The 12/13 January 1988 narrow cold-frontal rainband observed during MFDP/FRONTS 87. Part I: kinematics and thermodynamics

Abstract

Radiosonde data indicates a very weak convective instability below 1500-m altitude and a low-level jet of 30 m s-1 from SSW before the arrival of the front; a cooling of about 1°C associated with an airflow of 13 m s-1 from WSW after its passage. A composite of wind and reflectivity fields from 17 dual-Doppler radar analyses shows high reflectivity values, large convergence, and relatively intense vertical motions associated with this NCFR at the 1000-m altitude. A mean vertical cross section perpendicular to the surface front, derived from three successive high-resolution dual-Doppler scans, is used to examine the general characteristics of the air circulation. A structure apparently similar to that of a density current is observed. Analysis of the successive wind and reflectivity fields reveals some three-dimensional and time-dependent features. In particular, the frontal updraft underwent some evolution related to the formation and fall of precipitation. -from Authors