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Preprints
https://doi.org/10.5194/acp-2020-581
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2020-581
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 23 Jun 2020

Submitted as: research article | 23 Jun 2020

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This preprint is currently under review for the journal ACP.

Convective uplift of pollution from the Sichuan basin into the Asian monsoon anticyclone during the StratoClim aircraft campaign

Keun-Ok Lee1, Brice Barret1, Eric L. Flochmoën1, Pierre Tulet2, Silvia Bucci3, Marc von Hobe4, Corinna Kloss4,5, Bernard Legras3, Maud Leriche1,8, Bastien Sauvage1, Fabrizio Ravegnani6, and Alexey Ulanovsky7 Keun-Ok Lee et al.
  • 1Laboratoire d'Aérologie, Université de Toulouse, CNRS, UPS, Toulouse, France
  • 2Laboratoire de l'Atmosphère et des Cyclones, UMR8105, CNRS, Météo-France, Université de la Réunion, Saint-Denis de La Réunion, France
  • 3Laboratoire de Météorologie Dynamique, UMR CNRS 8539, IPSL ENS-PSL/Sorbonne Université/Ecole Polytechnique/Ecole des Ponts Paris Tech, Paris, France
  • 4Institute for Energy and Climate Research (IEK-7), Forschungszentrum Jülich GmbH, 52425 Jülich, Germany
  • 5LPC2E, CNRS/Université d'Orléans, France
  • 6Institute for Atmospheric Sciences and Climate of the National Research Council (CNR-ISAC), Bologna, Italy
  • 7Central Aerological Observatory (CAO), Moscow, Russia
  • 8Centre pour l'étude et la simulation du climat à l'échelle régionale, Université du Québec à Montréal, Montréal, Canada

Abstract. The StratoClim airborne campaign took place in Nepal from 27 July to 10 August 2017 to document the physical and chemical properties of the South Asian Upper Troposphere Lower Stratosphere (UTLS) during the Asian Summer Monsoon (ASM). In the present paper, simulations with the Meso-NH cloud-chemistry model at a horizontal resolution of 15 km are performed over the Asian region to characterize the impact of monsoon deep convection on the composition of Asian Monsoon Anticyclone (AMA) and on the formation of the Asian Tropopause Aerosol Layer (ATAL) during the StratoClim campaign. StratoClim took place during a break phase of the monsoon with an intense convective activity over south China and Sichuan. Comparisons between Brightness Temperature (BT) at 10.8 microns observed by satellite sensors and simulated by Meso-NH highlight the ability of the model to correctly reproduce the life cycle of deep convective clouds. Comparison between CO and O3 concentrations from Meso-NH and airborne observations (StratoClim and IAGOS) demonstrates that the model captures most of the observed variabilities. Nevertheless, for both gases, the model tends to overestimate the concentrations and misses some thin CO plumes related to local convective events probably because of a too coarse resolution, but the convective uplift of pollution is very well captured by the model. We have therefore focused on the impact of Sichuan convection on the AMA composition. A dedicated sensitivity simulation showed that the 7 August convective event brought large amounts of CO deep into the AMA and even across the 380 K isentropic level located at 17.8 km. This Sichuan contribution enhanced the CO concentration by ~ 15 % to reach more than 180 ppbv over a large area around 15 km height. Noteworthy, Meso-NH captures the impact of the diluted Sichuan plume on the CO concentration during a StratoClim flight south of Kathmandu highlighting its ability to reproduce the transport pathway of Sichuan pollution. According to the model, primary organic aerosol and black carbon particles originating from Sichuan are transported following the same pathway as CO. The large particles are heavily scavenged within the precipitating part of the convective clouds but remain the most important contributor to the particle mass in the AMA. Over the whole AMA region, the 7 August convective event resulted in a 0.5 % increase of CO over the 10–20 km range that lasted about 2 days. The impact of pollution uplift from three regions (India, China and Sichuan) averaged over the first 10 days of August has also been evaluated with sensitivity simulations. Even during this monsoon break phase, the results confirm the predominant role of India relative to China with respective contributions of 11 and 7 % to CO in the 10–15 km layer. Moreover, during this period a large part (35 %) of the Chinese contribution comes from the Sichuan basin alone.

Keun-Ok Lee et al.

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Short summary
In the present paper, simulations with the Meso-NH cloud-chemistry model at a horizontal resolution of 15 km are performed over the Asian region to characterize the impact of monsoon deep convection on the composition of Asian Monsoon Anticyclone (AMA) and on the formation of the Asian Tropopause Aerosol Layer (ATAL) during the StratoClim campaign.
In the present paper, simulations with the Meso-NH cloud-chemistry model at a horizontal...
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