Details

Autor(en) / Beteiligte

• Talib, Joshua
• Taylor, Christopher M.
• Klein, Cornelia
• Harris, Bethan L.
• Anderson, Seonaid R.
• Semeena, Valiyaveetil S.

Titel

The sensitivity of the West African monsoon circulation to intraseasonal soil moisture feedbacks

Ist Teil von

• Quarterly journal of the Royal Meteorological Society, 2022-04, Vol.148 (745), p.1709-1730

Ort / Verlag

Chichester, UK: John Wiley & Sons, Ltd

Erscheinungsjahr

2022

Quelle

Wiley Online Library All Journals

Beschreibungen/Notizen

• Intraseasonal soil moisture variability has the potential to feed back onto the West Africa monsoon circulation through its influence on surface turbulent fluxes and planetary boundary‐layer characteristics. Using satellite observations and an atmospheric reanalysis, we investigate intraseasonal soil moisture–atmosphere feedbacks triggered by large‐scale dynamics within the West African monsoon. Surprisingly, even though the surface response across the Sahel to strong convection is short‐lived (days) and precipitation accumulations are spatially and temporally heterogeneous, a coherent regional‐scale surface response to intraseasonal variability is observed. This surface response then feeds back onto the West African monsoon circulation. For example, during a dry intraseasonal event, Sahelian surface soil moisture significantly decreases, which elevates surface temperatures by 1.5 °C and shifts the monsoon circulation southward by approximately 1.5° latitude. Also, during a wet event the surface moistens and cools which leads to a northward monsoon shift. Alongside a low‐level wind response, the African Easterly Jet (AEJ) also responds to surface changes due to variations in the meridional temperature gradient. For example, an increased temperature gradient during a dry event intensifies and shifts the AEJ southward. The combined response of low‐level monsoon westerlies and the AEJ impacts low‐level shear and characteristics of strong convection. Elevated low‐level shear during a dry event promotes an intensification of deep convection across southern West Africa. This study provides new insight into the sensitivity of the West African monsoon circulation to intraseasonal soil moisture feedbacks and encourages similar research in other regions. An improved understanding and model representation of soil moisture–atmosphere feedbacks has the potential to improve forecasts beyond daily time‐scales and enhance early warning systems. Using observations and an atmospheric reanalysis, we show that the surface response to intraseasonal precipitation variability across West Africa feeds back onto the atmosphere and affects the West African monsoon circulation. For example, during dry intraseasonal events, surface warming and drying across the Sahel shifts the monsoon circulation and African Easterly Jet southwards. The atmospheric response to surface flux changes induced by intraseasonal precipitation variability changes the characteristics of intraseasonal variability of the West African monsoon.