Trend Analysis of Aerosol Optical Depth and &amp;amp;#197ngstr&amp;amp;#246m Exponent Anomaly over East Africa

Makokha, John Wanjala; Odhiambo, Jared O.; Godfrey, Juma S.

doi:10.4236/acs.2017.74043

Cited by 11 publications

(15 citation statements)

References 28 publications

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“…On the other hand, the enhanced aerosol loading during the local dry seasons could be attributed to increased anthropogenic activities (land preparations, biomass burning and forest fires) which release significant amount of smoke particles into the EA's atmosphere (Ngaina and Muthama, ; Makokha et al ., ). The stronger near‐surface winds during JJA over the arid and semi‐arid areas of north and eastern parts of Kenya (Figure (d)) could accelerate the formation of dust aerosols.…”

Section: Resultsmentioning

confidence: 97%

“…As aforementioned, the monthly variation in AOD over EA is closely associated with variations in emission sources, anthropogenic activities and seasonal cycles of precipitation. A combination of biomass burning (during December – February and June – July) and dust aerosols (locally derived and due to long‐range transport) could enhance the aerosol load during these months (Makokha et al , ). The low AOD during March–May and September–November is attributed to large wet deposition (Figure (a)) and reduced anthropogenic activities (de Graaf et al , ; Boiyo et al , ).…”

Section: Resultsmentioning

confidence: 99%

“…The monthly averaged temperature, wind speed and relative humidity at 850 hPa and spatial resolution of 0.75 × 0.75° were sourced from the European Centre for Medium‐Range Weather Forecasts (ECMWF), previously used by a number of authors over EA (Yang et al ., ; Ogwang et al ., ). However, the Climate Research Unit (CRU) temperature (Harris et al ., ) and Tropical Rainfall Measuring Mission (TRMM) (Huffman et al ., ) precipitation data sets derived at spatial resolutions of 0.5 × 0.5° and 0.25 × 0.25°, respectively, were preferred due to their better performance over the region (Kerandi et al ., ; Makokha et al ., ).…”

Section: Methodsmentioning

confidence: 97%

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Spatial variations and trends in AOD climatology over East Africa during 2002–2016: a comparative study using three satellite data sets

Boiyo

Kumar

Zhao

2018

Intl Journal of Climatology

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Aerosol optical depth (AOD) has become one of the most crucial parameters for climate change assessment. This study presents long‐term (2002–2016) spatio‐temporal distributions and trends in AOD over East Africa (EA) retrieved from the moderate‐resolution imaging spectroradiometer (MODIS) Aqua [Dark Target (DT) and Deep Blue (DB)] and multi‐angle imaging spectroradiometer (MISR). An inter‐comparison of AODs retrieved from different algorithms noticed significant positive correlations (r = 0.72 − 0.87) with MISR underestimating MODIS. Moderate (>0.5–0.8) to high (≥0.8) correlations in AOD exhibited over EA, with a few regions representing low (0–0.5) positive correlations. The spatial patterns of annual mean AOD were generally characterized by low (<0.2), moderate (0.2–0.35) and high (>0.35) centres over EA. The seasonal mean AODs over EA were found high (low) during the local dry (wet) seasons, with annual mean (±σ) values of 0.20 ± 0.01, 0.18 ± 0.01 and 0.20 ± 0.02 as observed by DT, DB and MISR, respectively. A single peak distribution of frequencies in AOD was observed by the three sensors in the interval 0.1–0.2, signifying a generally less polluted environment dominated by particular aerosol type. Linear trend analysis revealed an increase in AOD by 0.52, 0.57 and 0.74% year−1 as detected by MISR, DT and DB, respectively, and were consistent with those noted in key meteorological parameters. Furthermore, annual and seasonal spatial trends and tendencies revealed a general increase in AOD over EA, being positive and significant over the northern part of EA. Later, classification of major aerosol types over major cities in EA revealed dominance of continental (74.47%) followed by the mixed (16.22%) and biomass‐burning/urban‐industrial (8.02%) aerosols, with minor contributions from desert dust (1.03%) and clean maritime (0.32%) type of aerosols.

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Section: Resultsmentioning

confidence: 97%

Section: Resultsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 97%

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Spatial variations and trends in AOD climatology over East Africa during 2002–2016: a comparative study using three satellite data sets

Boiyo

Kumar

Zhao

2018

Intl Journal of Climatology

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“…Details and the map illustrating the study region and specifics on each site of study are as shown in [9]. .…”

Section: Description Of Study Areamentioning

confidence: 99%

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

Makokha¹,

Odhiambo²,

Shem³

2018

GEP

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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 , 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.

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“…Details and the map illustrating the study region and specifics over each site of study are as shown in [15].…”

Section: Description Of Study Area and Spectral Data Manipulationmentioning

confidence: 99%

Optical Characterization of Atmospheric Aerosols via Airborne Spectral Imaging and Self-Organizing Map for Climate Change Diagnostics

Makokha¹,

Odhiambo²

2018

OALib

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Self-Organizing Map (SOM) analysis is used to perform optical characterization of both Aerosol Optical Depth (AOD) and Ångström Exponent (ÅE) retrieved from Moderate-resolution Imaging Spectroradiometer (MODIS) in relation to Precipitation Rate (PR) from Tropical Rainfall Measurement Mission (TRMM) over selected East African sites from 2000 to 2014 and further diagnose climate change over the region if any. SOM reveals a marked spatial variability in AOD and ÅE that is associated to changing aerosol transport, urban heat islands, diffusion, direct emission, hygroscopic growth and their scavenging from the atmosphere specific to each site. Temporally, all sites except Mbita and Kampala indicate two clusters in AOD that are associated to prevailing dry and wet seasons over East Africa. Moreover, all sites except Mbita and Mount Kilimanjaro show two clusters in ÅE that are related to aerosol mode of generation and composition over the region. The single cluster in AOD and ÅE over Mbita indicate that aerosol characteristics over the site are influenced by biomass burning and local air circulation rather than the monsoon precipitation throughout the study period.

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Trend Analysis of Aerosol Optical Depth and &#197ngstr&#246m Exponent Anomaly over East Africa

Cited by 11 publications

References 28 publications

Spatial variations and trends in AOD climatology over East Africa during 2002–2016: a comparative study using three satellite data sets

Spatial variations and trends in AOD climatology over East Africa during 2002–2016: a comparative study using three satellite data sets

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

Optical Characterization of Atmospheric Aerosols via Airborne Spectral Imaging and Self-Organizing Map for Climate Change Diagnostics

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