Semitransparent cirrus clouds in the upper troposphere and their contribution to the particulate scattering in the tropical UTLS region

Contribution of semitransparent cirrus (STC) to the scattering properties of particulates in the UTLS region is examined over the Indian region using the lidar data from Gadanki (13.5°N, 79.2°E) and SAGE-II measurements from 30°S to 30°N in the longitude region 70–90°E within the feasibility of these measurements. While the contribution of STC to particulate optical depth (τp) in UT is found to be quite significant in the equatorial and off-equatorial regions in both the hemispheres during summer, this is very small during winter in the off-equatorial regions. Dense STCs in UT also influences the aerosol scattering below the cloud-base and above the cloud-top (LS). This STC influence in LS is quite significant in the northern hemisphere and almost insignificant over the southern hemisphere, where the STC-cover as well as its optical depth is relatively low. This hemispheric difference is attributed to relatively strong tropospheric convection in the northern hemisphere.

► STCs significantly contribute to optical scattering in the UT region.
► Dense STCs in the UT region influence aerosol scattering above and below the cloud.
► IGWs originating from deep convection during ASM transports particulates to LS region.
► B–D circulation could be playing an important role in the troposphere–stratosphere exchange during winter.