Long Term Assessment of Aerosol Radiative Forcing over Selected Sites of East Africa

John W Makokha,Jared O Odhiambo,Juma Godfrey Shem

doi:10.4236/gep.2018.64002

John W Makokha, Jared O Odhiambo + Show 1 more

Open Access

https://doi.org/10.4236/gep.2018.64002

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Abstract

Atmospheric aerosols have contributed to radiative forcing through direct and indirect mechanisms. Aerosol effects are important in computing radiative forcing estimates for the past, current and future climate. In this study, a comprehensive assessment of regional aerosol radiative forcing, Optical Properties of Aerosol and Clouds (OPAC) model (wavelength range of 0.25 - 4.0 μm) over selected sites in East Africa was done. Aerosol optical properties constituted the inputs of a Radiative Transfer Model (RTM). Op-tical properties investigated included Aerosol Optical Depth (AOD), Single Scattering Albedo (SSA) and Asymmetry Parameter (AP). Aerosol Radiative Forcing (ARF) during the study period at the surface (SFC), top of the atmosphere (TOA) and the atmosphere (ATM) was estimated to be -18.4 ± 1.4 W&#183m-2, +1.1 ± 0.3 W&#183m-2 and +19.5 ± 2.5 W&#183m-2, respectively. This corresponds to an increment in net atmospheric forcing at a heating rate of about 0.55 ± 0.05 K/day (0.41 ± 0.03 to 0.78 ± 0.03 K/day) in the lower troposphere. The study points out the significant role played by atmospheric aerosols in climate modification over the area of study. It is recommended that a further assessment be done in view of uncertainties that may impact on the findings and which were not within the scope of this research.

Highlights

Atmospheric aerosols are responsible for a radiative forcing (RF) of the atmosphere through multiple processes namely direct and indirect means [1]
This paper presents a comprehensive long term assessment of aerosol radiative forcing over the selected East African sites namely Nairobi (1 ̊S, 36 ̊E), Mbita (0 ̊S, 34 ̊E), Mau Forest Complex (0.0 ̊S - 0.6 ̊S; 35.1 ̊E - 35.7 ̊E), Malindi (2 ̊S, 40 ̊E), Mount Kilimanjaro (3 ̊S, 37 ̊E) and Kampala (0 ̊N, 32.1 ̊E) from 2000 to 2013
Assessment of radiative forcing due to aerosols is important in accounting for the cloud effect that has contributed to uncertainties in climate forcing estimates

Summary

Introduction

Atmospheric aerosols are responsible for a radiative forcing (RF) of the atmosphere through multiple processes namely direct and indirect means (the Intergovernmental Panel on Climate Change) [1]. The direct aerosol effect on RF is estimated to be −0.35 (−0.85 to +0.15) W∙m−2 (high confidence) [1]. The direct effective radiative forcing (ERF) is more negative than the direct RF (low confidence) and given a best estimate of about −0.45 (−0.95 to +0.05) W∙m−2 [1]. A recent estimate of aerosol RF over the Kenyan atmosphere was −0.48 W∙m−2 [2]

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