Abstract
Abstract. An extensive comparison of aerosol extinction has been performed using lidar and Stratospheric Aerosol and Gas Experiment (SAGE) II data over Gadanki (13.5° N, 79.2° E), a tropical station in India, following coincident criteria during volcanically quiescent conditions from 1998 to 2005. The aerosol extinctions derived from lidar are higher than SAGE II during all seasons in the upper troposphere (UT), while in the lower-stratosphere (LS) values are closer. The seasonal mean percent differences between lidar and SAGE II aerosol extinctions are > 100% in the UT and < 50% above 25 km. Different techniques (point and limb observations) played the major role in producing the observed differences. SAGE II aerosol extinction in the UT increases as the longitudinal coverage is increased as the spatial aerosol extent increases, while similar extinction values in LS confirm the zonal homogeneity of LS aerosols. The study strongly emphasized that the best meteorological parameters close to the lidar measurement site in terms of space and time and Ba (sr−1), the ratio between aerosol backscattering and extinction, are needed for the tropics for a more accurate derivation of aerosol extinction.
Highlights
The upper troposphere (UT) and lower stratosphere (LS) are regions of highly coupled dynamics and have created major scientific interest due to its particular role in radiative forcing and chemistry–climate coupling
The present attempt of an extensive comparison, utilizing an 8-year (1998–2005) data set from Stratospheric Aerosol and Gas Experiment (SAGE) II and lidar over a tropical location during volcanically quiescent conditions, to the best of our knowledge, is the first of its kind
These results suggest that aerosol extinction derived using a Ba value of 0.020 agrees more closely with the SAGE II profile in the LS than in the UT (Fig. 2d)
Summary
The upper troposphere (UT) and lower stratosphere (LS) are regions of highly coupled dynamics and have created major scientific interest due to its particular role in radiative forcing and chemistry–climate coupling. There was no evidence of ATAL in SAGE II at a date prior to 1998 Such evidence of ATAL and other changes in UTLS aerosol characteristics are vital, and observations using optical instruments (ground-based lidar, in situ balloon measurements) and satellites are essential to track the evolution of UTLS aerosols in various parts of the globe. Stratospheric Processes And their Role in Climate (SPARC) assessment (Thomason and Peter, 2006) stressed the need for more comparisons between lidar and satellite data both at midlatitudes and in the tropics, as there is a lack of statistics on the magnitude of differences between SAGE IImeasured and lidar-derived aerosol extinction values. The present attempt of an extensive comparison, utilizing an 8-year (1998–2005) data set from SAGE II and lidar over a tropical location during volcanically quiescent conditions, to the best of our knowledge, is the first of its kind
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