Asian Tropopause Aerosol Layer (ATAL) during El Niño: Impact on the Indian summer monsoon
Monday, 19 March 2018: 11:15
Salon Vilaflor (Hotel Botanico)
Suvarna S Fadnavis, Indian Institute of Tropical M, Pune, India, Jean-Paul Vernier, Science Systems and Applications, Inc., Hampton, VA, United States, Chaitri Roy, Indian Institute of Tropical Meteorology, CCCR, Pune, India, Ashok Karumuri, University of Hyderabad, University Centre for Earth and Space Sciences (UCESS), Hyderabad, India and T.P. Sabin, Indian Institute of Tropical Meteorology, Pune, India
Abstract:
Indian economy is facing challenges due to increase in drought frequency in the latest decades. Droughts are linked to heavy aerosol pollution and El Nino, both. Recent satellite observations revealed Asian Tropopause Aerosol Layer (ATAL) over the Asia (60-120E) associated with Asian summer Monsoon Rainfall (ISMR). In this study, we evaluated potential impacts of aerosols loading in the troposphere and ATAL during the monsoon season with co-occurring El Niño on the ISMR. We analyze sea surface temperature (SST), Total Ozone Mapping Spectrometer (TOMS) aerosol index datasets for the period 1979-2005, Multi-Angle Imaging Spectroradiometer (MISR) Aerosol Optical Depth (AOD) for the period 2000-2013. Our analysis of the TOMS and MISR observations indicate a higher-than-normal aerosol loading over the North-India during the summer monsoon season with a concurrent El Niño (Fig.1), which exacerbates the El Niño-induced negative rainfall anomalies over the Indian region. Our multi-ensemble sensitivity experiments with ECHAM5-HAMMOZ, a fully-coupled aerosol chemistry-climate model, confirm this finding.
Our model simulations indicate that during the monsoon season convective transport lifts-up the boundary layer aerosols from North-India and East-China to the upper troposphere contributing to the ATAL. During co-occurring El Ninos, a higher (than normal) amount of local emissions and dust transport from Saudi Arabia piles up over North India and Tibetan plateau (TP) region producing an aerosol column (1000 - 270 hPa). The subsidence over India associated with El Nino inhibits vertical transport to the ATAL. The thicker and wider ATAL is attributed to transport of anomalous amounts of sulfate aerosols from East Asia to India in the upper troposphere (Fig.2).
Our analysis depicts that during the monsoon season with co-occurring El Nino, this anomalous aerosol loading increases the stability of the mid-upper troposphere. It weakens the upper tropospheric warming, monsoon Hadley circulation and exacerbates the severity of drought associated with El Nino.
