Long-term trend analysis and climatology of tropical cirrus clouds using 16 years of lidar data set over Southern India
Other literature type
Pandit, A. K.
Gadhavi, H. S.
Venkat Ratnam, M.
Rao, S. V. B.
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<sup>−1</sup>. 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.