Evaluation of the Aerosol-Cloud Discrimination Techniques and Study of the Asian Tropopause Aerosol Layer (ATAL) Variability

Stratospheric aerosols play a crucial role in the earth’s atmosphere through their impacts on radiation, stratospheric ozone chemistry and the formation of cirrus clouds near the tropopause. Their optical properties have been monitored using space-borne occultation techniques for more than 4 decades with the Stratospheric Aerosol and Gas Experiment (SAGE) series of instruments. However, the study of aerosols in Upper Troposphere and Lower Stratosphere (UTLS), faces challenges due to the widespread presence of ice clouds. Several techniques, such as Extinction Color Ratio (ECR), Single Extinction Ratio (SER also known as TV13), and SAGE III/ISS Operational Aerosol Type Classification Method (SOATCM), have been developed to distinguish between aerosols and clouds. These methods are somewhat specific to cases and perform differently in various regions and at various times. A primary comparison of these techniques over the Asian Monsoon Anticyclone (AMA) shows somewhat similar results, but they vary significantly over the tropics. The study investigates whether SAGE data is reliable for studying the Asian Tropopause Aerosol Layer (ATAL) after filtering clouds. The analysis suggests that SAGE data is still sufficient for inferring and analyzing the ATAL feature. The study also examines the impact of these techniques on the ATAL and its variability. Furthermore, it delves into the interannual variability of the ATAL and investigates the reasons and sources for these variations. Additionally, a new modification to extinction color ratio (ECR) will be tested, with preliminary findings suggesting that the modifications perform better than the original ECR.