Seasonal forecasts of the Saharan Heat Low characteristics: A multi-model assessment

Cédric Gacial Ngoungué Langué (1, 2) , Christophe Lavaysse (1, 3) , Mathieu Vrac (4, 5) , Philippe Peyrille (6) , Cyrille Flamant (2)

1 IGE - Institut des Géosciences de l’Environnement
2 TROPO - LATMOS
3 JRC - European Commission - Joint Research Centre [Ispra]
4 LSCE - Laboratoire des Sciences du Climat et de l'Environnement [Gif-sur-Yvette]
5 ESTIMR - Extrèmes : Statistiques, Impacts et Régionalisation
6 CNRM - Centre national de recherches météorologiques

The Saharan Heat Low (SHL) is a key component of the West African monsoon system at synoptic scale and a driver of summertime precipitation over the Sahel region. Therefore, accurate seasonal precipitation forecasts rely in part on a proper representation of the SHL characteristics in seasonal forecasts models. This is investigated using the last versions of two seasonal forecast systems namely the SEAS5 and MF7 systems respectively from the European Center of Medium range Weather Forecasts (ECMWF) and Meteo-France. The SHL characteristics in the seasonal forecast models is assessed based on a comparison with the fifth ECMWF ReAnalysis (ERA5) for the period 1993-2016. The analysis of the modes of variability shows that the seasonal forecast models have issues with the timing of the SHL pulsations and the intensities when compared to ERA5. SEAS5 and MF7 show a cooling trend centered on the Sahara and a warming trend located in the eastern part of the Sahara, respectively. Both models tend to underestimate the inter-annual variability of the SHL. We also show that the seasonal forecast models detect the eastward and westward shift of the SHL during the monsoon season. The use of statistical bias correction methods significantly reduces the bias in the seasonal forecast models and improves the forecast score. Despite an improvement of prediction score, the SHL-related forecast skills of SEAS5 and MF7 remain weak for a lead time beyond 1 month.

Mots clés: Saharan Heat Low; seasonal forecast; bias correction; wavelet analysis; West African Monsoon system; Sahel Region; Precipitation

Domaines: Climatologie

Cédric Gacial Ngoungué Langué, Christophe Lavaysse, Mathieu Vrac, Philippe Peyrille, Cyrille Flamant. Seasonal forecasts of the Saharan Heat Low characteristics: A multi-model assessment. Weather and Climate Dynamics, 2021, 2, pp.893-912. ⟨10.5194/wcd-2-893-2021⟩. ⟨insu-03255675v2⟩