Articles | Volume 15, issue 24
Atmos. Chem. Phys., 15, 13833–13848, 2015
Atmos. Chem. Phys., 15, 13833–13848, 2015

Research article 16 Dec 2015

Research article | 16 Dec 2015

Long-term trend analysis and climatology of tropical cirrus clouds using 16 years of lidar data set over Southern India

A. K. Pandit1, H. S. Gadhavi1, M. Venkat Ratnam1, K. Raghunath1, S. V. B. Rao2, and A. Jayaraman1 A. K. Pandit et al.
  • 1National Atmospheric Research Laboratory, Gadanki-517 112, A. P., India
  • 2Department of Physics, Sri Venkateswara University, Tirupati-517502, A.P., India

Abstract. Sixteen-year (1998–2013) climatology of cirrus clouds and their macrophysical (base height, top height and geometrical thickness) and optical properties (cloud optical thickness) observed using a ground-based lidar over Gadanki (13.5° N, 79.2° E), India, is presented. The climatology obtained from the ground-based lidar is compared with the climatology obtained from 7 and a half years (June 2006–December 2013) of Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) observations. A very good agreement is found between the two climatologies in spite of their opposite viewing geometries and the differences in sampling frequencies. Nearly 50–55 % of cirrus clouds were found to possess geometrical thickness less than 2 km. Ground-based lidar is found to detect a higher number of sub-visible clouds than CALIOP which has implications for global warming studies as sub-visible cirrus clouds have significant positive radiative forcing. Cirrus clouds with mid-cloud temperatures between −50 to −70 °C have a mean geometrical thickness greater than 2 km in contrast to the earlier reported value of 1.7 km. Trend analyses reveal a statistically significant increase in the altitude of sub-visible cirrus clouds which is consistent with the recent climate model simulations. The mid-cloud altitude of sub-visible cirrus clouds is found to be increasing at the rate of 41 ± 21 m year−1. Statistically significant decrease in optical thickness of sub-visible and thick cirrus clouds is observed. Also, the fraction of sub-visible cirrus cloud is found to have increased by 9 % in the last 16 years (1998 to 2013). This increase is mainly compensated by a 7 % decrease in thin cirrus cloud fraction. This has implications for the temperature and water vapour budget in the tropical tropopause layer.

Short summary
We present the longest (1998 to 2013) cirrus cloud climatology over a tropical station using a ground-based lidar. A statistically significant increase is found in the altitude of sub-visible cirrus clouds. Also a systematic shift from thin to sub-visible cirrus cloud type is observed. Ground-based lidar is found to detect more number of sub-visible cirrus clouds than space-based lidar. These findings have implications to global warming and stratosphere-troposphere water vapour exchange studies.
Final-revised paper