Estimating the influence of precipitation variability by considering effect of middle atmosphere parameters on lower atmosphere over upper Blue Nile basin in Ethiopia

摘要

Precipitation over upper Blue Nile basin (UBNB) exhibits complex variability because of topographical features and the variability in tropopause temperature. The factors affecting its temporal and spatial distribution are not well known over the UBNB.Since precipitation is influenced by middle and lower atmosphere parameters such as greenhouse gases (carbon dioxide and methane), ozone concentration, incident solar radiation, gravity wave dispersion, cloud cover, and temperature. There is no study conducted to estimate precipitation variability using these parameters. In this study, we investigated the influence of precipitation variability by considering the effect of the middle atmosphere on lower atmospheres over UBNB in Ethiopia. Most of the data sets used in this study are derived from the European Centre for Medium-range Weather Forecast (ECMWF), in situ measurements and the Global monitoring division of National Oceanic and Atmospheric Administration. The results indicate that the correlation between ECMWF and in situ precipitation and temperature data is 0.82 and 0.32, respectively. The maximum ozone concentration is found during the summer season (6.2 x 10~(-3) kg m~(-2)). In this season, precipitation and cloud cover has positive correlations and both are negative correlations with temperature and incident solar radiation. The observed positive trend in temperature is associated with the enhancement of greenhouse gases. Cloud cover and ozone is quite useful for reduced incident solar radiation. Ozone is increased with temperature for all seasons except winter. Gravity wave dispersion affects the spatial distributions of temperature. Finally, we conclude that precipitation is directly influenced by temperature and incident solar radiation and indirectly affected by gravity waves, ozone concentration, and greenhouse gases. To draw a better conclusion, further study is needed with water vapor nuclei on precipitation variability in addition to middle atmospheric parameters.