On the Differences in the Intraseasonal Rainfall Variability between Western and Eastern Central Africa: Case of 10–25-Day Oscillations

Abstract

In this paper, we analyze the space-time structures of the 10–25 day intraseasonal variability of rainfall over Central Africa (CA) using 1DD GPCP rainfall product for the period 1996–2009, with an emphasis on the comparison between the western Central Africa (WCA) and the eastern Central Africa (ECA) with different climate features. The results of Empirical Orthogonal Functions (EOFs) analysis have shown that the amount of variance explained by the leading EOFs is greater in ECA than WCA (40.6% and 48.1%, for WCA and ECA, resp.). For the two subregions, the power spectra of the principal components (PCs) peak around 15 days, indicating a biweekly signal. The lagged cross-correlations computed between WCA and ECA PCs time series showed that most of the WCA PCs lead ECA PCs time series with a time scale of 5–8 days. The variations of Intraseasonal Oscillations (ISO) activity are weak in WCA, when compared with ECA where the signal exhibits large annual and interannual variations. Globally, the correlation coefficients computed between ECA and WCA annual mean ISO power time series are weak, revealing that the processes driving the interannual modulation of ISO signal should be different in nature or magnitude in the two subregions.

The observed synoptic scale precipitation relationship between Western Equatorial Africa and Eastern Equatorial Africa

“…Those identified using the GPCP dataset were generally in similar locations as those shown in Figure 1 (not shown). The 29°E longitude was chosen to divide Equatorial Africa (defined above) into WEA and EEA for consistency with previous studies (e.g., see Sandjon et al ., 2014, Figure 1) and with an operational weather forecasting model over Lake Victoria in EEA (e.g., see Woodhams et al ., 2018, Figure 1). The sub‐regions over ocean and those whose base‐points were located on 29°E were disregarded.…”

“…A few areas in central Equatorial Africa experience a bimodal rainfall cycle, while those outside the 5°S–5°N latitudinal band experience a unimodal rainfall cycle (e.g., Dunning et al ., 2016). Precipitation in Equatorial Africa is characterized by remarkable spatial variation at intraseasonal (e.g., Nguyen and Duvel, 2008), seasonal (e.g., Sandjon et al ., 2014; Fotso‐Kamga et al ., 2019) and interannual (e.g., Janowiak, 1988, Figure 2e) timescales. Because of the heterogeneity of precipitation over this region, previous studies delineated their areas of study into smaller sub‐regions, using either monthly totals (e.g., Indeje et al ., 2000; Dezfuli, 2011) or annual totals (e.g., Badr et al ., 2016).…”

Interannual variations in the amplitude of 25–70-day intraseasonal oscillations in Central Africa and relationship with ENSO

“…It is well known that in the tropics, the MJO is the dominant phenomenon of the atmospheric variability at intraseasonal timescales (10-90 days) (Madden and Julian 1994;Tazalika and Jury 2008;Tchakoutio et al 2014). In addition, many authors showed that MJO is largely responsible for the intraseasonal climate variance in the tropics and subtropics (Singh et al 1992;Mapande and Reason 2005;Pohl and Camberlin 2007;Maloney and Jeffrey 2008;Farnaz et al 2014).…”

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 notion of intraseasonal timescale then raised in the scientific community and since then, many authors studied the characteristics of intraseasonal rainfall variability in some regions in the tropics (e.g. Madden & Julian, 1971;Madden & Julian, 1972;Anderson et al, 1984;Madden & Julian, 1994;Sultan & Janicot, 2001;Jury & Mpeta, 2001;Tazalika & Jury, 2008;Maloney & Jeffrey, 2008;Tchakoutio et al, 2012;Tchakoutio et al, 2013a;Tchakoutio et al, 2013b;Tchakoutio et al, 2014). But the documentation on intraseasonal variability in tropical Africa is highly based on West Africa, East Africa and Southern Africa (e.g.…”

“…This confirms that CA a serious gap in the study of the tropical climate variability, though it is well-known that the intraseasonal modes such as MJO can substantially modulate rainfall variability at various timescales. In recent years, some authors started addressing the problem (Tchakoutio et al, 2012(Tchakoutio et al, , 2013a(Tchakoutio et al, , 2013b(Tchakoutio et al, , 2014, but in spite of their findings, the key challenge remains the best parameterization of ISOs for their use in the improvement of the rainfall prediction in tropical Africa.…”