Oceanic Forcing on Interannual Variability of Sahel Heavy and Moderate Daily Rainfall

Diakhaté, Moussa; Rodríguez‐Fonseca, Belén; Gómara, Íñigo; Mohíno, Elsa; Dieng, Abdou Lahat; Gaye, Amadou Thierno

doi:10.1175/jhm-d-18-0035.1

Cited by 38 publications

(30 citation statements)

References 47 publications

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“…For the Mediterranean (Figures 1-3 and Figure 6), evidence was given that statistical prediction of heavy daily precipitation based on SSTs is possible up to one month in advance (predicting August precipitation in July) over a widespread area of the Sahel. These results are consistent with previous studies, as a warmer Mediterranean is known to foster humidity supply and convergence over vast Sahel areas during boreal summer [15,21,34,37]. On the contrary, colder SSTs over the Mediterranean are generally linked with a drier Sahel.…”

Section: Discussionsupporting

confidence: 93%

“…In this paper, the novel Sea Surface temperature based Statistical Seasonal ForeCAST model (S4CAST; [36]) was utilized to exhaustively analyze the timing and spatial structure of the relation between Sahel heavy/extreme (75/95th percentile) daily precipitation events and skillful oceanic predictors identified in previous work: El Niño Southern Oscillation (ENSO) and the Mediterranean Sea [37]. To this aim, the NOAA Extended Reconstructed Sea Surface Temperature (SST) data set (ERSST), the Climate Hazards Group Infrared Precipitation with Station Data (CHIRPS) and the European Center for Medium-Range Weather Forecasts (ECMWF) ERA-Interim reanalysis were utilized for the period of 1982-2015.…”

Section: Discussionmentioning

confidence: 99%

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Statistical-Observational Analysis of Skillful Oceanic Predictors of Heavy Daily Precipitation Events in the Sahel

et al. 2020

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In this paper, the sea surface temperature (SST) based statistical seasonal forecast model (S4CAST) is utilized to examine the spatial and temporal prediction skill of Sahel heavy and extreme daily precipitation events. As in previous studies, S4CAST points out the Mediterranean Sea and El Niño Southern Oscillation (ENSO) as the main drivers of Sahel heavy/extreme daily rainfall variability at interannual timescales (period 1982–2015). Overall, the Mediterranean Sea emerges as a seasonal short-term predictor of heavy daily rainfall (1 month in advance), while ENSO returns a longer forecast window (up to 3 months in advance). Regarding the spatial skill, the response of heavy daily rainfall to the Mediterranean SST forcing is significant over a widespread area of the Sahel. Contrastingly, with the ENSO forcing, the response is only significant over the southernmost Sahel area. These differences can be attributed to the distinct physical mechanisms mediating the analyzed SST-rainfall teleconnections. This paper provides fundamental elements to develop an operational statistical-seasonal forecasting system of Sahel heavy and extreme daily precipitation events.

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Section: Discussionsupporting

confidence: 93%

Section: Discussionmentioning

confidence: 99%

Statistical-Observational Analysis of Skillful Oceanic Predictors of Heavy Daily Precipitation Events in the Sahel

et al. 2020

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“…The ERA5 dataset, a reanalysis product from the European Centre for Medium-Range Weather Forecasts (ECMWF, Hersbach et al, 2020), is used as a reference to evaluate the performance of the CMIP6 models in simulating the surface and atmospheric fields under present-day conditions. ERA5 has replaced ERA-Interim (Dee et al, 2011) that has been widely used to study the characteristics of the West African climate (Manzanas et al, 2014;Lavaysse et al, 2015;Kebe et al, 2016;Raj et al, 2018;Maranan et al, 2018;Diakhaté et al, 2019Diakhaté et al, , 2020Wainwright et al, 2019). ERA5 for instance shows an improvement of the rainfall representation over Burkina Faso (Tall et al, 2019), which is a part of the Sahelian region.…”

Section: Methodsmentioning

confidence: 99%

“…The difference of the wind divergence between 200 hPa and 850 hPa levels (DIV200/850) is used to evaluate the direction and intensity of the vertical air motion (Gómara et al, 2017;Diakhaté et al, 2019). Positive values of this difference (upper level minus low level) means that there is a low level convergence of the wind, an ascent and a divergence at high level.…”

Section: Methodsmentioning

confidence: 99%

Weakened impact of the Atlantic Niño on the future equatorial Atlantic and Guinean Coast rainfall

Worou

Goosse

Fichefet

et al. 2021

Preprint

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Abstract. The Guinea Coast is the southern part of the West African continent. Its summer rainfall variability mostly occurs on interannual timescales and is highly influenced by the sea surface temperature (SST) variability in the eastern equatorial Atlantic, which is known as the Atlantic Niño (ATL3). Using historical simulations from 31 General Circulation Models (GCMs) participating in the sixth phase of the Coupled Model Intercomparison Project (CMIP6), we first show that these models are able to simulate reasonably well the rainfall annual cycle in the Guinea Coast, with, however, a wet bias during boreal summer. This bias is associated with too high mean summer SSTs in the eastern equatorial and south Atlantic regions. Next, we analyze the near-term, mid-term and long-term changes of the Atlantic Niño mode relative to the present-day situation, in a climate with a high anthropogenic emission of greenhouse gases. We find a gradual decrease of the equatorial Atlantic SST anomalies associated with the Atlantic Niño in the three periods of the future. This result reflects a possible reduction of the Atlantic Niño variability in the future due to a weakening of the Bjerkness feedback over the equatorial Atlantic. In a warmer climate, an oceanic extension of the Saharan Heat Low over the North Atlantic and an anomalous higher sea level pressure in the western equatorial Atlantic relative to the eastern equatorial Atlantic weaken the climatological trade winds over the equatorial Atlantic. As a result, the eastern equatorial Atlantic thermocline is deeper and responds less to Atlantic Niño events. Among the models that simulate a realistic rainfall pattern associated with ATL3 in the present-day climate, there are 15 GCMs which project a decrease of the Guinean Coast rainfall response related to ATL3, and 9 GCMs which show no substantial change in the patterns associated with ATL3. In these 15 models, the zonal wind response to the ATL3 over the equatorial Atlantic is strongly attenuated in the future climate. Similar results are found when the analysis is focused on the rainfall response to ATL3 over the equatorial Atlantic. There is a higher confidence in the reduction of the rainfall associated with ATL3 over the Atlantic Ocean than over the Guinea Coast. We also found a decrease of the convection associated with ATL3 in the majority of the models.

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“…These studies have demonstrated the important role of sea surface temperatures (SSTs) with respect to the last drought over the Sahel (Folland et al,1986;Mohino et al, 2011;Rodríguez-Fonseca et al, 2015). Interannual variation of rainfall is also related to the phase of El Niño-Southern Oscillation (ENSO; Janicot et al,1996;Diakhaté et al, 2019;Hart et al, 2019). However, state-of-the-art climate models still struggle to reproduce precipitation variability and trends in West Africa through the historical period, which is mainly due to their low skill in simulating the observed SST teleconnections (Rowell, 2013).…”

Section: Introductionmentioning

confidence: 99%

サヘルの極端に深い対流に対する熱帯対流圏界面遷移層の低温化の影響

Kodera¹,

Eguchi

Ueyama

et al. 2021

Journal of the Meteorological Society of Japan

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Previous studies have suggested that the recent increase in tropical extreme deep convection, in particular over Asia and Africa during the boreal summer, has occurred in association with a cooling in the tropical lower stratosphere. The present study is focused on the Sahel region of West Africa, where an increased occurrence of extreme precipitation events has been reported over recent decades. The results show that the changes over West Africa since the 1980s involve a cooling trend in the tropical lower stratosphere and tropopause layer, combined with a warming in the troposphere. This feature is similar to that which might result from increased greenhouse gas levels, but is distinct from the interannual variation of precipitation associated with the transport of water vapor from the Atlantic Ocean.It is suggested that the decrease in the vertical temperature gradient in the tropical tropopause region enhances extreme deep convection over the Sahel, where penetrating convection is frequent, whereas tropospheric warming suppresses the shallower convection over the Guinea Coast. The essential feature of the recent changes over West Africa is therefore the depth of convection, rather than the total amount of surface precipitation.

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Oceanic Forcing on Interannual Variability of Sahel Heavy and Moderate Daily Rainfall

Cited by 38 publications

References 47 publications

Statistical-Observational Analysis of Skillful Oceanic Predictors of Heavy Daily Precipitation Events in the Sahel

Statistical-Observational Analysis of Skillful Oceanic Predictors of Heavy Daily Precipitation Events in the Sahel

Weakened impact of the Atlantic Niño on the future equatorial Atlantic and Guinean Coast rainfall

サヘルの極端に深い対流に対する熱帯対流圏界面遷移層の低温化の影響

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