Abstract:The heavy precipitation which caused by typhoon may lead to huge societal and economic losses,especially in the coastal regions of southeastern China.Based on the hourly rainfall data from 96 national stations in Zhejiang province,the performance of six regional and three global operational numerical weather prediction models for the typhoon-induced heavy precipitation during the 2021-2023 was evaluated.(1)For 24-hour accumulated precipitation,regional models demonstrate a higher Equitable threat score(ETS)and comprehensive scores in rainfall(greater than 0.1 mm)forecast than global models.However,obvious differences exist in torrential rain forecastg.ECMWF showed the best ETS for the In-fa and Doksuri processes,while CMA-TRAMS9 performed best for the Muifa.(2)Precipitation with an intensity greater than 10 mm·(3h)-1 was the major contributor to accumulated precipitation.The ETS for 3-hour heavy precipitation showed that regional models with resolution of 3 km slightly outperform the other models,and CMA-MESO3 had the best skill during the In-fa and Doksuri.(3)Both global and regional models overforecasted precipitation on eastern coast of Zhejiang during the In-fa and Doksuri.This positive bias was contributed to by both overestimated precipitation frequency and intensity.All models reasonably reproduced the early morning peak of precipitation amount before the landfall of In-fa,but the bias of the peak hour after the landfall of In-fa varied greatly between models.Among them,ECMWF,CMA-MESO3 and CMA-BJ9 were more accurate in predicting the main peak hour after landfall.In contrast,the forecasts of the diurnal variation were generally poor for all models before and after the landfall of Doksuri,with the exception of CMA-GD3 after landfall.The results provide users with the bias features and accuracy for the precipitation forecast among operational models,which may be helpful in the improvement of model forecast skill and weather forecasting services.

Abstract:In order to deepen the objective understanding of the formation mechanisms of tornadoes in Jiangsu and improve the accuracy of tornado monitoring and early warning,this paper investigates the rare EF3-level tornado case that occurred on 19 September 2023 in Funing,Jiangsu,an unprecedented event for September in the history of Jiangsu.The analysis focuses on the reality and disaster situation,weather background and environmental conditions,and multi-band radar collaborative observations.The results are as follows.(1)The"9.19"Funing EF3-Level tornado was a strong tornadic event that occurred under the background of Meiyu weather.The air flow branching in the 200 hPa weather pattern and the wedge-shaped cloud in the 13.3 μm infrared satellite imagery were important indicators of deep convective forcing and advanced prediction of"9.19"Funing tornado.(2)Sudden changes of thermal and dynamic conditions signaled an extremely unstable atmosphere with strong vertical ascent,serving as important potential indicators for the triggering of a strong tornado.At 20:00 BJT on September 19 at the Sheyang sounding station,the Convective Available Potential Energy(CAPE)increased to 2 288.7 J·kg-1,Convective Inhibition(CIN)decreased to 0.2 J·kg-1,the Lifting Condensation Level(LCL)plummeted to 1 005.0 hPa(69 m),and K index increased to 40.2℃.Vertical wind shear rose to 10.9 m·s-1(0-1 km),19.2 m·s-1(0-3 km),and 21.9 m·s-1(0-6 km).(3)The multi-band weather radar network in northern Jiangsu can provide ultra-low altitude data,with the lowest detection height ranging from 100 m to 350 m,which greatly meets the internal needs of tornado monitoring and early warning.The multi-band weather radar in northern Jiangsu had a good adaptive scanning capabilities on the"9.19"Funing tornado.Without manual intervention,Baoying XD radar can carry out reasonable Range Height Indicator(RHI)adaptive scanning,completely capturing the evolution and vertical flow field of tornadic supercell.The Scans clearly revealed key structural featares:a low-to-mid-level reflectivity factor core(RC)and dome structure;middle-to-high-level overhanging echoes;a"V"-shaped gap at 3-5 km height;and a northeast-to-southwest oriented weak echo band between overhanging echoes of the dome and the middle-to-high-level overhanging echoes.The flow field was characterized by the vortex tube circulation in the forward-flank inflow,high-altitude subsidence flow,and the divided rear-flank inflow jet.These results provide a valuable reference for the multi-band weather radar monitoring and warning of tornadoes using multi-band weather radar in Jiangsu and contribute to the objective understanding of tornadic physical processes.

Abstract:This study analyzes the characteristics of raindrop size distribution in the coastal areas and the northern regions of the South China Sea during pre-and post-monsoon periods.The study utilizes one-dimensional observation data from the Yongxing Island Observatory in the South China Sea from 2020 to 2022,and from three stations including Zhuhai,Guangzhou,and Foshan in Guangdong Province from 2018 to 2022.The analysis includes the Dm-Nw distribution characteristics in different flood seasons,the variations of the particle size distribution with rainfall intensity and diurnal variations,and the μ-Λand Z-Rrelationships.The results show that,influenced by lower aerosol concentrations and higher evaporation rates over the ocean,the number concentration of small raindrops in oceanic flood season precipitation is lower than that in coastal precipitation.For a given rainfall intensity,when it is less than 10 mm·h-1,the fitted spectra of medium-sized raindrops in oceanic and coastal precipitation show almost consistent trends across pre-and post-flood season.However,with increasing rainfall intensity,the difference in number concentration of medium and large raindrops among different precipitation types gradually increases.The number of large raindrops in both coastal and oceanic precipitation is mainly concentrated in the evening and nighttime during the post-flood season.The μ-Λrelationships within the same region show similarity.As Λ increases,the μ values of coastal pre-and post-flood season precipitation show significant differences,with the μ value of post-flood season precipitation being larger than that of the pre-flood season.This indicates that the concentration of small raindrops in pre-flood season precipitation is lower than that in post-flood season precipitation,and the high concentration of small raindrops is the reason for the relatively small μ.Furthermore,significant differences exist in the Z-R relationships at different latitudes.The raindrop diameter and number concentration in coastal post-flood season precipitation are both larger than those in the pre-flood season,while these parameters in oceanic pre-and post-flood season precipitation are similar.

Abstract:Investigating the spatiotemporal distribution and urban-suburban differences of lightning parameters is of great practical significance for understanding how the natural environment influences lightning activity and for improving urban lightning disaster prevention.Based on the monitoring data from the VLF/LF 3D lightning location system in Hubei Province(2015-2022),the DBSCAN algorithm was used to identify thunderstorm clusters.On this basis,mathematical and statistical methods are adopted for a comparative study on the distribution characteristics of lightning frequency,polarity,current intensity,and thunderstorm cloud cluster between urban and suburban areas.The results show a higher proportion of cloud lightning in urban areas,and an increasing trend for lightning density both in urban and suburban areas over the past 8 years,while lightning current intensity and average thunderstorm days decreased.The cloud-to-ground(CG)lightning parameters are more significantly affected by urbanization.Specifically,CG lightning density in suburban areas is 14.7%higher than that in urban areas.The average current intensity for both cloud and ground lightning in urban areas is higher than that in suburban areas,which means the CG lightning activity can produce higher lightning current intensity.The probability of current amplitude for CG lightning,which is less than 20 kA,is 6.6%higher in suburban areas when compared to the urban areas,and the shielding failure rate is also higher.Conversely,the probability of a current amplitude exceeding 100 kA is larger than 100 kA,is 0.5%higher in urban areas,and its back flashover rate is also higher.Both areas are dominated by small thunderstorm cloud,with average thunderstorm cluster areas of 77.2 km² and 81.7 km²,respectively.The occurrence probability for small thunderstorms is higher in urban areas,while the probability of large thunderstorms is higher in suburban areas.

Abstract:Currently,phased array weather radar has become increasingly widespread in China.Its efficient and flexible electronic scanning mode significantly improves the radar's observation efficiency,making it adaptable to different observation tasks.However,the instability of phased array antenna's performance parameters also poses new challenges for data quality control.To examine the rationality of multi-beam scanning mode of phased array radar and its impact on data quality,this study quantitatively compared observation data from three X-band dual-polarization phased array weather radars in Guangzhou and one S-band new-generation dual-polarization Doppler weather radar.The study evaluated sensitivity changes and observational deviations at various elevation angles,as well as their underlying causes,under both single-beam and multi-beam scanning modes.The results indicate that in the multi-beam mode,observation deviation in ZH and ZDR of the phased array radar increases with the beam direction deviating from the normal direction in the antenna array surface.The uneven distribution of antenna gain within the wide transmission beam causes data at various elevation angles to exhibit periodic fluctuations consistent with the transmission beamwidth.Through the proposed correction,the average observational deviation of ZHat different elevation angles in the multi-beam mode is controlled to approximately-0.6 dB.This study provides a scientific basis and framework for data quality control and advanced application of phased array radar.

Abstract:TRP(Tropical cyclone Remote Precipitation)often produces extreme precipitation events,the actual magnitude of which is larger than forecasted.Therefore,it is necessary to carry out research to improve the forecast accuracy of such pecipitation.This paper analyzed a TRP event in Zhejiang caused by the NO.20 typhoon"Khanun"(which made landfall in Guangdong Province)in 2017.The evolution and characteristics of the precipitation system were analyzed using ground observation and radar data,while the specific causes were investigated using NCEP CFSR reanalysis data(horizontal resolution 0.5 °×0.5 °).The results show that the rainstorm process had the following characteristics.(1)Under the guidance of the typhoon peripheral circulation,there were obvious water vapor channels in the lower layer to transport water vapor to the rainstorm area,accompanied by strong warm advection;(2)The tip of the low-level typhoon trough extended to Zhejiang and developed into a cut-off depression;(3)The rainstorm area was originally controlled by the subtropical high at 500 hPa,and a short-wave trough developed at the edge of the subtropical high during the precipitation process,accompanied by strong upward motion.Vorticity budget analysis showed that the initial disturbance for the development of the cut-off low was mainly provided by the horizontal convergence divergence term and the distortion term in the surface layer.Vorticity was then transmitted upward from the near-surface layer to 850-500 hPa,resulting in the development of depression in the low-level layer and the emergence of short-wave trough in the middle layer,while strengthening the upward movement and surface cyclone.The key mechanism for the strong precipitation was the transformation of the typhoon trough into a strong cut-off low due to intense warm advection and vertical vorticity transport at low level.For forecasting,it is crucial to monitor the intensity of warm advection at low level and the coupling of vorticity and vertical movement at low level.

Abstract:To explore the climatic characteristics and influencing factors of summer maximum temperatures in Guizhou Province,this study analyzed daily maximum temperature data from 84 national meteorological stations in Guizhou Province from June to August during 1972-2021,along with the subtropical high index,seven atmospheric circulation indices from the National Climate Center,and the NCEP/NCAR second reanalysis data.Methods such as empirical orthogonal function(EOF)expansion,Mann-Kendall non-parametric statistical test,Morlet wavelet analysis,and synthetic analysis were applied.The results show that there are multiple time-scale oscillations of mean maximum summer temperature in Guizhou Province,including quasi 2-4-year,quasi 8-year,and quasi 16-year cycles.An 8-year cycle is associated with anomalously high temperatures,while a 6-year cycle corresponds to anomalously low temperatures.Spatially,the maximum summer temperature is characterized by higher values in the eastern and southern regions,and lower values in the west.The leading EOF mode of summer maximum temperature shows a spatially consistent pattern across the province,counting for 78.67%of the variance,followed by a north-south dipole pattern,explaining 5.95%of the variance.The first mode of summer maximum temperature is significantly positively correlated with the ridge position of the subtropical high and the Tibetan Plateau index-1,and significantly negatively correlated with the Asian zonal circulation index and the East Asia Trough position index.The second mode is significantly negatively correlated with the area and intensity indices of the subtropical high,and significantly positively correlated with the Tibetan Plateau index-1,Tibetan Plateau index-2,and the India-Myanmar trough intensity index.When the summer maximum temperature is abnormally high,the 500 hPa geopotential height anomaly field over mid to high latitudes in Asia mainly exhibits a"positive-negative-positive"meridional structure.At this time,most areas in mid to high latitudes of China experence positive heght anomalies,while areas south of 30 °N are negative anomalies.When abnormally low temperature years,the anomaly field displays a"negative-positive-negative"pattern,with negative anomalies across most areas of China ecept South China.

Abstract:CMIP6 global climate model(GCM)is one of the primary tools for predicting future climate change.However,their outputs usually have a coarse spatial resolution(typically≥1 °),making them difficult to apply directly to regional-scale climate change studies.To address this issue,this study proposes a Terrain-Guided Multi-scale Residual Dense Network(TGMSRDN)downscaling model,aiming to improve the spatial resolution and accuracy of GCM daily mean temperature data for Southwest China.Specifically,the model constructs a Multi-scale Residual Dense Block(MSRDB)to extract of multi-scale feature information from the coarse-resolution temperature data.In addition,a Terrain-Guided Network(TGN)is designed to fully leverage topographic information.This network effectively aggregates temperature data with topographic information via an attention mechanism,thereby recovering finer spatial details in the temperature data.Comparative experiments conducted in Southwest China demonstrate that TGMSRDN can effectively improve the spatial resolution of the GCM daily mean temperature from 1 ° to 0.1 °,and performs better when compared with several advanced deep-learning-based super-resolution methods.Finally,the proposed model is applied to downscale the temperature projection data for the study area during 2015-2050 under four scenarios(SSP1-2.6,SSP2-4.5,SSP3-7.0,and SSP5-8.5).The results indicate that the annual mean temperature of the study area exhibits an increasing trend under all four scenarios.Notably,the temperature rise in the study area is projected to exceed 1.5 ℃ by 2050 under the SSP5-8.5 scenario.

Abstract:To explore the basic characteristics and patterns of landfalling hollow typhoons in Guangdong,this paper constructs an objective identification algorithm for landfalling hollow typhoons based on real-time wind field and tropical cyclone(TC)track data.Utilizing this algorithm,we identified hollow typhoons that made landfall in Guangdong from 2008 to 2022 and conducted a statistical analysis of their basic characteristics.The study found that all hollow typhoons that landed in Guangdong in the past 15 years originated from the central-northern South China Sea and the western part of the western Pacific Ocean.The highest proportion of landfalls occurred in western Guangdong(68%),with the majority concentrating during the late summer to autumn period(75%).These typhoons can be classified into four types:northwestward,westward,northward,and complex,with the northwestward type being the most prevalent(62.5%).Further statistical analysis reveals that for hollow typhoons making landfall on the eastern side of the Pearl River Estuary and in the area from the northeast of the Leizhou Peninsula to Maoming,the main gale regions are often distributed within a range of 80-160 km from the typhoon center.Conversely,for those making landfall in the southern part of Leizhou Peninsula,the gale regions are frequently distributed approximately 100-260 km from the center.The research also shows that hollow typhoons tend to be larger in size compared to normal TCs,and weaker TCs are more conducive to the formation of hollow structures.Furthermore,the difference between the inner-circle wind force and the central wind force of hollow typhoons tends to increase with the enhancement of landfall intensity.Composite analysis indicates that there is no significant difference in the large-scale circulation background between hollow typhoons and non-hollow typhoons.

Abstract:The precipitation measurement radar(PMR)carried by FY-3 Mercury is a new generation of active precipitation measurement load in China,which monitors typhoon,rainstorm and other disastrous weather systems.The PMR provides observation data from Ku and Ka bands,with a narrow width but high accuracy.The microwave imager(MERI-RM)installed on the same platform also has good precipitation measurement capabilities,and its wide cutting range can greatly improve the ground coverage for precipitation measurement.This article proposes using the DNN model to establish the relationship between the brightness temperature of the MWRI-RM and the reflectivity factor of the PMR,simulating the reflection signals of the main measurement channels of the PMR.At the same time,by using wide range observation geometry simulation technology,we establish observation geometry characteristics with the same width as the MWRI-RM,thus improving the observation range of the PMR,and ultimately obtain the PMR simulation data with the same width as the MWRI-RM.Through experimental testing of Typhoon Dussuri,it has been shown that this method can increase the observation width by 60%and achieve a fitting accuracy of 85%in rainfall areas.

Abstract:In recent years,the occurrence of multiple tropical cyclones(TCs)which consecutively impact the same region,resulting in significant economic losses,has become increasingly frequent.This study defines a compound TC event as an occurrence where the 50 km impact zones centered on the tracks of multiple TCs overlap spatially and the temporal interval between their impacts is no more than 10 days.Based on a dataset of Northwest Pacific TCs from 1949 to 2022 and TC disaster data in China from 1984 to 2022,we identify compound TC events and analyze their spatiotemporal characteristics of economic losses.The results indicate that:(1)From 1949 to 2022,an average of approximately 6.9 compound TC events occurred per decade,with significant differences in frequency across decades and a peak during 1960s.About 14.8%of the national territory was impacted by compound TC events,affecting not only traditionally vulnerable areas(such as the southeast coast)but also mid-to high-latitude coastal and adjacent inland regions,with the largest affected area observed in the 2010s.(2)In the years with recorded compound TC events from 1984 to 2022,direct economic losses from these events account for approximately 39%of total TC losses,increasing at a rate of 9.6%per decade,indicating a growing destructiveness of compound TC events.The average economic losses from high-intensity compound TCs were about 2.2 times greater than those of low-intensity compound TCs.(3)Economic losses from compound TC events are significantly higher than those from single TCs,highlighting the pronounced disaster amplification effect.Traditional TC-affected areas are particularly susceptible to high-intensity compound TCs,while mid-latitude regions exposed to low-intensity compound TCs are likely to incur severe economic losses,necessitating improvements in typhoon disaster prevention and mitigation capabilities.

Abstract:Extreme weather caused by typhoons poses significant threats to the lives and property of inland city residents.Therefore,studying the landfall characteristics of typhoons affecting inland cities has become increasingly important.The China Meteorological Administration(CMA)tropical cyclone best-track data and ground observation data from 1959 to 2023 were used to analyze the landfall characteristics of typhoons affecting Hefei Area.Based on wind-rain impact differences,the typhoons were divided into three categories:those with only high rainfall(OP),those with only strong winds(OW),and those with severe wind and rain(PW).The results show that:(1)Over 65 years,89 typhoons affected Hefei.OP,OW,and PW accounted for 17%,20%,and 8%,respectively,totaling 45%and highlighting the importance of high-impact typhoons.(2)Temporally,typhoon activity showed distinct phased changes,with active periods from the 1980s to 1990s and after 2016.Before 2000,OW events were predominant,while OP events increased significantly afterward.PW events had recurrence intervals of 10-20 years.Seasonally,July to September was the period of concentrated influence,with an increase in PW frequency from August to September.(3)In terms of landfall characteristics,Fujian was the most frequent landfall province(31.2%);43.7%of typhoons underwent secondary landfalls,with 94%of them first making landfall in Taiwan before striking Fujian and Zhejiang.The landing intensity was mainly at the typhoon level,but OW strength was generally weaker than OP events.(4)In terms of movement paths,48%followed a Type IV path(turning south of 30 °N),the secondary dominant paths for OP/PW and OW were Type II(northwest)and Type III(northward turning)while respectively,Significantly,Jiangxi Province and the Jiangsu-Zhejiang-Anhui border region were key transitional zones for high-impact typhoon paths,corresponding to the main influence channels for OP and OW.The research results provide data support for the assessment of typhoon disaster risks and the formulation of defense strategies in Hefei.

Abstract:Based on precipitation observations from 5 634 meteorological and hydrological stations in Guangdong Province,this study integrated radar quantitative precipitation estimation products using probability density function matching and optimal interpolation.The ART_1km precipitation fusion product was corrected using the space-time multiscale analysis system.Comparison with the domestic similar product ART_1km showed that both methods can effectively enhance product quality through integrating more site observations.The improvement included a reduced false alarm rate for precipitation below 2 mm·h-1 and smaller errors for precipitation over 20 mm·h-1,as well as decreased errors during the main flood season in site observations or topographically complex regions such as the western Leizhou Peninsula,coastal areas of western Guangdong,and mountainous areas of northern Guangdong.According to independent verification of a precipitation process,the fusion of station observations and radar information ere achieved through probability density function matching and optimal interpolation.This approach enhanced overall quality,especially in situations with poor spatial representation of stations,such as sparse sites,extreme and local precipitation.These showed relatively high false alarm rates.The space-time multiscale analysis could well capture the short-wave information of station observations,and had good effects in spatial representation of stations(e.g.,dense sites,continuous and stable precipitation structures,precipitation with low extreme intensity),but with a relatively high missing rate.Both methods exhibited measurable accuracy degradation in complex terrain regions.

Abstract:Based on the meteorological data of Zhongshan City,Guangdong Province,as well as the data on scale of aquaculture species and disaster losses,this study involved selecting key disaster-causing factors such as wind damage,heavy rainfall,and low temperatures;determining insurance trigger thresholds and premium rates of insurance compensation;and designing a tiered insurance compensation structure.These elements were used to develop aquaculture meteorological index insurance products and compile a customized agricultural meteorological index insurance scheme for Zhongshan,which was subsequently put into practice.The results show that:(1)By determining aquaculture insurance premium rates,selecting representative weather stations for insurance payouts,and designing the insurance payout structure in tiers at the town level,the developed insurance products can provide payouts tailored to specific towns.This reflects the varying disaster exposure of different towns in Zhongshan and effectively mitigates the risk of the spatial basis difference in agricultural insurance.(2)The"one town,one strategy"Zhongshan specialty agricultural insurance scheme covers the main meteorological disasters across the whole production chain of aquaculture,replacing single-peril aquaculture insurance products and significantly enhancing the satisfaction of farmers,insurance companies,and the government;(3)The successful implementation of meteorological index insurance products is strongly supported by robust policies and institutional frameworks.This practice has led to the formation of a replicable and transferable model of"Agriculture+Meteorology+Insurance"collaborative model,which can serve as a valuable reference for the implementation of aquaculture meteorological index insurance with similar characteristics.

Abstract:The first rainy season precipitation in South China is often characterized by heavy rainfall events lasting for more than 3 days,and even up to 10 days or more.These events,known as Persistent Heavy Rainfall Events(PHRE),result in severe flooding disasters in the region.Improving extended-range(10-30 days or 2-6 weeks in advance)precipitation forecast skill for the first rainy season is crucial.This paper focuses on the precipitation predictability sources of the first rainy season in South china,as well as the current application of numerical models,dynamical-statistical downscaling,and machine learning in the field of extended-range forecasting.The aim is to synthesize major advancements in extended-range precipitation forecasting for the first rainy season in South China.

Abstract:Based on observations from national meteorological and radiosonde stations,this study comprehensively evaluates the forecast performance of precipitation and low-level flow field over the Guangdong-Hong Kong-Macao region during the pre-flood season(April to June)from 2014 to 2018 using regional numerical weather prediction models with 9 km and 3 km horizontal resolutions.Traditional precipitation scoring methods and neighborhood technique were employed,along with various statistical indicators,to assess the differences in forecast skills between the models with different resolutions,focusing on both temporal and spatial variability.The study also analyzed the applicability of different resolutions and explored the relationship between the forecast skills for precipitation and low-level flow field,providing valuable insights for optimizing mesoscale models in future regional forecasts.The results show that:(1)Both the 9 km and 3 km resolution models exhibit relatively stable forecast performance for precipitation and low-level flow fields prior to the onset of the South China Sea summer monsoon.Both models show diurnal variations in forecasting capabilities,with improved accuracy during the 08:00 LST to 12:00 LST period,while their performance during the afternoon and night,which involve more complex physical processes,is comparatively inadequate.(2)The 9 km resolution model tends to overestimate precipitation amounts,whereas the 3 km model displays smaller temporal and spatial biases in overall forecasting,demonstrating more stable forecast skills,particularly with higher accuracy for light,moderate,and heavy rainfall events.The 3 km resolution model provides more precise predictions for precipitation following the monsoon onset and during the afternoon,with reduced forecast errors in complex terrains such as the Pearl River Delta and the northern mountainous regions of Guangdong.(3)Similarly,the 3 km resolution model excels in simulating low-level flow fields,particularly in near-surface temperature and specific humidity simulations,effectively capturing their variations during the afternoon.This model also demonstrates greater precision in simulating near-surface temperature and humidity over complex terrain areas.

Abstract:To evaluate the applicability of S/X-band weather radar networking in Guangxi,this study uses radar data to perform sequential processing:base data parsing,ZH-KDP attenuation correction,NVI-based single-station gridding,and maximum-value multi-radar mosaicking.The analysis then combines reflectivity and constant-altitude plan position indicator(CAPPI)data to assess the network's coverage during Typhoon Talim(2023,No.4).The results show the ZH-KDP-corrected X-band radar reflectivity,validated via radial profile,grid,and reflectivity comparisons obtained from multiple continuum scans,is reliable within a certain range.When applied to the Typhoon"Talim"rainstorm analysis,comparisons of 0.5,0.75,1.0,and 2.0 km CAPPI network reflectivity coverage between the S-band radar alone and the combined S/X-band radar network reveal that the addition of X-band radar improves the structure and smoothness of the data.This yields spatially wider coverage,effectively filling low-level blind zones and blocked gaps in Guangxi's new-generation weather radar.

Abstract:Using the Yearbook of Tropical Cyclone(1990-2019)from the China Meteorological Administration,ERA5 0.25 °×0.25 ° hourly reanalysis data,and 24-hour(20:00-20:00)rainfall observations from national stations in eastern Guangdong,this study classifies and analyzes the circulation characteristics of torrential rain in eastern Guangdong induced by westward-moving typhoons after landfall in Fujian Province.Statistical classification and composite analysis methods are employed.Results show that torrential rain occurs more frequently on the day after typhoon's landfall than on the landfall day itself.A mid-level position along the robust edge of a strong subtropical high favors heavy rainfall development.The low-level wind fields associated with heavy rain in eastern Guangdong are divided into three types:the typhoon trough type with prolonged precipitation duration;the southwesterly jet type where precipitation typically begins as the jet moves onshore,with rainfall intensity scaling with jet strength;and the southeasterly flow type where rainfall intensity is closely related to terrain,where windward slopes significantly enhance precipitation.Light-rainfall typhoons exhibit inherently weaker moisture convergence and vertical motion,which are insufficient to drive intense precipitation.Analysis of physical parameter configurations shows heavy-rainfall typhoons superior conditions than light-rainfall typhoons:the southwestern jet type has optimal warm and moist conditions and can generate widespread torrential rain even with moderate dynamic forcing;the typhoon trough type and southeasterly flow type exhibit peak dynamic but slightly inferior thermal conditions,with>100 mm rainfall areas collocated with upper-level divergence centers.Regarding moisture conditions,stronger eastward water vapor transport within typhoon circulation benefits moisture supply to eastern Guangdong,though attention should be paid to other developing tropical systems that may weaken or disrupt this moisture transport.

Abstract:Based on the ERA5 reanalysis data and China Meteorological Administration(CMA)tropical cyclone best track data from 1981 to 2022,this study analyzes the gale characteristics induced by offshore and northward-moving tropical cyclones(TCs)in Shanghai coastal areas.A quantitative momentum budget diagnostic equation is then utilized to investigate their dynamic mechanisms.The results show that:(1)Substantial discrepancy exists in the maximum impact wind intensities among different TCs,and the intensities are strongly affected by the distance of the TCs from Shanghai coastal waters.(2)The pressure gradient acceleration(PGA)and the vertical advection(VA)terms are the primary dynamical mechanisms for TC gales in Shanghai coastal areas.The PGA term accounts for the major contribution,followed by the VA term,with the intensity of both terms strengthen with wind intensities.(3)Enhanced pressure gradient directly strengthens the PGA term,while the downward transport of high momentum from the boundary layer jet amplifies the VA term above the boundary layer,ultimately driving the TC gales in the Shanghai coastal areas.These results establish important guidance for TC gale forecasting and have practical value for operational applications,thereby offering a scientific basis for disaster prevention and mitigation.

Abstract:This study investigates the interannual variability of landfalling tropical cyclones(TCs)in Guangdong during the post-flood season(1968-2022),using TC frequency data,reanalysis products,and sea surface temperature(SST)data.Through wavelet and composite analysis,we specifically explore the prominent bimodal characteristics in their interannual variability and their asymmetric relationship with SST.The main findings are as follows:(1)The frequency of landfalling TCs in Guangdong exhibits significant quasi-3-year and quasi-8-year bimodal periodic oscillations,with comparable amplitudes.(2)Under different modes,significant variations exist in atmospheric circulation configurations that influence TC landfalls.During years with more landfalling TCs for both quasi-3-year and quasi-8-year timescales,the Western Pacific Subtropical High(WPSH)shifts westward and strengthens,facilitating TC landfalls in Guangdong.Conversely,the WPSH configurations during less landfalling TC years are distinct for each mode.On the quasi-biennial timescale,the WPSH is weaker and retreats eastward,causing TCs to recurve northward prematurely;however,on the quasi-3-year timescale,the WPSH remains westward and strong,with significant anomalous easterlies on its southern flank that guide TCs westward.(3)The relationship between the landfalling TC frequency in Guangdong and SST is asymmetric.On the quasi-3-year timescale,years with more landfalling TCs are associated with significant positive winter SST anomalies in the equatorial eastern Pacific and from the tropical North Indian Ocean to the South China Sea(SCS).On the quasi-8-year timescale,more TC landfall years correspond to significant positive winter SST anomalies mainly in the equatorial central Pacific,while less TC landfall years generally exhibit positive winter SST anomalies across the entire tropical Indian Ocean.In addition,landfalling TC frequency tends to be higher in transition years from winter El Niño to summer La Niña conditions.This study enhances our understanding of the variability characteristics of landfalling TCs in Guangdong,and the identified asymmetric relationship with SST provides valuable guidance for improving short-term climate predictions of landfalling TC frequency in this region.