LOW-LEVEL JET STREAMS ASSOCIATED WITH ATMOSPHERIC COLD FRONTS - 7 CASE-STUDIES FROM THE FRONTS-87 EXPERIMENT

Sounding data collected during the European experiment FRONTS87 are us ed to investigate the dynamic structure of mid-latitude low-level jets associated with atmospheric cold fronts. These jets are identified as strong currents of relative warm and moist air, confined in the lower layers of the atmosphere (within the first two kilometers) ahead of c old fronts. The importance of the low-level jets lies on the fact that they can be responsible for the occurrence of strong winds near the s urface which sometimes can be disastrous, especially near coasts where frictional deceleration due to the land is minimum. Furthermore they are often associated with a narrow region of ascending motions just ah ead of the frontal surface which can account for strong precipitation at ground. The data to be discussed in this paper are provided from th e special upper air sounding stations deployed at Brittany, France, du ring FRONTS87. A comparison of seven case studies permitted to give a detailed picture of the jets characteristics and to better understand their dynamic structure.