LiDAR observations of the vertical distribution of aerosols in free troposphere: Comparison with CALIPSO level-2 data over the central Himalayas

Abstract

This study elucidates the seasonality in aerosol vertical profiles acquired using LiDAR measurements and compares it with the CALIPSO level-2 data products over central Himalayas. A detailed analysis on the vertical distribution of aerosols over the central Himalayan region is carried out during different seasons. We present intermittent observations that were made over Manora Peak (29.36° N, 79.45° E, 1951 m, AMSL) Nainital, during March 2012 to May 2013 amounting to a total of 360 h of LiDAR operation, out of which 57 suitable cases were subjected to further analysis. Aerosol loading in the vertical column was found to be highest with 3.40 (Mm sr)⁻¹ at 3.3 km during the spring and summer seasons (MAMJ-2012), and the lowest with 0.48 (Mm sr)⁻¹ at 2.5 km, during winter season (DJF 2012-13). The aerosol layer reaches to the maximum altitude of 5.6 km in the period of MAMJ-2012 and a minimum at 2.8 km in the winter (DJF). The highest value (124 Mm⁻¹ ) of extinction coefficient is found at 3.3 km, during MAMJ- 2012 and minimum (7 Mm⁻¹ ) at 2.5 km during the winter season. A comparison of ground based LiDAR observations with the CALIPSO satellite derived aerosol backscatter profiles has been carried out for 37 suitable cases. To determine the LiDAR ratio, AOD measurements from MODIS were used as constrain. The mean percent bias for different seasons is found to be + 18 ± 42%, +22 ± 28%, +32 ± 36% and +18 ± 51% for MAMJ-2012, SON-2012, DJF-2012e13 and MAM-2013 respectively.