On the Study of the Spatio-Temporal Variations in Intensity of 30 - 60-Day Intraseasonal Rainfall Oscillations in Central Africa Using Wavelet-Based Indices

The intraseasonal timescale is attractive in Central Africa (CA) where socio-economic activities are highly based on rainfall. The parameterization of intraseasonal oscillations (ISO) then remains a great challenge for the improvement of sub-seasonal to seasonal (S2S) prediction in this region. In this paper, we applied wavelet analysis on the 2.5° × 2.5° daily Outgoing Longwave Radiation (OLR, used here as rainfall proxy) to study the variations in the intensity of the 30 - 60-day intraseasonal rainfall oscillations over Central Africa within the last three decades (1980-2009). Results showed that the mean ISO intensity (ISOI) strongly fluctuates from day to another. The plots of monthly mean ISOIs revealed that the ISO activity is highly seasonal with above-normal ISO intensity during December-May and below-normal activity during June-November. The analysis of yearly mean ISOI showed that the ISOI exhibits strong interannual variations with the years of very low ISOIs such as 1982, 1994, 2001, 2007, 2009, 2015 and the years of very high ISOIs such as 1981, 1985, 1986, 989/1990, 1997, 2003, 2005. The regression analysis between ISOI and El Ni&#241o Southern Oscillation (ENSO) indices showed that even though the relationship between ISO and ENSO is nonlinear, warm ENSO (El Ni&#241o) events tend to reduce the ISOIs while cold ENSO (La Ni&#241a) events tend to increase it.