Shortwave Radiative Impacts of the Asian Tropopause Aerosol Layer (ATAL) using Balloon-borne In-situ measurements at three distinct locations in India

Abstract. The recurring presence of the Asian Tropopause Aerosol Layer (ATAL) in the Upper Troposphere Lower Stratosphere (UTLS) region, strongly linked with the Asian Summer Monsoon Anticyclone (ASMA), has garnered significant attention over the past decade. However, despite advances in instrumentation, studies quantifying the radiative impacts of ATAL aerosols in terms of radiative forcing and heating rates remain limited. This study aims to address this gap by evaluating the direct radiative effects of ATAL aerosols in the UTLS using in-situ measurements from the Balloon measurement of the Asian Tropopause Aerosol Layer (BATAL) campaigns conducted between 2014 and 2019 over three distinct locations in India: Gadanki (13.48° N, 79.18° E), Hyderabad (17.47° N, 78.58° E), and Varanasi (25.27° N, 82.99° E). The study considers three scenarios where UTLS aerosols are predominantly composed of sulfates, nitrates, or anthropogenic aerosols. Our findings reveal significant changes in aerosol radiative forcing, ranging from -0.015 to 0.03 Wm^-2 at the top of the atmosphere, -0.01 Wm^-2 to -0.16 Wm^-2 at the surface, and 0 to 0.19 Wm^-2 within the atmospheric column when transitioning from sulfate to nitrate and anthropogenic aerosol scenarios. UTLS aerosols were found to contribute 0.1 % to 2.3 % of the total columnar atmospheric forcing, with the highest contributions observed under the anthropogenic scenario. Notably, heating rate profiles indicate enhanced aerosol heating under anthropogenic scenarios, with rates reaching up to 0.03 K day^-1, particularly over Varanasi, compared to significantly lower rates under sulfate and nitrate scenarios. The study highlights the spatial variability in radiative impacts across different locations, reflecting the structural and dynamic complexities of ATAL within the ASMA region. It emphasizes the need for a comprehensive approach combining in-situ, satellite, and model-based retrievals to overcome current limitations and achieve a more accurate understanding of the net radiative impacts of ATAL aerosols.