Fluxes of sensible heat and momentum in the surface layer estimated from the profile measurements of wind and temperature at a tropical station

OLUWAGBEMIGA O. JEGEDE, PER LOFSTROM

Abstract

In this study the surface layer fluxes for both the sensible heat and momentum have been estimated at a tropical location; Osu, Nigeria (7º26' N, 4º35' E), using profile measurements of mean wind and temperature realized within the pre-monsoon season (January - March). Due to the weak surface winds that commonly exist in the area (for the study period, U was 1.24 m.s-1) and strong insolation, the daytime SL was frequently found to be within the free convection regime. Typically in the daytime, the sensible heat flux H~200 W.m-2 and the friction velocity u* ~ 0.2 m.s-1. At nighttimes, the ground-based temperature inversion was very pronounced (>0.33ºC.m-1) and it is such that the intensity of the turbulence in the nocturnal SL was weaker, shallower, sporadic and unsustained (H~ -5.0 W.m-2; * < 0.2 m.s-1). The frequency distribution of these derived fluxes (and the mean variables) for the observation period is also discussed.

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