Determining convective precipitation using cold cloud top temperatures and it’s impact on aviation industry over western part of Kenya.

Abstract

This study quantifies satellite infrared 10.8 μm band cold cloud top temperature data with convective rainfall by matching the cold cloud top temperature threshold values less than 255 K 0 (- 18 C 0 ) of the same spatial and temporal pixel domains with the convective rainfall events from ten synoptic stations. The period of study was for five years from January 2008 to December 2012 over western part of Kenya characterized by rapid variations of convective features which are difficult to detect in the absence of meteorological tracking and detection systems. Diagnostic techniques of using the derived satellite cold cloud top temperatures threshold values were investigated using statistical methods to assess the predictability potential with the aim of determining strength of indices associated with convective rainfall events. Significant negative correlations were observed between the convective rainfall and the cold cloud top temperature indices with the highest skill scores obtained during March, April and May long rainy season and October, November and December short rain season. Weak signals were observed during January, February, June, July, August and September. The results indicated that most convective rainfall events from all the zones occurred for cloud tops temperatures between 235 K 0 (-38 C 0 ) and 255 K 0 (-18 C 0 ) with the highest probability of detection at 90% over western zone during the month of April while all the zones recorded over 60% during the same month. The observed probability may be linked to Intertropical convergence zone (ITCZ) migratory characteristics over the region which reflects the intensity of the convective systems during the months of March to May. Correlation coefficient magnitude was highest at -0.8 indicating that as the cloud top temperature decreases the deep convective clouds extending to high altitude became more active signaling the possibility of more precipitable water over the region. This suggests that satellite information can be used during short and long rainy seasons as a proxy for convective rainfall. Thus satellite infrared information is useful in convective short range weather predictions notably in mitigation strategies of reducing the effects of adverse weather associated with icing, thunderstorms and downdrafts that are dangerous to aviation in the region.