Preprints
https://doi.org/10.5194/wcd-2021-19
https://doi.org/10.5194/wcd-2021-19

  26 Apr 2021

26 Apr 2021

Review status: this preprint is currently under review for the journal WCD.

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

Cedric G. Ngoungue Langue1,2, Christophe Lavaysse2,3, Mathieu Vrac4, Philippe Peyrille5, and Cyrille Flamant1 Cedric G. Ngoungue Langue et al.
  • 1Laboratoire Atmosphères, Milieux, Observations Spatiales (LATMOS) - UMR 8190 CNRS/Sorbonne Université/UVSQ, 78280 Guyancourt, France
  • 2Université Grenoble Alpes, CNRS, IRD, G-INP, IGE,38000 Grenoble, France
  • 3European Commission, Joint Research Centre (JRC), 21027 Ispra, VA, Italy
  • 4Laboratoire des Sciences du Climat et de l’Environnement, CEA Saclay l’Orme des Merisiers, UMR 8212 CEA-CNRS-UVSQ, Université Paris-Saclay & IPSL, 91191 Gif-sur-Yvette, France
  • 5Centre National de Recherches Météorologiques (CNRM) - Université de Toulouse, Météo-France, CNRS, 31057 Toulouse Cedex 1, France

Abstract. 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 under-estimate 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.

Cedric G. Ngoungue Langue et al.

Status: open (until 11 Jun 2021)

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Cedric G. Ngoungue Langue et al.

Cedric G. Ngoungue Langue et al.

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Short summary
This work is assessing the forecast of the temperature over the Sahara, a key driver of the West African monsoon, at seasonal time scale. The seasonal models are able to reproduce the climatological state and some characteristics of the temperature during the rainy season in the Sahel. But, because of errors in the timing, the forecast skill scores are significant only for the first 4 weeks.