Abstract:Based on station data and NCEP FNL 1°×1° reanalysis data from 2008 to 2012, the developing Yellow River cyclones passing over Bohai Sea are classified into Summer type and Spring type. In this paper, the structures and impact factors of the two types of cyclones, especially the moisture, thermal and dynamic effects of the Huang Bohai Sea are compared and analyzed. 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. The structures of the cyclones are baroclinic, but Summer type cyclone is with a warm center, while Spring type cyclone has remarkable baroclinicity. Upper level jet is at the south of cyclone in spring, the cyclonic wind shear at the jet left side keeps the cyclone, and the upper level momentum passes down into the back of Spring type cyclone, and meets the cold front secondary circulation and the flat sea surface, which is conducive to rapidly increasing low level cyclonic winds. In comparison, the upper level jet is at the north of cyclone in summer, and the upper level divergence of the jet right side and low level convergence strengthen together the ascending motion of summer cyclone, favoring strong cyclonic precipitation and condensation latent heat release. There is conversion of perturbation potential energy to kinetic energy when cyclones develop through the Bohai Sea that maintains and strengthens the cyclone momentum. In addition MPV calculations show that Summer type cyclones are with the deep and thick dry air sinking, which is favorable for the formation of heavy precipitation, but in Spring type the dry wet gradient is small and distributes in scattered patterns, corresponding to the small scale 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 in spring, but the water vapor transport is deficiency in spring. The low level wind speed of Spring type cyclone is significantly enhanced by sea surface 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.