Snowstorm over the Southwestern Coast of the Korean Peninsula Associated with the Development of Mesocyclone over the Yellow Sea

This study investigates the characteristics of a heavy snowfall event over the southwestern part of the Korean Peninsula on 4 December 2005. The snowstorm was a type of mesoscale maritime cyclone which resulted from barotropic instability, and diabatic heating from the warm ocean in continental polar air masses. Based on surface observations, radiosonde soundings, MTSAT-1R satellite data and the 10-km grid RDAPS （Regional Assimilation and Prediction System based on the PSU/NCAR MM5） data, the evolution of the mesocyclone is explained by the following dynamics; （1） In the initial stage, the primary role in the cyclogenesis process of the mesocyclone is a barotropic instability in the horizontal shear zone. （2） In the developing stage, the mesocyclone moves and deepens into a baroclinic zone corresponding to the surface heating and moistening. （3） In the mature stage, it is found that the mesocyclone is intensified by the destabilization caused by enhanced low-level heating and condensation, the moisture flux convergence, and the interaction between upper and lower-level potential vorticity anomalies. We suggest that a checklist with stepwise indicators responsible for development be prepared for the forecasting of heavy snowfall over the southwestern part of the Korean Peninsula.

Mesocyclone Evolution and Differences between Isolated and Embedded Supercells

A total of 61 supercells with mesocyclones lasting for at least 6 volume scans were investigated. These storm parameters and mesocyclone parameters were counted and compared to determine the salient differences between isolated supercells and embedded supercells in different regions. The results showed that the mesocyclone parameters had different evolution characteristics in three stages of mesocyclone. The storm parameters, mesocyclone parameters and severe weather phenomenon had significantly differences between isolated supercells and embedded supercells. The mesocyclone parameter differences determined the differences in the reflectivity structure and weather phenomenon. The higher base and top of mesocyclone for isolated supercells indicated that the isolated supercells had higher maximum reflectivity, maximum reflectivity height, cell-based vertically integrated liquid and top of storm cell, and significantly higher probability of hail or large hail than the embedded supercells. The descending lower base of mesocyclone at its mature stage in the region of Jianghuai Plain indicated that the supercells in this region had a higher probability of mesocyclone-induced tornado.

Single-Doppler Radar Analysis of a Mesocyclone in the Taiwan Strait

In this study, the kinematic and precipitation structures of a mesocyclone associated with a hook echo were analyzed using single Doppler radar data. The mesocyclone was embedded in a mesoscale convective rainband near northern Taiwan coastline on 10 September 2004. The synoptic environment was characterized by a moderate convective available potential energy （CAPE） and a moderate ambient vertical shear from surface to 5 km. In addition, a pronounced low-level mesoscale shear/convergence zone, which resulted from the interaction of two tropical depressions, was also identified in the northwest coast of Taiwan, providing a favorable dynamic condition for the development of the mesocyclone. Analyzing single Doppler dipole signature shows that this mesocyclone formed initially at low levels, then deepened and strengthened rapidly into mature stage with the vertical depth exceeding 8 km. The diameter of the mesocyclone decreased with the height at the time of vortexgenesis, and then evolved into columnar structure accompanied with the broader diameter in middle layer. The mesocyclone lasted for about 2 h. The Ground-Based Velocity Track Display （GBVTD） method was applied to retrieve the ax- isymmetric circulation of the mesocyclone. The GBVTD-derived primary circulation showed the radius of maximum wind （RMW） of the mesocyclone was about 5-6 km and varied from inward tilting to outward tilting with time. The axisymmetric radial wind field was initially characterized by a low-level inflow inside the RMW and outflow outside the RMW, respectively. The strongest reflectivity was associated with a stronger updraft near the RMW, and a weak downdraft was located at the center of the mesocyclone. Subsequently the downdraft and reflectivity near the mesocyclone center strengthened obviously, accompanied with the low-level outflow, strong updraft as well as high reflectivity extending outside the RMW. The relative tangential wind initially exhibited a wavenumber 1 asymmetric structure with the maximum wind region at the left portion of the meso cyclone and shifted counterclockwise with height. The axisymmetric tangential wind strengthened and reached its maximum intensity with a value about 20 m s^-1 at z=1 km. After that the axisymmetric tangential wind decreased rapidly, meanwhile the wave-1 asymmetric structure redeveloped with the maximum wind at the left-front of motion. In summary, the evolution and structure of the mesocyclone is similar to that observed within a non-supercell mesocyclone. It is worth to mention that the axisymmetric circulation characteristics of the mesocyclone at its mature stage are very similar to those observed in a mature typhoon. However, there are significant differences, i.e., the size is much smaller, the lifetime is much shorter, and the downdraft in the center is produced by precipitation instead of compensating subsidence.

Advanced Method for Forecasting and Warning of Severe Convective Weather and Local-scale Hazards

Hurricane Ida ferociously affected many south-eastern and eastern parts of the United States,making it one of the strongest hurricanes in recent years.Advanced forecast and warning tool has been used to track the path of the ex-Hurricane,Ida,as it left New Orleans on its way towards the northeast,accurately predicting significant supercell development above New York City on September 01,2021.This advanced method accurately detected the area with the highest possible level of convective instability with 24-h lead time and even Level 5,devised in the categorical outlooks legend of the system.Therefore,an extreme level implied a very high probability of the local-scale hazard occurring above the NYC.Cloud model output fields(updrafts and downdrafts,wind shear,near-surface convergence,the vertical component of relative vorticity)show the rapid development of a strong supercell storm with rotating updrafts and a mesocyclone.The characteristic hook-shaped echo signature visible in the reflectivity patterns indicates a signal for a highly precipitable(HP)supercell with the possibility of tornado initiation.Open boundary conditions represent a good basis for simulating a tornado that evolved from a supercell storm,initialized with initial data obtained from a real-time simulation in the period when the bow echo and tornado-like signature occurred.Тhe modeled results agree well with the observations.

Characterization and Application of S-Band Polarimetric Radar and X-Band Phased Array Radar for a Tornadic Storm Event on June 16,2022

The X-band phased array radar offers faster scanning speed and higher spatial resolution compared to the S-band radar,making it capable of enhancing tornado monitoring and early warning capabilities.This study analyzed the characteristics and nowcasting signals of a tornado case that occurred on June 16,2022 in the Guangzhou region.Our findings indicate that the violent contraction of rotation radius and the dramatic increase in rotation speed were important signal characteristics associated with tornado formation.The X-band phased array radar,with its high temporal and spatial resolution,provided an opportunity to capture early warning signals from polarimetric characteristics.The X-band phased array radar demonstrated noteworthy ability to identify apparent tornado vortex signature(TVS)features in a 10-minute lead time,surpassing the capabilities of the CINRAD/SA radar.Additionally,due to its higher scanning frequency,the Xband phased-array radar was capable of consistently identifying TVS with shorter intervals,enabling a more precise tracking of the tornado's path.The application of professional radars,in this case,provides valuable insights for the monitoring of evolutions of severe local storms and even tornadoes and the issuance of early warning signals.

Single-Doppler Radar Observations of a High Precipitation Supercell Accompanying the 12 April 2003 Severe Squall Line in Fujian Province

In this study,single Doppler radar data were used to examine the structure and evolution of a high precipitation（HP） supercell embedded in a cold front near Jianyang,Fujian Province on 12 April 2003.The synoptic environment was characterized by high humidity at low levels,moderate CAPE（convective available potential energy;1601 J kg^（-1））,moderate wind shear（22 m s^（-1） in 0-5 km）,and veering of the horizontal winds with height,similar to those HP supercells previously observed in midlatitudes.In addition,the calculated bulk Richardson number was only 16,suggesting favorable environmental conditions for supercell development. The documented storm was located at the leading edge of a squall line.It was initiated from a single cell at 0732 UTC.It evolved into a bow shape gradually,and then split into two separate storms along the storm motion direction through the apex of the bow echo.The left-moving storm dissipated rapidly, but the right-moving storm strengthened and evolved into an HP supercell,lasting for more than 1 h.The radar reflectivity of the HP supercell during its mature stage showed a typical low-level hook echo at the front flank of the storm with its maximum reflectivity beyond 70 dBZ.Above the hook echo,an elevated maximum reflectivity core accompanied by a bounded weak-echo region（BWER） and a down-shear echo overhanging aloft were clearly identified.The elevated BWER,marked by 40-50-dBZ reflectivity values,was surrounded by values of 60-70 dBZ.A well-defined mesocyclone lasted about 1 h and was collocated with the low-level WER and middle-level BWER.The radar-estimated time-height profiles of mesocyclone rotational velocity and diameter indicated that this mesocyclone formed initially at middle level,then deepened and strengthened rapidly with the vertical depth deeper than 8 km and rotational velocity stronger than 24 m s^（-1） at the mature stage,and later decayed rapidly.The GBVTD（ground-based velocity track display）-derived primary circulation showed that the maximum tangential wind of the mesocyclone appeared at middle level （3-5 km） with a value of about 20 m s^（-1）.The mean radial wind field was characterized with a low-level inflow below 4 km,and accompanied by stronger updraft near the mesocyclone center.Between 4 and 7 km.the tangential wind profile resembled a Rankine combined vortex with the radius of maximum wind （RMW） at 3 km.and there was outflow/inflow inside/outside of the RMW.Correspondingly,the vertical velocity indicated a stronger updraft at the RMW and a weak downdraft inside the RMW.Above 7 km,the outflow strengthened and extended outside the RMW. In summary,the reflectivity structures of the storm and the accompanying mesocyclone were similar to those midlatitude HP supercells proposed in Miller＇s paper in 1994.However,the evolution of the HP supercell,including its three stages：ordinary storm,bow echo,and storm splitting,was quite different from those documented before.

Analysis of Three Supercell Storms with Doppler Weather Radar Data

Three supercell storms on 24 June 2004（0624）,28 June 2003（0628）,and 27 September 2002（0927） induced different damages in Shandong Province.Storm 0927 was inferior in size and intensity to storms 0628 and 0624.The structure and evolvement of the three storms were analyzed in detail based on the WSR98D radar data in combination with weather charts.The results show that mesoscale surface convergence triggered release of instable energy,which resulted in severe convection.During the development stage,storms 0927,0628,and 0624 displayed multi-cell propagation,single-cell evolution,and multi-cell mergence,respectively.The storm tracks were similar：they were all right-moving supercell storms,i.e.,moving at an angle of 30°-70° to the right of the mean wind and at a speed of about 45%-70% of the mean wind speed.In the mature stage,the maximum reflectivity appeared at the low level in storm 0927,mid level in storm 0628,and mid-upper level in storm 0624.These storms possessed almost all typical features of supercell storms：weak echo region（WER）,bounded weak echo region（BWER）,and mesocyclone.An organized mesocyclone formed at the middle height of an updraft,deepened gradually downward and upward,and became a typical mid-level mesocyclone with strong updrafts.The vertical structures of airflows in the three storms were similar,i.e.,significant convergence at low level,nearly pure rotation at mid level,and divergent rotation at upper level.However,signatures of mid-level horizontal airflows in the three storms were different：at mid level,there was a single vortex in storm 0628,but a double-vortex flow pattern was seen in storms 0927 and 0624.The horizontal structure of the double-vortex flow was hard to be blown away by the environmental airflow,and thus the storms could persist for a longer period of time than the single vortex storm.