Radiative Forcing Estimation of Aerosols at an Urban Site near the Thar Desert Using Ground-Based Remote Sensing Measurements

Sunita Verma,Swagata Payra,Divya Prakash,Atul Kumar Srivastava

doi:10.4209/aaqr.2016.09.0424

Abstract

ABSTRACT The focus of present study is to quantify the radiation budget of aerosols over Jaipur (Northwestern, India) from 2011 to 2015. The Aerosol radiative forcing (ARF) has been determined for shortwave spectrum (0.3–3.0 µm) individually for the top of the atmosphere (TOA), bottom of the atmosphere (BOA) and within the atmosphere (ATM) over study region. Santa Barbara DISORT Atmospheric Radiative Transfer model (SBDART) is used to simulate the aerosols radiative effect. The inter-annual monthly average of ARF at TOA during 2011–2015 is found between –11.40 to –5.60 W m–2, while the ARF at BOA is found to be between –32.2 to –22.49 W m–2. Likewise, the ARF within the atmosphere (ATM) comes between 14.04 to 22.47 W m–2 over Jaipur. The SBDART model is run discretely for Dust period (DSP) and non-Dust Period (NDP) during the year 2012 to inspect the change in ARF during extreme events over the Jaipur site. During DSP, the net TOA and BOA forcing are found in the range –20.71 to –16.81 W m–2 and –45.15 to –39.6 W m–2, respectively, and net ATM forcing varies in the range 22.7 to 24.4 W m–2. For the NDP, the corresponding value varies in the range –10.1 to –6.6 W m–2 and –23.6 to –22.3 W m–2. The net ATM forcing during NDP is between 12.2 to 17.05 W m–2. The value of BOA increases more than ~67% during DSP than NDP. The more increase (–ve) in surface forcing represents the cooling of the surface during DSP. The results depict that dust over Jaipur in the vicinity of the Thar Desert is scattering in nature with high value (> 0.95) of SSA. The scattering is mostly high during summer and low in winter.

Highlights

Aerosols constitute prime uncertainty in the estimation of climate forcing (IPCC, 2007, 2013) due to scarce data representing aerosols and poor understanding of aerosolcloud interactions
The aerosols optical thickness (AOT) and single scattering albedo (SSA) values are designed in a recursive manner till the modelled and observed values match within ± 5% deviation
Ångström exponent (α) values obtained from OPAC shows more existence of coarse size aerosols which is validated with AE derived from MICROTOP

Summary

Introduction

Aerosols constitute prime uncertainty in the estimation of climate forcing (IPCC, 2007, 2013) due to scarce data representing aerosols and poor understanding of aerosolcloud interactions. The direct and indirect atmospheric radiative forcing by the dust has not been represented well in climate models (Tegen et al, 1996). The dust particles get transported to far off locations from their sources and over remote oceans with a combined action of convection and long-range transport of general circulation systems (Prospero et al, 2002). It exhibits high variability in the imaginary part of their refractive index (Ginoux et al, 2001; Zender et al, 2003; Seinfeld et al, 2004; Tegen et al, 2004) that shows the absorbing potentiality

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