Hydrodynamic instability in the cold-core low area and its effect on the weather

Abstract

Cold-core lows are poorly understood cyclones, but they significantly impact on the formation of weather conditions in Ukraine, especially in its central and western regions. In the paper, the evolution of a cold-core low, which is associated with the enlargement of rainfall areas with thunderstorms over the Western Europe and Ukraine. The low formed on July 21tst, 2014, in a deep cold trough of a Rossby wave over Atlantic Europe. During period 21-24 July the low was moving to the East and there were precipitation zones under its eastern part. Therefore, sizes of precipitation zones cannot always be explained by impact of front and thermic instability, in this paper it is tried to assess hydrodynamic instability in forming of precipitation in a cold-core low. The research method is based on the use of the linear theory of the hydrodynamic instability of the zonal flow with Rossby waves. To investigate barotropic instability fields of meridional profiles of absolute vorticity. It is shown that flow in which the low moved was barotropic unstable. Using baroclinic instability characteristics (Phillips’s criterion) Baroclinic zones were revealed in atmospheric fronts and in northern part of area in question. It has been shown that hydrodynamic instability, both barotropic and baroclinic, in the eastern part of the cold-core low leads to intensification of atmospheric processes on the fronts, which was revealed to strengthening of precipitation and in the enlargement of zones of their formation.

Keywords

• high-altitude cyclone, Rossby waves, rainfall zone, hydrodynamic instability, absolute vortex, Phillips criterion