset with the help of trajectory calculations combined with temporally and locally connected satellite data of nadir-pointing instruments, like IASI, to infer the distribution of NH₃ in the lower troposphere, as well as geostationary satellites to deduce the presence of convective influence.

Further, we performed experiments at the AIDA cloud and aerosol chamber laboratory (a) to support the analysis of the aerosol infrared spectral signature in remote sensing, (b) to investigate the conditions leading to the unexpected solid phase of AN particles as well as, (c) to study their potential to act as ice nucleating particles.

How to cite: Höpfner, M., Ungermann, J., Wagner, R., Spang, R., Riese, M., Stiller, G., Bucci, S., Friedl-Vallon, F., Johansson, S., Legras, B., Leisner, T., Möhler, O., Müller, R., Neubert, T., Orphal, J., Preusse, P., Rex, M., Saathoff, H., Stroh, F., and Wohltmann, I.: Solid ammonium nitrate aerosols: efficient ice nucleating particles in the upper troposphere during Asian monsoons investigated by aircraft, satellite and cloud-chamber, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7585, https://doi.org/10.5194/egusphere-egu2020-7585, 2020.

We use multiannual simulations with the chemistry-transport model CLaMS (Chemical Lagrangian Model of the Stratosphere) to analyze water vapour transport from the Asian monsoon region to the stratosphere. Further, we make comparisons of the transport characteristics from the Asian monsoon to the stratosphere with those of other source regions (e.g. from the tropics). In addition, we characterize the transport efficiency of the monsoon region compared to other source regions and bring our results into context with previous studies, which have focused on water vapour transport from the Asian monsoon to the stratosphere. These analyses are complementing the previously published work by Ploeger et al. (2017), who have analyzed mass transport from the Asian monsoon anticyclone to the stratosphere.

The presented findings have been recently published in Atmospheric Chemistry and Physics (Nützel et al., 2019).

References:

Ploeger, F., Konopka, P., Walker, K., and Riese, M.: Quantifying pollution transport from the Asian monsoon anticyclone into the lower stratosphere, Atmos. Chem. Phys., 17, 7055-7066, https://doi.org/10.5194/acp-17-7055-2017, 2017.

Nützel, M., Podglajen, A., Garny, H., and Ploeger, F.: Quantification of water vapour transport from the Asian monsoon to the stratosphere, Atmos. Chem. Phys., 19, 8947–8966, https://doi.org/10.5194/acp-19-8947-2019, 2019.

How to cite: Nützel, M., Podglajen, A., Garny, H., and Ploeger, F.: Quantification of water vapour transport from the Asian monsoon to the stratosphere , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9165, https://doi.org/10.5194/egusphere-egu2020-9165, 2020.

The Asian Tropopause Aerosol Layer (ATAL) has been found to be an aerosol layer with exceptionally high particle number concentrations in the UT/LS altitude range. During the StratoClim 2017 field campaign in Nepal we deployed the novel in-situ aerosol mass spectrometer ERICA (ERC Instrument for Chemical composition of Aerosols). It combines the methods of laser ablation mass spectrometry with flash vaporization/electron impact ionisation mass spectrometry in a single instrument to analyse the chemical composition of individual aerosol particles or small particle ensembles in the particle diameter range from 100 nm to 2 µm.

The quantitative analysis shows a strong contribution of ammonium nitrate (AN) to the ATAL aerosol concentration. In this layer, the AN concentrations can be as high as 1.5 µg per standard cubic meter. We present the vertical distribution of the mass concentrations of AN as well as other contributing species like sulphate and organics.

The single particle data from the laser ablation module of ERICA show a distinct particle type with nitrate and sulphate ions without the typical components of primary aerosol (soot, dust, metals) within the ATAL, indicating that a significant fraction of the ATAL aerosol consists of secondary particles formed in the upper troposphere.

How to cite: Appel, O., Hünig, A., Dragoneas, A., Molleker, S., Drewnick, F., and Borrmann, S.: Chemical composition of the ATAL aerosol measured by in-situ particle mass spectrometry, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9949, https://doi.org/10.5194/egusphere-egu2020-9949, 2020.

South Asia is one of the most heavily populated regions in the world with about 1.7 billion inhabitants. The diversity of human activities in the region make delineating the sources and magnitude of regional emissions complex. The major combustion sources in South Asia – predominantly anthropogenic – include wildfires and the burning of agricultural residues, garbage, biofuels, and fossil fuels. But regional aerosol loading is also heavily influenced by natural aerosols, primarily dust transported from as far as the Arabian Peninsula. Past studies have examined how irrigation expansion along with greenhouse gas (GHG) forcing have altered the surface energy budget, thereby affecting the transport of water vapor and altering South Asian Summer Monsoon (SASM) rainfall variability. However, there are still limited modelling studies that consider anthropogenic effects from anthropogenic aerosol loading in combination with irrigation and GHGs and how these factors collectively induce variability in the SASM. Using the NASA GISS-E2.1 model, this study elucidates the role of intensive agricultural activities on SASM, both at the onset of the Green Revolution (i.e., 1960s) and at present, isolating the individual roles of irrigation, anthropogenic aerosols, and GHGs. Specifically, we examine the impacts on SASM by using sensitivity runs to quantify how anthropogenic emissions from agriculture, urbanization as well as long- and short-term forcers have affected SASM from 1960-2014 using prescribed- and coupled-ocean runs. Understanding the roles of each of these influences on SASM can help to develop more effective climate interventions in the region and predict how SASM will influence and interact with the changing regional and global climate.

How to cite: Dhungel, S., Tsigaridis, K., and Bauer, S.: The Influences of Climate Forcers and Agricultural Activities on the South Asian Summer Monsoon, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11847, https://doi.org/10.5194/egusphere-egu2020-11847, 2020.

In-cloud aqueous-phase chemistry is known to decrease tropospheric ozone (O₃) via O₃+O₂^- with the major source of O₂^- being hydroperoxyl radicals (HO₂). Therefore, tropospheric O₃ is sensitive to aqueous-phase HO_x (HO_x=HO₂+OH) chemistry. However, most global atmospheric models do not represent this sink reasonably well since they lack explicit representation of in-cloud aqueous-phase chemistry. In this study, a new detailed aqueous-phase mechanism for the oxidation of water soluble oxygenated volatile organic compounds (OVOCs) is developed, suitable for global scale modelling. This improves the representation of aqueous-phase HO₂ and thus the removal of tropospheric O₃. The mechanism focuses on OVOCs containing up to three-carbon atoms. A detailed box-model analysis under low and high NO_x conditions is performed. Afterwards, the developed mechanism is implemented into the global atmospheric model ECHAM/MESSy (EMAC), which is capable to represent the described processes explicitly and integrates the corresponding ODE system with a Rosenbrock solver. EMAC is then used to estimate the global impact of the proposed mechanism with a focus on monsoon systems and biomass burning events. The implemented changes are evaluated using airborne campaign data like OMO for the Asian monsoon. The OVOC oxidation leads to an increase in ozone scavenging and a substantial reduction in tropospheric gas-phase chemical production of ozone. These changes in the free troposphere significantly reduce the modelled tropospheric ozone column, which is known to be overestimated by EMAC and global atmospheric models in general.

How to cite: Rosanka, S. and Taraborrelli, D.: Impact of in-cloud OVOC chemistry on tropospheric ozone, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10483, https://doi.org/10.5194/egusphere-egu2020-10483, 2020.

The Asian monsoon anticyclone is an important transport pathway for water vapor entering the global stratosphere. We use pentad-resolution gridded data from Aura Microwave Limb Sounder (MLS) satellite observations and CLaMS transport model simulations based on two atmospheric reanalyses to examine variations of water vapor in the lower stratosphere (100-68hPa) above the Asian summer monsoon during the warm seasons (May-September) of 2005 through 2017. Model outputs have been post-processed to facilitate direct comparison with MLS retrievals. A localized water vapor maximum is present in the upper troposphere and lower stratosphere above the Asian summer monsoon, with substantial interannual and intraseasonal variability superimposed on the mean seasonal cycle. The CLaMS simulations largely capture both the climatological distribution and variability of lower stratospheric water vapor but with a systematic moist bias, sharper spatial gradients, and larger variance in time relative to MLS. Applying principal component analysis to both vertical and horizontal variability of deseasonalized anomalies within this layer, we identify and describe the three leading modes of variability in lower stratospheric water vapor. The leading mode features regional-scale moistening or drying, with anomalies taking the same sign throughout the layer. Notably, cold point temperature anomalies are in phase with water vapor anomalies in the western part of the domain but out of phase in the eastern part of the domain, where the largest water vapor anomalies are located. The moist phase of this mode is also associated with systematically deeper convection through much of the monsoon domain. The second mode features a vertical dipole, with wet anomalies at 100 hPa (centered over the Persian Gulf but stretching across most of the domain) coupled with dry anomalies at 68 hPa and vice versa. This mode is linked to large anomalies in cold point temperature that span the southern part of the monsoon domain, with the moist phase at 100 hPa associated with warmer cold point temperatures. Warmer temperatures lead to negative anomalies in radiative heating in the lower stratosphere, which may in turn explain the dry anomalies at 68 hPa. The third mode features a horizontal dipole oriented east-to-west, with a deep layer of enhanced water vapor centered over the southeastern Tibetan Plateau coupled with dry anomalies in the west and vice versa. The moist phase of this mode is associated with more extensive cloud cover and deeper convection stretching across China from the eastern Tibetan Plateau. Cold point temperatures are colder and the upper-level monsoon anticyclone stronger in the eastern part of the domain, with opposing anomalies in the west. CLaMS is largely able to reproduce the first and third modes, but fails to capture the second mode and overemphasizes the importance of the third mode. Meanwhile, the monsoon season of 2017 emerges as a special case, with persistent large positive anomalies in lower stratospheric water vapor that are reproduced when CLaMS is driven using ERA-Interim but not when it is driven by MERRA-2. We discuss some possible explanations for these differences.

How to cite: Chen, J., Wright, J., Yan, X., and Konopka, P.: Water vapor variability in the Asian summer monsoon lower stratosphere from satellite observations and transport model simulations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21617, https://doi.org/10.5194/egusphere-egu2020-21617, 2020.

The variability of boreal spring Hadley circulation (HC) over the Asian monsoon domain over the last four decades is explored. The climatological distribution of the regional HC is symmetric of the equator, with the ascending branch around the equator and sinking branch around the subtropics in each hemisphere. The first dominant mode (EOF1) of the regional HC is equatorial asymmetric, with the main body in the Southern Hemisphere (SH) and the ascending branch to the north of the equator. This mode is mainly characterized by interannual variation and is related to El Niño-Southern Oscillation (ENSO). Significant negative sea surface temperature (SST) anomalies are observed over the tropical Indian Ocean (TIO) along with the development of La Niña events; however, the magnitude of SST anomalies in the southern Indian Ocean is greater than that in the northern counterpart, contributing to EOF1 formation. The spatial distribution of the second dominant mode (EOF2) is with the main body lying in the Northern Hemisphere (NH) and the ascending branch located to the south of the equator. The temporal variation of this mode is connected to the warming of the TIO. The warming rate of the southern TIO SST is faster than that in the northern counterpart, resulting in the southward migration of the rising branch. The above result indicates the critical role of the meridional distribution of SST on the variability of the regional HC.

How to cite: Wang, Y., Feng, J., Li, J., An, R., and Wang, L.: Variability of boreal spring Hadley circulation over the Asian monsoon domain and its relationship with tropical SST, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1389, https://doi.org/10.5194/egusphere-egu2020-1389, 2020.

Results from a transient 28 year simulation with the chemistry climate model EMAC with interactive modal aerosol scheme nudged to observed tropospheric meteorology (ERA-Interim) which includes about 500 volcanic SO₂ injections are compared with in situ aircraft observations in the UT/LS in the Asian Monsoon anticyclone. Enhanced SO₂ observed by STRATOMAS and enhanced sulfate aerosol observed by ERICA in the LS point to impact of several explosive eruptions of the Indonesian volcano Sinabung during summer 2017 seen by the OSIRIS satellite instrument. This is supported by freshly nucleated particles observed by COPAS in the UTLS. We present several sensitivity studies with EMAC with different assumptions on the injection patterns in comparison to the observations in July/August 2017.  
The monsoon dynamics distributes the volcanic material together with Asian pollution into the global lower stratosphere.

How to cite: Brühl, C., Schlager, H., Weigel, R., Appel, O., Borrmann, S., Lelieveld, J., and Schallock, J.: Volcanic influence on STRATOCLIM aircraft observations 2017 in the Asian Monsoon, studies with the transient CCM EMAC, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3958, https://doi.org/10.5194/egusphere-egu2020-3958, 2020.

We investigated the physical mechanism for late Indian Summer Monsoon onset over Kerala
(MOK). 14 early and 9 late onset years are selected based on the criteria when the onset is 5 days or
more prior and after normal onset date (i.e 1 st June according to India Meteorological Department)
respectively. Then, we perform composite analyses of mean May monthly and daily evolution during
early and late onset years to examine the differences in monsoon circulation features prior to the MOK.
We find that advection of Surface Air Temperature (SAT) from the northern to the southern China and
the eastern Tibetan Plateau (TP) plays an important role to modulate the MOK processes. In the late
onset years, more low-level jet (LLJ) from the Bay of Bengal (BOB) divert towards the east Asia before
the onset, which is due to an extension of the low sea level pressure and high SAT over the east Asia
(eastern TP, east-central China). This strengthens the low-level convergence and upper level divergence
over the eastern TP and southern China. As a result, a significant amount of moisture from the BOB
is transported towards the eastern TP and southern China. Thereby, a comparatively weaker LLJ and
deficit low-level moisture supply over the eastern BOB maintain the key roles in modulating the MOK
processes.

How to cite: Choudhury, D., Nath, D., and Chen, W.: The role of surface air temperature over the east Asia on the early and late Indian Summer Monsoon Onset over Kerala, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3820, https://doi.org/10.5194/egusphere-egu2020-3820, 2020.

Black carbon aerosol (BC) has a significant influence on regional climate changes due to its warming effect. Such changes will feedback to BC loadings. Here, the interactions between the BC warming effect and East Asian monsoon (EAM) in both winter (EAWM) and summer (EASM) are investigated using a regional climate model RegCM4, which essentially captures the EAM features and the BC variations in China. The seasonal mean BC optical depth is 0.021 over East Asia during winter, which is 10.5% higher than that during summer. Nevertheless, the BCs direct radiative forcing is 32% stronger during summer (+1.85 W/m²). The BC direct effect would induce lower air to warm by 0.11-0.12 K, which causes an meridional circulation anomaly associated with a cyclone at 20-30 ^oN and southerly anomalies at 850 hPa over East Asia. Consequently, the EAM circulation is weakened during winter but enhanced during summer. Precipitation is likely increased, especially in south China during summer (by 3.73%). Compared to BC changes due to EAM interannual variations, BC changes due to its warming effect are as important, but weaker. BC surface concentrations are decreased by 1~3% during both winter and summer, by 1~3%, while the columnar BC is increased in south China during winter. During the strongest monsoon years, the BC loadings are higher at lower latitudes than those during the weakest years, resulting in more southerly meridional circulation anomalies and BC feedbacks during both winter and summer. However, the interactions between the BC warming effect and EAWM/EASM are more intense during the weakest monsoon years.

How to cite: Zhuang, B., Wang, T., Li, S., Xie, M., Li, M., Chen, H., Wei, W., and Lin, H.: Interaction between the Black Carbon Aerosol Warming Effect and East Asian Monsoon, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6459, https://doi.org/10.5194/egusphere-egu2020-6459, 2020.

The StratoClim stratospheric aircraft campaign, taking place in summer over the Nepalese region, provided a wide dataset of observations of air composition inside the Asian Monsoon Anticyclone (AMA). To improve the understanding of the role of penetrating overshoot in the AMA region, we exploit the TRACZILLA Lagrangian simulations, computed on meteorological fields from ECMWF (ERA-Interim and ERA5) at 3h and 1h resolution and using both kinematic and diabatic vertical velocity approaches. The synergy with high-resolution observations of convective cloud top from the MSG1 and Himawari geostationary satellites is used to individuate the convective sources.

To evaluate the capability of the trajectory system to reproduce the transport in the UTLS we compare the simulations with the observed trace gases concentration. The ERA5 simulations appear to provide a higher consistency with observed data than ERA-Interim and show a better agreement between the diabatic and kinematic results. The best performance is given by the ERA5 with diabatic transport and, adopting this setting, we analyze the transport condition during the 8 flights of the campaign.

The aircraft sampled different convective plumes, often carrying pollutant compounds up to the UTLS level. The highest observed concentration of trace gases had been linked to fresh convective air (younger than a few days) coming from China, Pakistan and the North Indian region.

A vertical stratification is observed in the age of air: up to 15 km, the age of air is less than 3 days and these fresh air masses make up nearly the entire totality of the air composition. Above, a transition layer is identified between 15 km and 17 km (close to the tropopause), where the convective influence is still dominant and the ages range from one week to two. Finally, above this layer, the convective influence rapidly decreases toward zero and the mean air age increase to 20 days and more.

This study quantifies the contribution of direct injection of deep convection on the UTLS composition based on the aircraft measurements. Preliminary results of the upscale analysis based on the trajectories-satellites system will also be presented.

How to cite: Bucci, S., Legras, B., Sellitto, P., D'Amato, F., Viciani, S., Montori, A., Chiarugi, A., Ravegnani, F., Ulanovsky, A., Cairo, F., and Stroh, F.: Deep convective influence on the UTLS composition in the Asian Monsoon Anticyclone region: 2017 StratoClim campaign results, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10709, https://doi.org/10.5194/egusphere-egu2020-10709, 2020.

We investigate the radiative impacts of convectively detrained and in-situ formed ice crystals at uppermost altitudes with high-resolution ICON model runs in the Asian monsoon region. Radiatively, this area should be characterized by persistent longwave warming from thin and ubiquitous anvils and intermittent shortwave cooling from deep but infrequent convective systems. But how do different degrees of sophistication in the ice microphysics schemes modulate this picture? Three days coinciding with the StratoClim field campaign are simulated (6-9 August 2017), using two-moment microphysics, and in-situ ice water content (IWC) values and specific humidity profiles are used for validation. We calculate the shortwave and longwave radiative fluxes associated with IWC between 14 and 17 km over different timescales and examine the role of ambient dryness in anvil base radiative heating. We compare our results with the cloud-resolving Meso-NH simulation of Lee et al. ACP 2019 in which moist and ice layers were identified and tracked through the uppermost troposphere.

How to cite: Sullivan, S., Voigt, A., Krämer, M., Miltenberger, A., Khaykin, S., and Rolf, C.: Radiative impacts of convective anvil outflow in the Asian monsoon region, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11055, https://doi.org/10.5194/egusphere-egu2020-11055, 2020.

We study the confinement of the air inside the Asian monsoon anticyclone during summer using both kinematic and diabatic Lagrangian trajectories with ERA5 and ERA-Interim reanalysis, and observed clouds. The improved consistency of ERA5 is demonstrated. It is shown that the escape time from the anticyclone estimated to be 13 days is of the same order as the circulation time which implies weak confinement. Parcels found inside the anticyclone have been mostly detrained by convection above θ =364 K, by about 2.6%  of the high clouds over Asia, with a prevalence of continental sources which are located beneath. The Tibetan plateau is found to be the most efficient provider with 10% of its high clouds but this is entirely due to the higher level of cloud tops in this region, and not to any preferred path above.  Actually,  most parcels escape the plateau to rise. The mean trapping is shown to be described by a 1D model that combines a simple mean ascent and a constant erosion loss, without any need of a “chimney effect”. The vertical dilution is exponential with a e-folding scale of 15 K in potential temperature from 370 K onward. The mean age of parcels with respect to convection exhibits a minimum at the centre of the Asian monsoon anticyclone due to the permanent renewal by fresh convective air and largest values on the periphery as air spirals out.

The variability of the the confinement is strongly linked with the oscillations of the anticyclone between its Tibetan mode and its Iranian mode, and to break and active periods of monsoon rain. We show that this variability modulates also the moisture in the lower stratosphere with wet events following active convection and dry events following the breaks.

How to cite: Legras, B., Bucci, S., Chandra, S., and Kottayil, A.: Confinement of air in the Asian monsoon anticyclone and pathways of convective air to the stratosphere during summer season, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10170, https://doi.org/10.5194/egusphere-egu2020-10170, 2020.

The relation between the seesaw mode of the Interface between the Indian summer monsoon and East Asian summer monsoon (IIE) and the South China Sea summer monsoon trough (SCSSMT) and the Indian summer monsoon trough (ISMT) is investigated using two atmospheric reanalyses together with outgoing longwave radiation, sea surface temperature (SST), and gridded precipitation datasets. Canonical correlation analysis combined with empirical orthogonal functions, correlation, and composite analysis are employed. Results indicate that a stronger ISMT and SCSSMT resulting from colder SST over the tropical Indian Ocean and tropical east-central Pacific cause the IIE to deviate from its normal position in an anticlockwise direction, with a node at around 22°N. This leads to heavier than normal summer rainfall over the north-central Indian subcontinent and South China Sea, but weaker than normal from the low and middle reaches of the Yangtze River and South Korea to central Japan. A weaker ISMT and SCSSMT resulting from warmer SST over the tropical Indian Ocean and tropical east-central Pacific causes the IIE to deviate from its normal position in a clockwise direction, and the anomalous summer rainfall pattern is the opposite of that for the stronger troughs. Further analysis indicates that the SCSSMT plays a crucial role in the evolution of the IIE seesaw mode. The latitudinal difference between the IMST and SCSSMT may be one of the most important reasons for the formation of the IIE seesaw mode.

How to cite: Yang, R. W. and Wang, J.: Interannual variability of the seesaw mode of the interface between the Indian and East Asian summer monsoons, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21020, https://doi.org/10.5194/egusphere-egu2020-21020, 2020.

We will present trace gas measurements obtained by the airborne imaging limb sounder GLORIA (Gimballed Limb Observer for Radiance Imaging of the Atmosphere) instrument that has been operated on the Geophysica research aircraft in area of the Indian subcontinent with basis in Kathmandu, Nepal during the StratoClim campaign in July/August 2017.
We will show retrievals of two-dimensional trace-gas distributions derived from GLORIA observations in the UTLS (Upper Troposphere Lower Stratosphere) region during the Asian monsoon. Targeted gases are, amongst others, O₃, HNO₃, PAN, C₂H₂, and HCOOH. We will present an analysis of retrieval performance including diagnostics of spatial resolution and an estimated error budget.
In our contribution, we compare these GLORIA measurements with results of the atmospheric models EMAC (ECHAM/MESSy Atmospheric Chemistry) and CAMS (Copernicus Atmosphere Monitoring Service) reanalysis and discuss the influence of non-methane volatile organic compound emissions by sensitivity simulations with the EMAC model. Using trajectories from the models ATLAS and TRACZILLA, measured pollution trace gas plumes are connected to possible sources of origin. Due to the high convective activity in the region of the Asian monsoon, both trajectory sets consider vertical transport by convection, however in a different manner.
We show that there are very delicate structures of pollutant trace gases in the Asian monsoon UTLS, and that atmospheric models have difficulties in reproducing these structures, which is likely to be caused by insufficient vertical transport from convection in meteorological fields or by missing sources in the emission inventories used by the models.

How to cite: Johansson, S., Höpfner, M., Friedl-Vallon, F., Ungermann, J., Kirner, O., Bucci, S., Legras, B., Wohltmann, I., Wetzel, G., Glatthor, N., and Kretschmer, E.: Pollution trace gas distributions in the Asian monsoon UTLS derived from measurements of the airborne imaging limb sounder GLORIA during the StratoClim campaign, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6606, https://doi.org/10.5194/egusphere-egu2020-6606, 2020.

While the monsoon onset is recognized as a rapid, substantial, and sustained increase in rainfall over large parts of south Asia, the withdrawal marks the return to dry conditions. Normally, the south Asian summer monsoon onset occurs around 1^st June over extreme south of peninsular India, which gradually advances to extreme northwest of India by around 15^th July. The withdrawal starts from northwest India from around 1st September and from extreme south peninsular India by around 30th September. The determinations of the onset and withdrawal dates of monsoon have great economic significance for this region as they influence many agriculture and water resource management decisions in one of the most highly populated regions of the world. Several studies involving global model simulations have shown that changing aerosol emissions could result in significant changes in the seasonal mean precipitation distribution over India. A few studies also show that presence of absorbing aerosols in the foothills of Himalayas and over the Tibetan plateau could increase the moisture convergence over India thereby causing an advancement and intensification of the monsoon precipitation. However, most of the previous studies, which investigated the impact of anthropogenic emissions on the monsoon, are limited to understanding the impact of various emission changes on the seasonal mean monsoon characteristics. In the present study, we try to understand the sensitivity of the onset and withdrawal period of the south Asian summer monsoon system to changes in anthropogenic emissions using a climate model (CESM1.2). We diagnose the onset and withdrawal of the south Asian monsoon by analyzing the variability in vertically integrated moisture transport (VIMT) over the south Asian region and following the definition of hydrologic onset and withdrawal index (HOWI) defined by Fasullo et al. (2002). We examined the effect of changing emissions anthropogenic aerosol, greenhouse gases and both on the onset and withdrawal of the south Asian summer monsoon system. Our preliminary results suggest that increases in the emissions of aerosols and greenhouse gases from anthropogenic sources from pre-industrial to present day could possibly result in significant delay in the onset and advancement in withdrawal of the south Asian summer monsoon system thereby shortening the length of the monsoon season. More results with greater detail will be presented.

How to cite: Mishra, S., Ganguly, D., and Sharma, P.: Investigating the sensitivity of the onset and withdrawal of the south Asian summer monsoon system to changes in anthropogenic emissions using a climate model, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-14786, https://doi.org/10.5194/egusphere-egu2020-14786, 2020.

The StratoClim aircraft field campaign took place from Kathmandu, Nepal, in summer 2017 in
order to study the atmospheric composition, chemistry, and dynamics in the Asian Summer
Monsoon Anticyclone (ASMA) which is known to transport surface emissions to the mid-latitude
lower stratosphere and the stratosphere worldwide. Hydrogen cyanide (HCN) which is primarily
emitted from biomass burning and has a UTLS lifetime on the order of 1-2 years is a good tracer for
biomass burning import into the lower and free stratosphere.
HCN in the ASM Upper Troposphere and Lower Stratosphere (UTLS) was measured in-situ
employing the Chemical-Ionization Time-of-Flight Mass Spectrometer FUNMASS on board the
high-altitude research aircraft M55-Geophysica. The observed HCN mixing ratios in and above the
ASMA exhibit interesting vertical and horizontal signatures around the tropopause as well as in the
LS probably resulting from convective activity or air mass origin (AMO). We here compare
measured HCN to Lagrangian simulations by the ClaMS and TRACZILLA models which employ
two different approaches to represent higher-reaching convective events. The simulations succeed to
track some of the observed HCN features back to convective activity or AMO. The quality of the
reproduction and further outcomes on the atmospheric relevance will be discussed in the
presentation.

How to cite: Li, Y., Vogel, B., Plöger, F., Bucci, S., Legras, B., Viciani, S., D'Amato, F., and Stroh, F.: Results from a comparison of HCN measurements and Lagrangian backtrajectory analyses in the Asian Summer Monsoon Anticyclone, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19263, https://doi.org/10.5194/egusphere-egu2020-19263, 2020.