On the Key Dynamical Processes Supporting the 21.7 Zhengzhou Record-breaking Hourly Rainfall in China

An extremely heavy rainfall event occurred in Zhengzhou, China, on 20 July 2021 and produced an hourly rainfall rate of 201.9 mm, which broke the station record for mainland China. Based on radar observations and a convection-permitting simulation using the WRF-ARW model, this paper investigates the multiscale processes, especially those at the mesoscale,that support the extreme observed hourly rainfall. Results show that the extreme rainfall occurred in an environment characteristic of warm-sec...     

Sensitivity Analysis of Ensemble Simulations on a Torrential Rainfall Case over South China Using Multiple PBL and SL Parameterizations

A good representation of the interaction between the planetary boundary layer(PBL) and the surface layer(SL) in numerical models is of great importance for the prediction of the initiation and development of convection. This study examined an ensemble that consists of the available suites of PBL and SL parameterizations based on a torrential rainfall event over south China. The sensitivity of the simulations was investigated against objective measurements using multiple PBL and SL parameterization schemes. The main causes of the bias from different parameterization schemes were further analysed by comparing the good and bad ensemble members. The results showed that good members tended to underestimate the rainfall amount but presented a decent evolution of mesoscale convective systems that were responsible for the torrential rainfall. Using the total energy mass flux(TEMF) scheme, the bad members overestimated the amount and spatial coverage of rainfall. The failure of the bad member was due to a spurious convection initiation(CI) resulting from the overestimated high-θe elevated air. The spurious CI developed and expanded rapidly, causing intensive and extensive rainfall over south China. Consistent with previous studies, the TEMF scheme tends to produce a warmer and moister PBL environment. The detailed sensitivity analysis of this case may provide reference for the operational forecast of rainfall over south China using multiple PBL and SL parameterizations.     

青藏高原冬季积雪异常对东,南亚夏季风影响的初步数值模拟研究

利用一个耦合了简化的简单生物圈模式的大气环流谱模式（ＳＳｉＢ－ＧＣＭ），初步探讨了青藏高原冬季积雪异常对东、南亚夏季季风环流和降水的影响及其机理。结果表明，高原地区积雪增加将使随后地夏季东、南来季风明显减弱，主要表现为东、南亚季风区降水减少，索马里急流、印度季风的印度西南气流弱弱。另外，还提出欧亚大陆雪盖与整个高原雪盖和高原东部雪盖对东、南亚夏季风影响的敏感问题。与欧亚大陆雪盖相比，高原雪盖是影响     

Spatial characteristics of extreme rainfall over China with hourly through 24-hour accumulation periods based on national-level hourly rain gauge data

Hourly rainfall measurements of 1919 national-level meteorological stations from 1981 through 2012 are used to document,for the first time,the climatology of extreme rainfall in hourly through 24-h accumulation periods in China. Rainfall amounts for 3-,6-,12- and 24-h periods at each station are constructed through running accumulation from hourly rainfall data that have been screened by proper quality control procedures. For each station and for each accumulation period,the historical maximum is found,and the corresponding 50-year return values are estimated using generalized extreme value theory. Based on the percentiles of the two types of extreme rainfall values among all the stations,standard thresholds separating Grade I,Grade II and Grade III extreme rainfall are established,which roughly correspond to the 70th and 90th percentiles for each of the accumulation periods. The spatial characteristics of the two types of extreme rainfall are then examined for different accumulation periods. The spatial distributions of extreme rainfall in hourly through 6-h periods are more similar than those of 12- and 24-h periods. Grade III rainfall is mostly found over South China,the western Sichuan Basin,along the southern and eastern coastlines,and in the large river basins and plains. There are similar numbers of stations with Grade III extreme hourly rainfall north and south of 30°N,but the percentage increases to about 70% south of 30°N as the accumulation period increases to 24 hours,reflecting richer moisture and more prolonged rain events in southern China. Potential applications of the extreme rainfall climatology and classification standards are suggested at the end.     

珠江三角洲城市群对夏季降雨影响的初步研究

利用TRMM 2A25卫星降水数据和CMORPH同化数据对珠三角洲地区的降水分布特征进行了探讨,观测表明：珠三角城市群区域总体处于降水的低值中心,且对流降雨的低值中心尤为明显;同时近10 a珠三角核心城市区域降雨有减少的趋势,这种降水减少的趋势可能与珠三角城市化效应有关。本文进一步利用WRF模式模拟分析了珠三角城市群发展对夏季降雨的影响,结果表明珠三角城市化使得该区域降雨减少,其原因为城市化使得地表的蒸发减弱及其大气中的水分供应减少,同时也抬升了珠三角区域边界层高度相应增强了低层大气水汽垂直混合。     

下垫面对郑州城市强降水的影响:城市化及地形影响的数值模拟研究

利用WRF-ARW中尺度区域数值模式耦合单层城市冠层模式(slab-UCM),采用ERA-interim 0.5°×0.5°再分析资料作为初始场和边界条件,对2016年6月5日郑州地区发生的一次强对流天气进行模拟,并通过改变下垫面的土地利用类型与地形高度数据设置敏感性试验,探究了城市化及郑州西北部山脉地形对对流性强降水过程的影响。结果表明:1)此次强降水过程主要受高层的低槽系统影响,前期的对流不稳定层结为对流触发提供了有利的热力条件;2)城市热岛效应能够改变下垫面的热力状况,有利于在城市地区激发更强的上升运动,使降水向城区集中;3)郑州西北侧山脉激发的重力波能够使郑州地区对流增强;4)山脉能够阻挡低层干空气向郑州地区输送,因此山脉高度的削减造成郑州地区低层相对湿度减小,使雨滴蒸发冷却增强,进而导致与降水相联系的冷池的增强,雨带移速加快,进一步导致累积降水的减少。     

城市化对北京一次极端降水过程影响的数值分析

通过敏感性试验探讨了城市化对北京2011年6月23日局地极端降水事件的影响.结果表明耦合了城市冠层模式的WRF系统能较好地模拟出强降水的局地性和突发性特征,考虑了精细下垫面分类的敏感性试验模拟降水更接近实况;下垫面城市化对地表能量平衡影响明显,对大气的热量影响除加强地表对边界层大气向上感热输送外,还会减少局地地表蒸发及大气水分供应,增加边界层高度,并对移经本地的天气系统强度及水汽输送产生较明显的影响.     

Sensitivity study on the role of Western Ghats in simulating the Asian summer monsoon characteristics

The Advanced Research Weather Research and Forecasting (AR-WRF) model is used to study the influence of Western Ghats situated along the west cost of peninsular India in the mean characteristics of the Asian summer monsoon (ASM) through numerical simulations. A control simulation (CTRL) is carried out using 11-year (2000–2010) mean initial and lateral boundary conditions from the ERA-Interim reanalysis to simulate the mean atmospheric features of the ASM. The Modern-Era retrospective analysis for research and applications (MERRA) data along with the Tropical Rainfall Measuring Mission (TRMM, 3B42 daily rainfall) data are used to validate the CTRL simulation. The simulated dynamical features and precipitation characteristics during the ASM period agree well with the MERRA reanalysis and TRMM observations. In order to examine the role of Western Ghats on the mean characteristics of the ASM, a sensitivity simulation (NoWG) is carried out with orography reduced to surface over a domain bound between 5°–28°N and 72°–90°E, keeping all other conditions unchanged. This sensitivity analysis showed an enhancement in the low level monsoon flow over the Indian Ocean and peninsular India in the absence of Western Ghats. The prominent up-draft over the west coast of peninsular India observed in the CTRL simulation also decrease in the absence of Western Ghats. The simulated rainfall show a considerable decrease over the west coast and an enhancement over the east coast of peninsular India in the absence of Western Ghats. These simulations clearly depict the importance of Western Ghats in the circulation dynamics and rainfall features during the ASM period.     

“21·7”河南特大暴雨气象和水文雨量观测对比

2021年“21·7”河南特大暴雨打破我国大陆小时气象观测纪录,该极端天气事件位列2021年中国十大天气气候事件第2位。已有研究使用气象地面站雨量观测资料对此次过程进行雨情分析和极值统计,但降水时空分布不均匀,单一来源资料存在不确定性。通过对比气象站和水文站雨量资料,分析两套业务观测系统记录“21·7”河南特大暴雨过程的异同,发现气象站和水文站雨量在时间和空间分布上具有很好的一致性,两者不同等级的累积降雨落区、逐日和逐时降雨演变趋势均一致性强,但累积雨量和雨强极值的空间分布和数值存在差异,两套资料在暴雨中心（过程雨量大于600 mm）的系统性偏差小于1%。气象站和水文站的融合资料呈现比单一资料更细致的降雨分布、更全面的演变特征。此外,基于融合资料发现累积雨量排名前3位的城市（郑州、鹤壁、新乡）均具有累积雨量大、小时雨强极强、强降雨集中、雨强突然增长的特征,鹤壁和新乡最强降雨时段分别比郑州晚26 h和28 h。     

A numerical study of the influence of urban expansion on monthly climate in dry autumn over the Pearl River Delta, China

Summary In this study, we employed a regional model to simulate the impact of urban expansion on monthly climate in Pearl River Delta (PRD) region. Two experiments were performed by prescribing two different land covers in the PRD region. One land cover represents vegetation in the 1970s which is derived from the United States Geological Survey (USGS) data with 24-category (hereafter referred to as NU). The other land cover represents the current urban condition which is derived from remote sensing data acquired by the Moderate Resolution Imaging Spectroradiometer (MODIS) in 2004 (hereafter referred to as HU). Using the two land cover datasets, monthly climate of October 2004 was simulated, which was a very dry season in the PRD region. The results obtained from the numerical simulation show a distinct difference in simulated shelter-level temperature, humidity, surface fluxes and the height of planetary boundary layer (PBL) with two different land cover data sets being specified. The maximum difference in simulated monthly mean temperature over urban areas was 0.9 °C. A large temperature difference was found in urbanized area in Guangzhou, Dongguan, Zhongshan and Shenzhen. The monthly mean relative humidity in urban areas decreased by 1.4% as a result of urban expansion (from 59.2% in NU to 57.8% in HU). The maximum decrease in mixing ratio was 0.4 g/kg in Guangzhou and Dongguan, whereas the maximum decrease in relative humidity was 2.4%. There was an increase of sensible heat flux in developed lands and the maximum increase was 90 W m⁻². In contrast, latent hear flux in urban area decreased and the maximum decrease was 300 W m⁻². In addition, the increase in mean height of PBL ranged from 20 to 80 m (HU compared with NU), and the maximum change of the height was 180 m over urban area in city of Guangzhou.     

下垫面对郑州城市边界层风的影响

根据１９９３年１月和７月郑州市中心测点和南郊郑州气象观测站同步观测的地面和边界层气象资料,分析了郑州城市下垫面对边界层风的影响。结果表明,在地面气压梯度比较小且天气晴朗条件下,郑州存在城市热岛环流。受城市热岛环流影响,郊区地面风向指向市区;边界层８００ｍ以下,城市上空吹偏西风时同一高度上南郊风向偏于城市风向左侧,吹偏东风时同一高度上南郊风向偏于市区风向右侧;１２００ｍ以上,城市上空吹偏西风时,同一高度上南郊风向偏于城市风向右侧     

“21.7”郑州极端暴雨的形成过程及致灾机理分析

2021年7月19—21日,郑州地区出现了罕见的极端暴雨天气,过程累计降水量达到了732 mm,引发了严重的城市内涝,造成了巨大的人员和财产损失。利用国家级自动观测站逐小时降水数据和欧洲中期天气预报中心第五代大气再分析资料(ERA-5)分析了郑州地区"21.7"极端降水过程的降水特征以及其影响系统。结果表明:此次降水过程降水量大,持续时间长,强降水范围集中在郑州及周边地区,强降水时段集中在20日14时以后,其中郑州站20日17时小时降水量达到了201.9 mm·h^-1,超过了历史极值。降水过程中南亚高压东移,郑州位于200 hPa高空槽前,500 hPa副高加强西伸,与大陆高压对峙,郑州位于低压区形成低空辐合高空辐散的高低空配置。郑州低空850 hPa有东南急流发展,产生东风切变线同时伴随着地面辐合线影响郑州地区,东南急流也将西太平洋上的水汽输送至暴雨区,并在地形阻挡作用下在郑州地区汇集。低空急流与强降水在时间上有明显同步,急流在地形作用下产生的辐合抬升也在暴雨区形成强烈的垂直上升运动,对此次极端暴雨的产生和维持有明显的影响。     

NUMERICAL EXPERIMENTS ON THE EFFECT OF INDIAN SUBCONTINENT VEGETATION COVER ON SUMMER MONSOON

In the present paper,a global two-dimensional climate model developed by Chinese Academy of Meteorological Sciences (CAMS) with inclusion of a simple parameterization of land surface processes developed recently by Zhang and Li is used to investigate the effect of vegetation cover of the Indian subcontinent on summer monsoon circulation and its rainfall.First of all,we carried out a control experiment in which the distribution of vegetation species was based on obser-vations.Then,with removal of the vegetation cover on the subcontinent,a sensitivity experiment was performed.For both of the experiments,the integrations were made from the beginning of April to the end of July.The results show that,after the vegetation was removed from the subcontinent,the monthly mean updraft and the monsoon circulation to the south of the Plateau was weakened in June and July.Especially,the change was more manifest in June.Also,in the south side of the Plateau,the easterly component was strengthened in the lower troposphere,the monsoon rainfall was reduced over the central India.Moreover,the rainfall was obviously reduced over the southern India from the end of June to the beginning of July.     

青藏高原春季土壤湿度异常对我国夏季降水影响的模拟研究

利用耦合的全球海气模式（NCAR CCSM3）, 对青藏高原春季土壤湿度异常影响我国夏季7月降水的机制进行了数值模拟。结果表明, 高原6~62 cm深度的中层土壤湿度异常与表层土壤湿度异常有很好的一致性, 相对而言, 中层土壤湿度异常的持续性较好。若5月高原中层土壤偏湿, 则春末至夏初高原地面蒸发、 潜热通量增加, 而感热通量、 地面温度降低, 高原表面的加热作用减弱, 使得印度高压西撤偏晚, 环流系统的季节性转换偏晚, 东亚地区形成有利于我国夏季出现第I类雨型的环流分布形势, 使我国东部雨带偏北, 华北地区多雨, 江淮地区降水偏少, 华南地区降水偏多; 反之亦然。     

1948-2001年全球陆地春季降水长期变化的时空特征

利用全球陆地月降水资料(PREC／L)中3个月的资料，研究了1948—2001年全球陆地3—5月降水长期变化的时空特征。结果表明，1948—2001年，全球3—5月的降水量以负趋势为主要变化特征，明显减少的区域是：热带非洲、亚洲中西部、中国中东部、俄罗斯东部、南极的恩德比地和威尔克斯地等9个地区；降水量增加的区域是：俄罗斯西北部、美国西北部、加拿大西南部、南美洲南部、加拿大北部等7个地区。还研究了35个纬圈3—5月平均降水量的趋势系数。在分析全球季节降水量与ENSO的关系中，指出春季是春夏秋三季中最不显著的。     

Synergistic Effect of the Planetary-scale Disturbance,Typhoon and Meso-β-scale Convective Vortex on the Extremely Intense Rainstorm on 20 July 2021 in Zhengzhou

On 20 July 2021, northern Henan Province in China experienced catastrophic flooding as a result of an extremely intense rainstorm, with a record-breaking hourly rainfall of 201.9 mm during 0800–0900 UTC and daily accumulated rainfall in Zhengzhou City exceeding 600 mm(“Zhengzhou 7.20 rainstorm” for short). The multi-scale dynamical and thermodynamical mechanisms for this rainstorm are investigated based on station-observed and ERA-5 reanalysis datasets.The backward trajectory tracking shows that...     

利用CAM5.1模拟中国东部大规模城市化对东亚地区夏季大气环流及降水分布的影响

利用CAM5.1大气环流模式研究中国东部大规模城市化对东亚夏季大气环流及降水分布的影响。通过在模式中修改中国东部地区(22～42°N,110～125°E)城市比重的方法,探讨东亚地区夏季大气环流与降水等气象要素在一般城市化及极端城市化两种情景下的响应。结果表明:(1)CAM5.1模式能够很好地模拟出东亚地区夏季大气环流形势及降水分布。(2)城市比重增大后,晴空时地面吸收的净辐射增多,近地层气温升高,低层增温中心上空的大气由于受热产生上升运动,35°N以南的气流向增温区辐合,东亚夏季风出现增强的趋势,大量暖湿水汽往北输送,导致降水在中国北方地区增多而南方减少。(3)城市化的发展程度越高,它所产生的气候效应对各气象要素的影响就表现得越明显。     

A three-dimensional numerical sensitivity study of convection over the Florida peninsula

The Florida peninsula has the highest annual number of days with thunderstorms in the United States, partly due to sea breeze convergence. A three-dimensional mesoscale planetary boundary layer (PBL) model with the E- turbulence closure is used to investigate the relationship between sea breeze convergence and convection over the peninsula for two ambient wind cases during typical summer days.It is found that the spatial and temporal variation of the sea breeze convergence zones and the associated convective activities depend to a large extent on the direction and magnitude of the ambient wind. For the case of southeasterly ambient winds, a strong convergence zone and hence significant rainfall occur primarily along the west coast of the peninsula. The convergence zone and the associated rainfall shift towards the east coast for the case of southwesterly ambient winds. These are in agreement with the observations. In contrast to the southeasterly and southwesterly ambient winds, an intense convergence zone and rainfall occur near both coastlines of the peninsula under light ambient winds.It is also found that lake Okeechobee has a substantial influence on south Florida's mesoscale weather. A cloudless region is always present over the lake at least until late afternoon due to its own lake breeze circulation. Finally, increased roughness of the land surface appears to influence the temporal and spatial variation of the convection by determining the intensity of the vertical turbulent transport of heat and momentum.     

Observed Trends in Severe Weather Conditions Based on Humidex,Wind Chill,and Heavy Rainfall Events in Canada for 1953–2012

Observed trends in severe weather conditions based on public alert statements issued by Environment Canada are examined for Canada. Changes in extreme heat and extreme cold events represented by various humidex and wind chill indices are analyzed for 1953–2012 at 126 climatological stations. Changes in heavy rainfall events based on rainfall amounts provided by tipping bucket rainfall gauges are analyzed for 1960–2012 at 285 stations. The results show that extreme heat events, defined as days with at least one hourly humidex value above 30, have increased significantly at more than 36% of the stations, most of which are located south of 55°N; days with nighttime hourly humidex values remaining above 20 have increased significantly at more than 52% of the stations, most of which are located south of 50°N. Extreme cold events represented by days with at least one hourly wind chill value below ?30 have decreased significantly at more than 76% of the stations across the country. No consistent changes were found in heavy rainfall events. Because city residents are very vulnerable to severe weather events, detailed results on changes in extreme heat, extreme cold, and heavy rainfall events are also provided for ten urban centres.     

云南小时降水的时空分布变化研究

利用2005—2018年125个国家级台站小时降水观测数据研究云南小时降水时空分布特征。结果表明:云南年总降水量、不同持续时间降水量、极端强降水量及降水日变化空间分布差异很大。年降水量自西北向南增加,雨强自北向南增强,降水时长西部大于东部、南部略大于北部,年降水量受降水时长和雨强共同影响,降水时长影响最强,雨强影响较弱,这种特征在滇西北最突出,但滇东北的降水量与雨强相关更好。云南大部夜雨量多于昼雨量,滇东北和北部边缘夜雨特征最显著;降水日变化特征在云南北部为夜间单峰,西部边缘为清晨单峰,中部为夜间与午后峰值相当的双峰,南部也为夜间和午后双峰,但南部不同区域间主峰和次峰出现时间不同。云南南部降水贡献以短、中历时降水为主,北部则以长、超长历时降水为主。云南短时强降水发生次数的空间分布表现为自西北向东南增加;年发生站次数具有增加趋势,日变化特征为显著单峰,多在傍晚至入夜出现,且极端短时强降水更易在凌晨出现。这些小时降水时空分布特征很大程度上代表了低纬高原地区的降水特征。由于低值天气系统多影响低纬高原中北部,热带天气系统多影响南部,且低纬高原地形复杂,局地热力条件差异明显,这些因素造成该区域小时降水时空分布特征差异显著。