Hydroelectric power production from Garafiri dam and rainfall are essential elements with the observation of hydroelectric power production in West African power system,particularly in Guinea.This article focuses on t...Hydroelectric power production from Garafiri dam and rainfall are essential elements with the observation of hydroelectric power production in West African power system,particularly in Guinea.This article focuses on the study and the influence of climate variability on hydroelectric power production at Garafiri dam over 16-year period(2008-2023).The aim of this work is to show the correlation between rainfall anomalies and hydroelectric power production at Garafiri dam.The method used consists of calculating precipitation anomalies at Garafiri site and those for the production of hydroelectric power from Garafiri dam over the study period.This approach led us to calculate the anomalies,leading to the study on climatic variability,in order to establish correlation between rainfall and hydroelectric power dam’s production.The trend with the correlation found made it possible to carry out a significance test between these two variables.These results clearly show that rainfall in Garafiri site increases hydroelectric power production and vice versa,which explains the interdependence between these two parameters,i.e.climatic variability and hydroelectric power production.展开更多
The SST variability during the summer period in the northeastern tropical Atlantic region (NTA) is characterized by an alternation of warming/cooling which represents 87% of the total variability. The aim of this pape...The SST variability during the summer period in the northeastern tropical Atlantic region (NTA) is characterized by an alternation of warming/cooling which represents 87% of the total variability. The aim of this paper is to study the atmospheric responses as well as the precipitation associated with these oceanic conditions. Based on Reynolds’s SST from 1982 to 2019, a normalized Northern Tropical Atlantic index (NTAI) is computed into the region between 15° - 25°W;12° - 16°N and a composite analysis is then performed. It is shown that the NTAI is significantly correlated with the SST’s first principal component mode (PC1) in this region. Moreover, the composite of SST anomalies and atmospheric parameters exhibits a strong local ocean-atmosphere interaction which highly impacts the large-scale atmospheric circulation in West Africa, particularly in the western Sahel. An in-depth analysis shows that the atmospheric response to the warm (cold) SST is a cyclonic (anticyclonic) circulation in the lower layers near the West Africa Coast. This cyclonic (anticyclonic) circulation strengthens/reduces the moisture transport towards the continent in the low levels. In the middle layers of the atmosphere (500 hPa), the warm (cold) composite is associated with a decrease (increase) in the intensity of the African Easterly Jet (AEJ) whereas, in the upper atmosphere (200 hPa), the strengthening (weakening) of the Tropical Easterly Jet (TEJ) is observed. With regard to the composite precipitation field, a positive/negative SST anomaly is associated with significantly enhanced/reduced rainfall in the western Sahelian region. It is found that this relationship (correlation) increases as we are closer to the coasts.展开更多
Monthly means of boundary layer height (BLH) over West Africa are presented based on 36 years (1979-2014) of six-hourly ERA-Interim reanalysis. In this region, we found that there is a link between the West Africa Mon...Monthly means of boundary layer height (BLH) over West Africa are presented based on 36 years (1979-2014) of six-hourly ERA-Interim reanalysis. In this region, we found that there is a link between the West Africa Monsoon (WAM) and the monthly means of BLH in the summer. The trend and empirical orthogonal function (EOF) of BLH are presented, including the mid July variability of BLH with the precipitation. The dominant EOF of BLH accounts for around 42% of the variance with slightly large amplitude in the north while relatively small in the equatorial band. The second EOF which accounts for 16.4%, describes a longitudinal contrast with a zonal gradient. The relationship between BLH and precipitation is found using the canonical correlation analysis (CCA). Significant trends of the first and second pairs of BLH with precipitation are shown. The first and second CCA pair has a correlation of 68% and 60% with 12.2 and 10.8 degrees of freedom respectively. The critical correlation coefficients at the 95% level are 0.21 and 0.65 for the first and second CCA pairs respectively. This first CCA pair mostly determines the arid and semi-arid areas where the rate of explained regional variance is about 78% in the arid area and 73% in the semi-arid area. For the second pair of CCA, the rate of explained regional variance is more than 60% in the Guinea coast and wet equatorial area.展开更多
Haboob occurrence strongly impacts the annual variability of airborne desert dust in North Africa.In fact,more dust is raised from erodible surfaces in the early summer(monsoon)season when deep convective storms are c...Haboob occurrence strongly impacts the annual variability of airborne desert dust in North Africa.In fact,more dust is raised from erodible surfaces in the early summer(monsoon)season when deep convective storms are common but soil moisture and vegetation cover are low.On 27 June 2018,a large dust storm is initiated over North Africa associated with an intensive westward dust transport.Far away from emission sources,dust is transported over the Atlantic for the long distance.Dust plume is emitted by a strong surface wind and further becomes a type of haboob when it merges with the southwestward deep convective system in central Mali at 0200 UTC(27 June).We use satellite observations to describe and estimate the dust mass concentration during the event.Approximately 93%of emitted dust is removed the dry deposition from the atmosphere between sources(10°N–25°N;1°W–8°E)and the African coast(6°N–21°N;16°W–10°W).The convective cold pool has induced large economic and healthy damages,and death of animals in the northeastern side of Senegal.ERA5 reanalysis has shown that the convective mesoscale impacts strongly the climatological location of the Saharan heat low(SHL).展开更多
This research studies the capability of the Weather Research and Forecasting model coupled with the Chemistry/Aerosol module(WRF-Chem)with and without parametrization to reproduce a dust storm,which was held on 27th J...This research studies the capability of the Weather Research and Forecasting model coupled with the Chemistry/Aerosol module(WRF-Chem)with and without parametrization to reproduce a dust storm,which was held on 27th June 2018 over Sahara region.The authors use satellite observations and ground-based measurements to evaluate the WRF-Chem simulations.The sensitivities of WRF-Chem Model are tested on the replication of haboob features with a tuned GOCART aerosol module.Comparisons of simulations with satellite and ground-based observations show that WRF-Chem is able to reproduce the Aerosol Optical Depth(AOD)distribution and associated changes of haboob in the meteorological fields with temperature drops of about 9℃and wind gust 20 m·s–1.The WRF-Chem Convec-tion-permitting model(CPM)shows strong 10-meter winds induced a large dust emission along the leading edge of a convective cold pool(LECCP).The CPM indicates heavy dust transported over the West African coast(16°W-10°W;6°N-21°N)which has a potential for long-distance travel on 27th June between 1100 UTC and 1500 UTC.The daily precipitation is improved in the CPM with a spatial distribution similar to the GPM-IMERG precipitation and maxi-mum rainfall located at the right place.As well as raising a large amount of dust,the haboob caused considerable dam-age along its route.展开更多
This study aims to examine the atmospheric conditions characterising fog phenomena on the Senegalese coast focusing on two specific instances that occurred on April 3 and April 30,2023.These events were detected by th...This study aims to examine the atmospheric conditions characterising fog phenomena on the Senegalese coast focusing on two specific instances that occurred on April 3 and April 30,2023.These events were detected by the LIDAR Ceilometer installed at LPAOSF/ESP/UCAD and confirmed on the METARs of the meteorological stations at Dakar and Diass airports.The LIDAR’s backscatter signal showed that the fog of April 3 started around midnight with a vertical extension at 100 m altitude and dissipated around 10 a.m.The April 30 event characterized by a good vertical extension from the surface up to 300 m above sea level,was triggered just after 2 a.m.and lasted around 3 hours.The results showed that a decrease in temperature,accompanied by an increase in humidity and light wind,is favorable for the triggering and persistence of fog.Sea Level Pressure(SLP)anomaly fields show two distinct configurations.The April 3 event was characterized by a zonal dipole of SLP anomalies between the Sahara and the northern Senegalese coast,while the April 30 event was characterized by a meridional dipole between the Sahara and the Gulf of Guinea area as far as the equatorial Atlantic.A weakening of the pressure around the study area was observed in both cases,allowing moisture advection to favor the onset of fog.The hovmoller diagrams of relative humidity and wind show that a good vertical extension of humidity associated with a westerly wind in the lower layers plays an important role in the formation and persistence of fog.The presence of dry air associated with a weak easterly wind in the middle layers could explain the low vertical extension of the fog on April 3.A strong wind in the lower layers would be responsible for the premature dissipation of the April 30 fog.展开更多
In this study, we focused on describing the trends of Extreme Precipitation Indices (EPI) in Senegal and analyzing the significant links between their variability and key climatic factors such as the El Niño-Sout...In this study, we focused on describing the trends of Extreme Precipitation Indices (EPI) in Senegal and analyzing the significant links between their variability and key climatic factors such as the El Niño-Southern Oscillation Index (ONI), the Land-Ocean Temperature Index (LOTI), and the Land Surface Temperature Index (LST). Based on a century of daily rainfall data from various Senegalese stations, this study utilized twelve (12) EPIs calculated according to the definitions of the Expert Team on Climate Change Detection and Indices (ETCCDI). To analyze the temporal variation characteristics of extreme precipitation, the Mann-Kendall (MK) test was employed to perform a uniformity test on the precipitation data series. A dependence method through differentiation was used to remove data trends and observe correlations between the climate change indices ONI, LOTI, LST, and EPIs. An approach based on lagged correlations between the ONI index and the EPIs was applied to evaluate the predictability of extreme precipitation patterns in Senegal. Trend analysis indicates a significant decrease in total precipitation and frequency and intensity indices in most stations, while duration indices show no clear trend. Regarding their interannual variability, the analysis shows negative correlations between ONI and total precipitation, consistent with the known influence of ENSO on Sahel precipitation. Correlations with LOTI and LST indices, on the other hand, suggest that the Clausius-Clapeyron theory does not hold at Senegal’s latitudes, but that adjacent Atlantic ocean warming influence is crucial in modulating extreme precipitation patterns. Finally, on the predictability of extreme precipitation, the study shows a significant signal up to three months in advance with ENSO for 58% of the EPIs and up to two months in advance for 90% of the EPIs.展开更多
The period of the 70s and 80s was marked by a drought in the Sahelian coun-tries.However,since the beginning of the 21st century,these countries have experienced a resurgence of heavy rainfall and devastating floods,c...The period of the 70s and 80s was marked by a drought in the Sahelian coun-tries.However,since the beginning of the 21st century,these countries have experienced a resurgence of heavy rainfall and devastating floods,causing in-estimable socio-economic damage and losses.The objective of this work is to study the dynamics of atmospheric conditions associated with seventeen ex-treme rainfall events listed in the database of the Directorate of Civil Protection of Senegal and having caused significant socio-economic impacts between 2000 and 2017.This study was carried out using satellite products and atmospheric reanalysis data.The results of the analyses of the various atmospheric parame-ters studied show,at the synoptic scale,that extreme rainfall events are mainly modulated by African easterly waves.Strong moisture transport convergences in the lower tropospheric layers due to vortices associated with these waves are recorded.A response of this moisture convergence in the lower layers accom-panied by vertical moisture transport is highlighted by strong anomalies and wind divergence.This configuration corresponds to the presence of a vertically well-structured convective system.The analysis of atmospheric parameters such as relative vorticity,wind,relative humidity and precipitable water shows that they are good indicators to characterize rainfall extremes.The behavior of the anomalies of these variables shows the presence of a significant amount of moisture in the tropospheric column and the most marked pressure levels are between 850 and 700-hPa,and in the upper layers around 200-hPa.展开更多
The Republic of Guinea experiences a tropical climate marked by a dry season influenced by the Harmattan winds and a rainy season driven by the West African monsoon,with a mean annual rainfall of approximately 1835 mm...The Republic of Guinea experiences a tropical climate marked by a dry season influenced by the Harmattan winds and a rainy season driven by the West African monsoon,with a mean annual rainfall of approximately 1835 mm.This study examines precipitation trends using meteorological data from twelve synoptic stations over the period 1983-2013.Twelve precipitation indices,classified into four categories:hydrological,agro-hydrological,agronomic,and extreme precipitation indices,were analyzed to assess spatiotemporal variability.Trends were evaluated using the Mann-Kendall test at significance levels of 90%.Results reveal a pronounced north-south gradient in rainfall distribution,with the south receiving more abundant and intense precipitation.Agro-hydrological indices indicate that the rainy season begins around mid-January in southern regions,while the monsoon onset occurs nationwide by May 1st.Seven-day wet spells are frequent in the south,whereas dry spells predominate in northern areas.Conakry exhibits a high frequency of extreme wet events,in contrast to northern regions,which are more susceptible to severe dry conditions.Trend analysis shows a significant increase in wet-day indices,while indices related to dry days and extreme rainfall events display a statistically significant decrease.展开更多
文摘Hydroelectric power production from Garafiri dam and rainfall are essential elements with the observation of hydroelectric power production in West African power system,particularly in Guinea.This article focuses on the study and the influence of climate variability on hydroelectric power production at Garafiri dam over 16-year period(2008-2023).The aim of this work is to show the correlation between rainfall anomalies and hydroelectric power production at Garafiri dam.The method used consists of calculating precipitation anomalies at Garafiri site and those for the production of hydroelectric power from Garafiri dam over the study period.This approach led us to calculate the anomalies,leading to the study on climatic variability,in order to establish correlation between rainfall and hydroelectric power dam’s production.The trend with the correlation found made it possible to carry out a significance test between these two variables.These results clearly show that rainfall in Garafiri site increases hydroelectric power production and vice versa,which explains the interdependence between these two parameters,i.e.climatic variability and hydroelectric power production.
文摘The SST variability during the summer period in the northeastern tropical Atlantic region (NTA) is characterized by an alternation of warming/cooling which represents 87% of the total variability. The aim of this paper is to study the atmospheric responses as well as the precipitation associated with these oceanic conditions. Based on Reynolds’s SST from 1982 to 2019, a normalized Northern Tropical Atlantic index (NTAI) is computed into the region between 15° - 25°W;12° - 16°N and a composite analysis is then performed. It is shown that the NTAI is significantly correlated with the SST’s first principal component mode (PC1) in this region. Moreover, the composite of SST anomalies and atmospheric parameters exhibits a strong local ocean-atmosphere interaction which highly impacts the large-scale atmospheric circulation in West Africa, particularly in the western Sahel. An in-depth analysis shows that the atmospheric response to the warm (cold) SST is a cyclonic (anticyclonic) circulation in the lower layers near the West Africa Coast. This cyclonic (anticyclonic) circulation strengthens/reduces the moisture transport towards the continent in the low levels. In the middle layers of the atmosphere (500 hPa), the warm (cold) composite is associated with a decrease (increase) in the intensity of the African Easterly Jet (AEJ) whereas, in the upper atmosphere (200 hPa), the strengthening (weakening) of the Tropical Easterly Jet (TEJ) is observed. With regard to the composite precipitation field, a positive/negative SST anomaly is associated with significantly enhanced/reduced rainfall in the western Sahelian region. It is found that this relationship (correlation) increases as we are closer to the coasts.
文摘Monthly means of boundary layer height (BLH) over West Africa are presented based on 36 years (1979-2014) of six-hourly ERA-Interim reanalysis. In this region, we found that there is a link between the West Africa Monsoon (WAM) and the monthly means of BLH in the summer. The trend and empirical orthogonal function (EOF) of BLH are presented, including the mid July variability of BLH with the precipitation. The dominant EOF of BLH accounts for around 42% of the variance with slightly large amplitude in the north while relatively small in the equatorial band. The second EOF which accounts for 16.4%, describes a longitudinal contrast with a zonal gradient. The relationship between BLH and precipitation is found using the canonical correlation analysis (CCA). Significant trends of the first and second pairs of BLH with precipitation are shown. The first and second CCA pair has a correlation of 68% and 60% with 12.2 and 10.8 degrees of freedom respectively. The critical correlation coefficients at the 95% level are 0.21 and 0.65 for the first and second CCA pairs respectively. This first CCA pair mostly determines the arid and semi-arid areas where the rate of explained regional variance is about 78% in the arid area and 73% in the semi-arid area. For the second pair of CCA, the rate of explained regional variance is more than 60% in the Guinea coast and wet equatorial area.
基金This work is supported by UK Research and Innovation as part of the Global Challenges Research Fund,African SWIFT programme,grant number NE/P021077/1,The Agence Nationale de l’Aviation civile et de la Météorologie(ANACIM),ICARE Data and services center,University of Lille,the National Aeronautics and Space Administration(NASA)and National Oceanic and Atmospheric Administration(NOAA)are owed for sharing ground observations and satellite data.
文摘Haboob occurrence strongly impacts the annual variability of airborne desert dust in North Africa.In fact,more dust is raised from erodible surfaces in the early summer(monsoon)season when deep convective storms are common but soil moisture and vegetation cover are low.On 27 June 2018,a large dust storm is initiated over North Africa associated with an intensive westward dust transport.Far away from emission sources,dust is transported over the Atlantic for the long distance.Dust plume is emitted by a strong surface wind and further becomes a type of haboob when it merges with the southwestward deep convective system in central Mali at 0200 UTC(27 June).We use satellite observations to describe and estimate the dust mass concentration during the event.Approximately 93%of emitted dust is removed the dry deposition from the atmosphere between sources(10°N–25°N;1°W–8°E)and the African coast(6°N–21°N;16°W–10°W).The convective cold pool has induced large economic and healthy damages,and death of animals in the northeastern side of Senegal.ERA5 reanalysis has shown that the convective mesoscale impacts strongly the climatological location of the Saharan heat low(SHL).
文摘This research studies the capability of the Weather Research and Forecasting model coupled with the Chemistry/Aerosol module(WRF-Chem)with and without parametrization to reproduce a dust storm,which was held on 27th June 2018 over Sahara region.The authors use satellite observations and ground-based measurements to evaluate the WRF-Chem simulations.The sensitivities of WRF-Chem Model are tested on the replication of haboob features with a tuned GOCART aerosol module.Comparisons of simulations with satellite and ground-based observations show that WRF-Chem is able to reproduce the Aerosol Optical Depth(AOD)distribution and associated changes of haboob in the meteorological fields with temperature drops of about 9℃and wind gust 20 m·s–1.The WRF-Chem Convec-tion-permitting model(CPM)shows strong 10-meter winds induced a large dust emission along the leading edge of a convective cold pool(LECCP).The CPM indicates heavy dust transported over the West African coast(16°W-10°W;6°N-21°N)which has a potential for long-distance travel on 27th June between 1100 UTC and 1500 UTC.The daily precipitation is improved in the CPM with a spatial distribution similar to the GPM-IMERG precipitation and maxi-mum rainfall located at the right place.As well as raising a large amount of dust,the haboob caused considerable dam-age along its route.
文摘This study aims to examine the atmospheric conditions characterising fog phenomena on the Senegalese coast focusing on two specific instances that occurred on April 3 and April 30,2023.These events were detected by the LIDAR Ceilometer installed at LPAOSF/ESP/UCAD and confirmed on the METARs of the meteorological stations at Dakar and Diass airports.The LIDAR’s backscatter signal showed that the fog of April 3 started around midnight with a vertical extension at 100 m altitude and dissipated around 10 a.m.The April 30 event characterized by a good vertical extension from the surface up to 300 m above sea level,was triggered just after 2 a.m.and lasted around 3 hours.The results showed that a decrease in temperature,accompanied by an increase in humidity and light wind,is favorable for the triggering and persistence of fog.Sea Level Pressure(SLP)anomaly fields show two distinct configurations.The April 3 event was characterized by a zonal dipole of SLP anomalies between the Sahara and the northern Senegalese coast,while the April 30 event was characterized by a meridional dipole between the Sahara and the Gulf of Guinea area as far as the equatorial Atlantic.A weakening of the pressure around the study area was observed in both cases,allowing moisture advection to favor the onset of fog.The hovmoller diagrams of relative humidity and wind show that a good vertical extension of humidity associated with a westerly wind in the lower layers plays an important role in the formation and persistence of fog.The presence of dry air associated with a weak easterly wind in the middle layers could explain the low vertical extension of the fog on April 3.A strong wind in the lower layers would be responsible for the premature dissipation of the April 30 fog.
文摘In this study, we focused on describing the trends of Extreme Precipitation Indices (EPI) in Senegal and analyzing the significant links between their variability and key climatic factors such as the El Niño-Southern Oscillation Index (ONI), the Land-Ocean Temperature Index (LOTI), and the Land Surface Temperature Index (LST). Based on a century of daily rainfall data from various Senegalese stations, this study utilized twelve (12) EPIs calculated according to the definitions of the Expert Team on Climate Change Detection and Indices (ETCCDI). To analyze the temporal variation characteristics of extreme precipitation, the Mann-Kendall (MK) test was employed to perform a uniformity test on the precipitation data series. A dependence method through differentiation was used to remove data trends and observe correlations between the climate change indices ONI, LOTI, LST, and EPIs. An approach based on lagged correlations between the ONI index and the EPIs was applied to evaluate the predictability of extreme precipitation patterns in Senegal. Trend analysis indicates a significant decrease in total precipitation and frequency and intensity indices in most stations, while duration indices show no clear trend. Regarding their interannual variability, the analysis shows negative correlations between ONI and total precipitation, consistent with the known influence of ENSO on Sahel precipitation. Correlations with LOTI and LST indices, on the other hand, suggest that the Clausius-Clapeyron theory does not hold at Senegal’s latitudes, but that adjacent Atlantic ocean warming influence is crucial in modulating extreme precipitation patterns. Finally, on the predictability of extreme precipitation, the study shows a significant signal up to three months in advance with ENSO for 58% of the EPIs and up to two months in advance for 90% of the EPIs.
文摘The period of the 70s and 80s was marked by a drought in the Sahelian coun-tries.However,since the beginning of the 21st century,these countries have experienced a resurgence of heavy rainfall and devastating floods,causing in-estimable socio-economic damage and losses.The objective of this work is to study the dynamics of atmospheric conditions associated with seventeen ex-treme rainfall events listed in the database of the Directorate of Civil Protection of Senegal and having caused significant socio-economic impacts between 2000 and 2017.This study was carried out using satellite products and atmospheric reanalysis data.The results of the analyses of the various atmospheric parame-ters studied show,at the synoptic scale,that extreme rainfall events are mainly modulated by African easterly waves.Strong moisture transport convergences in the lower tropospheric layers due to vortices associated with these waves are recorded.A response of this moisture convergence in the lower layers accom-panied by vertical moisture transport is highlighted by strong anomalies and wind divergence.This configuration corresponds to the presence of a vertically well-structured convective system.The analysis of atmospheric parameters such as relative vorticity,wind,relative humidity and precipitable water shows that they are good indicators to characterize rainfall extremes.The behavior of the anomalies of these variables shows the presence of a significant amount of moisture in the tropospheric column and the most marked pressure levels are between 850 and 700-hPa,and in the upper layers around 200-hPa.
基金funded by the Guinean Government through the project for the training of 5000 Masters and 1000 PhDs under the Ministry of Higher Education,Scientific Research,and Innovation(MESRSI).
文摘The Republic of Guinea experiences a tropical climate marked by a dry season influenced by the Harmattan winds and a rainy season driven by the West African monsoon,with a mean annual rainfall of approximately 1835 mm.This study examines precipitation trends using meteorological data from twelve synoptic stations over the period 1983-2013.Twelve precipitation indices,classified into four categories:hydrological,agro-hydrological,agronomic,and extreme precipitation indices,were analyzed to assess spatiotemporal variability.Trends were evaluated using the Mann-Kendall test at significance levels of 90%.Results reveal a pronounced north-south gradient in rainfall distribution,with the south receiving more abundant and intense precipitation.Agro-hydrological indices indicate that the rainy season begins around mid-January in southern regions,while the monsoon onset occurs nationwide by May 1st.Seven-day wet spells are frequent in the south,whereas dry spells predominate in northern areas.Conakry exhibits a high frequency of extreme wet events,in contrast to northern regions,which are more susceptible to severe dry conditions.Trend analysis shows a significant increase in wet-day indices,while indices related to dry days and extreme rainfall events display a statistically significant decrease.
