Microphysical process of a cold vortex during its movement to the east – A case study

A cold vortex is an important weather system that can cause low temperatures and large
amounts of rainfall. Many scientific studies have focused on the climatological features of the
cold vortex along with its formation, maintenance, structure, circulation features and precipitation
distribution from a synoptic perspective. However, not many studies have been conducted related
to the microphysical processes in a cold vortex. In this paper, a model study is presented on the
microphysical features in a cloud system associated with a cold vortex system which lasted for four
days. The system formed, strengthened, split into two and dissipated while it moved towards the
east and brought extensive precipitation to the influenced area. The type and amount of precipitation
were not evenly distributed: liquid precipitation covered the whole area influenced by the cloud
system, while solid precipitation mainly covered high latitudes north of 48 N. In this case, the cloud
system was very cold and the 0 C; level was very low, with the result that the microphysical
features were dominated by cold cloud processes. The mixing ratio of liquid particles was very small,
and liquid particles only covered limited areas in the clouds. Due to the low temperature, there were
insucient cloud droplets throughout the whole system for the ecient production of rain droplets
by coalescence. The snow mixing ratio was largest, and ice and snow covered the whole cloud area,
with very little graupel, which occurred in only a small area. The distribution of the solid particles
was influenced by their growth through aggregation, the Bergeron process or accretion, resulting in
many snow particles. There were insucient liquid particles to support the formation of very large
particles such as graupel. Liquid precipitation was primarily caused by the melting of snow particles
precipitating out of the clouds; solid precipitation was also primarily caused by snow particles that
did not melt, along with some graupel.