Abstract:

Base on conventional meteorological observations and the National Centers for Environmental Prediction (NCEP) reanalysis data,the heavy rainfall distribution differences among three typical hollow typhoons (1710 “Haitang” on July 31,2017,1307 “Soulik” on July 13,2013,and 0709 “Sepat” on August 19,2007) landing in Fujian province were diagnostically analyzed.The results show that the divergence channels at high altitudes of the three typhoons are significantly different;typhoons of “Haitang” and “Sepat” both exhibit anticyclone outflows,while “Soulik” only has a single outflow channel.Vertical wind shear direction is useful to predict heavy rainfall area of typhoons “Haitang” and “Soulik”.The front zone of moisture and the intruding location of dry tongue greatly influence the formation of hollow structures and the difference in distributions of strong precipitation.The moist potential vorticity of the three typhoons is negative at low altitudes and positive at high altitudes,indicating a convectively unstable condition of the atmosphere at low altitudes.Wet positive pressure term provides major unstable conditions for the development of mesoscale convective systems (MCS) of “Haitang” and “Sepat”,while the wet positive pressure term and the wet baroclinic term both strengthen the development of MCS of “Soulik”,and the former term plays an important role in the formation of an asymmetric distribution of MCS.

Key words: Hollow typhoon, Heavy rainfall distribution, Cause analysis