METEOROLOGICAL DATA ACQUISITION AND SERVICE DELIVERY FOR WGC 2001 IN MAFIKENG, SOUTH AFRICA

Abstract

The World Gliding Championships for 2001, in which nineteen countries were expected to participate, was hosted by South Africa. This event took place over the central interior of South Africa and based from Mafikeng in the Northwest Province. Mafikeng is approximately 350km to the west of Johannesburg and 15km south of the Botswana border. Following the pre-world gliding championships of December 2000 a number of gaps in the meteorological observation network were noted. In order to bridge some of these gaps the South African Weather Service (SAWS) made a concentrated effort to upgrade and implement technology as far as finances and human resources would allow. In this paper attention will be given to several aspects with regard to the facilities at Mafikeng in December 2001. First of all general climatological statistics will be provided describing soaring weather in Mafikeng. This will be followed by a description of the changes and improvements made in order to provide the area with enough real time data to make weather forecasts feasible. Aspects such as the AWS network and instrumentation, available satellite imagery, numerical weather prediction model output, information technology and upper-air data will be addressed. In addition to the conventional radiosonde instrumentation package used to obtain information on the state of the upper atmosphere, a new, experimental method - called the glidersonde - will also be introduced at the Mafikeng championship. The glidersonde is a small unpowered autonomous sailplane that carries meteorological sensors for the collection of atmospheric data in comparable method to a a radiosonde. The glidersonde has a wingspan of less than two meters and an approximately total flying weight of 1.8 kilograms. The glidersonde contains a Global Positioning System (GPS) receiver and a small microcomputer used in determining relative position and making navigation decisions. The glidersonde is carried aloft by a conventional gas-filled balloon and measures pressure, temperature, humidity and position data as it ascends. At a present altitude, the glidersonde releases itself from the balloon. The aircraft naturally flies to a level attitude and the autonomous navigation system steers it to the home or alternative location. After reaching the home location, the glider circles while descending. At a preset altitude aboveground, a parachute deploys and the glidersonde is recovered. The vehicle can then be reused. The last part of the paper focuses on the different parameters for forecasting thermal soaring. The Mafikeng area is influenced by a tough line which marks the boundary between dry desert air to the southwest and humid air to the northeast. Along this air mass boundary large cumulonimbus clouds often form producing extensive thunderstorms. This is the typical summer weather pattern marking the rainy season in the interior of South Africa. The airfield is at 4200 ft above sea level, however the terrain is basically flat. Virtually all thermals in this area are purely convective. The area is characterizedby high-energy air in summer and forecasting the start of convection (and the first overdevelopment) is very much like putting a pot of water on a cooker and trying to predict where the firstbubble will pop up. The forecasting task in this area is thus not an easy one.