The scattering mechanism of squall lines with C-Band dual polarization radar. Part I: echo characteristics and particles phase recognition

Squall line is a kind of common mesoscale disaster weather. At present, there are few studies on the elaborate detection of squall line by dual polarization radar. With the dual polarization upgrade of weather radar network, we need to study the relationship between squall line echoes of base data and polarization data to reveal new echo phenomena and formation mechanisms. The relationship between radar parameters and atmospheric physical processes also need to be examined. Based on the NUIST CDP radar, a squall line in the Yangtze and Huaihe River basin that occurred from July 30 to 31, 2014 is analyzed. The results show that polarization parameters have obvious advantages in the characteristics analysis of size, phase state, shape and orientation of the water condensate particles. The phase states of water condensate particles in convection cell can be distinguished through comparative discussion. Several phase states exist in the squall line, including small, medium and large raindrops, melting hails, dry hails and ice crystal particles and the ZDR column can be used to identify the location of the main updraft. In addition, the polarization parameters are more sensitive to the melting layer. The gust front is presented as a narrow linear echo in Z affected by strong turbulence. It is an obvious velocity convergence line in V and approximately 0.70 in <font style="font-family:Symbol">r</font>HV. The ZDR can be used as a criterion to distinguish the horizontal and vertical scale of turbulence. The deforming turbulence, which is affected by environmental airflow, will cause an abnormally high ZDR in the gust front and a negative ZDR before and after the gust front. The variation of ZDR depends on the turbulence arrangement, orientation and relative position between turbulence and radar. These dual polarization parameter characteristics offer insights into understanding the structure and evolution of the squall line.