Influence of Indian Summer Monsoon on Tropopause, Trace Gases and Aerosols in Asian Summer Monsoon Anticyclone Observed by COSMIC, MLS and CALIPSO

The existence of the Asian Summer Monsoon Anticyclone (ASMA) during the summer in the northern hemisphere, upper troposphere and lower stratosphere (UTLS) region plays a significant role in confining the trace gases and aerosols for a long duration, thus affecting regional and global climate. Though several studies have been carried out, our understanding of the trace gases and aerosols variability in the ASMA is limited during different phases of the Indian monsoon. This work quantifies the role of Indian Summer Monsoon (ISM) activity on the tropopause, trace gases (Water Vapor (WV), Ozone (O-3), Carbon Monoxide (CO)) and aerosols (Attenuated Scattering Ratio (ASR)) obtained from the Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC), Microwave Limb Sounder (MLS), Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) satellite observations, respectively, during the period 2006-2016. Enhancement in the tropopause altitude, WV, CO, ASR and low tropopause temperatures, O-3 in the ASMA region is clearly noticed during peak monsoon months (July and August) with large inter-annual variability. Further, a significant increase in the WV and CO, and decrease in O-3 during the active phase of the ISM, strong monsoon years and strong La Nina years in the ASMA is noticed. An enhancement in the ASR values during the strong monsoon years and strong La Nina years is also observed. In addition, our results showed that the presence of deep convection spreading from India land regions to the Bay of Bengal with strong updrafts can transport the trace gases and aerosols to the upper troposphere during active spells, strong monsoon years and La Nina years when compared to their counterparts. Observations show that the ASMA is very sensitive to active spells, strong monsoon years and La Nina years compared to break spells, weak monsoon years and El Nino years. It is concluded that the dynamics play a significant role in constraining several trace gases and aerosols in the ASMA and suggested considering the activity of the summer monsoon while dealing with them at sub-seasonal scales.

Automated summary

The study found that the Indian Summer Monsoon (ISM) activity has a significant impact on the tropopause altitude, water vapor, carbon monoxide, attenuated scattering ratio, ozone, and lower tropopause temperatures in the Asian Summer Monsoon Anticyclone (ASMA) region, especially during the peak monsoon months of July and August. Additionally, significant increases in water vapor and carbon monoxide, as well as decreases in ozone, were observed during the active phase of the ISM, strong monsoon years, and strong La Nina years in the ASMA.