A Comparative Study Of Development Mechanism Of Yellow River Cyclone And Impact Of Huang-Bohai Sea Between Summer And Spring

Yellow river cyclone is frontal cyclone generated in the Hetao area and the Lower Yellow river, it is important in causing heavy rainfall in the Northeast and North of China. In recent years, the Bohai Sea region has become an important region of economic development, therefore, as an important weather system in the region, the formation and development of Yellow River cyclone is also of concern. Based on NCEP-FNL 1°×1° reanalysis data from 2008 to 2012, the Yellow River cyclones are classified into two types. In this paper, the structures and impact factors of two type cyclones, especially the moisture, thermal and dynamic effects of the Huang-Bohai Sea are compared and analyzed.Yellow cyclones are divided into ClassI and Ⅱ by its different generation, the classl is produced in the north of the Hetao area(37-44°N,104-114 °E) and the classⅡ is produced in the Yellow River (34-40°N,114-118 °E). Statistics show that the Annual difference of the number of Yellow River cyclone is large, the number of typel is more than type 2, the type 2 cyclone which maintain more than 12-h is with a high frequency in summer and spring. It is shown that the Summer-type cyclones are related to the wide area of heavy rainfall, while the Spring-type cyclones are related to large gale area instead of rain. So, the Yellow River cyclones are classified into Summer-type and Spring-type.According to the Vertical cross section along zonal direction of zonal temperature anomalies and relative humidity, The structures of two type cyclones are baroclinic, but Summer-type cyclone has warm center, Spring-type cyclone has remarkable baroclinicity, which plays an important part in the development of Yellow River cyclone. The relative humidity and the convergence of Moisture flux in summer is larger than that in spring, which is helpful for the heavy rainfall and latent heat of condensation.The upper and low level jets analysis show that upper level jet moves northward with the seasons. It is at the south of cyclone in spring and the north in summer, the Intensity and scope of upper level jet is larger in spring than that in summer.the southwest low level jet in the southeast of Summer cyclone center provide abundant moisture and unstable stratification, the northwest low level jet of spring cyclone provide less moisture and small preciptation. The Spring-type cyclone is with a large-scale and high-strength upper level correspond to a strong subsidence area which result in the upper level momentum passeing down and strengthening the ground cyclonic winds.Using MPV calculation results, the lower atmosphere stratification in summer is unstable, the higher atmosphere stratification in summer is stable, which is a favorable situation for strong precipitation, while in the spring are stable atmospheric stratification as a whole. Development of atmospheric wet baroclinic degrees indicate the intensity and area of precipitation, the relationship is more obvious in summer. The influence of the stretching of upper level potential vorticity is more important in spring than summer. The distribution of pseudo equivalent potential temperature in summer lead to convective instability in the lower atmosphere is conducive to development of the summer cyclone and to produce precipitation.Huang-Bohai Sea is the main vapor transport channel of cyclones which transports abundant moisture in summer because of the higher sea surface temperature than spring, but the water vapor transport is deficiency in spring. The low level wind speed of Spring-type cyclone is significantly enhanced by sea dynamic effect, while the effect does not work in Summer-type cyclone. Diabatic heating analysis over Bohai Sea indicates that latent heat plays an important role in Summer-type cyclone, while the sensible heat is more significant in Spring-type cyclone.The Sensitivity test of turning off the influence of the latent heat flux indicates that the latent heat flux plays an more important role in the summer cyclone than in the spring cyclone, in the test, the summer cyclone stagnate and disappear in the Bohai-sea,while the spring cyclone develop as control experiments,the test results and earlier diagnosis are consistent.The Sensitivity test of the change of sea surface temperature (SST)shows thatThe change of summer SST has a great influence on water vapor, thus affecting the intensity of summer cyclone,the water vapor increases obviously with the increase of SST, cyclone enhanced. As SST decreases, the water vapor decreased obviously, cyclone weakened. The changes of SST in spring has little effect on the intensity of cyclone, but making the cyclone center move to the warmer land, and changing the structure of the cyclone baroclinicity and the south wind. With SST increasing, the baroclinicity of the cyclone weakened, the lower troposphere wind speed of southern cyclone in the Huanghai-Sea is also reduced.