Department of Science, Technology and Engineering

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Browsing Department of Science, Technology and Engineering by Subject "East Africa"

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    Aerosol optical depth and precipitation rate projections over east africa utilizing self organizing map
    (The International Journal Of Science & Technoledge, 2017-03-01) Makokha, John Wanjala; Angeyo, H.K.; Muthama, John Nzioka
    Assessment of future aerosols impacts on both regional and global climate change requires a comprehensive projection tool that reliably provides information on aerosol evolution characteristics with high fidelity. In the current study, we propose an algorithm based on Self-Organizing Map (SOM) and Community Atmosphere Model 4 (CAM4) for long term Aerosol Optical Depth (AOD) and Precipitation Rate (PR) projections over East Africa. To start with, AOD and PR retrievals from Moderate Resolution Imaging Spectroradiometer (MODIS) and Tropical Rainfall Measurement Mission (TRMM) respectively were cross validated with simulation from CAM4 so as to assess the uncertainty between the measured and simulated retrievals from 2000 to 2014.The error analysis between CAM4 simulations and MODIS measurements (from 2000 to 2014)shows a close match where R2 varies from 0.58 to 0.83 with a corresponding RMSE of between 0.014 and 0.065 (for AOD). Likewise, the uncertainty between simulate and measured PR from CAM4 and TRMM showed an estimated R2 to range between 0.40 and 0.78 while the RMSE varied from 0.021 to 0.091 in the same period and study sites. Based on proposed SOM algorithm and simulated CAM4 retrievals over each study site, an increase of between 1.34-2.43 % for AOD and a decrease of between 1.03-1.98 % in PR are projected over the region by 2030.
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    Long term assessment of aerosol radiative forcing over selected sites of East Africa
    (scientific Research Publishing, 2018-03-08) Makokha, John Wanjala; Odhiambo, Jared Oloo; shem, Godfrey Juma
    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). Optical 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∙m−2, +1.1 ± 0.3 W∙m−2 and +19.5 ± 2.5 W∙m−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.