Climate Effects/Controls on Mesoscale Processes
NOAA/NWS/International Activities Office – Variability of the Intertropical Front and Rainfall over the West Africa Soudano-Sahel
LeLe, Lamb (primary – CIMMS at OU)
Funding Type: CIMMS Task III (Program Manager – Rob Masters)
Document the intra-seasonal characteristics of intertropical front (ITF) displacements during its northward movement at the beginning of the rainy season and its southward retreat at the end of the rainy season; investigate the relationship between the variability of the ITF latitudinal position and summer monsoon rainfall amount in West Africa Soudano-Sahelian countries where society needs improved weather and seasonal climate prediction.
The semi-arid region of West Africa is particularly sensitive to interannual fluctuation in the intertropical front position because it is only during one part of the year that the ITF extends far enough from its mean annual position for this region to receive normal annual rainfall. Space and time scales for analysis of the intraseasonal variability of sub-Sahelian rainfall and ITF displacement are determined. Analysis of daily dew point temperatures derived from observed stations daily minimum temperature and maximum relative humidity have been performed in a coherent area between 10o-25oN and 12oW-24oE for the period 1974- 2003, and a 10-day (dekad) mean ITF position time series was constructed. Analysis of the relationship suggests that a one of causes of the rainfall pattern variability results from a displacement of the ITF.
The 1958-2003 National Center for Environmental Prediction – National Center for Atmospheric Research (NCEP-NCAR) winds, vertical velocity, surface pressure, and sea surface temperature reanalysis data have been analyzed for extreme years in the tropical Atlantic sector and the core Sahelian rainfall season. Results show that during dry years in Sub Saharan Africa, the ITF is displaced southward from its long-term mean position and the related zone of convergence also experiences a southward shift. During wetter years, the opposite is true.
This project is ongoing.