Abstract
Abstract. This work quantifies the spatial distribution of different aerosol types, their seasonal variability and sources.The analysis of four years of CALIOP (Cloud–Aerosol LIdar with Orthogonal Polarization) vertically resolved aerosol data allows the identification of spatial patterns of desert dust and carbonaceous particles in different atmospheric layers. Clusters of Lagrangian back trajectories highlight the transport pathways from source regions during the dusty spring season. The analysis shows a prevalence of dust; at low heights it occurs frequently (up to 70% of available observations) and is distributed north of the Tibetan Plateau with a main contribution from the Gobi and Taklamakan deserts, and west of the Tibetan Plateau, originating from the deserts of southwest Asia and advected by the Westerlies. Above the Himalayas the dust amount is minor but still not negligible (occurrence around 20%) and mainly affected by the transport from more distant deserts sources (Sahara and Arabian Peninsula). Carbonaceous aerosol, produced mainly in northern India and eastern China, is subject to shorter-range transport and is indeed observed closer to the sources, while there is a limited amount reaching the top of the plateau. Data analysis reveals a clear seasonal variability in the frequencies of occurrence for the main aerosol types; dust is regulated principally by the monsoon dynamics, with maximal occurrence in spring. We also highlight relevant interannual differences, showing a larger presence of aerosol in the region during 2007 and 2008. The characterization of the aerosol spatial and temporal distribution in terms of observational frequency is a key piece of information that can be directly used for the evaluation of global aerosol models.
Highlights
Aerosol alters the radiative balance through absorption and scattering of the solar radiation (Lau et al, 2006) and influences cloud formation, greatly impacting the hydrological cycle (Kaufman et al, 2005)
Aerosol can modify the upwelling above the Himalaya with an intensification of the Indian monsoon that is strongly linked to the dust concentration around the plateau during the spring season (Lau et al, 2006)
The analysis focuses on aerosol layers defined in CALIOP data as desert aerosol, particles produced by combustion and composed mainly by soot and organic carbon, and a mix between dust and smoke which appears from this analysis to be the main typologies of particulate over the region
Summary
Aerosol alters the radiative balance through absorption and scattering of the solar radiation (Lau et al, 2006) and influences cloud formation, greatly impacting the hydrological cycle (Kaufman et al, 2005). The deposition of particulate on ice and snow affects their surface albedo and ice microphysics (Xu et al, 2009; Krinner et al, 2006), modifying the melting processes Such variations can be spatially highly inhomogeneous (Naz et al, 2011; Raina, 2010), suggesting that those changes may be caused by local forcings and, among. Kuhlmann and Quaas (2010) estimated the radiative forcing from different types of aerosol above the plateau to discuss the EHP hypothesis, while Gautam et al (2009) characterized the dust burden in the 2007 and 2008 pre-monsoon seasons. The first objective of this work is to provide a characterization of the spatial distribution of different aerosol type over the region of the Himalayan Plateau based on CALIPSO observations and individuate the seasonal variability over four years (2007–2010). Liu et al (2008), using Hysplit (Hybrid Single Particle Lagrangian Integrated Trajectory Model) back trajectories, showed that dust can be advected to the region from the Tarim Basin and the major deserts of northeastern India, Pakistan and Afghanistan
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