Spatial distribution and vertical structure of the MABL aerosols over Bay of Bengal during winter: Results from W-ICARB experiment P.R. Sinha a , R.K. Manchanda a , J.V. Subbarao a , U.C. Dumka a , S. Sreenivasan a , S. Suresh Babu b,n , K. Krishna Moorthy b a National Balloon Facility, Tata Institute of Fundamental Research, Hyderabad 500 062, India b Space Physics Laboratory, Vikaram Sarabhai Space Center, Tirvandrum 695 022, India article info Article history: Received 29 June 2010 Received in revised form 19 October 2010 Accepted 21 October 2010 Available online 20 November 2010 Keywords: Aerosol size distribution Bay of Bengal aerosol ICARB abstract The first ever in-situ measurements of size-segregated vertical profiles of aerosol in the marine atmospheric boundary layer (MABL) over the Bay of Bengal (BoB), made at five different locations during the winter Integrated Campaign of Aerosols, gases and Radiation Budget (W_ICARB) experiment is presented which showed large spatial variability in aerosol properties over BoB with high aerosol concentration over northern BoB ( 4500 cm 3 ) and low aerosol concentration ( r100 cm 3 ) over southern BoB with a moderate aerosol concentration (250–450 cm 3 ) over far east BoB. The altitude variation of aerosol number density is found to be steady in the convective boundary layer (up to  400 m) at all locations over BoB and above that the aerosol concentration is found to decrease, except at far eastern BoB. Over far eastern BoB, the altitude distribution of aerosol number concentration showed an increase at 600 m. Examination of the simultaneous air mass back trajectories along with the observations aerosol size distribution indicates that while the aerosols advected from IGP have a strong natural (coarse mode) component where as those from the east-Asia region are in general accumulation mode (anthropogenic) dominant. & 2010 Elsevier Ltd. All rights reserved. 1. Introduction Characterization of the physical, chemical and the optical properties of aerosols, along with their spatial and temporal variations has received significant attention because of their significant role in the atmospheric radiation budget and the climate change (IPCC, 2007, Moorthy et al., 2008). As such, the monitoring of the atmospheric aerosols and their spatio-temporal heteroge- neities (caused by the distributed nature of their sources and sinks, long-range transport at different altitudes and the mesoscale and synoptic scale atmospheric dynamics over the continent and adjoining oceans and short life time) is of great importance in assessing the aerosol radiative impact and its regional climate implications. Aerosols in the marine atmospheric boundary layer (MABL) are composed of mainly sea-salt and naturally produced sulfates (Blanchard and Cipriano, 1987; O’Dowd and Smith, 1993). Despite numerous investigation on aerosols from ground and space over the globe, the information on the size-segregated vertical profiles of aerosol has been reported only for few locations (Schr ¨ oder et al., 2002; Clarke et al., 1996; de Reus et al., 2001; Rankin et al., 2002; Ansmann et al., 1996; Krejci et al., 2005; Maletto et al., 2003, McKendry et al., 2004) and there exist no such measurements over the oceans adjoining Indian peninsula. How- ever, such information is very critical for impact assessment of aerosols, particularly when different aerosol types co-exist in the vertical column leading to structures in the altitude profile of the size distribution (eg., Satheesh et al., 2008). The altitude distribu- tion of aerosols also has important bearing in aerosol radiative forcing (Moorthy et al., 2009) and in the cloud microphysics particularly when the aerosols originate from urban/industrialized regions, with large abundance of black carbon (BC), sulfate and other submicron species (Kinne and Pueschel, 2001; Abel et al., 2005). From the simulations with the general circulation model (GCM), Haywood and Ramaswamy (1998) have shown that direct radiative forcing of a BC aerosol layer increases approximately by a factor of 5, if the layer is moved between the surface and 20 km. The tropical marine atmosphere is different in several respects from those of extra-tropical regions. Over the tropics the marine atmosphere is characterized by different layers such as surface layer, mixed layer, transition layer, cloud layer, and trade wind inversion (Alappattu et al., 2008). In addition, the tropical marine atmosphere is convectively unstable and it warms up continuously through the heat exchange of air–sea interface and through radiative processes, and shows marked spatial variability depending on the ocean dynamics. These processes would in-turn affect the vertical distribution of Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/jastp Journal of Atmospheric and Solar-Terrestrial Physics 1364-6826/$ - see front matter & 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.jastp.2010.10.011 n Corresponding author. Tel.: + 91 471 2562404. E-mail addresses: s_sureshbabu@vssc.gov.in, sureshsplvssc@gmail.com (S. Suresh Babu). Journal of Atmospheric and Solar-Terrestrial Physics 73 (2011) 430–438