A Numerical Study Of Cloud And Precipitation Microphysical Processes Of Cold Vortex Over Northeast China

The rainfall of two continuous cold vortexes over northeast China occurred during June 18 to 30 in 2009 have been synoptic analyzed and microphysical processes simulated in this paper. The reanalysis FNL data, observation data, including the sounding, and FY2C black body temperature are used to study the weather situation, dynamical and thermodynamical field, the water vapor transportation and the cloud microphysical characteristics of the Northeast cold vortex. The two sensitivity tests about ice microphysical processes and horizontal temperature and specific humidity advection are analyzed to find their key roles to rainfall of Northeast cold vortex.The position of the first cold vortex is more north than the second one, the cold air is always in the back of the cold vortex, which makes the cold vortex develop. On the contrast, the second vortex is without the cold air, so it disappears quickly. The clouds of vortex are in a comma shape, and there is obvious horizontal frontogenesis in the interface of dry and moisture air. The root-mean-squared (RMS) and the standard deviation manifest the successful simulation of the rainfall of the two cold vortexes. The main contribution term for the surface rainfall equation is the local water vapor convergence term in the domain mean and the convective regions. The ice water path and the liquid water path are both important in the two cold vortexes. The precipitation rate in the first cold vortex is larger than the second one, so the hydrometeor mixing ratio and the conversation rate are lager than the second one. The common points in the two cold vortexes are that, the two source of rain is the collection of cloud water by rain and the melting of graupel to rain. The cloud water source is the water vapor condensation. The conversation rate about graupel to rain is larger than the cloud water to rain, which demonstrates the large amount of the ice clouds.There are favorable dynamical, thermodynamical and the water vapor transportation conditions in the local abrupt convective rainfall in Fuyu county. The dry air in the middle level intrusion plays a key role for the convective rainfall. The evolutions of the radar reflectivity, liquid and ice hydrometeor are consistent with the rain belt. There is a high reflectivity in the onset period of the rain belt because of the mesoscale convective system. The vertical distributions of the five hydrometeors agree well with the vertical velocity. The mixing ratio of the ice hydrometeor is larger than the liquid hydrometeor, and the main contribution term for the surface rainfall and the microphysical processes are the same as the two cold vortexes. Similarities and differences are both exist in cold vortex rainfall and low latitude rainfall. The similarities are that the local convergence term is the main term for the surface rainfall rate and the two sources of rain are the same in the two kinds of precipitations. The differences are that liquid water path is the same large as the ice water path in the cold vortex rainfall while is two times as large as that in low latitude rainfall, the mixing ratio of the ice hydrometeor is larger than the liquid hydrometeor then the ice-water conversation rate is higher than the water microphysical conversation to produce rain in the cold vortex rainfall while the ice-water conversation rate is lower than the water microphysical conversation in the low latitude rainfall. That is due to the special thermodynamic and the dry intrusion of Northeast cold vortex.The two sensitivity tests about ice microphysical processes and horizontal temperature and specific humidity advection play key roles to rainfall of Northeast cold vortex rainfall. Without the ice microphysical processes, the amount of cloud water increases, surface precipitation regions shrink, the rain belt response to high level winds is quicker. The local convergence term weakens, and the absence of ice-water conversation makes the surface rainfall rate diminish evidently. Without the warm temperature advection, the environment temperature becomes colder, which is favorable to the ice hydrometeor generate, then the ice-water conversation becomes larger. The absence of positive specific humidity advection makes the environment moisture lower and the convergence term smaller, then the surface rainfall decreases. The absence of the negative specific humidity advection makes the environment moisture higher and the convergence term larger, the amount of hydrometeor increases and the ice-water conversation rate increases, ice microphysical processes became more active, then the surface rainfall rate increases.