Sensitivity analysis of aerosol optical and radiative properties over the climate sensitive Hindu Kush Himalayan region using sky radiometer observation

Abstract

The study examined sensitivity analysis of aerosol optical and radiative properties due to different versions of SKYRAD.pack module (i.e. versions 4.2 and 5.0) along with stability and performance of sky radiometer instruments (POM-01), operating at Hanle, Leh and Merak, located at high-altitude background sites in the most climate sensitive Hindu Kush Himalayan region. The study utilized long-term aerosol measurements during 2008–2024 for examining the stability and performance of the instruments. As a part of sensitivity analysis, coarse-mode aerosol optical depth (AOD) was found to be higher at version 4.2, while fine-mode AOD showed higher at version 5.0, but interestingly the variation of total AOD was found to be insignificant. Further, single scattering albedo (SSA) at version 5.0 was overestimated from 4.2 version. Among the parameters, aerosol asymmetry parameter (AS) showed significantly larger difference between the two versions with overestimation at 4.2 version. Such large differences of AS may be attributed to variations in aerosol radiative forcing parameters. Further, variation of $\pm$2% calibration constants (F0I) in the sensitivity analysis showed significant variation in the retrieval parameters. Aerosol volume size distribution at three sites showed dominantly tri-modal pattern at version 4.2, while version 5.0 showed dominance of bi-modal distribution, which may be attributed from significant variation of AS between the two versions. These findings highlighted the importance of performing calibration procedures frequently to ensure the quality controlled data at background sites in particular, and sensitivity analysis for aerosol retrieval parameters in different versions of the SKYRAD.pack software tool.