Synoptic Kelvin Type Perturbation Waves over Congo Basin During the Period 1979–2010

Water resources, agricultural and health on Central Africa depends on rainfall. What people really want to know is when and how much will it rain. The Congo basin region depends heavily on rainfall during spring and is characterized by high rainfall over the Cameroon Highlands. The associated precipitation over the Congo basin has unique characteristics compared to other continental regions in particular, a relatively small rainfall amount regarding to high cloudiness or lightning activity, attributed either to the abundance of aerosols or to relatively dry boundary layer that elevates the cloud base and decreases the amount of rain reaching the ground. The synoptic structure and inter-annual variability of Kelvin waves over the Congo basin from 1979 to 2010 are explored using outgoing longwave radiation (OLR) and National Centers for Environmental Prediction–National Center for Atmospheric Research (NCEP–NCAR) reanalysis data. Composite method shows that high values of synoptic Kelvin wave (SKW) index are located over Congo basin during March-June where the convective active phase favors the formation of convective synoptic systems. Mean composite SKWs structure shows that these waves propagate faster over land surface and dissipate with suppressed phase. Because convective instability is smaller, these waves cannot grow in Congo basin. High correlation between SKWs and precipitation time series occurs when the Kelvin waves lead the precipitation time series by about 4 days. The analysis of 32 years datasets (1979-2010) also shows that in some particular year, strong SKWs propagation exists with periods centered around 5 days. Otherwise, results show marked inter-annual variability of Kelvin wave activity over Congo basin associated with divergence and low level westerly trade winds.