CHARACTERISTICS OF THE NOCTURNAL BOUNDARY-LAYER - OKAUKUEJO, NAMIBIA,DURING SAFARI-92

During the Southern African Fire-Atmosphere Research Initiative (SAFAR I) in September and October 1992, nocturnal tethersonde soundings were carried out at Okaukuejo, measuring dry-bulb and dew-point temperatur e, ozone concentration, wind speed, and wind direction. These showed t he existence of a surface temperature inversion and a low-level wind m aximum on most nights. The inversion formed shortly after sunset, reac hed a maximum depth and strength at sunrise, and then gradually eroded from the surface upwards. The low-level jet (LLJ) started developing after the onset of inversion formation. Speeds in excess of 11 m s(-1) were not unusual. The height of the core of the jet ranged between 50 and 200 m above ground level and corresponded fairly closely with the level of the top of the inversion. While daytime thermal eddy convect ion prevailed, ozone in the boundary layer was well mixed, and no vert ical structure to ozone concentration was evident. With the onset of t he surface inversion ozone levels increased systematically with height from less than 10 ppbv near ground level to more than 30 ppbv at the LLJ core.