Severe Convective Weather Monitoring And Analysis Of The Mechanisms With Dual-Polarization Doppler Weather Radar

Dual-polarization Doppler radar has become an important tool for monitoring sudden severe weather events.The polarimetric parameters can accurately estimate the type and quantity of hydrometeors.During the evolution of precipitation,it can sensitively and delicately reflect the fine structural characteristics of precipitation clouds,helping to identify the echo structure of severe convective weather phenomena more accurately and understand the interaction between mesoscale kinematic and microphysical processes in severe convective weather processes,thus improving short-term forecasting.Considering that the application of polarimetric Doppler weather radar in China is still in its early stages,especially the high spatiotemporal resolution of fast and fine intelligent observation modes,various technical and application issues need to be addressed for monitoring and warning of severe convective weather.For example,when facing sudden disaster convective weather such as tornadoes,squall lines,thunderstorm winds,and extreme heavy precipitation,how can we utilize the wind-temperature-humidity structure characteristics of the entire troposphere to extract important precursor information?How can we use fine polarimetric parameters to understand the triggering and evolution mechanisms of severe convective weather,and gain in-depth knowledge of their different stages of kinematic structure and microphysical characteristics?How can we analyze the macro and microphysical processes expressed by polarimetric parameters using multisource observation data?How can we deepen our understanding of the differences in the efficiency of different types of heavy precipitation and reveal the macro and microphysical characteristics behind them to provide an improved basis for radar quantitative precipitation estimation methods?This paper carries out research on the above issues,and the main research contents and conclusions are summarized as follows:（1）It was found that there were ultralow temperatures and diverging areas（divergence）of the upper-level jet stream near the tropopause of the tornado,squall line and extreme heavy precipitation,which were the key premonitor characteristics easily ignored by monitoring and forecasting.Ultralow temperatures combined with high surface temperatures formed a strong temperature gradient in the vertical profile,and high-altitude divergence promoted kinematic uplift.Kinematic and thermal instability provide the environmental background for the occurrence and development of these three kinds of severe weather.（2）In the EF3 tornado event in Suzhou on May 14,2021,the formation of the supercell tornado underwent three merging processes,during which the storm cell echoes intensified,the vertical ascent speed increased(Z_DR column enhancement),and the vertical vorticity increased.Particularly,during the final merging process,the merging of two vortices resulted in a rapid reduction in the rotation radius of the new vortex,coupled with moderate cold pool intensity.This may serve as a"catalyst"for tornado formation.The velocity spectrum width reflects turbulence information,and its variations can be used as precursor signals for tornado warning.Through T-Matrix simulations,the Polarimetric Three-Body Scatter Signature（PTBSS）feature was revealed as an indicator for identifying hail and its size.The polarimetric parameters in the mature stage of the tornado were analyzed,along with the microphysical characteristics they represent.A comparison was made between the observation parameters of S-band and X-band dual-polarization radars,as well as the differences between the fine-resolution and operational-resolution of S-band dual-polarization radars.The observation of storm cell movement path bending and merging phenomena using dual-polarization radar led to the understanding of their interaction mechanisms based on fluid dynamics principles.A conceptual model of storm merging and interaction was proposed for the supercell tornado process based on this analysis.（3）In the squall line event in East China on May 10,2021,the vertical vorticity near the leading edge of the squall line had good indicative significance for the organization and evolution of squall line echoes.Positive vertical vorticity favored the intensification or maintenance of the echoes,while negative vertical vorticity indicated weakening.The evolution mechanisms of the"break"and"merge"structures during the movement of the squall line were discussed.The characteristics and mechanisms of rear inflow jet（RIJ）splitting to both sides near the top of the bow echo were studied,and a theoretical model was established to explain the formation of such structures.A new echo phenomenon,the double high-Z_DR bands（columns）,was discovered in the bulk of the warm sector squall line.The formation mechanism was explained from the perspectives of kinematic and microphysical structures.The generality of this echo phenomenon was confirmed based on two similar cases.The quasi-vertical profiles（QVPs）inverted from dual-polarization radar and GPM data were used to analyze the microscale vertical structure and evolutionary characteristics of the squall line,and a conceptual model of warm-sector bow echo was proposed based on the analysis.（4）In the rare extreme heavy rainfall event in Zhengzhou,Henan on July 20,2021,the macroscopic and microscale characteristics and evolutionary mechanisms of the record-breaking extreme hourly rainfall from 16:00 to 17:00 BT were the main focus.The FY-2G cloud-top brightness temperature indicated that the extreme short-duration heavy rainfall in Zhengzhou mainly occurred during the merging of medium and small-scale cloud clusters,which favored precipitation enhancement.The fine three-dimensional wind field of retrieval showed the presence of significant mesoscale vortices and convergence structures during the extreme heavy rainfall phase,which resulted in stationary and less-moving echoes,leading to localized extreme rainfall.The dual-polarization parameters exhibited deep convective characteristics.The formation mechanism of the"Z_DR arc"feature in the dual-polarization parameters during this phase was discussed.The dominance of warm-rain processes during the record-breaking extreme hourly rainfall phase was explained,highlighting the contribution of high concentration,medium-to-large-sized raindrops formed through effective collision-coalescence processes.From an observational perspective,significant collision and coalescence processes were confirmed during the rainfall drop descent.（5）A comparative analysis and summary of tornadoes,squall lines,and extreme heavy rainfall,three types of severe convective weather,were conducted from the aspects of weather background,echo structure characteristics,dual-polarization parameter characteristics,and microphysical parameter characteristics.The goal is to provide a theoretical basis and technical support for short-term warnings of such severe convective weather events.