Research On Characteristics Analysis And Identification Method Of Precipitation Melting Layer Based On GPM

The melting layer is an important place for the solid-liquid transformation of precipitation particles.The latent heat is released during this process,which influences the thermal structure of the atmospheric environment.Meanwhile,the melting layer is also one of the most important parameters in the study of precipitation,which is of great significance for accurate forecasting and disaster mitigation and prevention.The melting layer in the early research was mainly based on ground-based radar,and there was still a lack of global melting layer observations,which restricted the observation and research of tropical cyclone precipitation and the improvement of the ability to artificially affect the weather.The use of the satellite-borne dual-frequency rain-measuring radar provides new opportunities for observing the melting layer globally.Based on the global observation data of GPM DPR,this paper has carried out research on the distribution characteristics of precipitation melting,microphysical processes,hydrometeor distribution,and melting layer height identification.The main conclusions are as follows:1.The melting layer height product of GPM DPR overestimates the top height of the melting layer.In the developing or mature stage of tropical cyclones and when the latitude is less than 30°N,the height of the melting layer top is almost unchanged;in the dissipating stage and in areas above 30°N latitude,the height of the melting layer top decreases with the increasing latitude.The stratiform precipitation of tropical cyclones is stable,while convective precipitation has a wider distribution of DSD,Z_eand the height of the top of the melting layer due to its strong vertical convection.Near the height of the melting layer,the melting process and particle growth processes occur,such as freezing,adhesion,multiplying and rimming processes,and there are also fewer precipitation particles breaking up.2.Classification of hydrometeors in the precipitation of tropical cyclones during the developing,mature,and dissipating stages.The distribution of hydrometeor from high to low with altitude is snow particles,grizzly particles,mixed particles,and large(small)raindrops.Due to the strong updraft,small raindrops appear at the highest point of the mature stage;due to the weakest vertical convection of precipitation in the dissipating stage,the rimming process is slow,resulting in the solid particles above the melting layer being mainly snow particles.The identification result indirectly reflects the height of the melting layer of tropical cyclone precipitation.3.Propose a method for identifying the height of the melting layer top based on covariance wavelet transform(CWT).Among them,the use of Haar wavelet basis function to identify the top height of the melting layer has good stability and accuracy.The height of the melting layer top determined by the CWT method is related to the value of the dilation parameter a.It can be obtained through simulation that when the gradient and scale of the noise are greater than the gradient and scale of the height of the melting layer,the result will often be greatly affected.In addition,due to the influence of heavy rainfall near the ground,the CWT method may underestimate the height of the top of the melting layer.In response to this problem,we propose a melting layer height quality control algorithm.By comparing with the 0°C isothermal heights by radiosonde data,it is found that the identified melting layer top height is in good consistency with the 0°C isothermal heights.