The Asian summer monsoon influences global climate

About

The Asian summer monsoon transports ground-level air pollution into the upper troposphere and lower stratosphere and thereby influences the climate worldwide. We investigate the global impact of the Asian summer monsoon by combining innovative aircraft and satellite observations with process-oriented model simulations.

The most densely populated regions of the world and important source regions of air pollution and greenhouse gases are located in the area of the Asian summer monsoon. The monsoon season in Asia is characterized by strong convection over South Asia, which on the one hand leads to heavy rainfall, but also to the transport of anthropogenic greenhouse gases and air pollutants from ground-levels to altitudes of around 14-15 km (upper troposphere and lower stratosphere) within a few hours. In the altitude range of about 14 to 18 km, the Asian monsoon forms a high-pressure area that exists for about 3 months (~June to August) and extends in the form of an anticyclonic circulation system (clockwise rotation) from East Africa to the Pacific over the whole of South Asia. The polluted air is largely isolated from the surrounding air in this large-scale circulation system and can therefore be slowly transported to higher altitudes and then distributed further globally in the atmosphere.

The Asian summer monsoon is an important transport pathway for trace gases and particles that influence the radiative balance of the atmosphere, such as anthropogenic (CO2, CH4, N2O) and natural (e.g. water vapour) greenhouse gases, aerosol precursors (e.g. NH3) and aerosol particles. However, the transport of short-lived ozone-depleting trace gases (e.g. chlorine- or bromine-containing trace gases) into the extratropical upper troposphere and lower stratosphere also changes the chemical composition in this part of the Earth's atmosphere. Quantifying this change and its impact on the surface climate is an essential goal to assess the impact of the Asian summer monsoon on global climate. ICE-4 scientists led several aircraft campaigns to measure the air within the Asian monsoon anticyclone and its transport to northern mid-latitudes (e.g. to Europe). Innovative observations of the atmosphere on airplanes, balloons and satellites will be combined at ICE-4 with process-oriented model simulations to better understand the influence of the Asian summer monsoon on the global climate.

Research Topics

Unique aircraft observations over the North Indian subcontinent during the Asian summer monsoon in 2017 provide measurements of trace gases and aerosols at an unprecedented temporal and vertical resolution over an altitude range from the ground up to about 20 km. The evaluation of a series of remote sensing and in-situ measurements of aerosol particles indicate a strong contribution of solid ammonium nitrate particles to the aerosol layer at tropopause heights in the area of the Asian summer monsoon (Höpfner et al., 2019). Measurements of trace gases show a steady decrease in carbon monoxide (CO) and an increase in ozone (O3) up to 20 km altitude in the Asian monsoon region without showing strong discontinuities, i.e. no vertical transport barriers were found (von Hobe et al., 2021). Another important result concerns the insufficiently quantified CO2 sources in South Asia, which strongly contribute to the acceleration of the global CO2 increase. The measured CO2 profiles are successfully reconstructed by Lagrangian model simulations, which leads to a previously impossible explanation of the vertical structure of the greenhouse gas CO2 in the monsoon region and to a better source attribution (Vogel et al., 2023).

Increased quantities of short-lived ozone-depleting trace gases (e.g. CH2Cl2 ) have been observed in the Asian monsoon region and their transport to the northern latitudes has been demonstrated (Lauther et al., 2021). This transport could lead to a reduction in the stratospheric ozone layer. A highlight of recent ICE-4 activities is the PHILEAS aircraft measurement campaign in Alaska and Oberpfaffenhofen in the summer of 2023, during which the western part of the Asian monsoon anticyclone over the eastern Mediterranean and eddies over the Pacific, which contain an increased amount of short-lived ozone-depleting substances, aerosol particels and other pollutants, were investigated (Riese et al., 2024).

The scientific advances regarding the transport of ammonium nitrate, CO2 as well as ozone-depleting trace gases from the Asian monsoon into the global atmosphere may help to develop regulations of anthropogenic emissions of pollutants in Asia and may therefore have implications for policy measures.

Contact

Dr. Bärbel Vogel

ICE-4

Building 05.8 / Room 3003

+49 2461/61-6221

E-Mail
Latitudinal cross-section at about 90° E. The upward transport of air masses from the Asian monsoon region occurs in three distinct steps: First, very rapid uplift within the convective region to ∼ 360K (~9-10km) within the Asian monsoon anticyclone (within a few days); second, uplift above 360 K (to ∼ 20km) within the monsoon anticyclone (within a few months); and third, transport to heights above 460 K associated with the large-scale Brewer-Dobson circulation (within ∼ 1 year). The altitude coordinate shown here is potential temperature (400K ~ 17.5km); the thermal tropopause (black dots) and horizontal winds (black lines) are marked (adapted from Vogel et al., ACP, 2019).

Selection of ICE-4 publications

  • Höpfner, M., Ungermann, J., Borrmann, S., Wagner, R., Spang, R., Riese, M., Stiller, G., Appel, O., Batenburg, A. M., Bucci, S., Cairo, F., Dragoneas, A., Friedl-Vallon, F., Hünig, A., Johansson, S., Krasauskas, L., Legras, B., Leisner, T., Mahnke, C., Möhler, O., Molleker, S., Müller, R., Neubert, T., Orphal, J., Preusse, P., Rex, M., Saathoff, H., Stroh, F., Weigel, R., and Wohltmann, I.: Ammonium nitrate particles formed in upper troposphere from ground ammonia sources during Asian monsoons, Nature Geoscience, 12, 608–612, https://doi.org/10.1038/s41561-019-0385-8, 2019.
  • von Hobe, M., Ploeger, F., Konopka, P., Kloss, C., Ulanowski, A., Yushkov, V., Ravegnani, F., Volk, C. M., Pan, L. L., Honomichl, S. B., Tilmes, S., Kinnison, D. E., Garcia, R. R., and Wright, J. S.: Upward transport into and within the Asian monsoon anticyclone as inferred from StratoClim trace gas observations, Atmos. Chem. Phys., 21, 1267–1285, https://doi.org/10.5194/acp-21-1267-2021, 2021.
  • Lauther, V., Vogel, B., Wintel, J., Rau, A., Hoor, P., Bense, V., Müller, R., and Volk, C. M.: In situ observations of CH2 Cl2 and CHCl3 show efficient transport pathways for very short-lived species into the lower stratosphere via the Asian and the North American summer monsoon, Atmos. Chem. Phys., 22, 2049–2077, https://doi.org/10.5194/acp-22-2049-2022, 2022.
  • Vogel, B., Volk, C. M., Wintel, J., Lauther, V., Müller, R., Patra, P. K., Riese, M., Terao, Y., and Stroh, F.: Reconstructing high-resolution in-situ vertical carbon dioxide profiles in the sparsely monitored Asian monsoon region, Commun. Earth Environ, 4, 72, https://doi.org/10.1038/s43247-023-00725-5, 2023.
  • Riese M. and the PHILEAS Team, Quasi-horizontal transport of Asian summer monsoon air during the PHILEAS campaign in summer and autumn 2023, BAMS, 2024, in preparation.

Last Modified: 05.08.2024