Characteristics of Radar Echo Parameters and Microphysical Structure Simulation of a Short-Time Heavy Precipitation Supercell

By using the conventional observations, radar data, NCEP/NCAR FNL 1°×1° reanalysis data and numerical simulation data and with the construction and calculation of radar echo parameters, this paper presents the structural characteristics and physical processes of a short-time heavy precipitation supercell that occurred in the squall line process in Shanxi Province on 24 June 2020. The results show that this squall line event occurred in front of a surface cold front,combined with infiltration of low-level cold air and continuous increase of near-surface humidity in the afternoon. The surface mesoscale convergence line and mesoscale dew point front contributed to the development and systemization of the squall line by a large degree. The short-time extremely heavy precipitation in Pingshun County was caused by the development of a supercell from thunderstorm cells on the front side of the squall line. The characteristics of sharp increase in vertical integral liquid water content, persistent increase in reflectivity factor and continuous rise in the echo top height appeared about 23 min earlier than the severe precipitation, which has qualitative indicating significance for the nowcasting of short-time heavy precipitation. A quantitative analysis of the radar echo parameters suggests that the“sudden drop”of FV40was a precursor signal of cells’ coalescence and rapid development to the mature stage. The areal change of the echo core at the 6 km height was highly subject to the merging and developing of cells, the rapid change of hydrometeor particles in clouds and the precipitation intensity. Changes in the cross-sectional area of convective cells at different heights can indirectly reflect the changes of liquid particles and ice particles in clouds, which is indicatively meaningful for predicting the coalescing and developing-to-maturing of cells and heavy precipitation 30-45 min earlier.A comprehensive echo parameter prediction model constructed by the random forest principle can predict the magnitude of short-time heavy precipitation 40-50 min in advance. Numerical simulation reveals that large amounts of water vapor existed in the near-surface atmosphere, and that the cells rapidly obtained moisture from the ambient atmosphere and developed rapidly through maternal feeding. The cold cloud zone was narrow, upright and had a high stretch height. The upward motion in clouds was strong and deep, and very rich in liquid water content. The graupel particles had a large vertical distribution range, the coexistence area of graupel and snow was large, the height of raindrops was close to the surface with a wide horizontal scale, and the precipitation efficiency was high. These may be the important elements responsible for the occurrence of the short-time heavy precipitation that exceeded historical extreme values. On the basis of the above analyses, a comprehensive parameter(CP) prediction model is worked out, which can estimate the developing trend of supercells and the intensity of short-time heavy precipitation about 1 h in advance.

Spatio-Temporal Characteristics of Heavy Precipitation Forecasts from ECMWF in Eastern China

This study examines the spatio-temporal characteristics of heavy precipitation forecasts in eastern China from the European Centre for Medium-Range Weather Forecasts(ECMWF) using the time-domain version of the Method for Object-based Diagnostic Evaluation(MODE-TD). A total of 23 heavy rainfall cases occurring between 2018 and 2021 are selected for analysis. Using Typhoon “Rumbia” as a case study, the paper illustrates how the MODE-TD method assesses the overall simulation capability of models for the life history of precipitation systems. The results of multiple tests with different parameter configurations reveal that the model underestimates the number of objects’ forecasted precipitation tracks, particularly at smaller radii. Additionally, the analysis based on centroid offset and area ratio tests for different classified precipitation objects indicates that the model performs better in predicting large-area, fast-moving, and longlifespan precipitation objects. Conversely, it tends to have less accurate predictions for small-area, slow-moving, and shortlifespan precipitation objects. In terms of temporal characteristics, the model overestimates the forecasted movement speed for precipitation objects with small-area, slow movement, or both long and short lifespans while underestimating it for precipitation with fast movement. In terms of temporal characteristics, the model tends to overestimate the forecasted movement speed for precipitation objects with small-area, slow movement, or both long and short lifespans while underestimating it for precipitation with fast movement. Overall, the model provides more accurate predictions for the duration and dissipation of precipitation objects with large-area or long-lifespan(such as typhoon precipitation) while having large prediction errors for precipitation objects with small-area or short-lifespan. Furthermore, the model’s simulation results regarding the generation of precipitation objects show that it performs relatively well in simulating the generation of large-area and fast-moving precipitation objects. However, there are significant differences in the forecasted generation of small-area and slow-moving precipitation objects after 9 hours.

Spatial and Temporal Distribution of Different Grades of Short-time Precipitation in Xining City

Based on the hourly precipitation data from 4 observation stations of Xining City from June to September during 2005-2011,the temporal and spatial distribution characteristics of short-time precipitation were analyzed.The results show that the precipitation distribution in Xining region exhibited the less-more-less trend from southwest to northeast,while the torrential rain gradually increased from the northwest and southwest to the middle.The hourly general precipitation in Xining region had obviously seasonal characteristics,and its annual distribution showed wavy changes,but the annual variation of short-time heavy precipitation and rainstorm was very obvious.Furthermore,short-time heavy precipitation was concentrated from 18:00 to 24:00,followed by 03:00-07:00 on the following day.The occurrence time of short-time rainstorm accorded with short-time heavy precipitation.It offers a useful reference for the accurate and timely short-term forecast.

Analysis on Precipitation Efficiency of the “21.7” Henan Extremely Heavy Rainfall Event

A record-breaking heavy rainfall event that occurred in Zhengzhou,Henan province during 19–21 July 2021 is simulated using the Weather Research and Forecasting Model,and the large-scale precipitation efficiency(LSPE)and cloud-microphysical precipitation efficiency(CMPE)of the rainfall are analyzed based on the model results.Then,the key physical factors that influenced LSPE and CMPE,and the possible mechanisms for the extreme rainfall over Zhengzhou are explored.Results show that water vapor flux convergence was the key factor that influenced LSPE.Water vapor was transported by the southeasterly winds between Typhoon In-Fa(2021)and the subtropical high,and the southerly flow of Typhoon Cempaka(2021),and converged in Zhengzhou due to the blocking by the Taihang and Funiu Mountains in western Henan province.Strong moisture convergence centers were formed on the windward slope of the mountains,which led to high LSPE in Zhengzhou.From the perspective of CMPE,the net consumption of water vapor by microphysical processes was the key factor that influenced CMPE.Quantitative budget analysis suggests that water vapor was mainly converted to cloud water and ice-phase particles and then transformed to raindrops through melting of graupel and accretion of cloud water by rainwater during the heavy precipitation stage.The dry intrusion in the middle and upper levels over Zhengzhou made the high potential vorticity descend from the upper troposphere and enhanced the convective instability.Moreover,the intrusion of cold and dry air resulted in the supersaturation and condensation of water vapor,which contributed to the heavy rainfall in Zhengzhou.

Objective Identification and Climatic Characteristics of Heavy-Precipitation Northeastern China Cold Vortexes

The northeastern China cold vortex(NCCV)plays an important role in regional rainstorms over East Asia.Using the National Centers for Environmental Prediction Final reanalysis dataset and the Global Precipitation Measurement product,an objective algorithm for identifying heavy-precipitation NCCV(HPCV)events was designed,and the climatological features of 164 HPCV events from 2001 to 2019 were investigated.The number of HPCV events showed an upward linear trend,with the highest frequency of occurrence in summer.The most active region of HPCV samples was the Northeast China Plain between 40°–55°N.Most HPCV events lasted 3–5 days and had radii ranging from 250 to 1000 km.The duration of HPCV events with larger sizes was longer.About half of the HPCV events moved into(moved out of)the definition region(35°–60°N,115°–145°E),and half initiated(dissipated)within the region.The initial position was close to the western boundary of the definition region,and the final position was mainly near the eastern boundary.The locations associated with the precipitation were mostly concentrated within 2000 km southeast of the HPCV systems,and they were farther from the center in the cold season than in the warm season.

Analysis of Heavy Precipitation Process in North China from August 23 to 24, 2020

In order to better understand the formation mechanism of rainstorm in China and promote disaster prevention and reduction, based on the meteorological data of National Meteorological Information Center and Japan Meteorological Agency, this paper draws the isobaric surface map of 850 hPa and 500 hPa, relative humidity and precipitation distribution map. In this study, synoptic methods were used to analyze the heavy precipitation process in North China from August 23th to 24th, 2020. The results show that 1) The formation of short-term heavy precipitation requires sufficient water vapor and very strong upward movement;2) the heavy precipitation in August 23th to 24th 2020 in North China was influenced by the upper-level trough line, cold vortex and cold front, which made the warm and cold air strongly converge over North China, resulting in strong convective weather;3) the heavy rainfall over North China was also influenced by Typhoon Bawei, which caused maximum precipitation and air humidity.

Comparative Analysis of Two Short-time Strong Precipitation Processes

By means of conceptual model prediction, two short-time strong precipitation processes in Xiamen on June 12th and 14th, 2008 were analyzed from the aspects of real precipitation, weather situation, physical parameter and radar echo. The results showed that two short-time strong precipitation processes had complete different weather backgrounds, so physical quantities which could reflect atmospheric thermal and dynamic characteristic were different, as well as the characteristic and evolution process of radar echo, and it revealed that two short-time strong precipitation processes in Xiamen had various formation mechanisms and evolution processes. Therefore, many data should be combined to grasp different vantage points in precipitation forecast.

Comparative Analysis of Climate Characteristics of Extremely Short-Time Severe Precipitation in Guizhou Based on Two Types of Rainfall Data

In order to fill the gaps of the research on the data of automatic weather stations(referred to as automatic stations)not used for the climate characteristics of extremely short-time severe precipitation in Guizhou Province,the climate characteristics of extremely short-time severe precipitation in Guizhou Province were compared and analyzed based on the hourly precipitation data of the automatic stations and the national weather stations(referred to as the national stations)from April to September during 2010-2019.The results show that the average state of maximum hourly precipitation of all stations(the automatic stations and the national stations)and national stations both are representative,but the data of all stations are more representative when the maximum hourly precipitation is extreme.The 99.5 th quantile is the most reasonable threshold of extremely short-time severe precipitation in each station.The spatial distribution of extremely short-time severe precipitation intensity in all stations and national stations is generally that the southern region is stronger than the northern region,and the intensity values are concentrated in the range of 40-50 mm/h.All stations data can better reflect the distribution characteristics of<40 and≥50 mm/h.The national stations data underestimates the precipitation intensity in the southern and northeastern marginal areas of Guizhou,and slightly exaggerates the precipitation intensity in the northern part of Guizhou.The monthly and diurnal variations of the frequency of extremely short-time severe precipitation in all stations and national stations are very obvious and the variation trend is the same,but the intensity of extremely short-time severe precipitation has no obvious monthly variation characteristics.There is no significant diurnal variation in the intensity of extremely short-time severe precipitation in all stations,but the diurnal variation in the data of national stations is significant.Since the frequency of extremely short-time severe precipitation in national stations is less,the diurnal variation in the intensity of extremely short-time severe precipitation in all stations is more statistically significant.

Climatic trends of different intensity heavy precipitation events concentration in China

Based on 740 stations of daily precipitation datasets in China, the precipitation- concentration degree (PCD)and precipitation-concentration period (PCP)ofdifferentintensity durative precipitation eventswere calculated to analyze theirstatisticalcharacteristics,mainly including spatial and temporaldistributions,variations and climatic trends ofthe two parameters ofthe durative heavy precipitation events in China.Itis proved thatthese two parameters ofheavy rainfallcan display the temporalinhomogeneity in the precipitation field.And itis also found thatthere is a good positive relationship between the precipitation-concentration degree and annualrainfallamountin the Eastern and CentralChina.Thismethod can beapplied in flood assessmentand climatechangefields.

Diagnosis of a Heavy Precipitation Process in Northern Guangxi

[Objective] The aim was to analyze one strong precipitation process in Northern Guangxi from May 27 to 28 in 2010.[Method] By dint of 2.5×2.5 NCEP reanalysis data,physical quantities such as the water vapor flux,pseudo-equivalent temperature,Non-geotropic wet Q vector in one front rainstorm process in north Guangxi from May 27 to 28 in 2010 was expounded.The forecast application of Non-geotropic wet Q vector in rainstorm falling area in Guangxi during early flood period was discussed.[Result] The water vapor in Bay of Bengal transported to Guangxi and formed convergence lifting movement in north Guangxi,which provided favorable water vapor transportation condition for the generation of strong precipitation in north Guangxi.The 850 hPa pseudo-equivalent temperature front (close area) moved southward to the north part of Guangxi.North Guangxi was in pseudo-equivalent temperature area.The highly wet unstable energy of lower layer and the cold air penetrating downward from the middle layer led to potential instability in the lower level established in northern Guangxi,which thus provided certain thermal condition for the strong precipitation process;Northern Guangxi was in the overlap region of the maximum gradient region of contour Qx at 850 hPa and stronger negative areas of ▽Q,which provided favorable dynamic condition for the rainstorm process in northern Guangxi in the future.[Conclusion] The study provided reference in accordance to the forecast of rainstorm.

Application of Electrocoagulation and Electrolysis on the Precipitation of Heavy Metals and Particulate Solids in Washwater from the Soil Washing

Soil washing, ex situ mechanical technique, is one of the few permanent treatment alternatives to remove metal contaminants from soils by employing physical separation based on mineral processing technologies to remove discrete particles or metal-bearing particles and/or chemical extraction based on leaching or dissolving process to extract the metals from the soils into an aqueous solution. However, washwater remained from soil washing process contains discrete particulate particles along with heavy metals as solution phase to be treated separately, as well as this process can produce large amount of sludge that requires further treatment, slow metal precipitation, poor settling, the aggregation of metal precipitates. Electrical treatments including electrocoagulation and electrolysis can be effective in removing these substances from washwater. This paper reviews the theoretical models in applying electrocoagulation and electrolysis to remove heavy metals and discrete particulate particles in washwater by examining and comparing the status of washwater treatment technologies which have been undertaken, mostly in the US and EU for the period 1990-2012.

Changes in Typhoon Regional Heavy Precipitation Events over China from 1960 to 2018

In earlier studies,objective techniques have been used to determine the contribution of tropical cyclones to precipitation(TCP)in a region,where the Tropical cyclone Precipitation Event(TPE)and the Regional Heavy Precipitation Events(RHPEs)are defined and investigated.In this study,TPE and RHPEs are combined to determine the Typhoon Regional Heavy Precipitation Events(TRHPEs),which is employed to evaluate the contribution of tropical cyclones to regional extreme precipitation events.Based on the Objective Identification Technique for Regional Extreme Events(OITREE)and the Objective Synoptic Analysis Technique(OSAT)to define TPE,temporal and spatial overlap indices are developed to identify the combined events as TRHPE.With daily precipitation data and TC best-track data over the western North Pacific from 1960 to 2018,86 TRHPEs have been identified.TRHPEs contribute as much as 20%of the RHPEs,but100%of events with extreme individual precipitation intensities.The major TRHPEs continued for approximately a week after tropical cyclone landfall,indicating a role of post landfall precipitation.The frequency and extreme intensity of TRHPEs display increasing trends,consistent with an observed positive trend in the mean intensity of TPEs as measured by the number of daily station precipitation observations exceeding 100 mm and 250 mm.More frequent landfalling Southeast and South China TCs induced more serious impacts in coastal areas in the Southeast and the South during 1990-2018 than1960-89.The roles of cyclone translation speed and"shifts"in cyclone tracks are examined as possible explanations for the temporal trends.

Characteristics Analysis on Short-Time Heavy Rainfall during the Flood Season in Shanxi Province, China

In order to provide a reference for the correct forecasting of short-term heavy rainfall and better disaster prevention and mitigation services in Shanxi Province, China, it is very important to carry out systematic research on short-term heavy precipitation events in Shanxi Province. Based on hourly precipitation data during the flood season (May to September) from 109 meteorological stations in Shanxi, China in 1980-2015, the temporal and spatial variation characteristics of short-time heavy rainfall during the flood season are analyzed by using wavelet analysis and Mann-Kendall test. The results show that the short-time heavy rainfall in the flood season in Shanxi Province is mainly at the grade of 20 - 30 mm/h, with an average of 97 stations having short-time heavy rainfall each year, accounting for 89% of the total stations. The short-time heavy rainfall mainly concentrated in July and August, and the maximal rain intensity in history appeared at 23 - 24 on June 17, 1991 in Yongji, Shanxi is 91.7 mm/h. During the flood season, the short-time heavy rainfalls always occur at 16 - 18 pm, and have slightly different concentrated time in different months. The main peaks of June, July and August are at 16, 17 and 18 respectively, postponed for one hour. Short-time heavy rainfall overall has the distribution that the south is more than the north and the east less than the west in Shanxi area. In the last 36 years, short-time heavy rainfall has a slight increasing trend in Shanxi, but not significant. There is a clear 4-year period of oscillation and inter-decadal variation. It has a good correlation between the total precipitation and times of short-time heavy rainfall during the flood season.

Investigating the initiation and propagation processes of convection in heavy precipitation over the western Sichuan Basin

青藏高原大地形和四川盆地西侧的陡峭地形过渡带,夏季暴雨频发,易带来泥石流等次生地质灾害。本文选定该地区2010年8月的一次暴雨过程,研究了伴随对流尺度降水的强对流的激发和传播。具体借助于垂直动量方程,并将扰动气压分离为动力和浮力分量,通过动力扰动气压梯度、浮力扰动气压梯度、以及浮力等几种强迫作用的不平衡,探索对流激发和传播的主导因子。经分析发现,在本次暴雨过程中,较之动力过程,热力作用对对流的激发和传播发挥着更为重要的作用。

Sensitivity of warm-sector heavy precipitation to the impact of anthropogenic heating in South China

为探讨人为热(AH)对华南暖区暴雨的影响,该文利用WRF-SLUCM模式并考虑适当的AH释放,对2014年5月8日发生在珠江三角洲(PRD)的暖区暴雨进行了数值模拟。有无AH效应的模拟结果分析表明,降水对AH的影响敏感,AH效应使得城区总降水量减少约10%。影响的可能机制为:AH增加导致的热力场和流场再分布,使得局地辐合向PRD边界区域转移增强城乡边界的对流和降水;PRD城区内更为均质的城市热环境减小了热力对比削弱了辐合,从而降低了城区降水。

SPATIO-TEMPORAL VARIATION CHARACTERISTICS OF EXTREMELY HEAVY PRECIPITATION FREQUENCY OVER SOUTH CHINA IN THE LAST 50 YEARS

This paper comprehensively studies the spatio-temporal characteristics of the frequency of extremely heavy precipitation events over South China by using the daily precipitation data of 110 stations during 1961 to 2008 and the extremely heavy precipitation thresholds determined for different stations by REOF, trend coefficients, linear trend, Mann-Kendall test and variance analysis. The results are shown as follows. The frequency distribution of extremely heavy precipitation is high in the middle of South China and low in the Guangdong coast and western Guangxi. There are three spatial distribution types of extremely heavy precipitation in South China. The consistent anomaly distribution is the main type. Distribution reversed between the east and the west and between the south and the north is also an important type. Extremely heavy precipitation events in South China mainly occurred in the summer-half of the year. Their frequency during this time accounts for 83.7% of the total frequency. In the 1960 s and 1980 s, extremely heavy precipitation events were less frequent while having an increasing trend from the late 1980 s. Their climatological tendency rates decrease in the central and rise in the other areas of South China, and on average the mean series also shows an upward but insignificant trend at all of the stations. South China's frequency of extremely heavy precipitation events can be divided into six major areas and each of them shows a different inter-annual trend and three of the representative stations experience abrupt changes by showing remarkable increases in terms of Mann-Kendall tests.

Diagnosis of Moist Vorticity and Moist Divergence for a Heavy Precipitation Event in Southwestern China

A regional heavy precipitation event that occurred over Sichuan Province on 8–9 September 2015 is analyzed based on hourly observed precipitation data obtained from weather stations and NCEP FNL data.Two moist dynamic parameters,i.e.,moist vorticity(mζ)and moist divergence(mδ),are used to diagnose this heavy precipitation event.Results show that the topography over southwestern China has a significant impact on the ability of these two parameters to diagnose precipitation.When the impact of topography is weak(i.e.,low altitude),mζ cannot exactly depict the location of precipitation in the initial stage of the event.Then,as the precipitation develops,its ability to depict the location improves significantly.In particular,mζ coincides best with the location of precipitation during the peak stage of the event.Besides,the evolution of the mζcenter shows high consistency with the evolution of the precipitation center.For mδ,although some false-alarm regions are apparent,it reflects the location of precipitation almost entirely during the precipitation event.However,the mδ center shows inconsistency with the precipitation center.These results suggest that both mζ and mδ have a significant ability to predict the location of precipitation.Moreover,mζ has a stronger ability than mδ in terms of predicting the variability of the precipitation center.However,when the impact of topography is strong(i.e.,high altitude),both of these two moist dynamic parameters are unable to depict the location and center of precipitation during the entire precipitation event,suggesting their weak ability to predict precipitation over complex topography.

Influence of North Pacific SST on heavy precipitation events in autumn over North China

本文主要研究了华北秋季(9月)强降水频次发生年代际变化的可能原因。分析指出,华北秋季强降水频次在2000/01年发生了年代际增强,而它的变化与北太平洋海温变化密切相关。2000/01年之前,影响华北强降水的海温关键区主要位于中国东部海域;2000/01年海温关键区向东偏移,正是这种偏移使得西北太平洋副热带高压增强,向华北地区的水汽输送增加,从而使得华北地区发生强降水的概率增加。进一步研究指出,北太平洋海温年际变率的变化可能是造成海温与华北秋季强降水频次显著相关区发生东移的原因,更多的原因还需要深入研究。

Diagnostic Analysis of Potential Vorticity in a Heavy Precipitation Process in Qujing in September 2017

Based on the observation data from the automatic rainfall station and NCEP/NCAR reanalysis data,circulation analysis and diagnosis analysis of potential vorticity in a heavy rainfall process in September 2017 in Qujing were conducted.The results show that the heavy rainfall was mainly affected by the convergence zone between the two high pressures and shear line system,the precipitation area developed from the west to the southeast of Qujing,and the heavy rainfall area was concentrated in the central area.The southerly airflow in the middle and lower layers of the troposphere provided favorable water vapor conditions for heavy precipitation.The precipitation was characterized by high intensity,strong suddenness and small time scale.The heavy precipitation was concentrated from 04:00 to 06:00 on September 6.The high-and low-value centers of dry potential vorticity PV at 500 h Pa were indicative of the activities of cold and warm air in the process of heavy rainfall,and representative of the development of the convergence zone and the activities of shear line.That is to say,the high-value zone of dry potential vorticity PV at 500 h Pa was strengthened to penetrate into the center of Yunnan,leading the northerly airflow to the convergence zone.The deep southerly airflow in the relatively low-value zone of PV was uplifted to the north,converging the cold and warm air at the front of the convergence zone,resulting in heavy precipitation in Qujing.The high-value zone of wet potential vorticity MPV at 700 h Pa can also indicate the characteristics of unstable warm and humid air flow activity.MPV1<0,and MPV2>0,which easily caused the unstable energy release of wet convection and formed heavy precipitation.

Convective/Large-scale Rainfall Partitions of Tropical Heavy Precipitation in CMIP6 Atmospheric Models

Convective/large-scale(C/L)precipitation partitions are crucial for achieving realistic rainfall modeling and are classified in 16 phase 6 of the Coupled Model Intercomparison Project(CMIP6)atmospheric models.Only 4 models capture the feature that convective rainfall significantly exceeds the large-scale rainfall component in the tropics while the other 12 models show 50%–100%large-scale rainfall component in heavy rainfall.Increased horizontal resolution generally increases the convective rainfall percentage,but not in all models.The former 4 models can realistically reproduce two peaks of moisture vertical distribution,respectively located in the upper and the lower troposphere.In contrast,the latter 12 models correspond to three types of moisture vertical profile biases:(1)whole mid-to-lower tropospheric wet biases(60%–80%large-scale rainfall);(2)mid-tropospheric wet peak(50%convective/large-scale rainfall);and(3)lower-tropospheric wet peak(90%–100%large-scale rainfall).And the associated vertical distribution of unique clouds potentially causes different climate feedback,suggesting accurate C/L rainfall components are necessary to reliable climate projection.