Elevated aerosol layers and their radiative impact over Kanpur during monsoon onset period

Abstract

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.

Enhancement of Atmospheric Stability by Anomalous Elevated Aerosols During Winter in China

“…Figure shows that the aerosol particles are uplifted above 2 km and can even be transported to 4–5 km in EAL years. This result is comparable to the results of EALs in India (Sarangi et al, ). Aerosol flux initially increases then decreases with the increase in longitude, and the maximum aerosol flux is located at approximately 112°E (center line over Eastern China).…”

“…However, a weak decrease of −0.04 K/day in heating rate is observed at the near surface due to the reduction in incoming solar radiation resulting from anomalous EALs. The opposite heating rate changes for the warming in the upper atmosphere and cooling on the surface are consistent with other estimates in literature (Sarangi et al, 2016;Wang et al, 2018), which indicated that these changes can further enhance inversion of in the lower troposphere .…”

“…This situation regulates atmospheric stability and affects atmospheric convection and regional climate circulation (Liu et al, ). Elevated aerosol layers (EALs) refer to high‐level aerosol layers that are mainly distributed above 2 km and generated by regional transport and local emissions, convective uplift, specific synoptic conditions, topography, and other related factors (Sarangi et al, ; Wang et al, ; Zhang et al, ). In comparison with near‐surface aerosols, EALs have distinct interactions with incoming solar radiation (Kumar et al, ).…”

Large contrast in the vertical distribution of aerosol optical properties and radiative effects across the Indo-Gangetic Plain during SWAAMI-RAWEX campaign

“…10 A very recent work, synergizing these measurements, with models and satellite data (Govardhan et al, 2017) has highlighted the potential of these elevated absorbing aerosols in aggravating stratospheric ozone loss or in delaying the recovery of ozone depletion in the past. Sarangi et al (2016) have reported enhanced stability of lower free troposphere due to these elevated aerosols over the IGP, while Dipu et al (2013) have found alteration in cloud 15 water content due to these layers.…”

CALIPSO lidar level 3 aerosol profile product: version 3 algorithm design

“…Quality screening procedures for the beta level 3 aerosol product were initially reported by Winker et al (2013). In subsequent years, researchers have adopted these procedures explicitly (Sarangi et al, 2016;Marinou et al, 2017) while others have adopted variations on these procedures, citing the level 3 aerosol product as a reference (Ge et al, 2014;Todd and Cavazos-Guerra, 2016). This paper documents the averaging and quality screening methods used to generate the version 3 level 3 aerosol 15 profile product.…”