Dynamic Diagnosis and Mechanism Analysis of Yellow River Cyclone Induced Bohai Storm Tide

Using the digital 6.7 μm satellite water vapor image and NCEP/NCAR 1°×1° reanalysis data,the synoptic and dynamic processes of Yellow River cyclone induced Bohai storm tide is diagnosed based on the dry intrusion and potential vorticity theories.The result shows that the storm tide occurred during the adjustment of Eurasia mid-and high-latitude circulations,east moving and development of unstable low tough and the rebuilding of East Asian trough.Northerly gale wind induced by strongly developed Yellow River cyclone forced the sharp increase of tide over Bohai tide sharply bloomed.Dry cold air from tropopause with high potential vorticity intruded into lower level troposphere shown as dark area in vapor image,when the dry cold air encountered with warm moist and wet air from low troposphere,it was distorted into an axe-shaped dry air area which manifested a strong horizontal deformation.Then the cyclone rapidly strengthened when it moved to the area with bigger potential vorticity from upper to lower levels.It followed by the mature of cyclone when the spiral structure can be found in the dry and wet area.In the center of cyclone where the dry air with lower θw superposed the warm air with higher θw,which increased the potential instability.The mechanism of rapid intensification of cyclone can be shown as follows: Firstly,the downward intrusion of dry air into low level;secondly the reduction of static stability of atmosphere and augmentation of absolute vorticity;finally,the quick development of cyclone.The isallobairc gradient,pressure gradient,downward propagation of upper level momentum and divergence of super-low-level jet all contributed to the gale wind during the Bohai storm tide.