Multi-scale organization of water vapor over low and mid-tropical Africa

Abstract

In this study, data from the Southern Hemisphere ADditional OZonesondes (SHADOZ) are used to compute the spatially averaged water vapour (WVg) over low and mid-tropical Africa. Based on the SHADOZ stations, reanalysis data from the National Centres for Environmental Prediction and Atmospheric Research (NCEP/NCAR) were partitioned into four grid cells: (1) over Ascension [10.0°S to 7.5°S, 12.5°W to 15.0°W]; (2) Nairobi [0.0° N to 2.5°S, 35.0°E to 37.5°E]; (3) Irene [27.5°S to 25.0°S, 27.5°E to 30.0°E] and (4) Reunion [22.5° S to 20.0° S, 55.0° E to 57.5°E]. The mean Water Vapour (WV) was computed over these grid cells to obtain (WVg). The temporal scales of WVg fluctuations have been analyzed using wavelet transforms and Principal Components. Analysis (PCA) of the WVg wavelet-transformed coefficients was used to demonstrate spatial organization of WV. The results indicate that WV exhibits localized spatial coherence patterns. Further, the analysis show strong seasonal dependence of WV which is associated with global and local atmospheric circulation