Analysis of Water Vapor over Nigeria Using Radiosonde and Satellite Data

The Satellite Application Facility on Climate Monitoring (CM-SAF) focuses on retrieving geophysical parameters from satellite data by using inversion schemes that are based on radiative transfer theory. In this study, the focus is on the daily mean vertically integrated water vapor [i.e., total precipitable water vapor (TPW)] and the monthly mean layered vertically integrated water vapor [i.e., low-level precipitable water vapor (LPW), midlevel precipitable water vapor (MPW), and upper-level precipitable water vapor] obtained from CM-SAF Germany for the 2004-08 period and for 20 radiosonde stations distributed over Nigeria. The mean annual cycle shows a structure with two maxima, in May and September, respectively, for all low-and midlevel water vapor in the coastal and Guinea savannah regions, whereas at the midland and Sahelian regions, an almost constant maximum lasting between May and September occurs. The two-maxima structure manifested by TPW, LPW, and MPW at the coastal and Guinea savannah regions and the single maximum exhibited by them at the midland and the Sahelian regions are in synchronism with the movement of the intertropical discontinuity. In addition, comparisons have been made between the precipitable water from CM-SAF (CM-SAF PWV) and precipitable water from radiosonde (RS-PWV). Comparisons of the products at the seasonal scale show that CM-SAF PWV at all levels is larger than that of RS-PWV. In addition, a seasonal intercomparison between them shows that CM-SAF PWV and RS-PWV agree significantly at all of the stations that were investigated.