MESOSCALE STRUCTURE OF LINE CONVECTION AT SURFACE COLD FRONTS

In this paper we consider 15 cases of line convection at ana‐cold fronts which have been observed by radar. Although line convection can be a simple two‐dimensional feature, it is usually broken up into line elements having lengths from a few to many tens of kilometres separated by somewhat smaller gaps. The passage of a line element is accompanied by a short burst of heavy precipitation, a temperature drop of about 2degC, a sudden veer and decrease in wind speed, and a pressure jump of 1 to 2 mb. If a gap between line elements passes over a station, however, the changes can occur gradually over a period of up to an hour. Despite the variable size of the line elements, they are found to share common characteristics. They are always oriented slightly clockwise with respect to the synoptic cold front. They all move with the same velocity as their neighbours on a given front, with a component parallel to the front in the direction of the strong low‐level flow which occurs ahead of the front. Moreover, the line elements tend to travel in a fairly predictable manner, largely unaffected by topography and with the major features having lifetimes of several hours. Copyright © 1979 Royal Meteorological Society