Water Vapour Transport Over Africa and the Atlantic Ocean During Summer 1979

Cadet, Daniel; Nnoli, N. O.

doi:10.1002/qj.49711347609

Cited by 82 publications

(24 citation statements)

References 16 publications

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“…Fontaine et al [2003], using NCEP-NCAR Reanalysis, identified the Sudanian and Guinean regions as sink areas in JAS and emphasized the weight of moisture advection in the interannual variability of rainfall. Their results are consistent with those of Cadet and Nnoli [1987] and Gong and Eltahir [1996], but in contrast with those of Brubaker et al [1993], Nicholson et al [1997], and also more recently Nieto et al [2006], who support the idea that recycling represents a significant contribution to the annual mean and interannual variability.…”

Section: Introductionsupporting

confidence: 85%

“…[43] Using a similar approach, Cadet and Nnoli [1987] estimate E as a residual and find also too large values (around 10 mm d −1 ) in the Sudanian zone in JAS. More recent studies using NWP model simulations found contrasting results.…”

Section: Annual Mean and Seasonal Cyclesupporting

confidence: 74%

“…For instance, coherent displacements of the moisture convergence band are observed and an increased MFC occurs over the Sahel in wet years. It may be due to an enhancement of the low-level moisture flux and a decrease of wind strength in the AEJ (the "main moisture artery" over West Africa according to Cadet and Nnoli [1987], which would be consistent with Fontaine et al [2003].…”

Section: Interannual Variabilitymentioning

confidence: 86%

“…[4] Studies of the West African water cycle are few. Cadet and Nnoli [1987] investigated water transport over West Africa and the Atlantic Ocean for the summer 1979 using winds from a European Centre for Medium-Range Weather Forecasts (ECMWF) analysis and humidity fields from satellite-based retrievals. They estimated water budgets and investigated the respective roles of evaporation over the Gulf of Guinea and evapotranspiration north to the Guinean coast.…”

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

West African Monsoon water cycle: 1. A hybrid water budget data set

Meynadier¹,

Bock²,

Guichard³

et al. 2010

J. Geophys. Res.

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[1] This study investigates the West African Monsoon water cycle with the help of a new hybrid water budget data set developed within the framework of the African Monsoon Multidisciplinary Analyses. Surface water and energy fluxes are estimated from an ensemble of land surface model simulations forced with elaborate precipitation and radiation products derived from satellite observations, while precipitable water tendencies are estimated from numerical weather prediction analyses. Vertically integrated atmospheric moisture flux convergence is estimated as a residual. This approach provides an advanced, comprehensive atmospheric water budget, including evapotranspiration, rainfall, and atmospheric moisture flux convergence, together with other surface fluxes such as runoff and net radiation. The annual mean and the seasonal cycle of the atmospheric water budget are presented and the couplings between budget terms are discussed for three climatologically distinct latitudinal bands between 6°N and 20°N. West Africa is shown to be alternatively a net source and sink region of atmospheric moisture, depending on the season (a source during the dry season and a sink during the wet season). Several limiting and controlling factors of the regional water cycle are highlighted, suggesting strong sensitivity to atmospheric dynamics and surface radiation. Some insight is also given into the underlying smaller-scale processes. The relationship between evapotranspiration and precipitation is shown to be very different between the Sahel and the regions more to the south and partly controlled by net surface radiation. Strong correlations are found between precipitation and moisture flux convergence over the whole region from daily to interannual time scales. Causality is also established between monthly mean anomalies. Hence, precipitation anomalies are preceded by moisture flux convergence anomalies and followed by moisture flux divergence and evapotranspiration anomalies. The results are discussed in comparison to other studies.

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Section: Introductionsupporting

confidence: 85%

Section: Annual Mean and Seasonal Cyclesupporting

confidence: 74%

Section: Interannual Variabilitymentioning

confidence: 86%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

West African Monsoon water cycle: 1. A hybrid water budget data set

Meynadier¹,

Bock²,

Guichard³

et al. 2010

J. Geophys. Res.

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show abstract

“…Especially, the density of radiosonde stations in Africa is very sparse [Parker et al, 2008]. Moreover, biases in these observations have been diagnosed and their impact on NWP products has been evidenced Agustí-Panareda et al, 2009], It is thus not surprising that poor consensus emerged from the past water cycle studies over West Africa which used either NWP products or directly radiosonde data [Lamb, 1983;Cadet and Nnoli, 1987;Brubaker et al, 1993;Fontaine et al, 2003;Bielli and Roca, 2009].…”

Section: Introductionmentioning

confidence: 99%

West African Monsoon water cycle: 2. Assessment of numerical weather prediction water budgets

et al. 2010

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[1] Water budgets from European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA)-Interim and National Centers for Environmental Prediction (NCEP) Reanalysis I and II are intercompared and compared to GPS precipitable water and to the 6 year hybrid budget data set described in part 1 of this study. Deficiencies are evidenced in the reanalyses which are most pronounced over the Sahel.Results from operational models (ECMWF Integrated Forecast System, NCEP Global Forecast System, and ARPEGE-Tropiques) and the special ECMWF African Monsoon Multidisciplinary Analyses reanalysis confirm and help understanding these findings. A bias (∼1-2 mm d −1 ) in precipitation and evapotranspiration leads to an unrealistic view of West Africa as a moisture source during the summer. North of the rainband (13°N-16°N), moisture flux convergence (MFC) shows a minimum in the NCEP models and divergence in the ECMWF models not consistent with the hybrid data set. This feature, added to presence of a deep layer of northerly dry air advected at midlevels (800-400 hPa), is thought to block the development of deep convection in the models and the northward propagation of the monsoonal rainband. The northerly flow is part of a shallow meridional circulation that is driven by the Saharan heat low. This circulation appears too strong in some of the models, a possible consequence of the too-approximate representation of physical processes and land surface properties over the Sahel. In most of the models, evapotranspiration shows poor connection with precipitation. This is linked with large analysis increments in precipitable water, soil moisture, and MFC. Despite the large biases affecting the water budget components in the models, temporal variations (seasonal and interannual) might nevertheless be recovered with reasonable accuracy.

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Sources of Sahelian‐Sudan moisture: Insights from a moisture‐tracing atmospheric model

et al. 2016

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The summer rainfall across Sahelian‐Sudan is one of the main sources of water for agriculture, human, and animal needs. However, the rainfall is characterized by large interannual variability, which has attracted extensive scientific efforts to understand it. This study attempts to identify the source regions that contribute to the Sahelian‐Sudan moisture budget during July through September. We have used an atmospheric general circulation model with an embedded moisture‐tracing module (Community Atmosphere Model version 3), forced by observed (1979–2013) sea‐surface temperatures. The result suggests that about 40% of the moisture comes with the moisture flow associated with the seasonal migration of the Intertropical Convergence Zone (ITCZ) and originates from Guinea Coast, central Africa, and the Western Sahel. The Mediterranean Sea, Arabian Peninsula, and South Indian Ocean regions account for 10.2%, 8.1%, and 6.4%, respectively. Local evaporation and the rest of the globe supply the region with 20.3% and 13.2%, respectively. We also compared the result from this study to a previous analysis that used the Lagrangian model FLEXPART forced by ERA‐Interim. The two approaches differ when comparing individual regions, but are in better agreement when neighboring regions of similar atmospheric flow features are grouped together. Interannual variability with the rainfall over the region is highly correlated with contributions from regions that are associated with the ITCZ movement, which is in turn linked to the Atlantic Multidecadal Oscillation. Our result is expected to provide insights for the effort on seasonal forecasting of the rainy season over Sahelian Sudan.

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Water Vapour Transport Over Africa and the Atlantic Ocean During Summer 1979

Cited by 82 publications

References 16 publications

West African Monsoon water cycle: 1. A hybrid water budget data set

West African Monsoon water cycle: 1. A hybrid water budget data set

West African Monsoon water cycle: 2. Assessment of numerical weather prediction water budgets

Sources of Sahelian‐Sudan moisture: Insights from a moisture‐tracing atmospheric model

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