Features of upper troposphere and lower stratosphere aerosols observed by lidar over Gadanki, a tropical Indian station

Upper troposphere (UT) and lower stratosphere (LS) aerosol characteristics are studied over a tropical station Gadanki (13.5 degrees N, 79.2 degrees E), using 532-nm Nd:YAG lidar during 2001-2005. Scattering ratios (SR) and aerosol extinction are found to exhibit seasonal and interannual variations in UT (10-15 km) and LS (18-30 km). SR is about 1.00-1.2 in the 10- to 30-km altitude region. Aerosol extinction is about 0.5-6 x 10(-3) km(-1). SR in UT in 2001 and 2004 during winter is lower than that of summer, whereas LS winter profiles are found to have higher SR values. SR values apparently experience a shift in altitude corresponding to the seasonal change in tropopause indicating a relation between the two. UT integrated extinction is about 2.5 times higher than LS extinction. The correlation between UT and LS monthly mean aerosol extinction was weak and negative with a coefficient of 0.4. UT and LS aerosol extinctions over Gadanki are found to exhibit an increasing trend during 2001-2005. The percentage contribution of integrated aerosol extinction in the 10- to 30-km region to aerosol optical depth (AOD) is about 12%. Correlation coefficient between monthly mean AOD and the 10- to 30-km integrated extinction is about 0.6. The increasing trends in UT and LS aerosols seem to support the finding that emissions from subtropical and tropical Asia may have already started to influence the amount of sulfur containing gases reaching UT and LS. This becomes relevant in the climate change context as it has been shown that increasing aerosol abundances may be impacting the monsoon.