The Turkana Jet and its role in interannual variability

Low-level jets have been shown to play an important role in climate, particularly precipitation. One such jet exists in the narrow Turkana Channel of northern Kenya. This feature has received little attention, despite brief field work in the 1980s that showed its speeds can exceed 50 ms-1 just 500 m above the surface. Notably, it lies in an arid region noted for extreme year-to-year variability of rainfall. This paper presents the first detailed evaluation of its spatio-temporal characteristics and also examines for the first time its impact on rainfall. The results show that the Turkana Jet is a nocturnal feature with maximum speeds between 0000Z and 0600 Z in all months that it is present. The jet is best developed September through April, but the period in which it is present varies greatly from year to year. Its core is at roughly 3N, 37E and generally lies at roughly 850 hPa. When speeds are particularly strong, the core is elevated to 800 to 750 hPa. On occasion the core is as high as 700 hPa. It is generally strongest in September but the month of peak intensity also varies greatly from year to year. There are distinct patterns of divergence and convergence associated with the jet and these change markedly as the jet's intensity changes. We are currently investigating the impact of these changes on daily and monthly rainfall and will present preliminary results of this investigation.