Diagnosis of a Moist Thermodynamic Advection Parameter in Heavy-Rainfall Events

A moist thermodynamic advection parameter, defined as an absolute value of the dot product of hori- zontal gradients of three-dimensional potential temperature advection and general potential temperature, is introduced to diagnose frontal heavy rainfall events in the north of China. It is shown that the parameter is closely related to observed 6-h accumulative surface rainfall and simulated cloud hydrometeors. Since the parameter is capable of describing the typical vertical structural characteristics of dynamic, thermodynamic and water vapor fields above a strong precipitation region near the front surface, it may serve as a physical tracker to detect precipitable weather systems near to a front. A tendency equation of the parameter was derived in Cartesian coordinates and calculated with the simulation output data of a heavy rainfall event. Results revealed that the advection of the parameter by the three-dimensional velocity vector, the covariance of potential temperature advection by local change of the velocity vector and general potential temperature, and the interaction between potential temperature advection and the source or sink of general potential temperature, accounted for local change in the parameter. This indicated that the parameter was determined by a combination of dynamic processes and cloud microphysical processes.

ANALYSIS OF A TORNADO-LIKE SEVERE STORM IN THE OUTER REGION OF THE 2007 SUPER TYPHOON SEPAT

When super typhoon Sepat came close to the Fujian coastline on the night of 18 August 2007 (coded as 0709 in Chinese convention), an associated tornado-like severe storm developed at 2307–2320 Beijing Standard Time in Longgang, Cangnan County, Wenzhou Prefecture, Zhejiang Province approximately 300 km away in the forward direction of the typhoon. The storm caused heavy losses in lives and property. Studying the background of the formation of the storm, this paper identifies some of its typical characteristics after analyzing its retrieval of Doppler radar data, vertical wind shear and so on. Synoptic conditions, such as unstable weather processes and TBB, are also studied.

A Potential Risk Index Dataset for Landfalling Tropical Cyclones over the Chinese Mainland(PRITC dataset V1.0)

A dataset entitled“A potential risk index dataset for landfalling tropical cyclones over the Chinese mainland”(PRITC dataset V1.0)is described in this paper,as are some basic statistical analyses.Estimating the severity of the impacts of tropical cyclones(TCs)that make landfall on the Chinese mainland based on observations from 1401 meteorological stations was proposed in a previous study,including an index combining TC-induced precipitation and wind(IPWT)and further information,such as the corresponding category level(CAT_IPWT),an index of TC-induced wind(IWT),and an index of TC-induced precipitation(IPT).The current version of the dataset includes TCs that made landfall from 1949-2018;the dataset will be extended each year.Long-term trend analyses demonstrate that the severity of the TC impacts on the Chinese mainland have increased,as embodied by the annual mean IPWT values,and increases in TC-induced precipitation are the main contributor to this increase.TC Winnie(1997)and TC Bilis(2006)were the two TCs with the highest IPWT and IPT values,respectively.The PRITC V1.0 dataset was developed based on the China Meteorological Administration’s tropical cyclone database and can serve as a bridge between TC hazards and their social and economic impacts.

EFFECTS OF PACIFIC SSTA ON SUMMER PRECIPITATION OVER EASTERN CHINA, PART I: OBSERVATIONAL ANALYSIS

With the methods of REOF (Rotated Empirical Orthogonal Function), the summer precipitation from 43 stations over eastern China for the 1901 – 2000 period was examined. The results show that South China and Southwest China, the middle and lower reaches of Changjiang River, North China and the southwestern of Northeast China are the three main areas of summer rainfall anomaly. Furthermore, correlation analysis is used in three time series of three mostly summer rainfall modes and four seasonal Pacific SSTA (Sea Surface Temperature Anomaly), and the results suggest that the Pacific SSTA which notably causes the summer rainfall anomaly over eastern China are the SSTA of the preceding winter over Kuroshio region of Northwest Pacific, SSTA of the preceding spring in the eastern and central equatorial Pacific, and SSTA of the current summer in the central region of middle latitude. The relationship between summer precipitation over eastern China and SSTA of Pacific key regions was further verified by SVD (Singular Value Decomposition) analysis. The composite analysis was used to analyze the features of atmospheric general circulation in the years of positive and negative precipitation anomaly. Its results were used to serve as the base of numerical simulation analysis.

EFFECTS OF PACIFIC SSTA ON SUMMER PRECIPITATION OVER EASTERN CHINA, PART II: NUMERICAL SIMULATIONS

Based on an observational analysis, seven numerical experiments are designed to study the impacts of Pacific SSTA on summer precipitation over eastern China and relevant physical mechanism by NCAR CCM3. The numerical simulation results show that preceding winter SSTA in the Kuroshio region leads to summer precipitation anomaly over the Yangtze River valleys by modifying atmospheric general circulation over eastern Asia and middle-high latitude. West Pacific subtropical high is notably affected by preceding spring SSTA over the middle and east of Equator Pacific; SSTA of the central region of middle latitude in the corresponding period causes the summer rainfall anomaly over eastern China so as to trigger the atmospheric Eurasia-Pacific teleconnection pattern.

ANALYSIS OF RAINSTORMS ASSOCIATED WITH SIMILAR TRACK TROPICAL CYCLONES HAITANG (0505) AND BILIS (0604)

It is generally thought that the influence of comparable track typhoons is approximately similar, but in fact their wind and especially their rainstorm distribution are often very different. Therefore, a contrastive analysis of rainstorms by tropical cyclones (TCs) Haitang (0505) and Bilis (0604), which are of a similar track, is designed to help understand the mechanism of the TC rainstorm and to improve forecasting skills. The daily rainfall of TC Haitang (0505) and Bilis (0604) is diagnosed and compared. The result indicates that these two TCs have similar precipitation distribution before landfall but different precipitation characteristics after landfall. Using NCEP/GFS analysis data, the synoptic situation is analyzed; water vapor transportation is discussed regarding the calculated water vapor flux and divergence. The results show that the heavy rainfall in the Zhejiang and Fujian Provinces associated with Haitang (0505) and Bilis (0604) before landfall results from a peripheral easterly wind, a combination of the tropical cyclone and the terrain. After landfall and moving far inland of the storm, the precipitation of Haitang is caused by water vapor convergence carried by its own circulation; it is much weaker than that in the coastal area. One of the important contributing factors to heavy rainstorms in southeast Zhejiang is a southeast jet stream, which is maintained over the southeast coast. In contrast, the South China Sea monsoon circulation transports large amounts of water vapor into Bilis – when a water-vapor transport belt south of the tropical cyclone significantly strengthens – which strengthens the transport. Then, it causes water vapor flux to converge on the south side of Bilis and diverge on the north side. Precipitation is much stronger on the south side than that on the north side. After Bilis travels far inland, the cold air guided by a north trough travels into the TC and remarkably enhances precipitation. In summary, combining vertical wind shear with water vapor transportation is a good way to predict rainstorms associated with landing tropical cyclones.

A NUMERICAL STUDY OF THE EFFECT OF TAIWAN ISLAND TERRAIN ON TYPHOON HAITANG (0505) TRACK

The track of Typhoon Haitang (0505), which passed through the Taiwan Island and landed again, has been successfully simulated by using the non-hydrostatic mesoscale atmospheric model MM5. Its structure is analyzed on the landing stage, and it is found that there exist good relationships between the typhoon abnormal moving track and its asymmetry structure. The effect of terrain of Taiwan Island on the typhoon Haitang, which made it rotate before landing and present a"V"type abnormal moving track in Taiwan straits, has also been simulated. Further analysis shows that the terrain of Taiwan Island not only directly affects the typhoon moving track, but also changes the typhoon track by affecting its asymmetric structure. Therefore, the typhoon asymmetric structure and the effect of terrain of Taiwan Island together results in the abnormal rotating track. The terrain of Taiwan Island tends to increase the SW-NE asymmetric structure of the typhoon and has different effect on SE-NW asymmetric structure during the landfall process of typhoon Haitang before entering and moving out of the Taiwan straits.

IMPROVEMENT OF NUMERICAL SIMULATION OF TYPHOON RANANIM (0414) BY USING DOPPLER RADAR DATA

Typhoon Rananim (0414) has been simulated by using the non-hydrostatic Advanced Regional Prediction System (ARPS) from Center of Analysis and Prediction of Storms (CAPS). The prediction of Rananim has generally been improved with ARPS using the new generation CINRAD Doppler radar data. Numerical experiments with or without using the radar data have shown that model initial fields with the assimilated radar radial velocity data in ARPS can change the wind field at the middle and high levels of the troposphere; fine characteristics of the tropical cyclone (TC) are introduced into the initial wind, the x component of wind speed south of the TC is increased and so is the y component west of it. They lead to improved forecasting of TC tracks for the time after landfall. The field of water vapor mixing ratio, temperature, cloud water mixing ratio and rainwater mixing ratio have also been improved by using radar reflectivity data. The model’s initial response to the introduction of hydrometeors has been increased. It is shown that horizontal model resolution has a significant impact on intensity forecasts, by greatly improving the forecasting of TC rainfall, and heavy rainstorm of the TC specially, as well as its distribution and variation with time.

A STUDY ON VARIABLE QUANTITATIVE PRECIPITATION ESTIMATION USING DOPPLER RADAR DATA

With the pros and cons of the traditional optimization and probability pairing methods thoroughly considered, an improved optimal pairing window probability technique is developed using a dynamic relationship between the base reflectivity Z observed by radar and real time precipitation I by rain gauge. Then, the Doppler radar observations of base reflectivity for typhoons Haitang and Matsa in Wenzhou are employed to establish various Z-I relationships, which are subsequently used to estimate hourly precipitation of the two typhoons. Such estimations are calibrated by variational techniques. The results show that there exist significant differences in the Z-I relationships for the typhoons, leading to different typhoon precipitation efficiencies. The typhoon precipitation estimated by applying radar base reflectivity is capable of exhibiting clearly the spiral rain belts and mesoscale cells, and well matches the observed rainfall. Error statistical analyses indicate that the estimated typhoon precipitation is better with variational calibration than the one without. The variational calibration technique is able to maintain the characteristics of the distribution of radar-estimated typhoon precipitation, and to significantly reduce the error of the estimated precipitation in comparison with the observed rainfall.

A STUDY OF RAPID DECAY TYPHOONS IN OFFSHORE WATERS OF CHINA

On the basis of NCEP/NCAR reanalysis data and yearbooks of CMA tropical cyclones, statistical analysis is performed for 1949—2013 offshore typhoons subjected to rapid decay(RD). This analysis indicates that RD typhoons are small-probability events, making up about 2.2% of the total offshore typhoons during this period. The RD events experience a decadal variation, mostly in the 1960 s and 1970 s(maximal in the 1970 s), rapidly decrease in the 1980 s and 1990 s and quickly increase from 2000. Also, RD typhoons show remarkable seasonal differences: they arise mainly in April and July-December, with the prime stage being in October-November. The offshore RD typhoons occur mostly in the South China Sea(SCS) and to a lesser extent in the East China Sea(ECS); however, none are observed over the Huang Sea and Bo Sea.Composite analysis and dynamic diagnosis of the RD typhoon-related large-scale circulations are performed.Physical quantities of the composite analysis consist of 500-h Pa height and temperature fields, vapor transfer, vertical wind shear(VWS), density of core convection(DCC), and high-level jet and upper-air outflow of the typhoon. The results suggest that(1) at the 500-h Pa height field, the typhoon is ahead of a westerly trough and under the effects of its passing trough;(2) at the temperature field, the typhoon is ahead of a temperature trough, with an invading cold tongue present;(3) at the vapor transfer field, water transfer into the RD typhoon is cut off; and(4) at higher levels, the related jet weakens and the outbreak of convection becomes attenuated in the typhoon core. In addition, VWS bears a relation to the RD typhoon; in particular, strong VWS favors RD occurrence.The differences in RD events between the SCS and ECS show that for the RD, the VWS of the ECS environmental winds is markedly stronger in comparison with its SCS counterpart. The cold advection invading into the typhoons is more intense in the SCS than in the ECS, and the low-level vapor transfer and high-level outflow are weaker in the SCS RD typhoons.Data analysis shows that sea surface temperature(SST), VWS, and DCC can be employed as efficient factors to predict RD occurrence. With appropriate SST, VWS, and DCC, a warning of RD occurrence can be given 36, 30-36,and 30 h, respectively, in advance. These values suggest that atmospheric SST responses lag. Owing to this time lag,the prediction of RD typhoons is possible.

The impact of Typhoon Lekima (2019) on East China: a postevent survey in Wenzhou City and Taizhou City

Typhoon Lekima(2019)struck Zhejiang Province on 10 August 2019 as a supertyphoon,which severely impacted Zhejiang Province.The typhoon killed 45 people and left three others missing,and the total economic loss reached 40.71 billion yuan.This paper reports a postdisaster survey that focuses on the storm precipitation,flooding,landslides,and weather services associated with Typhoon Lekima(2019)along the southeastern coastline of Zhejiang Province.The survey was conducted by a joint survey team from the Shanghai Typhoon Institute and local meteorological bureaus from 26 to 28 August,2019,approximately two weeks after the disaster.Based on this survey and subsequent analyses of the results,we hope to develop countermeasures to prevent future tragedies.

POST-DISASTER SURVEY OF TYPHOON MEGI IN WENZHOU CITY

This paper reports the post-disaster results due to Typhoon Megi. The survey was conducted by a joint survey team of Shanghai Typhoon Institute in 14 December 2016, with the support of Wenzhou Meteorological Bureau and some meteorological departments in disaster areas. The survey results show that Typhoon Megi brought torrential rain and heavy rainstorm to the southern of Wenzhou City. The precipitation characters of Typhoon Megi are strong intensity, high accumulation, long duration and broken historical record. Typhoon winds affected wide,with large peripheral wind. According to the needs of defense and emergency rescue of Typhoon Megi,Wenzhou meteorological departments made every effort, including closely monitor, strengthening consultation, roll forecast, timely warning, active reporting, and targeted service. In order to provide scientific reference for government decision, the service of weather protection and disaster relief were done well. The results of typhoon forecast shows as follows.(1) The track, landing location and time of typhoon forecast were basically consistent with the actual situation.(2) The wind forecast was close to the actual.(3) The forecasted area precipitation was slightly lower, and the extreme value of process precipitation was too low. While the prediction of Dongtou Island Station was too high, this investigation shows that we are still insufficient in forecasting precipitation grades of typhoons breaking historical records, especially for precipitation quantification and meticulous prediction. In this case, more attention should be paid as below. 1) Effect of topography on precipitation enhancement. 2) Summary of similar cases. 3) Improve the defense ability and residents' awareness of risk. 4)Combine modem methods of early warning information with traditional methods. 5) Quantitative, fixed-pointed and precision forecast. 6) Rapid access of referent information to forecasters, 7) Modern monitoring technology(3 S, unmanned aerial vehicle) should be used for disaster investigation, monitor and hidden trouble detection.8) Carry out the renovation of the engineering construction design standards, impact assessment and structure of buildings.

A simplified index to assess the combined impact of tropical cyclone precipitation and wind on China

Relationships between tropical cyclone(TC)precipitation,wind,and storm damage are analyzed for China based on TCs over the period from 1984 to 2013.The analysis shows that the maximum daily areal precipitation from stations with daily precipitation of ≥50 mm and the sum of wind gusts of ≥13.9 m/s can be used to estimate the main damage caused by TCs,and an index combining the precipitation and wind gust of a TC(IPWT)is defined to assess the severity of the combined impact of precipitation and wind.The correlation coefficient between IPWT and the damage index for affecting TCs is 0.80,which is higher than that for only precipitation or wind.All TCs with precipitation and wind affecting China are divided intofive categories,Category 0 to Category 4,based on IPWT,where higher categories refer to higher combined impacts of precipitation and wind.The combined impact category is closely related to damage category and it can be used to estimate the potential damage category in operational work.There are 87.7%,72.9%,69.8%,and 73.4%of cases that have the same or one category difference between damage category and combined impact category for Categories 1,2,3,and 4,respectively.IPWT and its classification can be used to assess the severity of the TC impact and of combined precipitation and wind conveniently and accurately,and the potential damage caused by TCs.The result will be a good supplementary data for TC intensity,precipitation,wind,and damage.In addition,IPWT can be used as an index to judge the reliability of damage data.Further analysis of the annual frequency of combined precipitation-wind impact categories reveals no significant increasing or decreasing trend in impact over China over the past 30 years.

Numerical Study of a Mesoscale Vortex in the Planetary Boundary Layer of the Meiyu Front

It was found that the heavy rainfall event along the Meiyu front in the lower reaches of the Yangtze River on 23 June 2009 was connected with a mesoscale disturbance vortex, which originated from the planetary boundary layer (PBL) and developed upward later and was discovered by using the Shuman-Shapiro filtering method. The mesoscale disturbance vortex in the PBL (PMDV) in this process corresponded well to the short-time rainstorm in the Doppler radar echo. Analysis of the high-resolution simulation results from the Advanced Weather Research and Forecasting Model (ARW) showed that there were several surface disturbances along the southern warm section of the Meiyu front prior to the generation of the PMDV. The PMDV interacted with the mesoscale convective system (MCS) and intensified the local convective precipitation. The north and southwest flows in the PBL converged at the time of the PMDV formation. Meanwhile, a southwesterly jet on the top of the PBL to the south side of the vortex reinforced the ascending motion and convergence. Hence, it is concluded that the PMDV was generated when the strong cold air flows north of the shear line encountered the southwest flow south of the shear line. The convergence line in the PBL, the intensification of the southwest wind, and the southward aggression of the north wind were critical for the development of the PMDV. The release of latent heat was found crucial for the formation of the PMDV as it facilitated the convergence at low levels.

A Numerical Study of the Severe Heavy Rainfall Associated with Typhoon Haitang (2005)

Typhoons landing in the central and north of Fujian Province often seriously impact Zhejiang Province. Much attention has been given to exceptionally torrential rain in the South/North Yandang mountainous regions in the southeast of Zhejiang Province associated with typhoon-landing.Typhoon Haitang (2005) is a typical case of such a category,which landed in Huangqi Town of Lianjiang County in Fujian Province, and meanwhile greatly impacted Southeast Zhejiang.A numerical simulation has been performed with the PSU/NCAR non-hydrostatic model MM5V3 to study the torrential rain associated with Typhoon Haitang. The comparison of simulated and observed rainfalls shows that the MM5V3 was able to well simulate not only the intensity but also the locations of severe heavy rain of Typhoon Haitang,especially the locations of the south/north heavy rain center areas in the South/North Yandang mountainous regions.Meanwhile,the diagnostic analysis has been also carried out for better understanding of the severe heavy rain mechanism by using the model output data of high resolution.The diagnostic analysis indicates that the westward tilt of the axis of vorticity from lower layer to upper layer over the south heavy rain center area and the coupled structure of convergence in the lower layer and divergence in the upper level over the north heavy rain center area,were both propitious to stronger upward motion in the layers between the mid and upper atmosphere, and the secondary circulation induced by the vertical shear of the ambient winds further strengthened the upward motion in the heavy rain areas.After Haitang passed through Taiwan Island into the Taiwan Strait, the water vapor east of Taiwan Island was continuously transferred by typhoon circulation towards South Wenzhou,leading to the torrential rainfall in the South Yandang mountainous region south of Wenzhou. Subsequently,Haitang moved northwards,the water vapor belt east of Taiwan Island slowly advanced northwards,the precipitation rate obviously enhanced in the North Yandang mountainous region north of Wenzhou.After landing in Fujian Province,Haitang moved northwestwards,the water vapor belt coming from the Taiwan Strait merged into the strong water vapor belt from the ocean surface east of Taiwan Island, and passed through the north of Wenzhou,resulting in the torrential rainfall in the north of Wenzhou.The specific moisture transport passage offered abundant water vapor condition for torrential rainfalls associated with Haitang.The unstable stratification at the middle and lower layers over rainstorm areas also provided favorable thermal condition for torrential rainfall.The sensitivity simulation experiments of terrain effect on Haitang's heavy rain were also conducted.The moisture flow derived by Haitang's southeast flow, which was perpendicular to the South and North Yandang Mountain ranges,played an important role in the torrential rainfall associated with Haitang.The experimental results show that orographic lifting contributed greatly to the enhancement of precipitation,and made the distribution of precipitation more uneven.Some causes for typhoon heavy rainfalls in the south and north of Wenzhou are common,but some causes different.The common aspects are strong ascending motion forced by vertical wind shear,sustained unstable stratification,and amplification effect of orography on precipitation,while different aspects are dynamic structure,conditions for maintenance of unstable stratification,and moisture transport condition.

A Numerical Simulation Study of Typhoon Rananim(0414)

用高分辨率的非静水力学的模型 ARPS (先进地区性的预言系统) ，台风 Rananim (0414 ) 被使用 CINRAD Doppler 雷达数据模仿。在台风前后的结果乍见陆地证明模型 ARPS 表现很好模仿轨道，中心压力的变化，以及 Rananim 的严重大雨。同时，模仿的合成反射率与观察雷达相比是合成反射率。数字结果表明 Rananim 的不均匀的结构在它向西偏斜在以后起一个重要作用乍见陆地。 Rananim ( 0414 )上的地面效果的敏感模拟实验也被调查，并且东南的中国的地面在它的轨道稍微向右转并且显然增加它的紧张的 Rananim 上有重要效果，但是当台风是远的离开海岸线时，地面仅仅稍微影响暴风雨紧张在期间它的乍见陆地。结果证明地志的上升极大地作出贡献到降水改进，并且使降水的分发更不平。[出版摘要]

Impact of physical representations in CALMET on the simulated wind field over land during Super Typhoon Meranti(2016)

A WRF(Weather Research and Forecasting Model)/CALMET(California Meteorological Model)coupled system is used to investigate the impact of physical representations in CALMET on simulations of the near-surface wind field of Super Typhoon Meranti(2016).The coupled system is configured with a horizontal grid spacing of 3 km in WRF and 500 m in CALMET,respectively.The model performance of the coupled WRF/CALMET system is evaluated by comparing the results of simulations with observational data from 981 automatic surface stations in Fujian Province.The root mean square error(RMSE)of the wind speed at 10 m in all CALMET simulations is significantly less than the WRF simulation by 20%^30%,suggesting that the coupled WRF/CALMET system is capable of representing more realistic simulated wind speed than the mesoscale model only.The impacts of three physical representations including blocking effects,kinematic effects of terrain and slope flows in CALMET are examined in a specified local region called Shishe Mountain.The results show that before the typhoon landfall in Xiamen,a net downslope flow that is tangent to the terrain is generated in the west of Shishe Mountain due to blocking effects with magnitude exceeding 10 m/s.However,the blocking effects seem to take no effect in the strong wind area after typhoon landfall.Whether being affected by the typhoon strong wind or not,the slope flows move downslope at night and upslope in the daytime due to the diurnal variability of the local heat flux with magnitude smaller than 3 m/s.The kinematic effects of terrain,which are speculated to play a significant role in the typhoon strong wind area,can only be applied to atmospheric flows in stable conditions when the wind field is quasinondivergent.