Analysis of Dual Polarization and Wind Field Inversion Characteristics of a Heavy Rainstorm in Changsha
This study aims to help forecasters to apply dual polarization and phased array radar products in the analysis of rainstorm process.The heavy rainstorm in Changsha on April 25,2022,is analyzed by using S-band dual-polarization radar and X-band phased-array radar.The findings are as follows:(1)The precipitation echo belt changed from a northeast-southwest orientation to an east-west orientation.The high value region(≥1.0 dB)of difference reflectance factor(ZDR)showed zonal distribution,and the train effect caused the heavy rain in Changsha.(2)Multiple convective cells were arranged in an east-west direction and extended to a height of 6km.The expansion of ZDR and KDP columns above the height of the melting layer indicated that strong upward airflow provided favorable conditions for water droplets to break through the melting layer and form supercooled water droplets.Below the height of the melting layer of convective cells,most ZDR values were positive,with noticeable high values of ZDR and KDP in the bottom layer.This indicated large horizontal raindrop diameters and high number concentrations,corresponding to strong rainfall.(3)When minute rainfall exceeded 1 m,KDP ranged from 1.7 ° to 2.4 °·km-1,and KDP cavities appeared.When minute rainfall exceeded 2 mm,KDP ranged from 2.4 ° to 3.1 °·km-1.(4)The three-dimensional wind field of phased-array radar inversion showed that during the heavy precipitation,strong southwest wind in front and south of the zonal precipitation echo carried water vapor,contributing to the heavy rain process.The deep shear line facilitated the maintenance of banded echo,with a strong bow echo accompanied by cyclonic wind fields and strong divergence in the upper wind field.Guided by the airflow,the banded echo continuously passed through Changsha,forming the train effect.(5)The vertical section of three-dimensional wind field and intensity showed distinct anvil-shaped echoes during the heaviest precipitation period.The strong echo center was influenced by power lift and water vapor transport conditions.As winds changed to the northwest or west at mid-low levels,the echo gradually weakened,and minute rainfall decreased sharply.The above analysis indicates that dual polarization products can help indicate convective rainfall,and the three-dimensional wind field retrieved by X-band phased array radar effectively depicts the characteristics of convective intensity,convergence,and divergence.
heavy raindual-polarization radarphased-array radartrain effectZDRKDP
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