EUMeTrain: Case Study on Prefrontal Convergence

Author

Jarno Schipper - ZAMG
Veronika Zwatz-Meise - ZAMG

Introduction

The case study will deal with the development of a prefrontal convergence line. Several convective cells develop on July 30th ahead of a front stretching from the Baltic States towards Northern Italy. The case is associated to large amount of precipitation. The development and the onset of this convective event is shown using several MSG channels and RGBs as also several NWP parameters.

Meteosat 8 Enhanced IR10.8 image - 30th July 2005:17 UTC
Several convective cells can be seen over Central Europe.

The aim of this case study is to:

There are two synoptic-scale environments which lead to the development of convective Convergence Lines: the leading area of frontal cloud bands and the cold air region behind frontal cloud bands. Weak relation to parameters typical for these regions and contributing to upward motion such as temperature advection (warm advection) or vorticity advection (positive vorticity advection) are found in connection to these events. As these convective lines can be regarded as small scale phenomena Local Area Models (LAM) have to be studied for a deeper explanation. The cloudiness within the convergence lines is the result of the production of upward motion due to low level convergence which is the result of different processes. These Convergence Lines also show a life cycle during the day time dependant on solar radiation with a maximum of convection in the early afternoon.

The Pre-frontal convective line that is described in this case study is influenced by an approaching frontal system as well as the diurnal variation of solar radiation. To be able to follow the case study from the beginning it is preferable to study the chapter dealing with non-orographic convergence lines from the “Manual of Synoptic Satellite Meteorology”.