Abstract
The economy of Tanzania heavily depends on agriculture sector which is primarily rain-fed. In this paper, we compute the moist potential vorticity (MPV) and evaluate its usefulness to describe annual cycles of rainfall. We also modify the convective vorticity vector ((CVV) ) which was defined as the cross product of absolute vorticity and the gradient of equivalent potential temperature to moist potential vorticity vector ((MPVV) ). This vector is calculated as a cross product of absolute vorticity and the gradient of moist air entropic potential temperature. The performance of (MPVV) to describe the annual cycles of rainfall over different regions in Tanzania is analyzed. Twenty six (26) years (1976-2001) daily data of air temperature, specific humidity, zonal and meridional components of the wind at 850 and 600hPa from numerical output generated by the Rossby Center regional climate model version four (RCA4) are used for computation of MPV and (MPVV) at 700hPa. The statistical relationship between (MPVV) and MPV against observed rainfall data from 22 synoptic meteorological stations using Pearson correlation coefficient indicate that (MPVV) bears strong and statistically significant correlation coefficient to rainfall than MPV suggesting its potential use as predictor of annual cycles of rainfall over different regions in Tanzania.
Highlights
The general circulation models (GCMs) represent the most satisfactory approach for predicting climate change (IPCC, 2013)
The results presented in this study contribute on the existing predictors that are used for development of empirical models for seasonal climate prediction
This suggests that MPVVx, and MPVV can be used as predictors of rainfall over different regions where they have shown strong correlation coefficient, and high coefficient of determination at significant −−−−→
Summary
The general circulation models (GCMs) represent the most satisfactory approach for predicting climate change (IPCC, 2013). GCMs have coarse spatial resolutions and cannot resolve small scale features such as orography, and land use land change that characterize the climate of many regions in the world This makes their climate simulations of limited use in impact studies of climate change on for instance biodiversity, ecosystem services, agricultural systems, species distributions, conservation planning, and other landscape related matters (Villegas and Jarvis, 2010; Daniels et al, 2012; Tumbo et al, 2012; Xiaoduo et al, 2012; Hassan et al, 2013; Vigaud et al, 2013). The concept of Potential Vorticity (PV) has long history in the study of fluid dynamics It has been used in meteorology and oceanography for many years back (see Bjerknes, 1898a; Rossby, 1939; Ertel, 1942). The conservative and invertibility properties of PV form the bases of understanding many important atmospheric flow processes
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