LiDAR observations of the vertical distribution of aerosols in free troposphere: Comparison with CALIPSO level-2 data over the central Himalayas Raman Solanki a, b , Narendra Singh a, * a Aryabhatta Research Institute of Observational Sciences, Nainital 263 002, Uttarakhand, India b Department of Physics and Astrophysics, University of Delhi, India highlights  Yearlong LiDAR observation and aerosol layers over the central Himalayas.  Comparison and validation of CALIPSO aerosol backscatter with LiDAR data.  Strong variability in vertical profiles of aerosol extinction coefficient. article info Article history: Received 13 June 2014 Received in revised form 2 September 2014 Accepted 30 September 2014 Available online 2 October 2014 Keywords: LiDAR Aerosol backscatter LiDAR ratio Long range transport CALIPSO Bias 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 2012e13). 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 þ18 ± 42%, þ22 ± 28%, þ32 ± 36% and þ18 ± 51% for MAMJ-2012, SON-2012, DJF-2012e13 and MAM-2013 respectively. © 2014 Elsevier Ltd. All rights reserved. 1. Introduction Aerosols play a vital role in the earth ' s radiation budget, cloud formation and climate change. The measurements of vertical dis- tribution of aerosol are critical to assess the radiative impact of aerosol on the surface and atmosphere (Liu et al., 2012; Kaufman et al., 1997; Pelon et al., 2008). In addition, aerosols influence the lifetime and microphysical properties of clouds, precipitation rates, and tropospheric photochemistry (Towmey, 1977; IPCC, 2001). Due to the presence of distinct aerosol layers, the columnar properties can be entirely different from the surface properties of aerosol (Ramanathan et al., 2001). Considering such an importance, numerous efforts were made from ground based and space borne observations to study aerosol distribution and properties, along with model simulations around the globe, but such studies are very limited over the Indian region particularly those having the infor- mation on the vertical distribution of aerosol. Over the Indian re- gions, satellite based observations have demonstrated very high pollution loadings in terms of aerosol optical depth (AOD), partic- ularly over the Indo-Gangetic Plain (IGP) region. Although inte- grated columnar properties of aerosols over the central Himalayas have been studied extensively (Sagar et al., 2004; Guleria et al., 2012) but a very limited study on vertical profile exists over * Corresponding author. ARIES, Atmospheric Science, Manora Peak, Nainital, Uttarakhand 263002, India. E-mail address: narendra@aries.res.in (N. Singh). Contents lists available at ScienceDirect Atmospheric Environment journal homepage: www.elsevier.com/locate/atmosenv http://dx.doi.org/10.1016/j.atmosenv.2014.09.083 1352-2310/© 2014 Elsevier Ltd. All rights reserved. Atmospheric Environment 99 (2014) 227e238