SummaryLatitude-time cross-sections of precipitation across the West African region indicate that a strong relation exists between the May-September cycle of precipitation in the Sahel and the January-December cycle in the moist Southern sector. It is demonstrated that while the promiment precipitation band moves with the Inter-tropical discontinuity (ITD) in its South-North annual course, another important atmospheric mechanism, the Walker circulation (WC) influences the precipitation in the South where the ITD control breaks down. The effects, on the Sahel region's precipitation, of these atmospheric mechanisms, along with albedo variation are associated with a bio-physical feed-back mechanism forced, in the main, by ocean-atmosphere interaction.
Zusammenfassung Der Niederschlag in West-Afrika und sein Zusammenhang mit vorherrschenden atmosph~ifischen MechanismenZeifliche Breiten-Querschnitte des Niederschlags durch West-Afrika lassen erkennen, dat~ eine enge Beziehung zwischen der Niederschlagsperiode vom Mai bis September im Sahel und der Niederschlagsperiode von Januar bis Dezember im feuchten SiJdabschnitt besteht. Es wird gezeigt, daft, w/ihrend sich das Hauptniederschlagsband mit der innertropischen Diskontinuit/it (ITD) mit ihrer im Jahresgang in Richtung SiJd-Nord erfolgenden Verschiebung verlagert, als anderer bedeutender atmosph~irischer Mechanismus die Walker-Zirkulation (WC) den Niederschlag im Stiden beeinflufit, wo die Wirkung der ITD aufh6rt. Der Einflufi dieser atmosphiirischen Mechanismen auf den Niederschlag in der SahelRegion im Zusammenhang mit einer .~nderung der Albedo ist mit einem biophysikalischen RiJckkopplungsmechanismus verbunden, der haupts~ichlich durch die Wechselwirkung zwischen Ozean und Atmosph~ire erzwungen wird.
Dataset consisting of hourly global and diffuse solar radiation measured over the period February 1992 and December 2002 have been utilized to investigate the diurnal and seasonal variations of hourly and daily clearness index together with the diffuse fraction at a tropical station Ile-Ife (7.5°N, 4.57°E), Nigeria. Statistical analysis (the frequency and cumulative frequency distribution of the hourly and daily clearness index) and subsequent characterization of the sky conditions over the station based on these were also done, and their implications for solar energy utilization in the area discussed.Daytime ( Statistical analysis of hourly and daily clearness index showed that the local sky conditions at the station were almost devoid of clear skies and overcast skies (clear skies and overcast skies occurred for only about 3.5% and 4.8% of the time respectively). The sky conditions were rather predominantly cloudy (cloudy skies occurred for about 88% of the time) all the year round.
A relationship of the form W = aqb(a, b constants) has been established between precipitable water W(cm) aloft and the surface specific humidity, q(g/kg) over West Africa using an analysis of variance (ANOVA) technique on upper air climatological data spanning over a decade.Owing to the difference in the climatological patterns of the precipitable water between the southern and northern zones of the region, no single relationship was found suitable for both zones. Earlier models, generally of the form: In W = A + B t d ( A , B constants and td, dew-point temperature (OF)) tried on the same basis were found to be rather inadequate over the region.3.154).
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.