scholarly journals Temporal variability of mineral dust concentrations over West Africa: analyses of a pluriannual monitoring from the AMMA Sahelian Dust Transect

2010 ◽  
Vol 10 (3) ◽  
pp. 8051-8101 ◽  
Author(s):  
B. Marticorena ◽  
B. Chatenet ◽  
J. L. Rajot ◽  
S. Traoré ◽  
M. Coulibaly ◽  
...  
Keyword(s):  
West Africa ◽  
Rainy Season ◽  
Seasonal Cycle ◽  
Mineral Dust ◽  
General Pattern ◽  
Regional Scale ◽  
Surface Wind ◽  
Dry Season ◽  
Dust Concentration ◽  
Dust Content

Abstract. The Sahelian belt is known to be a region where the mineral dust content is among the highest observed on Earth. In the framework of the AMMA (African Monsoon Multidisciplinary Analysis) International Program, a transect of 3 ground based stations, the "Sahelian Dust Transect" (SDT), has been deployed in order to obtain quantitative information on the mineral dust content and its variability over the Sahel. The three stations, namely Banizoumbou (Niger), Cinzana (Mali) and M'Bour (Senegal) are aligned around 14° N along the east-west main pathway of the Saharan and Sahelian dust towards the Atlantic Ocean. We discuss data collected between January 2006 and December 2008 to investigate the main characteristics of the mineral dust concentration over West Africa and their connection with the dominant meteorological situations. The succession of the dry season during which the Sahel is under the influence of the dry Harmattan wind and the wet season induced by the entrance of the monsoon flow is clearly identified from the basic meteorological parameters (air temperature and moisture, wind direction). Atmospheric dust concentrations at the three stations exhibit a similar seasonal cycle, with a monthly maximum during the dry season and a minimum occurring during the rainy season, indicating that the general pattern of dust concentration is similar at regional scale. This seasonal cycle of the dust concentrations is not phased with the seasonal cycle of surface wind velocity suggesting that it is mainly controlled by Saharan dust transport. A decrease in the dust concentration is observed when moving from Niger to Senegal. However, local dust emissions induced by strong surface winds are responsible for the occurrence of extremely high daily concentrations observed at the beginning of the rainy season.

scholarly journals Temporal variability of mineral dust concentrations over West Africa: analyses of a pluriannual monitoring from the AMMA Sahelian Dust Transect

2010 ◽  
Vol 10 (18) ◽  
pp. 8899-8915 ◽  
Author(s):  
B. Marticorena ◽  
B. Chatenet ◽  
J. L. Rajot ◽  
S. Traoré ◽  
M. Coulibaly ◽  
...  
Keyword(s):  
West Africa ◽  
Rainy Season ◽  
Seasonal Cycle ◽  
Mineral Dust ◽  
General Pattern ◽  
Regional Scale ◽  
Surface Wind ◽  
Dry Season ◽  
Dust Concentration ◽  
Saharan Dust

Abstract. The Sahelian belt is known to be a region where atmospheric levels of suspended mineral dust are among the highest observed on Earth. In the framework of the AMMA (African Monsoon Multidisciplinary Analysis) International Program, a transect of 3 ground based stations, the "Sahelian Dust Transect" (SDT), has been deployed in order to obtain quantitative information on the mineral dust content and its variability over the Sahel. The three stations, namely Banizoumbou (Niger), Cinzana (Mali) and M'Bour (Senegal) are aligned around 14° N along the east-westward main pathway of the Saharan and Sahelian dust towards the Atlantic Ocean. We discuss data collected between January 2006 and December 2008 to investigate the main characteristics of the mineral dust concentration over West Africa and their connection with the dominant meteorological situations. The succession of the dry season during which the Sahel is under the influence of the dry Harmattan wind and the wet season induced by the entrance of the monsoon flow is clearly identified from the basic meteorological parameters (air temperature and moisture, wind direction). Atmospheric dust concentrations at the three stations exhibit a similar seasonal cycle, with a monthly maximum during the dry season and a minimum occurring during the rainy season, indicating that the general pattern of dust concentration is similar at regional scale. This seasonal cycle of the dust concentrations is not phased with the seasonal cycle of surface wind velocity locally measured, suggesting that it is mainly controlled by Saharan dust transport. Local dust emissions induced by strong surface winds are responsible for the occurrence of extremely high daily concentrations observed at the beginning of the rainy season. A decrease in the dust concentration is observed when moving from Niger to Senegal.

scholarly journals Radiative forcing associated with a springtime case of Bodélé and Sudan dust transport over West Africa

2010 ◽  
Vol 10 (4) ◽  
pp. 8811-8858 ◽  
Author(s):  
C. Lemaître ◽  
C. Flamant ◽  
J. Cuesta ◽  
J.-C. Raut ◽  
P. Chazette ◽  
...  
Keyword(s):  
West Africa ◽  
Heating Rate ◽  
Radiative Forcing ◽  
Mineral Dust ◽  
Regional Scale ◽  
Longwave Radiation ◽  
Heating Rates ◽  
Dust Layer ◽  
In Situ Observations

Abstract. The radiative forcing due to mineral dust over West Africa is investigated using the radiative code STREAMER, as well as remote sensing and in situ observations gathered during the African Monsoon Multidisciplinary Analysis Special Observing Period (AMMA SOP). We focus on two days (13 and 14 June 2006) of an intense and long-lasting episode of dust being lifted in remote sources in Chad and Sudan and transported across West Africa in the African easterly jet region, during which airborne operations were conducted at the regional scale, from the southern fringes of the Sahara to the Gulf of Guinea. Profiles of heating rates are computed from airborne LEANDRE 2 and space-borne CALIOP lidar observations using two mineral dust model constrained by airborne in situ data and ground-based sunphotometer obtained during the campaign. Complementary space-borne observations (from MODIS) and in-situ observations such as dropsondes are also used to take into account a realistic infrared contribution of the water vapour. We investigate the variability of the heating rate on the vertical within a dust plume, as well as the contribution of longwave radiation to the heating rate and the radiative forcing of dust during the nighttime. The sensitivity of the so-derived heating rate is also analyzed for some key variables for which the associated uncertainties are quite large. During daytime, the warming associated with the presence of dust was found to be between 1.5 K day−1 and 4 K day−1, on average, depending on altitude and latitude. Strong warming (i.e. heating rates as high as 8 K day−1) was also observed locally in some limited part of the dust plumes. Obviously, during nighttime much smaller values of heating/cooling are retrieved (less than ±1 K day−1) but large enough to modify the low tropospheric equilibrium. Furthermore, cooling is observed as the result of the longwave forcing in the dust layer, while warming is observed below the dust layer, in the monsoon layer.

scholarly journals The role of aerosol–radiation–cloud interactions in linking anthropogenic pollution over southern west Africa and dust emission over the Sahara

2019 ◽  
Vol 19 (23) ◽  
pp. 14657-14676 ◽  
Author(s):  
Laurent Menut ◽  
Paolo Tuccella ◽  
Cyrille Flamant ◽  
Adrien Deroubaix ◽  
Marco Gaetani
Keyword(s):  
West Africa ◽  
Mineral Dust ◽  
Surface Wind ◽  
Dust Emission ◽  
Longwave Radiation ◽  
Atmospheric Composition ◽  
Anthropogenic Emissions ◽  
Dust Emissions ◽  
Aerosol Cloud ◽  
The Impact

Abstract. The aerosol direct and indirect effects are studied over west Africa in the summer of 2016 using the coupled WRF-CHIMERE regional model including aerosol–cloud interaction parameterization. First, a reference simulation is performed and compared with observations acquired during the Dynamics-aerosol-chemistry-cloud interactions in West Africa (DACCIWA) field campaign which took place in June and July 2016. Sensitivity experiments are also designed to gain insights into the impact of the aerosols dominating the atmospheric composition in southern west Africa (one simulation with halved anthropogenic emissions and one with halved mineral dust emissions). The most important effect of aerosol–cloud interactions is found for the mineral dust scenario, and it is shown that halving the emissions of mineral dust decreases the 2 m temperature by 0.5 K and the boundary layer height by 25 m on a monthly average (July 2016) and over the Saharan region. The presence of dust aerosols also increases (decreases) the shortwave (longwave) radiation at the surface by 25 W m−2. It is also shown that the decrease of anthropogenic emissions along the coast has an impact on the mineral dust load over west Africa by increasing their emissions in the Saharan region. It is due to a mechanism where particulate matter concentrations are decreased along the coast, imposing a latitudinal shift of the monsoonal precipitation and, in turn, an increase of the surface wind speed over arid areas, inducing more mineral dust emissions.

The Madden–Julian Oscillation’s Influence on Spring Rainy Season Precipitation over Equatorial West Africa*

2015 ◽  
Vol 28 (22) ◽  
pp. 8653-8672 ◽  
Author(s):  
Fisseha Berhane ◽  
Benjamin Zaitchik ◽  
Hamada S. Badr
Keyword(s):  
Indian Ocean ◽  
West Africa ◽  
Rainy Season ◽  
Regional Scale ◽  
Relative Strength ◽  
Boreal Summer ◽  
Kelvin Wave ◽  
Equatorial Wave ◽  
The Indian Ocean ◽  
Rain Rates

Abstract This paper characterizes the influence of the Madden–Julian oscillation (MJO) on spring rainy season (March–June) convection variability over equatorial West Africa (EWA) and investigates mechanisms of association. It is found that the MJO has a significant impact on convection and precipitation anomalies over the region. Over large portions of EWA, MJO impacts on rainfall constitute a difference on the order of 20%–50% from average daily rain rates for the season. This impact is primarily due to the direct influence of the eastward movement of the MJO convective core into EWA, which is associated with westerly low-level wind anomalies that advect moisture from the Atlantic Ocean to the region. In addition, equatorial Rossby and Kelvin waves triggered by MJO convection anomalies over the Indian Ocean have a significant and systematic influence on EWA spring rainy season precipitation. The Kelvin wave contribution and the relative strength of the direct MJO convective influence compared to that of equatorial wave activity differs from findings of studies that have examined MJO influence on EWA during boreal summer. In addition, MJO is found to influence precipitation extremes during spring rains in a manner that is not observed in summer. Importantly, in this analysis the influences of MJO convection and each of the MJO-associated convectively coupled equatorial waves frequently coincide, reaching EWA approximately 20 days after MJO convection initiates in the Indian Ocean. This coincident timing enhances the total MJO impact on the region, and it also implies that MJO events have potential for prediction of regional-scale convection and rainfall anomalies over EWA in this season.

scholarly journals Transport and vertical structure of aerosols and water vapor over West Africa during the African monsoon dry season

2009 ◽  
Vol 9 (1) ◽  
pp. 1831-1871
Author(s):  
S.-W. Kim ◽  
P. Chazette ◽  
F. Dulac ◽  
J. Sanak ◽  
B. Johnson ◽  
...  
Keyword(s):  
Water Vapor ◽  
West Africa ◽  
Biomass Burning ◽  
Surface Wind ◽  
Dry Season ◽  
Water Vapor Transport ◽  
Dust Particles ◽  
Tropospheric Aerosol ◽  
Biomass Burning Aerosol ◽  
High Concentrations

Abstract. We present observations of tropospheric aerosol and water vapor transport over West Africa and the associated meteorological conditions during the AMMA SOP-0 dry season experiment, which was conducted in West Africa in January–February 2006. This study combines data from ultra-light aircraft (ULA)-based lidar, airborne in-situ aerosol and gas measurements, standard meteorological measurements, satellite-based aerosol measurements, airmass trajectories, and radiosonde measurements. At Niamey (13.5° N, 2.2° E) the prevailing surface wind was from the northeast bringing dry dusty air from the Sahara desert. High concentrations of mineral dust aerosol were typically observed from the surface to 1.5 or 2 km associated with the Saharan airmasses. At higher altitudes the prevailing wind veered to the south or southeast bringing relatively warm and humid airmasses from the biomass burning regions to the Sahel (<10° N). These elevated layers had high concentrations of biomass burning aerosol and were typically observed between altitudes of 2–5 km. Meteorological analyses show these airmasses were advected upwards over the biomass burning regions through large-scale ascent, presumably driven by surface heating rather than pyro-convection. Aerosol vertical profiles obtained from the space-based lidar CALIOP onboard CALIPSO during January 2007 also showed the presence of dust particles (depolarization ~30%, color ratio <0) at low levels (<1.5 km) and biomass burning smoke aerosol (depolarization ratio <10%) between 2 and 5 km. CALIOP data indicated that these distinct continental dust and biomass burning aerosol layers likely mixed as they advected further south over the tropical Atlantic Ocean.

scholarly journals Pengaruh Suhu Permukaan Laut (SPL) terhadap Curah Hujan di Perairan Bali menggunakan Data Citra Satelit

2021 ◽  
Vol 4 (2) ◽  
pp. 1
Author(s):  
Ni Kadek Martini ◽  
I Wayan Nuarsa ◽  
I Wayan Gede Astawa Karang
Keyword(s):  
Correlation Coefficient ◽  
Strong Correlation ◽  
Rainy Season ◽  
Regional Scale ◽  
Time Lag ◽  
Dry Season ◽  
High Variability ◽  
Sea Surface ◽  
Weather Element ◽  
Level 3

Rainfall is a weather element. Sea surface temperatures (SST) affects precipitation. SST and rainfall have a high variability which can be measured by satellite. At a regional scale, a research of the effect of SST on rainfall analyzed island rainfall, which means that there is still little research on rainfall in the waters. This study purposed to find out the variability and correlation between SST and rainfall in the Bali waters.  It used satellite MODIS and TRMM for 10 years, started from 2010 to 2019. The data used was SST MODIS and rainfall TRMM level 3 with the geographic coordinates boundaries area 114.4281o East - 115.7145o East, and 7.8168o South 8.9868o South. The method of this study was correlation analyzed with time lag between of SST and rainfall. The variability of SST in the Bali waters were ranged from 25,2 oC to 31,6 oC. Furthermore, the variability of rainfall was ranged from 0 mm to 556,92 mm. The changes patterns of SST and precipitation in Bali water were related to the season in each month. The data showed that the SST was warmer in the rainy season compared to the SST in the dry season. Besides, the rainfall increases when entering the rainy season, and the decreases when entering the dry season. The correlation between SST and rainfall in this waters area ranged from weak to strong. Correlation formed in the rainy season is negative with a correlation coefficient between -0.34 to -0.74. However, in the dry season there was a positive correlation with a correlation coefficient ranging from 0.77 to 0.92.

scholarly journals Radiative heating rates profiles associated with a springtime case of Bodélé and Sudan dust transport over West Africa

2010 ◽  
Vol 10 (17) ◽  
pp. 8131-8150 ◽  
Author(s):  
C. Lemaître ◽  
C. Flamant ◽  
J. Cuesta ◽  
J.-C. Raut ◽  
P. Chazette ◽  
...  
Keyword(s):  
West Africa ◽  
Heating Rate ◽  
Mineral Dust ◽  
Regional Scale ◽  
Longwave Radiation ◽  
Radiative Heating ◽  
Heating Rates ◽  
Dust Layer ◽  
In Situ Observations

Abstract. The radiative heating rate due to mineral dust over West Africa is investigated using the radiative code STREAMER, as well as remote sensing and in situ observations gathered during the African Monsoon Multidisciplinary Analysis Special Observing Period (AMMA SOP). We focus on two days (13 and 14 June 2006) of an intense and long lasting episode of dust being lifted in remote sources in Chad and Sudan and transported across West Africa in the African easterly jet region, during which airborne operations were conducted at the regional scale, from the southern fringes of the Sahara to the Gulf of Guinea. Profiles of heating rates are computed from airborne LEANDRE 2 (Lidar Embarqué pour l'étude de l'Atmosphère: Nuages Dynamique, Rayonnement et cycle de l'Eau) and space-borne CALIOP (Cloud Aerosol Lidar and Infrared Pathfinder Satellite Observations) lidar observations using two mineral dust model constrained by airborne in situ data and ground-based sunphotometer obtained during the campaign. Complementary spaceborne observations (from the Moderate-resolution Imaging Spectroradiometer-MODIS) and in-situ observations such as dropsondes are also used to take into account the infrared contribution of the water vapour. We investigate the variability of the heating rate on the vertical within a dust plume, as well as the contribution of both shortwave and longwave radiation to the heating rate and the radiative heating rate profiles of dust during daytime and nighttime. The sensitivity of the so-derived heating rate is also analyzed for some key variables for which the associated uncertainties may be large. During daytime, the warming associated with the presence of dust was found to be between 1.5 K day−1 and 4 K day−1, on average, depending on altitude and latitude. Strong warming (i.e. heating rates as high as 8 K day−1) was also observed locally in some limited part of the dust plumes. The uncertainty on the heating rate retrievals in the optically thickest part of the dust plume was estimated to be between 0.5 and 1.4 K day−1. During nighttime much smaller values of heating/cooling are retrieved (less than ±1 K day−1). Furthermore, cooling is observed as the result of the longwave forcing in the dust layer, while warming is observed below the dust layer, in the monsoon layer.

scholarly journals Effects of seasonal variation in temperature and cultivar on yield and yield determination of irrigated groundnut (Arachis hypogaea) during the dry season in the Sahel of West Africa

1998 ◽  
Vol 131 (4) ◽  
pp. 439-448 ◽  
Author(s):  
B. R. NTARE ◽  
J. H. WILLIAMS ◽  
B. J. NDUNGURU
Keyword(s):  
West Africa ◽  
Arachis Hypogaea ◽  
Growth Rates ◽  
Rainy Season ◽  
Sowing Date ◽  
Crop Growth ◽  
Dry Season ◽  
Pod Yield ◽  
Sowing Dates ◽  
Yield Determination

In the Sudano-Sahelian zone of West Africa there is potential for groundnut (Arachis hypogaea L.) to be grown as a dry-season crop where irrigation is available. However, there are substantial variations in the temperatures during the post-rainy season that can be expected to influence growth and yield. An experiment at the ICRISAT Sahelian Centre was done in order to study the effect of sowing date on phenology, yield and the processes of yield determination for four groundnut cultivars under irrigation in the dry seasons of 1990/91 and 1991/92. Starting on 15 November, eight sowing dates at 2-weekly intervals were tested. Sowing date significantly affected phenology (time to emergence, flowering and maturity) with groundnut sown in November/December taking the longest time to reach these phenological stages. November and December sowings gave the highest pod yield within each year, despite the lowest crop growth rates (B), and yield declined progressively as sowing occurred later (50% decrease by March) despite increasing B. The observed responses appear to have been due to the effect of temperature differences during the pod-filling phase on partitioning. Partitioning (p) to pods was optimized at c. 30 C, with some indication of cultivar differences in partitioning response to temperature. Across all the environments, cultivars displayed substantial differences in yield stability. When sown late, yields were low and lines with high partitioning were the best. When sown early in the post-rainy season, cultivars with a high B value were the better choices. Plant habit differences and B suggest that radiation interception was a limitation to yield, particularly when the crops were sown in the cool months of the year. However, haulm yield and crop growth rates were not consistently affected by sowing date across the years, and cultivars demonstrated different degrees of stability for B. It is concluded that where pod has a price advantage over fodder, irrigated groundnut for the dry season should be sown in November to allow the crop to develop under the relatively cool temperatures that maximize pod yield. Further agronomic research is suggested to maximize B for individual cultivars for given sowing dates.

scholarly journals Prevalence and Severity of Nattrassia mangiferae Root and Stem Rot Pathogen of Cassava in Bénin

Plant Disease ◽  
2005 ◽  
Vol 89 (1) ◽  
pp. 12-16 ◽  
Author(s):  
W. Msikita ◽  
B. Bissang ◽  
B. D. James ◽  
H. Baimey ◽  
H. T. Wilkinson ◽  
...  
Keyword(s):  
West Africa ◽  
Root Rot ◽  
Rainy Season ◽  
Disease Incidence ◽  
Macrophomina Phaseolina ◽  
Dry Season ◽  
Stem Cuttings ◽  
Storage Roots ◽  
Fusarium Spp ◽  
Nattrassia Mangiferae

Root rot pathogens were found through diagnostic surveys in all departments (regions) of Bénin, West Africa, to affect 86 to 100% and 96 to 100% of cassava fields during the dry and rainy seasons, respectively. Disease incidence in individual fields ranged between 0 and 53%, and averaged 16 to 27% per department. Nattrassia mangiferae was consistently the most frequently isolated root rot pathogen (56% in the dry season and 22 to 52% in the rainy season). Pathogenicity of N. mangiferae was confirmed on four cultivars of cassava using stem cuttings and storage roots. For all four cultivars, N. mangiferae significantly reduced the number of roots. Lesions (3 to 15 cm long) formed on the lower stem portion of all inoculated plants, whereas control plants remained symptom free. On storage roots, the disease profile was similar to that formed on stem cuttings. Other root rot pathogens detected during the dry season were Macrophomina phaseolina (14.2%), Fusarium spp. (11.8%), Botryodiplodia theobromae (7.7%), and Pythium spp. (2.9%). During the rainy season, Fusarium spp. were the second most commonly isolated root rot pathogens in three departments (Atlantique, Borgou, and Mono). In Oueme and Zou, B. theobromae was the second most isolated root rot pathogen (ranging between 24 and 28%) during the rainy season. During the same season, Pythium spp. were pronounced in Borgou (18%), followed by Mono (11%), Atlantique (9%), Atacora (8%), Oueme (5%), and Zou (6%). Results of the study are discussed with a view to creating awareness of the destructive power of N. mangiferae, a hitherto poorly recognized root rot pathogen of cassava in Bénin and West Africa in general.

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