春夏季节黄河气旋经渤海发展时影响因子对比研究

利用2008—2012年台站资料、NCEP(National Centers for Environ mental Prediction) FNL(Final Operational Global Analysis)1°×1°再分析资料，将近5年经过渤海持续发展的黄河气旋分为夏季型和春季型，采用动态合成法对两类气旋的结构和黄渤海海域的热力、动力、水汽等影响因子进行对比分析。结果表明：经过渤海时，夏季型气旋主要伴随大范围的强降水，而春季型气旋主要形成强风区。春夏季黄河气旋均为冷暖交汇的斜压性结构，但夏季型有偏暖中心，斜压性弱于春季型。春季高空急流位于气旋南部，其左侧正涡度区维持气旋的深厚，且气旋后部高空动量下传与锋面二级环流及平坦海面配合有利于气旋低层大风迅速增强。夏季高空急流位于气旋北部，高空强辐散区和低层辐合区配置加强了气旋中的上升运动，有利于气旋强降水和凝结潜热释放。气旋发展阶段，扰动位能向动能的转化，支持气旋动能的维持与加强。湿位涡计算显示，夏季气旋中有深厚的干空气下沉，干湿梯度强，尺度大，有利于气旋的强降水，春季气旋中干湿梯度小，分布零散，对应降水强度和范围均小。黄渤海为气旋主要水汽输送通道，夏季海温相对春季高，水汽充沛，春季水汽辐合量仅为夏季三分之一。海洋下垫面作用对春季气旋影响大，在夏季作用不明显。夏季海面潜热加热影响为主，春季感热加热影响明显。

Comparative Study of Impact Factors of the Yellow River Cyclones over the Bohai Sea in Spring and Summer

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.