Comparisons of the atmospheric hydrologic processes depicted by the operational ECMWF analyses with the corresponding forecasts at medium range over tropical Africa

This study compares the atmospheric components of regional tropical Africa hydrologic cycle diagnosed from analyses and operational 120 hours forecast both from European Center for Medium Range Weather Forecast (ECMWF). Analyses are extracted from global level-III-b atmospheric data archive and forecasts are T213L31 model outputs for summer 1995 within the domain 30°N - 20°S and 30°W - 40°E. Some Biases are highlighted and intraseasonal variability analyzed and compared with simulations.

The simulations agree quite well with analysis of position and northward migration of Intertropical Convergence Zone (ITCZ). It is worth noting that strong underestimation (minus 50%) of TPW exists over Sahara and around 15°S. This bias is probably due to subsidence associated to Hadley circulation stronger than observed. A significant moisten bias is found over the oceanic part of ITCZ. Approximations and assumptions in the mass flux scheme for deep convection are probably the major factors in producing this bias.

Analyses data indicate that water vapor transport at low levels (1000 - 850hPa) dominates the overall moisture circulation in the troposphere. In the middle and upper troposphere, zonal easterly transport is dominant with peaks over Sahel and around the great Lakes region. Although water vapor transport is relatively well simulated in the model, some biases are presented. Predicted moisture transport was stronger over west Africa and extremely weaker than observed over east Africa in the lower troposphere.

Analysis of flux divergence showed strong evaporation over the southern Atlantic coast of Africa and precipitation over land, particularly evident in August. The model poorly depicted those features.