Global Journals Inc. (USA)

 Journal

 Multiyear Analysis Of Ground-Based Sunphotometer (AERONET) Aerosol Optical Properties And Its Comparison With Satellite Observations Over West Africa

 Ayodeji Oluleye, Kehinde Olufunso Ogunjobi, A. Bernard, Akintomide Afolayan Akinsanola

 2012

The Sahelian West Africa (Long 20W:20E, Lat 0:30N) by its climatological and geographical conditions is a key region for the characterization of global atmospheric aerosol optical properties. This study evaluates the spatial and temporal variation of the Aerosol Optical Depth (AOD440nm), aerosol particle size characterization (Angstrom exponent (?440-675nm) at four locations (Agoufou, Banizoumbou, Cape Verde and Ilorin) over a period of January 2005 to December 2009. Results of the day-today AOD440nm variations as well as the seasonal and annual variations are presented in order to establish the aerosol climatology in the region. We compared satellite derived data of Total Ozone Mapping Spectrometer-Aerosol Index (TOMS-AI), MODIS (Terra and Aqua) with those of ground-based Sunphotometer AERONET measurements. In general, there exits good relationship between MODIS (Terra and Aqua) and the ground-based AERONET measurements with correlation coefficients, R2 › 0.8 reported in all stations. However low coefficients (as low as 0.40) were obtained in all the stations for regressions between TOMS AI and ground-based Sunphotometer AERONET data. Abstract-The Sahelian West Africa (Long 20W:20E, Lat 0:30N) by its climatological and geographical conditions is a key region for the characterization of global atmospheric aerosol optical properties. This study evaluates the spatial and temporal variation of the Aerosol Optical Depth (AOD 440nm), aerosol particle size characterization (Angstrom exponent (? 440-675nm) at four locations (Agoufou, Banizoumbou, Cape Verde and Ilorin) over a period of January 2005 to December 2009. Results of the day-today AOD 440nm variations as well as the seasonal and annual variations are presented in order to establish the aerosol climatology in the region. We compared satellite derived data of Total Ozone Mapping Spectrometer-Aerosol Index (TOMS-AI), MODIS (Terra and Aqua) with those of ground-based Sunphotometer AERONET measurements. In general, there exits good relationship between MODIS (Terra and Aqua) and the ground-based AERONET measurements with correlation coefficients, R 2 › 0.8 reported in all stations. However low coefficients (as low as 0.40) were obtained in all the stations for regressions between TOMS AI and ground-based Sunphotometer AERONET data. 

 Modeling Earth Systems And Environment

 Journal

 Dynamic Response Of Monsoon Precipitation To Mineral Dust Radiative Forcing In The West Africa Region

 Julius Adekola Akinyoola · V. O. Ajayi · B. J. Abiodun · K. O. Ogunjobi · Imoleayo E. Gbode · Stephen Bunmi Ogungbenro

 2008

Mineral dust over West Africa region modulates summer monsoon through direct radiative forcing. This study examined the impact of mineral dust radiative forcing on West Africa Monsoon variability with the aid of Regional Climate Model (RegCM4) at 50 km grid resolution driven by ERA Interim re-analysis. Three experiments were performed; first with the non-dust aerosol version of the model (CONTROL), and second with the dust aerosol module (DUST) and with an increase in the dust concentration (DOUBLE DUST). The simulation was run from October, 2004 to December, 2005 over West Africa domain with the first 3 months taken as spin up for model stability. The result shows that there was no significant change with Control and Dust case experiment but as the dust AOD increases from 1.0 to 2.0, radiation flux at the Top of Atmosphere changes from ? 60 to ? 80 W/m² in the Double dust experiment. The Surface Long-wave Radiation Flux of 8.0 W/m² remains unchanged in both cases. The Outgoing Long-wave Radiation (OLR) flux changes from 2.0 to 4.0 W/m² indicating reduction in convective formation and as well as decrease in precipitation of 2 mm/day in the Sahel, while precipitation increases from 2 to 4 mm/day in the Guinea coast region. There was also strengthening of TEJ core and weakening of AEJ above average as dust concentration increases in some parts of the region during the monsoon period. The air temperature increases from 22.5 to 38.5 °C in both cases from coastal area to Sahelian region of West Africa. It was concluded that substantial amount of dust concentration in the atmosphere could trigger and increase radiative forcing of aerosols thereby sensitive to monsoon variability and results in enhancement of precipitation amount in the Guinea coast and reduction of precipitation amount in the Sahel region of West Africa. Meanwhile, there is need to inquire more into difference aerosol concentration per specie that can trigger or increase radiative forcing in the atmosphere. 

 Theoretical And Applied Climatology

 Journal

 The Synoptic And Optical Characteristics Of The Harmattan Dust Spells Over Nigeria

 Kehinde Olufunso Ogunjobi, Ajayi Vincent, Ifeoluwa Adebowale Balogun, Zhuanshi He

 2008

The synoptic and optical characteristic of days during severe dust spells of December 1998, January 2000, February 2001, Marchstract">The synoptic and optical characteristic of days during severe dust spells of December 1998, January 2000, February 2001, March 2003 and January 2005 at Ilorin (8°19?N, 4°20?E), Nigeria are investigated in this study. For example, during the severe dust 2003 and January 2005 at Ilorin (8°19?N, 4°20?E), Nigeria are investigated in this study. For example, during the severe dust storm of 5 January 2005 a strong synoptic-scale ridge developed which caused a shift in the position of the anticyclone over storm of 5 January 2005 a strong synoptic-scale ridge developed which caused a shift in the position of the anticyclone over the desert region. These conditions led to a higher pressure gradient, and in turn resulted in the generation of dust at the the desert region. These conditions led to a higher pressure gradient, and in turn resulted in the generation of dust at the 900?hPa level and wind speeds of up to ?13?m/s over the source region between Bilma (18°12?N, 12°55?E), Faya Largeau (17°55?N, 900?hPa level and wind speeds of up to ?13?m/s over the source region between Bilma (18°12?N, 12°55?E), Faya Largeau (17°55?N, 19°07?E) and Maiduguri (11°50?N, 13°09?E) during the dust spells. Spectral aerosol optical depth ?a?, Angström parameters (?440-500?nm and ?) derived from sunphotometer measurements and horizontal visibility (km) were used to study aerosol optical characteristics 19°07?E) and Maiduguri (11°50?N, 13°09?E) during the dust spells. Spectral aerosol optical depth ?a?, Angström parameters (?440-500?nm and ?) derived from sunphotometer measurements and horizontal visibility (km) were used to study aerosol optical characteristics during and after the winter “harmattan” dust days. It was found that the daily mean ?a500?nm during the dust episodes ranged between 0.31 and 3.28, with an average of 0.98 ± 0.50. ?a? showed a pronounced temporal trend, with maximum dust loading during intense dust haze as ?a500?nm increased from a daily average value of 0.68 ± 0.48 to values >2.0 during severe dust spells. Daily mean spectral variationsaximum dust loading during intense dust haze as ?a500?nm increased from a daily average value of 0.68 ± 0.48 to values >2.0 during severe dust spells. Daily mean spectral variations of the Angstrom exponent ? show striking changes especially at high ?a?, when coarse mode aerosol dominate the accumulation mode aerosol. During the dust spells of 1998–2005 average horizontal of the Angstrom exponent ? show striking changes especially at high ?a?, when coarse mode aerosol dominate the accumulation mode aerosol. During the dust spells of 1998–2005 average horizontal visibility was reduced to as low as 1.66 ± 0.34?km at Ilorin with an increase in average ?a500?nm and ? to ?2.06 ± 0.48 and 1.87 ± 0.49, respectively. However, for cases with strong biomass burning aerosol ?a500?nm = 0.67 with ? and ? = 1.02 ± 0.08 and 0.31 ± 0.06, respectively. In some cases, smoke particles mix with desert dust to produce visibility was reduced to as low as 1.66 ± 0.34?km at Ilorin with an increase in average ?a500?nm and ? to ?2.06 ± 0.48 and 1.87 ± 0.49, respectively. However, for cases with strong biomass burning aerosol ?a500?nm = 0.67 with ? and ? = 1.02 ± 0.08 and 0.31 ± 0.06, respectively. In some cases, smoke particles mix with desert dust to produce intermediate values of ?. A trajectory analysis at three different levels (200, 500 and 1000?magl) during a severe dust and intermediate values of ?. A trajectory analysis at three different levels (200, 500 and 1000?magl) during a severe dust and biomass burning episode were further used to explain the transport of aerosols to Ilorin, Nigeria. biomass burning episode were further used to explain the transport of aerosols to Ilorin, Nigeria.