Search

The frequency of flash floods resulting from heavy rainfall over West Africa has increased in recent years with serious socio‐economic consequences. Therefore, the need to utilize numerical weather prediction models to forecast heavy rainfall events reliably is also rising at many operational meteorological centres in West Africa. This paper evaluates the performance of the Consortium for Small‐scale Modelling (COSMO) model of the German Meteorological Services (DWD) in predicting rainfall over West Africa for high‐impact rainfall events that occurred between 19 and 26 August 2017. The paper aims to investigate the synoptic forcings modulating daily rainfall variability during that period. Results show that COSMO simulates adequately the spatio‐temporal variability of rainfall distribution over West Africa, though with inherent biases. COSMO displays a decreasing skill in producing spatial rainfall distribution as rainfall amounts tend to 30 mm and above. Additionally, areas of heavy rainfall, mostly about 100–300 km southwest of the core of the Africa Easterly Jet (AEJ), often coincide with areas of decreasing mean sea level pressure of at least 0.6 hPa and areas of increasing convective available potential energy of at least 500 J/kg. Although not in all cases, the trough of the Africa Easterly Wave (AEW) is always located to the east of these areas. We show that not every storm, especially east of the prime meridian, is associated with an AEW trough. COSMO is able to reproduce the atmospheric dynamics modulating the daily rainfall variability, in addition to capturing the daily propagation of the AEW trough, and the core of the AEJ. However, the reproducibility skill of the model in predicting atmospheric dynamics may not transform into the predictive skill of the model in producing rainfall. Nevertheless, operational forecasters may be able to determine likely areas of heavy rainfall by estimating the position of the AEJ core based on the position of areas of the least falling pressure from COSMO. Finally, the incorporation of the fractions skill score metric based on the neighbourhood approach could also assist operational forecasters to decide at which scale a severe weather alert can be issued. [ABSTRACT FROM AUTHOR]

ABSTRACT The ability of numerical models in reproducing the observed statistical links between the sea surface temperature of central and eastern tropical Pacific Ocean is analysed in this paper. Significant links in the whole spectrum of frequency were studied for models of the World Climate Research Program (WCRP-CMIP3/IPCC-AR4) using the methodology of wavelet coherence. During the second half of the twentieth century, in-phase or quasi-in-phase links in oscillations of 2-6 years, a lack of relation in oscillations of 8-12 years and time lagged links in the longest periodicities are detected in the observed dataset. Some of the analysed models are able to reproduce the observed relationships in oscillations shorter than 6 years and few of them also reproduce the lacks of significant relation in the band of 8-12 years. On the other hand, all models have serious problems representing the observed time lagged links in the longest waves. The analysis shows that climate models are still unable to reproduce specific features of tropical Pacific interactions with potential effect on the Southern Hemisphere atmospheric circulation and, in particular, the South American climatic variability. [ABSTRACT FROM AUTHOR]