Wind, temperature and humidity distribution at some cold fronts over SE. England

Abstract

AbstractRecent evidence from frequent radar‐sonde soundings at Crawley (Sussex) has been studied along with earlier published evidence to establish that a marked fall in humidity occurs directly above the front in a more or less random sample of cold fronts crossing southern England. This usually happens at levels above 700 mb and without a corresponding fall of temperature or any considerable change in wind direction at these levels.Evidence from trajectories shows that the dry warm air is drawn from a cold source and warmed dynamically before it enters the frontal zone. At this stage it is usually moving faster than, and in the same direction, as the warm moist air and this contributes to the formation of a marked humidity gradient at the junction of the two air masses.The air may sometimes be ascending at this junction, but there is no clear evidence that a wedge of cold air (where it exists) has anything to do with the vertical motion.