Analysis on environmental conditions and characteristics of dual-polarization parameters of two rainstorms caused by typhoons in Dalian

Using the S-band dual-polarization Doppler weather radar data of Dalian and Yingkou,combined with conventional meteorological observation data and 1°×1° reanalysis data from the National Centers for Environmental Prediction (NCEP),the environmental conditions and characteristics of dual-polarization parameter of two typhoon cases in Dalian were analyzed.The results show that: both typhoons experienced extratropical transition during their northward movement due to interaction with the westerly trough.Frontalogenesis of both cold and warm fronts occurred in the northern and northwestern parts of the systems.The dense belt of θse caused by typhoon approaching to the north side of cold air of Dalian was one of the triggering conditions for heavy precipitation.Compared with typhoon Yanhua,the precipitation area of typhoon Meihua was closer to the upper-level jet.The continuous strengthening of the frontal zone and the intrusion of cold air in the middle and lower troposphere allowed the system to obtain more moisture and energy,and the upward motion extended to the upper troposphere,resulting in stronger precipitation intensity.Z、Z_DR、K_DP were in an increasing trend in general with the increase of precopication intensity and raindrop size.CC was above 0.95,and exhibited little difference basically.When hourly rainfall intensity is lower than 30 mm·h^-1 ,the dual-polarization weather radar data exist high correlations.The correlations of Z and K_DP are superior to Z_DR.Stronger convergent lifting is beneficial to enhance the water vapor transportation,the probability of droplet coalescence after collision increases as large diameter and dense precipitation particles form high precipitation efficiency,which is an important factor in generating short-duration heavy precipitation.