Abstract:An extraordinary extreme heavy rainfall event during 19—22.July 2021 (“21.7” EHRE) attacked Henan Province of North China Plain (NCP) and led to tremendous catastrophes due to the record-breaking rainfall.Previous studies mainly focus on the individual case study of the “21.7” EHRE,which cannot give a general view of circulation characteristic from the climatic perspective,particularly for the extraordinary precipitation extremes with a rare occurrence.Based on 12-hourly observed precipitation data from rain gauge stations during 1960—2021 from CMA (China Meteorological Administration) and NCEP/NCAR reanalysis data,this study investigated the typical synoptic patterns responsible for the summer regional extreme precipitation events (REPEs) over NCP during 1960—2021 via the spectral clustering method and systematically revealed how the “21.7” EHRE occurred.Results show that the “21.7” EHRE occurred under a rare synoptic pattern featured by a distant typhoon over western Pacific accompanied by the farther northwestward extended western Pacific subtropic high (WPSH) and northeastward extended South Asia high (SAH).This synoptic pattern only contributes 5.97％ of the total summer REPE occurrences over NCP but can lead to much stronger precipitation extremes.The water vapor transported by the strong southeasterly winds between the Typhoon In-Fa and WPSH from the western Pacific to Henan,and the intense ascending motion caused by wind shear between lower and upper troposphere over Henan Province led to the occurrence of the “21.7” EHRE.In addition,diagnosis analysis based on quasi-geostrophic omega equation indicates that the positive feedback on intense ascending motion and diabatic heating at lower troposphere over Henan province and surrounding areas distinguishes the “21.7” EHRE from the others under the same synoptic pattern.This study investigates the dominant large-scale synoptic pattern of the “21.7” EHRE in Henan to figure out the formation mechanism of the rarest REPEs in a climatic aspect.Findings of this study provide a novel perspective on characterizing and predicting future precipitation extremes in NCP by linking the occurrence and distribution of REPEs with the synoptic patterns.

Abstract:Soil moisture plays a significant role in global terrestrial water cycles and interactions between land and atmosphere,serving as a crucial factor in hydrologic and climate applications.Due to its long-term memory on time scales ranging from several weeks to months,soil moisture is valuable for weather and climate forecasts.Additionally,it profoundly influences plant photosynthesis,especially during extreme precipitation events and droughts.Accurate and continuous high-resolution soil moisture datasets are essential for analyzing the response of soil moisture to extreme events.However,in situ observations of soil moisture are inadequate due to the sparse distribution of stations,necessitating reliable datasets with fine coverage and accuracy.
Three primary types of high-resolution soil moisture datasets exist:remote sensing data,reanalysis data,and machine learning-enhanced data based on ground-based observations.However,the ability of these datasets to accurately capture the responses of soil moisture to droughts and extreme precipitation events in the middle and lower reaches of the Yangtze River remains uncertain.This study assessed five soil moisture products—Soil Moisture Active Passive (SMAP),Soil Moisture and Ocean Salinity (SMOS),European Space Agency Climate Change Initiative (ESA CCI),European Reanalysis 5 (ERA5),and Soil Moisture of China by in situ data (SMCI)—to investigate their accuracy in capturing the responses of soil moisture to precipitation anomalies in this region.
Precipitation datasets were used to identify years with extremely dry and wet Meiyu seasons based on the standard deviations of total precipitation in June and July.Extremely dry (2013 and 2018) and wet (2016 and 2020) years were identified.The responses of the soil moisture datasets to extreme precipitation and drought events in the study area were then compared.The results showed that all five products could reflect the spatial distribution of soil moisture,but SMOS had lower values than the other products,and its spatial variations differed somewhat from the others.SMAP,SMCI,and ERA5 reasonably captured the responses of soil moisture to extreme precipitation,while SMOS did not accurately reflect these responses.The responses of SMOS and ESA CCI soil moisture to extreme drought events differed from the other products,whereas ERA5 and SMCI demonstrated more accurate spatial responses to drought conditions.Overall,while all five products provided reasonable spatial distributions of soil moisture over the study area,their performances in capturing response to climate extremes varied substantially.Therefore,the accuracy of these datasets needs to be evaluated under different conditions,especially during droughts and extreme precipitation events.This study enhances our understanding of soil moisture variations in the middle and lower reaches of the Yangtze River and guides the use of various soil moisture datasets for examining responses to climatic extremes.

Abstract:Using NCEP/NCAR reanalysis data,ERSST v5 sea surface temperature data,and an atmospheric circulation model,we analyzed the mechanisms and relative contributions of tropical Indo-Pacific ocean SST anomalies to the high-temperature event in the middle and lower reaches of the Yangtze River basin during the summer of 2022.The study shows that the summer of 2022.recorded the highest temperatures in the middle and lower reaches of the Yangtze River basin in the past 40 years,with an area mean anomalous temperature of 1.52.℃.The spatial distribution of positive temperature anomalies in this region was highly uneven,with the maximum anomalies located to the west of the Henan-Hubei border.This positive temperature anomaly event was influenced by both La Niña and the negative phase of the IOD.After removing the ENSO and IOD signals,the anomalous temperatures in the middle and lower reaches of the Yangtze River were 1.23 and 1.37 ℃,respectively.When both ENSO and IOD signals were removed,the temperature anomaly was 1.13 ℃,indicating that tropical Indian Ocean and Pacific SST anomalies contributed 25.66％ to the summer high-temperature anomalies in this region.The atmospheric Matsuno-Gill response to the La Niña event caused an anticyclonic circulation anomaly from the middle and lower reaches of the Yangtze River to the Northwest Pacific region.The negative phase IOD event enhanced the subtropical high in the western Pacific by strengthening the easterly anomalies over the Maritime Continent.The strengthened western Pacific subtropical high favored maintaining anomalous subsidence motion in the middle and lower reaches of the Yangtze River basin,facilitating the occurrence of the high-temperature event.These results provide a scientific basis for understanding the extreme high-temperature events in the middle and lower reaches of the Yangtze River basin during summer.

Abstract:Based on NCEP/NCAR daily reanalysis data and observations from 124 meteorological stations in Yunnan Province,we analyze the extreme features and low-frequency oscillation characteristics of the abnormally low temperature event in Yunnan from April to June 2022.We also investigate the evolution of the spatial configuration of low-frequency circulation systems in the middle and lower troposphere.The results are as follows: 1) In the late spring and early summer (April-June) of 2022,Yunnan experienced a rare extreme low temperature event under the backdrop of climate warming.The average temperature was the fifth lowest on record for this period since 1961 and the lowest since 1991.Average temperatures at 42.stations reached or broke historical records for the same period.2) There was a significant 10—20 d period for average temperatures in Yunnan in late spring and early summer of 2022,with a variance contribution of 45.7％.This 10—20 d oscillation was closely related to actual temperature drops.3) During the 10—20 d low-frequency oscillation,phase 7 corresponded to the maximum temperature decrease and phase 3 to the maximum temperature increase over Yunnan.At 500 hPa,Yunnan was influenced by northerly (southerly) airflow between a low-frequency anomalous high-pressure (low-pressure) system around Lake Baikal and a low-frequency anomalous low-pressure (high-pressure) system near the Sea of Japan in phase 7 (phase 3).Simultaneously,the region from eastern China to the South China Sea was mainly controlled by low-frequency northward (southward) wind at 700 hPa,which correlated with cooling (warming) areas.Yunnan was mainly under control of the low-frequency easterly (westerly) air flow and also located in the cooling (warming) area.The sea level pressure field showed an enhanced and southward-moving Siberian high-pressure system,bringing cold air from high to low latitudes,affecting temperature changes in Yunnan,and contributing to the strong cold air process.4) At 500 hPa,low-frequency positive height anomalies propagated southward from high latitudes to Lake Baikal,while low-frequency positive height anomalies at middle and low latitude moved eastward from Mediterranean Sea to Lake Baikal.The synergistic effect of these two low-frequency wave trains facilitated the generation,strengthening,and maintenance of abnormally low temperatures in eastern China and Yunnan from April to June 2022.5) In late spring and early summer of 2022,the South Branch Westerly Trough Index and the Siberian High Pressure Index in the 10—20 d low-frequency oscillation showed the best correlation with low-frequency temperatures in Yunnan at 7 and 5 d,respectively.These indices can effectively predict abnormal low-temperature processes in Yunnan.

Abstract:With global warming,extreme precipitation events are becoming more frequent and intense,affecting broader regions and presenting significant global challenges.The Qinghai-Xizang Plateau,known as the “roof of the world,” has a unique geographical position and fragile ecosystem,making it particularly sensitive to climate change.Extreme precipitation events exacerbate the uneven spatial and temporal distribution of water resources across the Qinghai-Xizang Plateau and trigger natural disasters such as landslides,mudslides,and floods,posing severe risks to local populations and ecosystems.
This paper provides a comprehensive review of recent research on summer extreme precipitation over the Qinghai-Xizang Plateau,focusing on four key aspects:1) definitions and indices of extreme precipitation;2) characteristics of summer extreme precipitation over the Qinghai-Xizang Plateau;3) factors influencing extreme summer precipitation over the Qinghai-Xizang Plateau;and 4) disaster risks and future projections of summer extreme precipitation over the Qinghai-Xizang Plateau.The percentile threshold method is widely used to define extreme precipitation,revealing a pattern of “less in the northwest and more in the southeast” across the Qinghai-Xizang Plateau.There is a notable increasing trend in extreme precipitation,characterized by extended durations and a greater contribution to total precipitation.
Extreme precipitation over the Qinghai-Xizang Plateau is highly sensitive to both natural and anthropogenic factors.The determinants are complex and multifaceted,involving interactions with global warming,atmospheric circulation patterns,and multi-scale weather systems.Key dynamic and thermodynamic factors,such as ascending motions,moisture transport and convergence,and enhanced atmospheric convective instability,create conditions conducive to the intensification of extreme precipitation.Future climate model projections consistently suggest an intensification of the global water cycle,increasing the frequency and magnitude of extreme precipitation under continued global warming.These trends are more pronounced under high-emission scenarios compared to moderate and low-emission scenarios,posing significant challenges to the Qinghai-Xizang Plateau's fragile ecosystems and socio-economic advancement.
While considerable progress has been made in understanding extreme precipitation over the Qinghai-Xizang Plateau,many complex issues require further investigation.This review aims to summarize current knowledge and highlight future research directions,enhancing our unders tanding of extreme precipitation patterns and their impacts on the Qinghai-Xizang Plateau and surrounding regions.By providing theoretical insights into the challenges posed by climate change on the Qinghai-Xizang Plateau,this paper seeks to inform more effective responses to the evolving threats of global warming and extreme precipitation events.

Abstract:Cold spells are significant winter weather events that affect eastern China,posing risks to public safety and property.Various factors contribute to the occurrence of these cold spells,including anomalies in the polar vortex,tropical sea surface temperature,Arctic Oscillation,and stratosphere-troposphere coupling.One key form of stratosphere-troposphere coupling is Rossby wave reflection,which can alter tropospheric circulation and trigger cold spells.Previous studies,such as Matthias and Kretschmer(2020),have linked North American cold spells to wave reflection over Siberia and Canada,primarily involving wave numbers 1 and 2.However,the characteristics of cold spells in eastern China remain underexplored,particularly those influenced by higher wave numbers.
To address this gap,we analyzed cold spell events in eastern China from 2000 to 2020,selecting cases based on the intensity and duration of cooling.We calculated the E-P flux for wave components 1—4,identifying events influenced by wave reflection.From this analysis,we identified 6 cases influenced by wave reflection of waves 1—2.and 8 cases influenced by wave reflection of waves 3—4.This study focuses on the anomalies associated with Rossby waves 3—4 and their impact on cold spells in eastern China,using synthetic analysis of the 8 cases influenced by wave reflection of waves 3—4 with ERA5 reanalysis data.
Our findings indicate anomalies in Rossby waves 3—4 are closely linked to the Ural high.Prior to cold spells,the stratospheric polar vortex showed a distinct 3-wave structure,with the mid-to-upper stratosphere (500—600 K) polar vortex shifting towards Eurasia and extending its northern edge to northern Europe.This displacement resulted in abnormal easterly zonal winds over high-latitude Eurasia,promoting downward Rossby wave activity fluxes.The lower stratospheric polar vortex (450 K) elongated towards East Asia,forming wave reflection near the tropopause characterized by upward fluxes over western Europe and downward fluxes over eastern Europe.This reflection pattern intensified the Ural high,facilitating the onset of cold spells in China.We propose a regional reflection index,defined as the difference between the eddy heat fluxes over western Europe and eastern Europe at 200 hPa.The index peaked approximately one week before the coldest temperatures were recorded,demonstrating strong correlation with temperature changes associated with cold spells influenced by waves 3—4 in eastern China.This index could serve as a valuable tool for forecasting and early warning of cold spells.
This study reveals that,in addition to wave components 1—2,wave reflection involving components 3—4 can also occur under specific conditions,contributing to cold spells in eastern China.Future research will examine the 6 cases influenced by wave reflection of waves 1—2,comparing the circulation characteristics and mechanisms between cold spells influenced by waves 1—2.and waves 3—4.

Abstract:Typhoons can cause significant damage,and accurate forecasting of their paths is crucial for mitigating their impact.This study investigates the sudden northward turn of Typhoon In-Fa (2021),which veered nearly 90 degrees northward,using the WRF model to perform accurate numerical simulations combined with analyses of upper atmospheric circulation and basic airflow patterns.The findings indicate that the northward turn of Typhoon In-Fa was driven by several key factors:1) As Typhoon In-Fa approached Taiwan,its track shifted northward due to the strengthening and westward expansion of the western pacific Subtropical high,combined with the deepening of the upper-level long-wave trough over China and the blocking influence of a low-pressure vortex near Japan,which prevented further westward movement.Concurrently,the northward surge of cross-equatorial flow altered the basic airflow from a northeasterly to a southwesterly direction,enhancing the northward movement trend.2) The continuous eastward shift of the mid-latitude longwave trough over China and the eastward retreat of the subtropical high led to the formation of a significant positive potential vorticity center north of the center of Typhoon In-Fa,accompanied by counterclockwise positive potential vorticity advection on the northwest side of the center.This altered the structure of the potential vorticity field near the typhoon center,slowing its westward trajectory and steering it northward.3) The vertical shear of the ambient wind near the typhoon center was unfavorable for westward movement but facilitated northward movement due to the distribution of high and low values,with lower values north of the typhoon center.4) Both simulation experiments indicated persistent wind speed asymmetry around the typhoon center,with the 500 hPa wind speed maximum shifting from the west to the east side of the typhoon center.The presence of southerly winds on the right side of the typhoon increased the northward component of its movement,significantly contributing to its abrupt northward turn.5) In the unstable energy field,a low-energy tongue developed on the west side of the typhoon,promoting movement into the unstable atmospheric junction region.These findings highlight that the sudden northward turn of Typhoon In-Fa was driven by a combination of thermodynamic factors,providing valuable insights for improving typhoon track forecasts.

Abstract:Amidst the backdrop of global warming,rainstorms have become increasingly frequent in North China,posing significant threats to both the socio-economic fabric and health and safety of the population.The convergence of the subtropical high over the northwestern Pacific and Typhoons “Dussuri” (No.5) and “Kanu” (No.6) in 2023 precipitated an extreme rainstorm event in North China from 08:00 BST on July 29 to 08:00 BST on August 2,2023,resulting in considerable social disruption.Utilizing hourly precipitation data from national meteorological stations provided by the National Meteorological Information Center of the China Meteorological Administration,this study analyzes the temporal and spatial distributions of hourly heavy rainfall (HHR) and statistically compare three types of heavy rainfall events(HREs)with varying durations to elucidate their characteristics.The findings indicate that:(1) HHR during this event exhibited high intensity and localized patterns,contributing over 20％ to the total precipitation.Areas such as the eastern foothills of the Taihang Mountains,including western Beijing and central and southwestern Hebei,recorded the highest precipitation amounts and the most active precipitation frequencies.The dual typhoons facilitated sustained water vapor transport to the North China Plain,which was enhanced by orographic lifting by the Taihang Mountains,promoting the persistence and intensification of HHR.(2) HHR experienced 6 periods,with the third peak showing the highest cumulative precipitation,frequency,and longest duration.During the stages influenced by the “Dussuri” residual vortex,warm shear lines,and easterly winds,as well as southerly or southwestern jets,HHR was most active during the stage associated with the “Dussuri” residual vortex,totaling 257 occurrences with a maximum precipitation of 73.5 mm.(3) Among the three HRE types,long-duration events (>12.hours) were most frequent,accounting for 54.5％,followed by short-duration events (1—6 hours) at 32.9％,and medium-duration events (7—12.hours) at 12.6％.Precipitation amounts for long-duration HREs typically exceeded 180 mm,while those for short and medium durations are mostly ranged from 20 to 60 mm.(4) Spatial analyses show that long-duration HREs had higher frequencies and precipitation amounts compared to shorter events.Beijing and Hebei were particularly prone to high precipitation amounts and frequencies during long-duration events.This study underscores critical role of the Taihang Mountain's terrain in influencing HHR during heavy rainstorm events in North China,suggesting that the mechanisms driven by refined terrain features warrant further detailed investigation.Future studies could employ numerical simulation experiments to delve deeper into these dynamics.

Abstract:Aircraft turbulence is a significant meteorological event impacting flight safety.This study analyzes the temporal and spatial distribution characteristics of aircraft turbulence on major air routes across China,as well as the underlying causes of observed turbulence patterns.The analysis utilizes 6 498 Pilot Reports (PIREPs),employing data quality control and kernel density analysis.Results reveal that aircraft turbulence over China exhibits a distinct multi-scale temporal distribution.From 2011 to 2016,the incidence of turbulence showed an increasing trend,stabilizing after 2013.Seasonally,turbulence frequency and intensity peak during winter and spring,while they diminish during summer and autumn.Monthly variations follow a “funnel-shaped” pattern,and daily variations exhibit a clear “three-peak” characteristic.Regionally,turbulence frequency is higher in eastern China compared to western regions.Notably,turbulence along the main north-south air routes forms a large “comma” shape,stretching from North China through Nanchang to Chengdu.The altitude of turbulence also shows regional distinctions:North China experience the most high-altitude turbulence,while mid-altitude turbulence predominates in East and Southwest China.Xinjiang is notable for its prevalence of low-altitude turbulence.The spatiotemporal distribution of turbulence in China is primarily influenced by the upper-level jet stream,with wind shear contributing to low-altitude turbulence in Xinjiang.

Abstract:Accurate understanding of microphysical characteristics of short-term heavy rainfall is crucial to improve the monitoring and warning capabilities of severe convective weather such as short-term heavy rainfall and accurate understanding of raindrop size distribution (DSD) characteristics of short-term heavy rainfall is also the key to improve the forecasting and early warning capabilities of it.Currently there are still few studies on DSD statistical characteristics of short-term heavy rainfall.Most studies either focus on the rainstrom process under the influence of a certain weather system or contrastive studies on different weather types.Studies on the DSD characteristics of short-term heavy rainfall under the influence of different weather systems are rare.Furthermore,most of the research is based on the observations of a single station or several stations,so the results have some limitations due to the local site observations.In this paper,based on automatic weather station data and disdrometer data during 2019—2020 in summer in Jiangsu Province,the short-term heavy rainfall is divided into four types:Meiyu 20,Meiyu 50,Typhoon 20 and Typhoon 50 according to different weather types (Meiyu and typhoon) and different rainfall intensities (20—50 and >50 mm·h^-1).The different DSD characteristics in different types of short-term heavy rainfall with different intensity is further analyzed to deepen the understanding of the differences of microphysical characteristics of the different types of short-term heavy rainfall.Statistical results show that the average raindrop particle size (number concentration) of Meiyu-type short-term heavy rainfall (SHR) is obviously higher (lower) than that of typhoon-type SHR on the whole.The contribution of small raindrops (diameter≤2.mm) to typhoon-type SHR is significantly more than that to Meiyu-type SHR.Furthermore,with the increase of rainfall intensity,the large raindrop number concentration and the average raindrop particle size of Meiyu-type SHR with intensity over 50 mm·h^-1increased significantly compared with Meiyu-type SHR with intensity between 20 and 50 mm·h^-1.Similarly,the number concentration of typhoon-type SHR with intensity over 50 mm·h^-1 increased significantly but the growth of particle size is not obvious compared with typhoon-type SHR with intensity between 20 and 50 mm·h^-1.Therefore,the typhoon-type SHR with different intensities is mainly contributed by high concentration of small particle size raindrops,while the extreme Meiyu-type SHR is contributed by larger raindrops,and the DSD characteristics are more complex.Similar observation conclusions are also obtained through typical case study.It shows that the DSD of Meiyu-type SHR is more obvious than that of typhoon-type SHR.

Abstract:With the economic development of southern Sichuan,ground-level ozone (O₃) and particulate matter less than 2.5 μm in aerodynamic diameter (PM_2.5) have emerged as major pollutants detrimental to human health.In response to air pollution challenges,the Chinese Government implemented the “Air Pollution Prevention and Control Action Plan” in 2013 and the “Three-Year Action Plan to Win the Blue Sky Defense War” in 2018.This study evaluates the effectiveness of control measures for PM_2.5 and O₃ in southern Sichuan post-implementation and aims to provide a theoretical and scientific basis for the coordinated management of these pollutants.We analyze the temporal variations in PM_2.5 and O₃ concentrations in four cities in southern Sichuan (Zigong,Neijiang,Luzhou,and Yibin) from 2015 to 2020.Zigong,identified as the most polluted among the cities,serves as a case study to investigate the correlations between PM_2.5 and O₃ concentrations and various influencing factors.The study utilizes backward trajectory clustering,source emission intensity analysis,and potential source analysis to assess the impact of regional pollutant transport on Zigong.The results indicate that:1) From 2015 to 2020,the annual average concentration of PM_2.5 in southern Sichuan showed a declining trend with a 38.9％ reduction,while the annual average concentration of O₃ showed a slight increasing trend,rising by 8.2％.These trends suggest that current control strategies are effective for PM_2.5 but may be insufficient for O₃,highlighting the need for enhanced O₃ management strategies.2) The monthly average PM_2.5 concentration exhibits a “U” shape,with the lowest values in July and August and the highest from December to February.In contrast,the monthly average O₃ concentration exhibits an “M” shape,peaking in July and August with secondary peaks in April and May.These patterns suggest that PM_2.5 control should be prioritized in winter,while O₃ control should be emphasized in spring and summer.3) In Zigong,PM_2.5 concentration shows significant positive correlations with CO,NO₂,and SO₂ concentrations,while O₃ concentration is significantly positively correlated with temperature and negatively correlated with relative humidity.4) The regional transport of PM_2.5 and O₃ in Zigong is predominantly influenced by local air masses.Radiation levels and anthropogenic emission intensities along air trajectories significantly affect PM_2.5 and O₃ concentrations.The primary potential source areas for these pollutants are located within the Sichuan Basin and parts of Guizhou.Given the regional transport influnece,there is a need for strengthened regional collaborative governance,joint prevention and control efforts,enhanced source control,accelerated replacement of VOC-containing materials,and increased utilization of clean energy soucres.The study employs Pearson correlation analysis to preliminarily identify relationships between PM_2.5 and O₃,and various influencing factors.Future research will include a more quantitative analysis of these relationships,including the impact of temperature on photochemical reactions,the role of relative humidity in PM_2.5 wet deposition,and the effects of atmospheric diffusion conditions on pollutant concentrations.These analyses will provide precise quantification of the specific impacts of each influencing factor on PM_2.5 and O₃ pollution,thereby enhancing the objectivity and reliability of the research findings.

Abstract:Radar is the most effective tool for detecting hail.In the 1960s and 1970s,the widespread use of rain measurement radar (e.g.,Danka 41 in the UK and domestic radars such as 711,713,etc.) enabled the identification of hail clouds through radar echo features like hook-shaped,finger-shaped,and V-shaped notches.The introduction of Doppler weather radar in the late 1980s and early 1990s provided more accurate data,including radial velocity,for effective hail cloud identification.However,four factors affect the accuracy of hail cloud recognition: 1)single radar limitations such as detection range,distance attenuation,blind spots,and Earth’s curvature;2)the requirement for forecasters to possess high echo analysis skills;3)the variability of classic hail cloud characteristics with orientation,elevation,and distance;4)the limited number of PUP terminals for single radar use,insufficient for county-level forecasters.Radar mosaics can effectively compensate for some of these limitations,especially through web-based radar mosaic CR (Combined Reflectivity) products,which are accessible via computers,tablets,and mobile phones for simple and convenient operation.
The radar mosaic CR product gathers data from multiple radars simultaneously (within ±3 min).The blind spot of one radar is covered by another,and the inter-radar distance of 100—150 km is optimal for detection,minimizing issues related to angle blind spots,Earth’s curvature,and distance attenuation.The four key elements for identifying hail clouds on the CR product chart are: 1)echo intensity of 60 dBZ and strong echo core≥65 dBZ,2)strong echo in horizontal and vertical areas,3)strong echo gradient of 30—60 dBZ,and 4)weak echo length formed by cloud anvils.For example,in Jiangxi,hail echo intensity is typically≥60 dBZ,with larger hail having strong echo nuclei above 65 dBZ.A strong echo area of 60 dBZ should be ≥100 km²,although smaller hail may represent a smaller area.The vertical thickness of the strong echo (≥6 km) is also significant,though Jiangxi radar mosaics lack CAPPI products for this measurement.The strong echo gradient indicates hail echo walls,with a steep gradient suggesting a shorter distance.The weak echo formed by cloud anvils reflect the high-altitude wind's “pumping” effect.Using the radar mosaic CR product,identifying hail clouds based on these four elements is nearly 100％ successful,with a false report rate below 20％,primarily due to seasonal variability in element thresholds.Adding the vertical area of the strong echo can reduce the false alarm rate.
Automated identification of hail-inducing echoes based on these four elements involves specific algorithms: 1)echo intensity identification through comparison of adjacent points;2)strong echo area identification using clustering and scatter contour algorithms;3)strong echo gradient determination by comparing the distance between 30 dBZ and 60 dBZ;4)cloud anvil echo calculation by measuring the 10 dBZ distance from the 30 dBZ edge along the high-altitude wind direction.Results indicate that hail may occur when the radar mosaic CR is ≥60 dBZ,and the Strong Echo Area (SEA) is ≥100 km²,the Strong Echo Gradient (SEG) is ≤8 km,and the Cloud Anvil Echo (CAE) ratio is between 1∶2.and 1∶3.Most hail in Jiangxi occurs in supercells,though some micro supercells with SEA=18 km² may also produce hail under suitable conditions.
A method for identifying hail clouds based on these four elements was verified through six hail processes in Jiangxi from 2022.to 2023.The identified hail cloud areas matched actual hail areas,with a false alarm rate of 10％—20％.Future efforts should focus on reducing false alarm rates by incorporating strong echo vertical area and vertical integrated liquid water content elements.This research provides practical experience for simple,fast,and automatic identification of hail weather.