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Elevated aerosol layers and their radiative impact over Kanpur during monsoon onset period
Author(s) -
Sarangi Chandan,
Tripathi S. N.,
Mishra A. K.,
Goel A.,
Welton E. J.
Publication year - 2016
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
eISSN - 2169-8996
pISSN - 2169-897X
DOI - 10.1002/2015jd024711
Subject(s) - aerosol , environmental science , atmospheric sciences , angstrom exponent , radiative transfer , radiative forcing , daytime , climatology , extinction (optical mineralogy) , monsoon , meteorology , physics , geology , mineralogy , quantum mechanics
Accurate information about aerosol vertical distribution is needed to reduce uncertainties in aerosol radiative forcing and its effect on atmospheric dynamics. The present study deals with synergistic analyses of aerosol vertical distribution and aerosol optical depth (AOD) with meteorological variables using multisatellite and ground‐based remote sensors over Kanpur in central Indo‐Gangetic Plain (IGP). Micro‐Pulse Lidar Network‐derived aerosol vertical extinction ( σ ) profiles are analyzed to quantify the interannual and daytime variations during monsoon onset period (May–June) for 2009–2011. The mean aerosol profile is broadly categorized into two layers viz., a surface layer (SL) extending up to 1.5 km (where σ decreased exponentially with height) and an elevated aerosol layer (EAL) extending between 1.5 and 5.5 km. The increase in total columnar aerosol loading is associated with relatively higher increase in contribution from EAL loading than that from SL. The mean contributions of EALs are about 60%, 51%, and 50% to total columnar AOD during 2009, 2010, and 2011, respectively. We observe distinct parabolic EALs during early morning and late evening but uniformly mixed EALs during midday. The interannual and daytime variations of EALs are mainly influenced by long‐range transport and convective capacity of the local emissions, respectively. Radiative flux analysis shows that clear‐sky incoming solar radiation at surface is reduced with increase in AOD, which indicates significant cooling at surface. Collocated analysis of atmospheric temperature and aerosol loading reveals that increase in AOD not only resulted in surface dimming but also reduced the temperature (∼2–3°C) of lower troposphere (below 3 km altitude). Radiative transfer simulations indicate that the reduction of incoming solar radiation at surface is mainly due to increased absorption by EALs (with increase in total AOD). The observed cooling in lower troposphere in high aerosol loading scenario could be understood as a dynamical feedback of EAL‐induced stratification of lower troposphere. Further, the observed radiative effect of EALs increases the stability of the lower troposphere, which could modulate the large‐scale atmospheric dynamics during monsoon onset period. These findings encourage follow‐up studies on the implication of EALs to the Indian summer monsoon dynamics using numerical models.