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

Clément Tchawoua,Tengeleng Siddi,Alain Tchakoutio Sandjon,Armand Nzeukou

doi:10.1155/2014/434960

Clément Tchawoua, Tengeleng Siddi + Show 2 more

Open Access

https://doi.org/10.1155/2014/434960

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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.

Highlights

The monitoring and prediction of climate in the tropics remain a crucial problem in the scientific community
From the difference between physical features of eastern Central Africa (ECA) and western Central Africa (WCA), one central question we may ask is “what could be the difference in the intraseasonal oscillations (ISO) patterns between WCA and ECA?” Some of the previous studies revealed two dominant frequency bands (10–25 and 25–60 days) at the intraseasonal timescale in tropical Africa [12,13,14], but for this study, we focused on the case of 10–25-day band
In Fourier decomposition, the importance of a given frequency in a time series can be quantified by the spectral variance, defined as the amplitude of the harmonic corresponding to the this frequency

Summary

Introduction

The monitoring and prediction of climate in the tropics remain a crucial problem in the scientific community. The notion of intraseasonal variability (ISV) arose in the scientific community and many authors used different rainfall or rainfall proxy datasets to study ISV in the tropics [10, 11]. Some of these authors have studied the ISV in precipitation for different geographical regions of Africa. [19] used one-Degree Daily Global Precipitation Climatology Project (1 DD GPCP) higher resolution rainfall product to study the ISO patterns in CA, but they considered the whole area (15∘S–15∘N, 0–50∘N) and did not take into account the contrast patterns between western and eastern parts of the region with different climate features.

Data and Methods

Results and Analysis

Summary and Conclusions