Measuring Temperature and Humidity Distributions in Thermal Updrafts

Abstract

This study employs a miniaturized chilled mirror hygrometer mounted on the Discus-2c DLR research glider to measure updraft thermodynamics in the convective atmospheric boundary layer, with particular focus on the role of humidity. A flight strategy transecting thermals parallel and perpendicular to the main wind direction was chosen and 26 thermal transects were conducted over three flights. Updraft width, velocity as well as temperature, and humidity within thermals and in the surrounding air were measured. Despite large scattering, results showed an average temperature excess of 0.075 K in thermals. The mean relative contribution of humidity to the density difference between thermals and the surrounding air was 17.4%. This data was compared with previous studies and LES simulations. Furthermore, the horizontal fine structure of humidity and temperature in and around thermals displayed non-uniform characteristics in wind direction and perpendicular to the wind direction.