Abstract:

Using the ERA5 reanalysis data of August 28-29 in 2012 and September 7-8 in 2019 with a horizontal resolution of 0.25°×0.25°, ground observation data, and the China Meteorological Administration tropical cyclone optimal moving path data, the diagnosis and analysis of wet potential vorticity of two typhoons "Bolaven" and "Lingling" with similar moving path northward causing heavy rainfalls in Northeast China were carried out.The results show that the heavy rainfalls caused by typhoons correspond well with the dense zone of pseudo-equivalent potential temperature (θ_se), and the rainfall is mainly located on the warm side of the dense zone of θ_se.The stronger the front zone is, the greater the rainfall is.Both typhoon processes have convectively unstable stratification in the early rainfall period, which provides initial energy accumulation for typhoon rainfall.The wet symmetry instability at the initial moment is the main factor for the occurrence of heavy rainfall on the northwest side of the typhoon center.During the time of rainfall enhancement, the instability of atmospheric convection is involved again, indicating that the instability of low-level convection provides the main energy for the rapid enhancement of rainfall.The absolute values of the wet barotropic term (MPV1) and the wet baroclinic term (MPV2) in the lower layer experienced an increase first, followed by decrease, and then changing to increase again, and the heavy rainfall mainly distributes in the intermediate period of the two extreme values.The rainstorm belts in central Jilin province caused by the two northward typhoons have a good correspondence with the negative MPV2 and positive MPV1 areas at the lower level of 850 hPa.

Key words: Typhoon, Heavy rainfall, Wet barotropic term (MPV1), Wet baroclinic term (MPV2)