Contrasting changes in cloud optical properties and the influence of aerosols, meteorology and radiation feedback in the Himalaya Karakoram region

The spatio-temporal variations in cloud optical properties and the influence of aerosols, radiation feedback and meteorological parameters were investigated at high altitudes of Diamir, Gilgit and Skardu in the Himalaya Karakoram (HK) region of northern Pakistan from 2004 to 2016. The aerosol optical depth (AOD) depicted significant variation with high values during spring months as compared to other months. The results revealed high values of cloud fraction (CF), cloud water path (CWP) and cloud optical depth (COD) in winter months, while contrasting response was observed in summer months. Due to Twomey effect, clouds become thicker and brighter with maximum COD and liberation of latent heat, which modifies temperature gradient of vertical profile. Similarly, an uneven distribution of cloud effective radius (CER) was observed throughout the study period. An increasing trend of cloud top temperature (CTT) from February to September was observed, while an opposite response was found from September to January during the study period. Likewise, minimum and maximum cloud top pressure (CTP) was found in February and November, respectively. AOD is positively correlated with CF and COD due to high humidity and the existence of hydrophilic aerosols. The results of AOD and CER correlation were in good agreement with Twomey effect. However, AOD showed contrasting relationship with CWP over Diamir and Gilgit. The negative relationships of AOD with CTP and CTT indicated the suppression of precipitation process and variability of meteorological parameters. In addition, a positive correlation was observed between COD and CTP against top of the atmosphere shortwave cloud radiative forcing (TOASWCRF), which indicates the cooling effect due to increasing COD and CTP. With TOASWCRF, a variation in CWP and CER may also lead to cooling effect due to reflection of solar radiations. While the meteorology depicted an uneven relationship with cloud optical properties at observation sites. © 2020 Elsevier B.V.