Meteorology

Observing and chasing thunderstorms

Thunderstorms are of the most beautiful and spectacular atmospheric phenomena, however, they often cause severe and dangerous weather conditions at the surface of Earth. Severe thunderstorms may cause heavy amounts of rainfall, hail, lightning and damaging winds to occur. They may even spawn flash floods, gust fronts and tornadoes. On the positive side thunderstorms are responsible for a huge portion of the rainfall of the summer rainfall region of South Africa. Thunderstorms develop in an unstable atmosphere, where rising air parcels cool down more slowly than their environment. Severe thunderstorms develop in an atmosphere with strong vertical wind shear, that is, where the wins speeds quickly increases with height over the lower few kilometers of the atmosphere.

In this project we will be studying thunderstorms more closely. We will be using satellite and radar data, as well as data collected from surface weather stations and balloon soundings. During the project we will make a number of visits to the National Forecasting Office of the South African Weather Service, where we will meet weather forecasters that predict thunderstorms on an operational basis. We will also visit the Irene Weather Station of the South African Weather Service, where we will participate in sending a weather balloon into the atmosphere. We'll analyze the temperature and wind data obtained from this balloon sounding in order to learn more about the vertical wind shear and temperature profile of the atmosphere, and how these aspects contribute to thunderstorm formation. Most exciting perhaps, is that we will make our own measurements of thunderstorm outflow. Our strategy will be to identify developing thunderstorms on a radar image and to predict their path of motion. We will then quickly set up a series of thermometers in the path of the thunderstorm. With this experiment we hope to take measurements of the gust front caused when cold air from the thunderstorm core sinks to the surface of Earth and spreads out horizontally as a strong wind (gust front).

Participants

• Dr. Francois A. Engelbrecht