The raindrop size distribution(DSD) is a significant characteristic of precipitation physics,which plays a crucial role in improving the accuracy of radar quantitative precipitation estimation and prediction.There is ...The raindrop size distribution(DSD) is a significant characteristic of precipitation physics,which plays a crucial role in improving the accuracy of radar quantitative precipitation estimation and prediction.There is an effect of atmospheric circulation and weather sy stems in South China,with frequent precipitation and differences in regional features,resulting in a limited understanding of the DSD characteristics and their impact mechanisms in the region. In this study,six ground-based two-dimensional video di sdrometers(2DVDs) were used to analyze the DSD of inland and coastal in South China during the five-year(2016-2020) monsoon seasons(April to September),ERA5 reanalysis data and MODIS cloud property products were also used to investigate the dynamics and microphysical characteristics of monsoon precipitation.Compared to inland rainfall,coastal rainfall has a higher conentration of small,medium,and diameter of less than 4.7 mm large raindrops.Considering the contributions to precipitation,the inland and coastal rainfall are dominated by convective rain,accounting for 74.8% and 84.7% of the total rainfall,respectively.The coastal rainfall has a higher the mass-weiglited mean diameter(D_(m)) value than the inland rainfall D_(m) for both the stratiform and convective rainfall.The logarithmic mean of the generalized intercept parameter(log_(10)N_(w)) in inland stratiform rain is greater than that in coastal areas,while convective rain is relatively small.Due to the impact of precipitation types and climate conditions,The Z-R relationship between inland and coastal rainfall also shows obvious differences.Compared to inland areas,there is more frequent convective activity,relatively moist near-surface conditions,and lower cloud droplet number concentrations,which contribute to larger D_(m) of raindrops in coastal areas.This study deepens the understanding of changes in South China's coastal and inland DSD and provides support for improving numerical weather forecasting in the region.展开更多
The characteristics of summertime raindrop size distribution(DSD) and associated relations in the semi-arid region over the Inner Mongolian Plateau(IMP) were investigated,utilizing five-year continuous observations by...The characteristics of summertime raindrop size distribution(DSD) and associated relations in the semi-arid region over the Inner Mongolian Plateau(IMP) were investigated,utilizing five-year continuous observations by a PARSIVEL2disdrometer in East Ujimqin County(EUC),China.It is found that only 7.94% of the 15 664 one-min precipitation samples meet classification criteria as convective rain(CR),but its contribution to the total rainfall amount is 63.87%.Notably,40.72% of the rainfall comes from large-sized raindrops(D> 3 mm),despite the fact that large-sized raindrops account for only 1.73% of the CR total number concentration.Further results show that the mean value of mass-weighted mean diameters(Dm) is larger(2.43 mm) and generalized intercepts(lgN_(W)) is lower(3.19) in CR,aligning with a "continentallike" cluster,which is mainly influenced by the joint impact of in-cloud ice-based processes and the below-cloud environmental background.Also,the empirical relationships of shape-slope(μ-Λ),radar reflectivity-rain rate(Z-R),and rainfall kinetic energy(KE_(time)-Rand KE_(time)-Z) are localized.To quantitatively analyze the impact of DSD parameters on kinetic energy estimation,power-law KE_(time)-R and KE_(time)-Z relationships are derived based on the normalized gamma distribution.N_(W)takes precedence over μ in affecting variabilities of multiplicative coefficients,especially for KE_(time)-R relationship where the multiplicative coefficient is proportional to N_(W)^(-0.287).It should be noted that although the proportion of CR occurring throughout the summer is small,raindrops with lower N_(W) and larger Dmwill generate higher KE_(time),which will bring a higher potential risk of soil erosion in semi-arid regions over IMP.展开更多
Seasonal variations of rainfall microphysics in East China are investigated using data from the observations of a twodimensional video disdrometer and a vertically pointing micro rain radar. The precipitation and rain...Seasonal variations of rainfall microphysics in East China are investigated using data from the observations of a twodimensional video disdrometer and a vertically pointing micro rain radar. The precipitation and rain drop size distribution(DSD) characteristics are revealed for different rain types and seasons. Summer rainfall is dominated by convective rain,while during the other seasons the contribution of stratiform rain to rainfall amount is equal to or even larger than that of convective rain. The mean mass-weighted diameter versus the generalized intercept parameter pairs of convective rain are plotted roughly around the "maritime" cluster, indicating a maritime nature of convective precipitation throughout the year in East China. The localized rainfall estimators, i.e., rainfall kinetic energy–rain rate, shape–slope, and radar reflectivity–rain rate relations are further derived. DSD variability is believed to be a major source of diversity of the aforementioned derived estimators. These newly derived relations would certainly improve the accuracy of rainfall kinetic energy estimation, DSD retrieval, and quantitative precipitation estimation in this specific region.展开更多
The characteristics of raindrop size distribution （DSD） over the Tibetan Plateau and southern China are studied in this paper, using the DSD data from April to August 2014 collected by HSC-PS32 disdrometers in Nagqu...The characteristics of raindrop size distribution （DSD） over the Tibetan Plateau and southern China are studied in this paper, using the DSD data from April to August 2014 collected by HSC-PS32 disdrometers in Nagqu and Yangjiang, com- prising a total of 9430 and 63661-rain raindrop spectra, respectively. The raindrop spectra, characteristics of parameter variations with rainfall rate, and the relationships between reflectivity factor （Z） and rainfall rate （R） are analyzed, as well as their DSD changes with precipitation type and rainfall rate. The results show that the average raindrop spectra appear to be one-peak curves, the number concentration for larger drops increase significantly with rainfall rate, and its value over southern China is much higher, especially in convective rain larger drops, especially for convective rain in southern China. Standardized Gamma distributions better describe DSD for All three Gamma parameters for stratiform precipitation over the Tibetan Plateau are much higher, while its shape parameter （,u） and mass-weighted mean diameter （Dm）, for convective precipitation, are less. In terms of parameter variation with rainfall rate, the normalized intercept parameter （Nw） over the Tibetan Plateau for stratiform rain increases with rainfall rate, which is opposite to the situation in convective rain. The/1 over the Tibetan Plateau for stratiform and convective precipitation types decreases with an increase in rainfall rate, which is opposite to the case for Dm variation. In Z-R relationships, like ＂Z = ARb＇＇, the coefficient A over the Tibetan Plateau is smaller, while its b is higher, when the rain type transfers from stratiform to convective ones. Furthermore, with an increase in rainfall rate, parameters A and b over southern China increase gradually, while A over the Tibetan Plateau decreases sub- stantially, which differs from the findings of previous studies. In terms of geographic location and climate over the Tibetan Plateau and southern China, the precipitation in the pre-flood seasons is dominated by strong convective rain, while weak convective rain occurs frequently in northern Tibet with lower humidity and higher altitude.展开更多
Microphysical characteristics of the raindrop size distribution(RSD)in Typhoon Morakot(2009) have been studied through the PARSIVEL disdrometer measurements at one site in Fujian province,China during the passage of t...Microphysical characteristics of the raindrop size distribution(RSD)in Typhoon Morakot(2009) have been studied through the PARSIVEL disdrometer measurements at one site in Fujian province,China during the passage of the storm from 7 to 10 August 2009.The time evolution of the RSD reveals different segments of the storm.Significant difference was observed in the microphysical characteristics between the outer rainband and the eyewall;the eyewall precipitation had a broader size distribution(a smaller slope) than the outer rainband and eye region.The outer rainband and the eye region produced stratiform rains while the eyewall precipitation was convective or mixed stratiform-convective.The RSD was typically characterized by a single peak distribution and well represented by the gamma distribution.The relations between the shape(μ)and slope(Λ)of the gamma distribution and between the reflectivity(Z)and rainfall rate(R)have been investigated.Based on the NW-Dm relationships,we suggest that the stratiform rain for the outer rainband and the eye region was formed by the melting of graupel or rimed ice particles,which likely originated from the eyewall clouds.展开更多
The characteristics of the raindrop size distribution(DSD)during regional freezing rain(FR)events that occur throughout the phase change(from liquid to solid)are poorly understood due to limited observations.We invest...The characteristics of the raindrop size distribution(DSD)during regional freezing rain(FR)events that occur throughout the phase change(from liquid to solid)are poorly understood due to limited observations.We investigate the evolution of microphysical parameters and the key formation mechanisms of regional FR using the DSDs from five disdrometer sites in January 2018 in the Jianghan Plain(JHP)of Central China.FR is identified via the size and velocity distribution measured from a disdrometer,the discrete Fréchet distancemethod,surface temperature,human observations,and sounding data.With the persistence of precipitation,the emergence of graupel or snowflakes significantly reduces the proportion of FR.The enhancement of this regional FR event is mainly dominated by the increase in the number concentration of raindrops but weakly affected by the diameters.To improve the accuracy of quantitative precipitation estimation for the FR event,a modified second-degree polynomial relation between the shapeμand slopeΛof gamma DSDs is derived,and a new Z-R(radar reflectivity to rain rate)relationship is developed.The mean values of mass-weighted mean diameters(D_(m))and generalized intercepts(lgN_(w))in FR are close to the stratiform results in the northern region of China.Both the melting of tiny-rimed graupels and large-dry snowflakes are a response to the formation of this regional FR process in the JHP,dominated by the joint influence of the physical mechanism of warm rain,vapor deposition,and aggregation/riming coupled with the effect of weak convective motion in some periods.展开更多
The objective of this research was to acquire a raindrop size distribution(DSDs)retrieved from C-band polarimetric radar observations scheme for the first time in south China.An observation period of the precipitation...The objective of this research was to acquire a raindrop size distribution(DSDs)retrieved from C-band polarimetric radar observations scheme for the first time in south China.An observation period of the precipitation process was selected,and the shape-slope(μ-Λ)relationship of this region was statistically analyzed using the raindrop sample observations from the two-dimensional video disdrometer(2DVD)at Xinfeng Station,Guangdong Province.Simulated data of the C-band polarimetric radar reflectivity ZHHand differential reflectivity ZDRwere obtained through scattering simulation.The simulation data were combined with DSD fitting to determine the ZDR-Λand log10(ZHH/N0)-Λrelationships.Using Xinfeng C-band polarimetric radar observations ZDRand ZHH,the raindrop Gamma size distribution parametersμ,Λ,and N0were retrieved.A scheme for using C-band polarimetric radar to retrieve the DSDs was developed.This research revealed that during precipitation process,the DSDs obtained using the C-band polarimetric radar retrieval scheme are similar to the 2DVD observations,the precipitation characteristics of rainfall intensity(R),mass-weighted mean diameter(Dm)and intercept parameter(Nw)with time obtained by radar retrieval are basically consistent with the observational results of the 2DVD.This scheme establishes the relationship between the observations of the C-band polarimetric radar and the physical quantities of the numerical model.This method not only can test the prediction of the model data assimilation system on the convective scale and determine error sources,but also can improve the microphysical precipitation processes analysis and radar quantitative precipitation estimation.The present research will facilitate radar data assimilation in the future.展开更多
AIM：To provide a side-by-side analysis of the summary of safety and effectiveness data（SSED）submitted to the FDA for the KAMRA and Raindrop corneal inlays for the correction of presbyopia.METHODS：SSED reports subm...AIM：To provide a side-by-side analysis of the summary of safety and effectiveness data（SSED）submitted to the FDA for the KAMRA and Raindrop corneal inlays for the correction of presbyopia.METHODS：SSED reports submitted to the FDA for KAMRA and Raindrop were compared with respect to loss of corrected distance visual acuity（CDVA）,adverse event rates,induction of astigmatism,retention of contrast sensitivity,stability of manifest refractive spherical equivalent（MRSE）,and achieved monocular uncorrected near visual acuity（UNVA）at 24mo.RESULTS：Totally 442/508 of KAMRA patients and344/373 Raindrop patients remained enrolled in the clinical trials at 24mo.The proportion of KAMRA and Raindrop patients who lost≥2 lines of CDVA at 24mo was 3.4%and1%,respectively.The adverse event rate was comparable between the devices.No significant inductions of astigmatism were noted.Both technologies induced a transient myopic shift in MRSE followed by a hyperopic shift and subsequent stabilization.Totally 87%of KAMRA and 98%of Raindrop patients attained a monocular UNVA of J5（20/40）or better at 24mo,28%of KAMRA and 67%of Raindrop patients attained a monocular UNVA of J1（20/20）or better at 24mo.CONCLUSION：Both devices can be considered safe and effective,however,the results of corneal inlay implantation are mixed,and long-term patient satisfaction will likely depend on subjective expectations about the capabilities of the inlays.Variability in surgical technique and postoperative care within and between the two clinical trials diminishes the comparative power of this article.展开更多
While heavy rainfall frequently takes place in southern China during summer monsoon seasons,quantitative precipitation forecast skills are relatively poor.Therefore,detailed knowledge about the raindrop size distribut...While heavy rainfall frequently takes place in southern China during summer monsoon seasons,quantitative precipitation forecast skills are relatively poor.Therefore,detailed knowledge about the raindrop size distribution(DSD)is useful in improving the quantitative precipitation estimation and forecast.Based on the data during 2018-2022 from 86stations in a ground-based optical disdrometer measurement network,the characteristics of the DSD in Guangdong province are investigated in terms of the particle size distribution(N(D)),mass-weighted mean diameter(Dm) and other integral DSD parameters such as radar reflectivity(Z),rainfall rate(R) and liquid water content(LWC).In addition,the effects of geographical locations,weather systems(tropical cyclones,frontal systems and the summer monsoon) and precipitation types on DSD characteristics are also considered.The results are shown as follows.1) Convective precipitation has a broader N(D) and larger mean particle diameter than the stratiform precipitation,and the DSD observations in Guangdong are consistent with the three-parameter gamma distribution.The relationships between the Z and R for stratiform and convective precipitation are also derived for the province,i.e.,Z=332.34 R1.32and Z=366.26R1.42which is distinctly different from that of the Next-generation Weather Radar(NEXRAD) Z-R relationship in United States.2) In the rainy season(April-September),the Dm, R and LWC are larger than those in the dry season(OctoberMarch).Moreover the above parameters are larger,especially in mid-May,which is the onset of the South China Sea summer monsoon.3) The spatial analysis of DSD shows that the coastal station observations indicate a smaller Dmand a larger normalized intercept parameter(log10Nw),suggestive of maritime-like rainfall.Dmis larger and log10Nwis smaller in the inland area,suggestive of continental-like rainfall.4) Affected by such weather systems as the tropical cyclone,frontal system and summer monsoon,the DSD shows characteristics with distinct differences.Furthermore,frontal system rainfall tends to present a continental-like rainfall,tropical cyclone rainfall tends to have a maritime-like rainfall,and summer monsoon rainfall characteristic are between maritime-and continental-like cluster(raindrop concentration and diameter are higher than continental cluster and maritime cluster,respectively.)展开更多
The diurnal variation in the vertical structure of the raindrop size distribution(RSD)associated with stratiform rain at Kototabang,West Sumatra(0.20°S,100.32°E),was investigated using micro rain radar(MRR)o...The diurnal variation in the vertical structure of the raindrop size distribution(RSD)associated with stratiform rain at Kototabang,West Sumatra(0.20°S,100.32°E),was investigated using micro rain radar(MRR)observations from January 2012 to August 2016.Along with the MRR data,the RSD from an optical disdrometer and vertical profile of precipitation from the Tropical Rainfall Measuring Mission were used to establish the microphysical characteristics of diurnal rainfall.Rainfall during 0000–0600 LST and 1800–2400 LST had a lower concentration of small drops and a higher concentration of large drops when compared to rainfall during the daytime(0600–1800 LST).The RSD stratified on the basis of rain rate(R)showed a lower total concentration of drops and higher mass-weighted mean diameter in 0000–0600 LST and1800–2400 LST than in the daytime.During the daytime,the RSD is likely governed by a riming process that can be seen from a weak bright band(BB).On the other hand,during 0000–0600 LST and 1800–2400 LST,the BB was stronger and the rainfall was associated with a higher concentration of midsize and large drops,which could be attributed to more active aggregation right above the melting layer with minimal breakup.Diurnal variation in the vertical profile of RSD led to a different radar reflectivity(Z)–R relationship in the rain column,in which Z during the periods 0000–0600 LST and1800–2400 LST was larger than at the other times,for the same R.展开更多
Simulation results of the WDM6 scheme and the Thompson scheme,both of which are commonly-used double-moment bulkmicrophysics schemes,are compared within theWeather Research and Forecasting model.The purpose of the com...Simulation results of the WDM6 scheme and the Thompson scheme,both of which are commonly-used double-moment bulkmicrophysics schemes,are compared within theWeather Research and Forecasting model.The purpose of the comparison is to study the difference in the aspects of the warm-rain hydrometeor number concentrations,the droplet size distributions,and the budgets of the rain mixing ratio and number concentration.It is found that the WDM6 scheme overestimates the ratio and the amount of large precipitation,and underestimates those of small precipitation,compared to the Thompson scheme.The cloud number concentration(CNC)predicted in the WDM6 scheme is one to three orders ofmagnitude smaller than that of the Thompson scheme,which is set to the specific valueof CNC.The cloud droplet spectra of the WDM6 scheme are broader.The WDM6 scheme produces a larger rain number concentration and smaller mass mean diameter of raindrops under the influence of both warm and cold rain processes—specifically,autoconversion and melting of snow and graupel.The WDM6 scheme produces a larger autoconversion rate and smaller total melting rate of snow and graupel than the Thompson scheme in the rain mixing ratio budget.The sign of the difference in the rain-cloud collection varieswith region,and the rain-cloud collection process together with evaporation of rain have a major influence on the sign of the surface precipitation difference between the two schemes.展开更多
In the issue of rainfall estimation by radar through the necessary relationship between radar reflectivity Z and rain rate R (Z-R), the main limitation is attributed to the variability of this relationship. Indeed, se...In the issue of rainfall estimation by radar through the necessary relationship between radar reflectivity Z and rain rate R (Z-R), the main limitation is attributed to the variability of this relationship. Indeed, several pre-vious studies have shown the great variability of this relationship in space and time, from a rainfall event to another and even within a single rainfall event. Recent studies have shown that the variability of raindrop size distributions and thereby Z-R relationships is therefore, more the result of complex dynamic, thermody-namic and microphysical processes within rainfall systems than a convective/stratiform classification of the ground rainfall signature. The raindrop number and size at ground being the resultant of various processes mentioned above, a suitable approach would be to analyze their variability in relation to that of Z-R relation-ship. In this study, we investigated the total raindrop concentration number NT and the median volume di-ameter D0 used in numerous studies, and have shown that the combination of these two ‘observed’ parame-ters appears to be an interesting approach to better understand the variability of the Z-R relationships in the rainfall events, without assuming a certain analytical raindrop size distribution model (exponential, gamma, or log-normal). The present study is based on the analysis of disdrometer data collected at different seasons and places in Africa, and aims to show the degree of the raindrop size and number implication in regard to the Z-R relationships variability.展开更多
Freezing rain(FZR)presents significant risks to energy,transportation,and agriculture,leading to substantial economiclossesandcasualties,particularlyinsouthwestern,central,andeasternChina,withonlyoccasionaloccurrences...Freezing rain(FZR)presents significant risks to energy,transportation,and agriculture,leading to substantial economiclossesandcasualties,particularlyinsouthwestern,central,andeasternChina,withonlyoccasionaloccurrences in northern China.This study investigates an extreme,large-scale FZR event that occurred during 8–9 November 2021 in Heilongjiang Province of Northeast China,marking the region’s most intense FZR since 1958.Surface station observations revealed distinct characteristics of the FZR,and the stations were classified into three types by using the k-means clustering:stations with continuous FZR(FZR_Con),stations with FZR of mixed hydrometeor types(FZR_Mix),and stations with FZR transitioning to rain(FZR_Rain).Vertical atmospheric temperature and humidity profiles significantly influenced the raindrop size distribution(DSD)for the three station types.All three station types exhibited an inversion layer in the upper atmosphere,though they formed through two distinct mechanisms:(1)the supercooled warm rain mechanism and(2)the melting mechanism.This study found that the massweighted mean diameters(D--m)were larger than those observed in FZR events in central China and in stratiform rain in northern and northwestern China.FZR_Mix,which formed through the supercooled warm rain mechanism,exhibited the largest D_(m) among the three types.In contrast,FZR_Con and FZR_Rain formed through the melting mechanism,involving the melting of ice crystals and snow particles.The drier refreezing layer in FZR_Rain,compared to FZR_Con,resulted in a lower normalized number concentration(N_(w))and a larger D_(m).Positive exponential relationships between D_(m) and R(precipitation rate),as well as N_(w) and R,across all FZR types,highlighting dominant role of microphysical processes such as collision and coalescence.Variations in the gamma distribution parameters—shape(μ)and slope(λ)—as well as in the radar Z–R relationships among the FZR types further underscore differences in the microphysical processes and regional precipitation characteristics.This study enhances our understanding of the macro-and microphysical properties of FZR formed through different mechanisms,providing valuable reference for improved radar-based precipitation estimation in mid-and high-latitude regions.展开更多
Knowledge of raindrop size distribution(RSD)is essential for understanding microphysical processes occurring within cloud and precipitation systems,as well as for enhancing the capabilities of numerical models and rad...Knowledge of raindrop size distribution(RSD)is essential for understanding microphysical processes occurring within cloud and precipitation systems,as well as for enhancing the capabilities of numerical models and radar-based quantitative precipitation estimation(QPE).However,observation and study of RSD,especially its temporal and spatial variability,remain quite limited in specific regions.One such region is Southeast China.In this paper,four years of disdrometer data from a south coastal plain site(CPS)and a north hilly inland site(HIS)in the Fujian Province of Southeast China are analyzed and compared to elucidate the characteristics and discrepancies of RSD between these two distinct climatological sites.On this basis,empirical relations between the parameters of Gamma distribution and between radar reflectivity factor(Z)and rain rate(R)are proposed.The results are summarized as follows.(1)In the cases of light to moderate rains,HIS exhibits a higher(lower)concentration of small-size(midsize and large)raindrops with diameters of D<1 mm(1≤3 and D≥3 mm),compared to CPS.Conversely,as the rain intensity increases,the raindrop concentrations across all size categories at CPS gradually exceed those at HIS.(2)RSDs at both sites broaden and exhibit elevated concentrations across most diameter categories as the rain rate increases.(3)For rainfalls with rain rates below 5 mm h^(-1),collision and coalescence dominate,resulting in unimodal rain spectra at both sites;whereas for stronger rainfalls,breakup intensifies,leading to the development of bimodal rain spectra.(4)HIS experiences more stratiform rains but fewer,weaker convective rains than CPS.Stratiform RSD at HIS possesses more small and large raindrops but fewer midsize raindrops compared to CPS,whereas convective RSD at CPS possesses higher concentrations across all diameter categories.(5)Accordingly,specific Z–R relations at these two sites are proposed and validated for two real cases,demonstrating that the accuracy of radar QPE is effectively improved based on the proposed Z–R relations.展开更多
Based on the stochastic collision-coalescence equation for cloud droplets and the definition of the autoconversion rate from cloud droplets to raindrops(ARCR),this study analyzes and derives an ARCR equation from the ...Based on the stochastic collision-coalescence equation for cloud droplets and the definition of the autoconversion rate from cloud droplets to raindrops(ARCR),this study analyzes and derives an ARCR equation from the collision-coalescence process.This equation narrows the integration range of the stochastic collision-coalescence equation,providing a theoretical basis for accurately and efficiently calculating the ARCR.Utilizing the results of the turbulent collision kernel and turbulent collision efficiency,as well as the ARCR equation,an accurate and efficient model for the ARCR was established.Modeling results indicate the following:(1)The ARCR increases with the enhancement of turbulence.The rate of increase was fastest when the turbulent dissipation rate was between 0 and 20 cm^(2)s^(-3),slower when it was between 20 and 50 cm^(2)s^(-3),and intermediate when it was between 50 and 500 cm^(2)s^(-3).(2)Compared to the case without turbulence,the ARCR increased by approximately 20% when the turbulent dissipation rate was 100 cm^(2)s^(-3),and by over 100% when it was 500 cm^(2)s^(-3).Therefore,turbulence has a significant impact on the ARCR only when the turbulent dissipation rate exceeds 100 cm^(2)s^(-3).(3)The influence of turbulence on ARCR results increases with an increase in cloud water content.When there was no turbulence and the cloud water content exceeded 0.68 g m^(-3),a strong linear relationship existed between cloud water content and the ARCR.(4)The effect of turbulence on the ARCR results decreases rapidly with an increase in the cloud droplet number concentration.(5)The impact of turbulence on the ARCR becomes stronger with a decrease in the shape parameter,which corresponds to the increase in the relative dispersion of the cloud droplet spectrum(i.e.,as the cloud droplet spectrum broadens).展开更多
Mêdog and Nagqu are two typical regions of the Tibetan Plateau with different geographical locations and climate regimes.These differences may lead to discrepancies in the raindrop size distributions(DSDs)and pre...Mêdog and Nagqu are two typical regions of the Tibetan Plateau with different geographical locations and climate regimes.These differences may lead to discrepancies in the raindrop size distributions(DSDs)and precipitation microphysical processes between the two regions.This paper investigates discrepancies in the DSDs using disdrometer data obtained during the rainy season in Mêdog and Nagqu.The DSD characteristics are studied under five different rainfall rate categories and two precipitation types(stratiform and convective).For the total datasets,the number concentrations of drops with diameters D>0.6(D<0.6)mm are higher(lower)in Nagqu than in Mêdog.The fitted normalized gamma distributions of the averaged DSDs for the five rainfall rate categories show that Nagqu has a larger(lower)mass-weighted mean diameter D_(m)(normalized intercept parameter,lgNw)than Mêdog does.The difference in D_(m)between Nagqu and Mêdog increases with the rainfall rate.Convective clusters in Nagqu could be identified as continental-like,while convective precipitation in Mêdog could be classified as maritime-like.The relationships between the shape factorμand slope parameterΛof the gamma distribution model,the radar reflectivity Z,and the rainfall rate R are also derived.Furthermore,the possible causative mechanism for the notable DSD variation between the two regions during the rainy season is illustrated using reanalysis data and automated weather station observations.Cold rain processes are mainly responsible for the lower concentrations of larger drops observed in Nagqu,whereas warm rain prevails in Mêdog,producing abundant small drops.展开更多
Characteristics of raindrop size distribution during summer are studied by using the data from six Parsivel disdrometers located in the northeastern Tibetan Plateau.The analysis focuses on convective and stratiform pr...Characteristics of raindrop size distribution during summer are studied by using the data from six Parsivel disdrometers located in the northeastern Tibetan Plateau.The analysis focuses on convective and stratiform precipitation at high altitudes from 2434 m to 4202 m.The results show that the contribution of stratiform and convective precipitation with rain rate between 1≤R<5 mm h^(-1)to the total precipitation increases with altitude,and the raindrop scale and number concentration of convective precipitation is larger than that for stratiform precipitation.The droplet size spectra of both stratiform and convective precipitation shows a single peak with a peak particle size between 0.31–0.50 mm,and they have essentially the same peak particle size and number concentration at the same altitude.The maximum spectral widths of stratiform clouds are between 4 mm and 5 mm,while those of convective clouds range from 4 mm to 8 mm.The Gamma distribution is more suitable than the Marshall-Palmer distribution in terms of the actual raindrop spectrum distribution.The stratiform precipitation particles are smaller with higher number concentration,while the opposite is true for the convective precipitation particles.The convective precipitation particles drop faster than stratiform precipitation particles when the particle size exceeds 2 mm,and the falling velocity of raindrops after standard curve fitting is underestimated during the observation period.Moreover,conventional radar estimation methods would underestimate the precipitation in the Northeastern Tibetan Plateau.展开更多
In this study,a regional Parsivel OTT disdrometer network covering urban Zhengzhou and adjacent areas is employed to investigate the temporal-spatial variability of raindrop size distributions(DSDs)in the Zhengzhou ex...In this study,a regional Parsivel OTT disdrometer network covering urban Zhengzhou and adjacent areas is employed to investigate the temporal-spatial variability of raindrop size distributions(DSDs)in the Zhengzhou extreme rainfall event on 20 July 2021.The rain rates observed by disdrometers and rain gauges from six operational sites are in good agreement,despite significant site-to-site variations of 24-h accumulated rainfall ranging from 198.3 to 624.1 mm.The Parsivel OTT observations show prominent temporal-spatial variations of DSDs,and the most drastic change was registered at Zhengzhou Station where the record-breaking hourly rainfall of 201.9 mm over 1500-1600 LST(local standard time)was reported.This hourly rainfall is characterized by fairly high concentrations of large raindrops,and the mass-weighted raindrop diameter generally increases with the rain rate before reaching the equilibrium state of DSDs with the rain rate of about 50 mm h^(−1).Besides,polarimetric radar observations show the highest differential phase shift(K_(dp))and differential reflectivity(Z_(dr))near surface over Zhengzhou Station from 1500 to 1600 LST.In light of the remarkable temporal-spatial variability of DSDs,a reflectivity-grouped fitting approach is proposed to optimize the reflectivity-rain rate(Z-R)parameterization for radar quantitative precipitation estimation(QPE),and the rain gauge measurements are used for validation.The results show an increase of mean bias ratio from 0.57 to 0.79 and a decrease of root-mean-square error from 23.69 to 18.36 for the rainfall intensity above 20.0 mm h^(−1),as compared with the fixed Z-R parameterization.This study reveals the drastic temporal-spatial variations of rain microphysics during the Zhengzhou extreme rainfall event and warrants the promise of using reflectivity-grouped fitting Z-R relationships for radar QPE of such events.展开更多
基金National Natural Science Foundation of China(U2242203, 41975138, 42075086, 42275008)Guangdong Basic and Applied Basic Research Foundation (2023A1515011971)Science Technology Research Program of Guangdong Meteorological Service (GRMC2021Q01)。
文摘The raindrop size distribution(DSD) is a significant characteristic of precipitation physics,which plays a crucial role in improving the accuracy of radar quantitative precipitation estimation and prediction.There is an effect of atmospheric circulation and weather sy stems in South China,with frequent precipitation and differences in regional features,resulting in a limited understanding of the DSD characteristics and their impact mechanisms in the region. In this study,six ground-based two-dimensional video di sdrometers(2DVDs) were used to analyze the DSD of inland and coastal in South China during the five-year(2016-2020) monsoon seasons(April to September),ERA5 reanalysis data and MODIS cloud property products were also used to investigate the dynamics and microphysical characteristics of monsoon precipitation.Compared to inland rainfall,coastal rainfall has a higher conentration of small,medium,and diameter of less than 4.7 mm large raindrops.Considering the contributions to precipitation,the inland and coastal rainfall are dominated by convective rain,accounting for 74.8% and 84.7% of the total rainfall,respectively.The coastal rainfall has a higher the mass-weiglited mean diameter(D_(m)) value than the inland rainfall D_(m) for both the stratiform and convective rainfall.The logarithmic mean of the generalized intercept parameter(log_(10)N_(w)) in inland stratiform rain is greater than that in coastal areas,while convective rain is relatively small.Due to the impact of precipitation types and climate conditions,The Z-R relationship between inland and coastal rainfall also shows obvious differences.Compared to inland areas,there is more frequent convective activity,relatively moist near-surface conditions,and lower cloud droplet number concentrations,which contribute to larger D_(m) of raindrops in coastal areas.This study deepens the understanding of changes in South China's coastal and inland DSD and provides support for improving numerical weather forecasting in the region.
基金supported by the National Natural Science Foundation of China(Grant Nos.42325503,42075063,42075066,and 42021004)the Hubei Provincial Natural Science Foundation and the Meteorological Innovation and Development Project of China(Grant No.2023AFD096)the Beijige Foundation of NJIAS(Grant No.BJG202304).
文摘The characteristics of summertime raindrop size distribution(DSD) and associated relations in the semi-arid region over the Inner Mongolian Plateau(IMP) were investigated,utilizing five-year continuous observations by a PARSIVEL2disdrometer in East Ujimqin County(EUC),China.It is found that only 7.94% of the 15 664 one-min precipitation samples meet classification criteria as convective rain(CR),but its contribution to the total rainfall amount is 63.87%.Notably,40.72% of the rainfall comes from large-sized raindrops(D> 3 mm),despite the fact that large-sized raindrops account for only 1.73% of the CR total number concentration.Further results show that the mean value of mass-weighted mean diameters(Dm) is larger(2.43 mm) and generalized intercepts(lgN_(W)) is lower(3.19) in CR,aligning with a "continentallike" cluster,which is mainly influenced by the joint impact of in-cloud ice-based processes and the below-cloud environmental background.Also,the empirical relationships of shape-slope(μ-Λ),radar reflectivity-rain rate(Z-R),and rainfall kinetic energy(KE_(time)-Rand KE_(time)-Z) are localized.To quantitatively analyze the impact of DSD parameters on kinetic energy estimation,power-law KE_(time)-R and KE_(time)-Z relationships are derived based on the normalized gamma distribution.N_(W)takes precedence over μ in affecting variabilities of multiplicative coefficients,especially for KE_(time)-R relationship where the multiplicative coefficient is proportional to N_(W)^(-0.287).It should be noted that although the proportion of CR occurring throughout the summer is small,raindrops with lower N_(W) and larger Dmwill generate higher KE_(time),which will bring a higher potential risk of soil erosion in semi-arid regions over IMP.
基金primarily supported by the National Key Research and Development Program of China(Grant No.2017YFC1501703)the National Natural Science Foundation of China(Grant Nos.41875053,41475015 and 41322032)+1 种基金the National Fundamental Research 973 Program of China(Grant Nos.2013CB430101 and 2015CB452800)collected by a National 973 Project(Grant No.2013CB430101)
文摘Seasonal variations of rainfall microphysics in East China are investigated using data from the observations of a twodimensional video disdrometer and a vertically pointing micro rain radar. The precipitation and rain drop size distribution(DSD) characteristics are revealed for different rain types and seasons. Summer rainfall is dominated by convective rain,while during the other seasons the contribution of stratiform rain to rainfall amount is equal to or even larger than that of convective rain. The mean mass-weighted diameter versus the generalized intercept parameter pairs of convective rain are plotted roughly around the "maritime" cluster, indicating a maritime nature of convective precipitation throughout the year in East China. The localized rainfall estimators, i.e., rainfall kinetic energy–rain rate, shape–slope, and radar reflectivity–rain rate relations are further derived. DSD variability is believed to be a major source of diversity of the aforementioned derived estimators. These newly derived relations would certainly improve the accuracy of rainfall kinetic energy estimation, DSD retrieval, and quantitative precipitation estimation in this specific region.
基金supported jointly by the China Meteorological Administration Special Public Welfare Research Fund (Grant No. GYHY201406001)the National (Key) Basic Research and Development (973) Program of China (Grant No. 2012CB417202)the National Natural Science Foundation of China (Grant No. 41175038)
文摘The characteristics of raindrop size distribution （DSD） over the Tibetan Plateau and southern China are studied in this paper, using the DSD data from April to August 2014 collected by HSC-PS32 disdrometers in Nagqu and Yangjiang, com- prising a total of 9430 and 63661-rain raindrop spectra, respectively. The raindrop spectra, characteristics of parameter variations with rainfall rate, and the relationships between reflectivity factor （Z） and rainfall rate （R） are analyzed, as well as their DSD changes with precipitation type and rainfall rate. The results show that the average raindrop spectra appear to be one-peak curves, the number concentration for larger drops increase significantly with rainfall rate, and its value over southern China is much higher, especially in convective rain larger drops, especially for convective rain in southern China. Standardized Gamma distributions better describe DSD for All three Gamma parameters for stratiform precipitation over the Tibetan Plateau are much higher, while its shape parameter （,u） and mass-weighted mean diameter （Dm）, for convective precipitation, are less. In terms of parameter variation with rainfall rate, the normalized intercept parameter （Nw） over the Tibetan Plateau for stratiform rain increases with rainfall rate, which is opposite to the situation in convective rain. The/1 over the Tibetan Plateau for stratiform and convective precipitation types decreases with an increase in rainfall rate, which is opposite to the case for Dm variation. In Z-R relationships, like ＂Z = ARb＇＇, the coefficient A over the Tibetan Plateau is smaller, while its b is higher, when the rain type transfers from stratiform to convective ones. Furthermore, with an increase in rainfall rate, parameters A and b over southern China increase gradually, while A over the Tibetan Plateau decreases sub- stantially, which differs from the findings of previous studies. In terms of geographic location and climate over the Tibetan Plateau and southern China, the precipitation in the pre-flood seasons is dominated by strong convective rain, while weak convective rain occurs frequently in northern Tibet with lower humidity and higher altitude.
基金National Natural Science Foundation of China(40730948,40830958,40921160382)National Grand Fundamental Research 973 Program of China(2009CB421502)
文摘Microphysical characteristics of the raindrop size distribution(RSD)in Typhoon Morakot(2009) have been studied through the PARSIVEL disdrometer measurements at one site in Fujian province,China during the passage of the storm from 7 to 10 August 2009.The time evolution of the RSD reveals different segments of the storm.Significant difference was observed in the microphysical characteristics between the outer rainband and the eyewall;the eyewall precipitation had a broader size distribution(a smaller slope) than the outer rainband and eye region.The outer rainband and the eye region produced stratiform rains while the eyewall precipitation was convective or mixed stratiform-convective.The RSD was typically characterized by a single peak distribution and well represented by the gamma distribution.The relations between the shape(μ)and slope(Λ)of the gamma distribution and between the reflectivity(Z)and rainfall rate(R)have been investigated.Based on the NW-Dm relationships,we suggest that the stratiform rain for the outer rainband and the eye region was formed by the melting of graupel or rimed ice particles,which likely originated from the eyewall clouds.
基金supported by the National Natural Science Foundation of China(Grant Nos.41875170 and 41675136)the National Key Research and Development Program of China(2018YFC1507201 and 2018YFC1507905)the Guangxi Key Research and Development Program(AB20159013)。
文摘The characteristics of the raindrop size distribution(DSD)during regional freezing rain(FR)events that occur throughout the phase change(from liquid to solid)are poorly understood due to limited observations.We investigate the evolution of microphysical parameters and the key formation mechanisms of regional FR using the DSDs from five disdrometer sites in January 2018 in the Jianghan Plain(JHP)of Central China.FR is identified via the size and velocity distribution measured from a disdrometer,the discrete Fréchet distancemethod,surface temperature,human observations,and sounding data.With the persistence of precipitation,the emergence of graupel or snowflakes significantly reduces the proportion of FR.The enhancement of this regional FR event is mainly dominated by the increase in the number concentration of raindrops but weakly affected by the diameters.To improve the accuracy of quantitative precipitation estimation for the FR event,a modified second-degree polynomial relation between the shapeμand slopeΛof gamma DSDs is derived,and a new Z-R(radar reflectivity to rain rate)relationship is developed.The mean values of mass-weighted mean diameters(D_(m))and generalized intercepts(lgN_(w))in FR are close to the stratiform results in the northern region of China.Both the melting of tiny-rimed graupels and large-dry snowflakes are a response to the formation of this regional FR process in the JHP,dominated by the joint influence of the physical mechanism of warm rain,vapor deposition,and aggregation/riming coupled with the effect of weak convective motion in some periods.
基金National Key R&D Program of China(2018YFC1507401)Science and Technology Planning Project of Guangdong Province(2017B020244002)+1 种基金National Natural Science Foundation of China(41975138,41705020)Natural Science Foundation of Guangdong Province(2019A1515010814)。
文摘The objective of this research was to acquire a raindrop size distribution(DSDs)retrieved from C-band polarimetric radar observations scheme for the first time in south China.An observation period of the precipitation process was selected,and the shape-slope(μ-Λ)relationship of this region was statistically analyzed using the raindrop sample observations from the two-dimensional video disdrometer(2DVD)at Xinfeng Station,Guangdong Province.Simulated data of the C-band polarimetric radar reflectivity ZHHand differential reflectivity ZDRwere obtained through scattering simulation.The simulation data were combined with DSD fitting to determine the ZDR-Λand log10(ZHH/N0)-Λrelationships.Using Xinfeng C-band polarimetric radar observations ZDRand ZHH,the raindrop Gamma size distribution parametersμ,Λ,and N0were retrieved.A scheme for using C-band polarimetric radar to retrieve the DSDs was developed.This research revealed that during precipitation process,the DSDs obtained using the C-band polarimetric radar retrieval scheme are similar to the 2DVD observations,the precipitation characteristics of rainfall intensity(R),mass-weighted mean diameter(Dm)and intercept parameter(Nw)with time obtained by radar retrieval are basically consistent with the observational results of the 2DVD.This scheme establishes the relationship between the observations of the C-band polarimetric radar and the physical quantities of the numerical model.This method not only can test the prediction of the model data assimilation system on the convective scale and determine error sources,but also can improve the microphysical precipitation processes analysis and radar quantitative precipitation estimation.The present research will facilitate radar data assimilation in the future.
文摘AIM：To provide a side-by-side analysis of the summary of safety and effectiveness data（SSED）submitted to the FDA for the KAMRA and Raindrop corneal inlays for the correction of presbyopia.METHODS：SSED reports submitted to the FDA for KAMRA and Raindrop were compared with respect to loss of corrected distance visual acuity（CDVA）,adverse event rates,induction of astigmatism,retention of contrast sensitivity,stability of manifest refractive spherical equivalent（MRSE）,and achieved monocular uncorrected near visual acuity（UNVA）at 24mo.RESULTS：Totally 442/508 of KAMRA patients and344/373 Raindrop patients remained enrolled in the clinical trials at 24mo.The proportion of KAMRA and Raindrop patients who lost≥2 lines of CDVA at 24mo was 3.4%and1%,respectively.The adverse event rate was comparable between the devices.No significant inductions of astigmatism were noted.Both technologies induced a transient myopic shift in MRSE followed by a hyperopic shift and subsequent stabilization.Totally 87%of KAMRA and 98%of Raindrop patients attained a monocular UNVA of J5（20/40）or better at 24mo,28%of KAMRA and 67%of Raindrop patients attained a monocular UNVA of J1（20/20）or better at 24mo.CONCLUSION：Both devices can be considered safe and effective,however,the results of corneal inlay implantation are mixed,and long-term patient satisfaction will likely depend on subjective expectations about the capabilities of the inlays.Variability in surgical technique and postoperative care within and between the two clinical trials diminishes the comparative power of this article.
基金National Natural Science Foundation of China(42075014,41975138)Natural Science Foundation of Guangdong Province(2022A1515011814,2021A1515011539,2020A1515010602)+3 种基金Open Grants of State Key Laboratory of Severe Weather(2022LASW-B15)Radar Application and Short-term Severe-weather Predictions and Warnings Technology Program(GRMCTD202002)Key Scientific and Technological Research Project of GRMC(GRMC2020Z03)Water Resource Science and Technology Innovation Program of Guangdong Province(2022-02)。
文摘While heavy rainfall frequently takes place in southern China during summer monsoon seasons,quantitative precipitation forecast skills are relatively poor.Therefore,detailed knowledge about the raindrop size distribution(DSD)is useful in improving the quantitative precipitation estimation and forecast.Based on the data during 2018-2022 from 86stations in a ground-based optical disdrometer measurement network,the characteristics of the DSD in Guangdong province are investigated in terms of the particle size distribution(N(D)),mass-weighted mean diameter(Dm) and other integral DSD parameters such as radar reflectivity(Z),rainfall rate(R) and liquid water content(LWC).In addition,the effects of geographical locations,weather systems(tropical cyclones,frontal systems and the summer monsoon) and precipitation types on DSD characteristics are also considered.The results are shown as follows.1) Convective precipitation has a broader N(D) and larger mean particle diameter than the stratiform precipitation,and the DSD observations in Guangdong are consistent with the three-parameter gamma distribution.The relationships between the Z and R for stratiform and convective precipitation are also derived for the province,i.e.,Z=332.34 R1.32and Z=366.26R1.42which is distinctly different from that of the Next-generation Weather Radar(NEXRAD) Z-R relationship in United States.2) In the rainy season(April-September),the Dm, R and LWC are larger than those in the dry season(OctoberMarch).Moreover the above parameters are larger,especially in mid-May,which is the onset of the South China Sea summer monsoon.3) The spatial analysis of DSD shows that the coastal station observations indicate a smaller Dmand a larger normalized intercept parameter(log10Nw),suggestive of maritime-like rainfall.Dmis larger and log10Nwis smaller in the inland area,suggestive of continental-like rainfall.4) Affected by such weather systems as the tropical cyclone,frontal system and summer monsoon,the DSD shows characteristics with distinct differences.Furthermore,frontal system rainfall tends to present a continental-like rainfall,tropical cyclone rainfall tends to have a maritime-like rainfall,and summer monsoon rainfall characteristic are between maritime-and continental-like cluster(raindrop concentration and diameter are higher than continental cluster and maritime cluster,respectively.)
基金supported by the 2019 Basic Research Grants from the Ministry of ResearchTechnology and Higher Education(Grant No.T/3/UN.16.17/PT.01.03/PD-Kebencanaan/2019)。
文摘The diurnal variation in the vertical structure of the raindrop size distribution(RSD)associated with stratiform rain at Kototabang,West Sumatra(0.20°S,100.32°E),was investigated using micro rain radar(MRR)observations from January 2012 to August 2016.Along with the MRR data,the RSD from an optical disdrometer and vertical profile of precipitation from the Tropical Rainfall Measuring Mission were used to establish the microphysical characteristics of diurnal rainfall.Rainfall during 0000–0600 LST and 1800–2400 LST had a lower concentration of small drops and a higher concentration of large drops when compared to rainfall during the daytime(0600–1800 LST).The RSD stratified on the basis of rain rate(R)showed a lower total concentration of drops and higher mass-weighted mean diameter in 0000–0600 LST and1800–2400 LST than in the daytime.During the daytime,the RSD is likely governed by a riming process that can be seen from a weak bright band(BB).On the other hand,during 0000–0600 LST and 1800–2400 LST,the BB was stronger and the rainfall was associated with a higher concentration of midsize and large drops,which could be attributed to more active aggregation right above the melting layer with minimal breakup.Diurnal variation in the vertical profile of RSD led to a different radar reflectivity(Z)–R relationship in the rain column,in which Z during the periods 0000–0600 LST and1800–2400 LST was larger than at the other times,for the same R.
基金sponsored by the National Natural Science Foundation of China [grant number 41530427]
文摘Simulation results of the WDM6 scheme and the Thompson scheme,both of which are commonly-used double-moment bulkmicrophysics schemes,are compared within theWeather Research and Forecasting model.The purpose of the comparison is to study the difference in the aspects of the warm-rain hydrometeor number concentrations,the droplet size distributions,and the budgets of the rain mixing ratio and number concentration.It is found that the WDM6 scheme overestimates the ratio and the amount of large precipitation,and underestimates those of small precipitation,compared to the Thompson scheme.The cloud number concentration(CNC)predicted in the WDM6 scheme is one to three orders ofmagnitude smaller than that of the Thompson scheme,which is set to the specific valueof CNC.The cloud droplet spectra of the WDM6 scheme are broader.The WDM6 scheme produces a larger rain number concentration and smaller mass mean diameter of raindrops under the influence of both warm and cold rain processes—specifically,autoconversion and melting of snow and graupel.The WDM6 scheme produces a larger autoconversion rate and smaller total melting rate of snow and graupel than the Thompson scheme in the rain mixing ratio budget.The sign of the difference in the rain-cloud collection varieswith region,and the rain-cloud collection process together with evaporation of rain have a major influence on the sign of the surface precipitation difference between the two schemes.
文摘In the issue of rainfall estimation by radar through the necessary relationship between radar reflectivity Z and rain rate R (Z-R), the main limitation is attributed to the variability of this relationship. Indeed, several pre-vious studies have shown the great variability of this relationship in space and time, from a rainfall event to another and even within a single rainfall event. Recent studies have shown that the variability of raindrop size distributions and thereby Z-R relationships is therefore, more the result of complex dynamic, thermody-namic and microphysical processes within rainfall systems than a convective/stratiform classification of the ground rainfall signature. The raindrop number and size at ground being the resultant of various processes mentioned above, a suitable approach would be to analyze their variability in relation to that of Z-R relation-ship. In this study, we investigated the total raindrop concentration number NT and the median volume di-ameter D0 used in numerous studies, and have shown that the combination of these two ‘observed’ parame-ters appears to be an interesting approach to better understand the variability of the Z-R relationships in the rainfall events, without assuming a certain analytical raindrop size distribution model (exponential, gamma, or log-normal). The present study is based on the analysis of disdrometer data collected at different seasons and places in Africa, and aims to show the degree of the raindrop size and number implication in regard to the Z-R relationships variability.
基金Supported by the Hubei Provincial Natural Science Foundation and Meteorological Innovation and Development Project of China(2023AFD096,2022CFD122,and 2023AFD100)Science and Technology Development Fund of Hubei Meteorological Bureau(2023Y18)+3 种基金Qinghai Province 2023 Key R&D and Transformation Plan(2023-SF-111)Special Program for Innovation and Development of China Meteorological Administration(CXFZ2022J010)Natural Science Foundation of Wuhan(2024020901030454)CMA Meteorological Observation Centre Field Experiment Project in 2024(GCSYJH24-30)。
文摘Freezing rain(FZR)presents significant risks to energy,transportation,and agriculture,leading to substantial economiclossesandcasualties,particularlyinsouthwestern,central,andeasternChina,withonlyoccasionaloccurrences in northern China.This study investigates an extreme,large-scale FZR event that occurred during 8–9 November 2021 in Heilongjiang Province of Northeast China,marking the region’s most intense FZR since 1958.Surface station observations revealed distinct characteristics of the FZR,and the stations were classified into three types by using the k-means clustering:stations with continuous FZR(FZR_Con),stations with FZR of mixed hydrometeor types(FZR_Mix),and stations with FZR transitioning to rain(FZR_Rain).Vertical atmospheric temperature and humidity profiles significantly influenced the raindrop size distribution(DSD)for the three station types.All three station types exhibited an inversion layer in the upper atmosphere,though they formed through two distinct mechanisms:(1)the supercooled warm rain mechanism and(2)the melting mechanism.This study found that the massweighted mean diameters(D--m)were larger than those observed in FZR events in central China and in stratiform rain in northern and northwestern China.FZR_Mix,which formed through the supercooled warm rain mechanism,exhibited the largest D_(m) among the three types.In contrast,FZR_Con and FZR_Rain formed through the melting mechanism,involving the melting of ice crystals and snow particles.The drier refreezing layer in FZR_Rain,compared to FZR_Con,resulted in a lower normalized number concentration(N_(w))and a larger D_(m).Positive exponential relationships between D_(m) and R(precipitation rate),as well as N_(w) and R,across all FZR types,highlighting dominant role of microphysical processes such as collision and coalescence.Variations in the gamma distribution parameters—shape(μ)and slope(λ)—as well as in the radar Z–R relationships among the FZR types further underscore differences in the microphysical processes and regional precipitation characteristics.This study enhances our understanding of the macro-and microphysical properties of FZR formed through different mechanisms,providing valuable reference for improved radar-based precipitation estimation in mid-and high-latitude regions.
基金Supported by the National Key Research and Development Program of China(2023YFC3007501)Natural Science Foundation of Fujian Province of China(2023J011337)Innovation Ability Promotion Plan Project of Chengdu University of Information Technology(KYQN202307)。
文摘Knowledge of raindrop size distribution(RSD)is essential for understanding microphysical processes occurring within cloud and precipitation systems,as well as for enhancing the capabilities of numerical models and radar-based quantitative precipitation estimation(QPE).However,observation and study of RSD,especially its temporal and spatial variability,remain quite limited in specific regions.One such region is Southeast China.In this paper,four years of disdrometer data from a south coastal plain site(CPS)and a north hilly inland site(HIS)in the Fujian Province of Southeast China are analyzed and compared to elucidate the characteristics and discrepancies of RSD between these two distinct climatological sites.On this basis,empirical relations between the parameters of Gamma distribution and between radar reflectivity factor(Z)and rain rate(R)are proposed.The results are summarized as follows.(1)In the cases of light to moderate rains,HIS exhibits a higher(lower)concentration of small-size(midsize and large)raindrops with diameters of D<1 mm(1≤3 and D≥3 mm),compared to CPS.Conversely,as the rain intensity increases,the raindrop concentrations across all size categories at CPS gradually exceed those at HIS.(2)RSDs at both sites broaden and exhibit elevated concentrations across most diameter categories as the rain rate increases.(3)For rainfalls with rain rates below 5 mm h^(-1),collision and coalescence dominate,resulting in unimodal rain spectra at both sites;whereas for stronger rainfalls,breakup intensifies,leading to the development of bimodal rain spectra.(4)HIS experiences more stratiform rains but fewer,weaker convective rains than CPS.Stratiform RSD at HIS possesses more small and large raindrops but fewer midsize raindrops compared to CPS,whereas convective RSD at CPS possesses higher concentrations across all diameter categories.(5)Accordingly,specific Z–R relations at these two sites are proposed and validated for two real cases,demonstrating that the accuracy of radar QPE is effectively improved based on the proposed Z–R relations.
基金supported by the Science and Technology Development Fund of Chinese Academy of Meteorological Sciences(CAMS)(Grant No.2024KJ001)。
文摘Based on the stochastic collision-coalescence equation for cloud droplets and the definition of the autoconversion rate from cloud droplets to raindrops(ARCR),this study analyzes and derives an ARCR equation from the collision-coalescence process.This equation narrows the integration range of the stochastic collision-coalescence equation,providing a theoretical basis for accurately and efficiently calculating the ARCR.Utilizing the results of the turbulent collision kernel and turbulent collision efficiency,as well as the ARCR equation,an accurate and efficient model for the ARCR was established.Modeling results indicate the following:(1)The ARCR increases with the enhancement of turbulence.The rate of increase was fastest when the turbulent dissipation rate was between 0 and 20 cm^(2)s^(-3),slower when it was between 20 and 50 cm^(2)s^(-3),and intermediate when it was between 50 and 500 cm^(2)s^(-3).(2)Compared to the case without turbulence,the ARCR increased by approximately 20% when the turbulent dissipation rate was 100 cm^(2)s^(-3),and by over 100% when it was 500 cm^(2)s^(-3).Therefore,turbulence has a significant impact on the ARCR only when the turbulent dissipation rate exceeds 100 cm^(2)s^(-3).(3)The influence of turbulence on ARCR results increases with an increase in cloud water content.When there was no turbulence and the cloud water content exceeded 0.68 g m^(-3),a strong linear relationship existed between cloud water content and the ARCR.(4)The effect of turbulence on the ARCR results decreases rapidly with an increase in the cloud droplet number concentration.(5)The impact of turbulence on the ARCR becomes stronger with a decrease in the shape parameter,which corresponds to the increase in the relative dispersion of the cloud droplet spectrum(i.e.,as the cloud droplet spectrum broadens).
基金the Second Tibetan Plateau Scientific Expedition and Research(STEP)program(Grant No.2019QZKK0105)the National Natural Science Foundation of China(Grant No.41775036).
文摘Mêdog and Nagqu are two typical regions of the Tibetan Plateau with different geographical locations and climate regimes.These differences may lead to discrepancies in the raindrop size distributions(DSDs)and precipitation microphysical processes between the two regions.This paper investigates discrepancies in the DSDs using disdrometer data obtained during the rainy season in Mêdog and Nagqu.The DSD characteristics are studied under five different rainfall rate categories and two precipitation types(stratiform and convective).For the total datasets,the number concentrations of drops with diameters D>0.6(D<0.6)mm are higher(lower)in Nagqu than in Mêdog.The fitted normalized gamma distributions of the averaged DSDs for the five rainfall rate categories show that Nagqu has a larger(lower)mass-weighted mean diameter D_(m)(normalized intercept parameter,lgNw)than Mêdog does.The difference in D_(m)between Nagqu and Mêdog increases with the rainfall rate.Convective clusters in Nagqu could be identified as continental-like,while convective precipitation in Mêdog could be classified as maritime-like.The relationships between the shape factorμand slope parameterΛof the gamma distribution model,the radar reflectivity Z,and the rainfall rate R are also derived.Furthermore,the possible causative mechanism for the notable DSD variation between the two regions during the rainy season is illustrated using reanalysis data and automated weather station observations.Cold rain processes are mainly responsible for the lower concentrations of larger drops observed in Nagqu,whereas warm rain prevails in Mêdog,producing abundant small drops.
基金jointly sponsored by the Second Tibetan Plateau Atmospheric Sciences Experiment(STEP)(Grant No.2019QZKK010406)the National Natural Science Foundation of China(Grant No.42165008)Natural Science Foundation of Technology Department of Qinghai Province(Grant No.2021-ZJ-745)。
文摘Characteristics of raindrop size distribution during summer are studied by using the data from six Parsivel disdrometers located in the northeastern Tibetan Plateau.The analysis focuses on convective and stratiform precipitation at high altitudes from 2434 m to 4202 m.The results show that the contribution of stratiform and convective precipitation with rain rate between 1≤R<5 mm h^(-1)to the total precipitation increases with altitude,and the raindrop scale and number concentration of convective precipitation is larger than that for stratiform precipitation.The droplet size spectra of both stratiform and convective precipitation shows a single peak with a peak particle size between 0.31–0.50 mm,and they have essentially the same peak particle size and number concentration at the same altitude.The maximum spectral widths of stratiform clouds are between 4 mm and 5 mm,while those of convective clouds range from 4 mm to 8 mm.The Gamma distribution is more suitable than the Marshall-Palmer distribution in terms of the actual raindrop spectrum distribution.The stratiform precipitation particles are smaller with higher number concentration,while the opposite is true for the convective precipitation particles.The convective precipitation particles drop faster than stratiform precipitation particles when the particle size exceeds 2 mm,and the falling velocity of raindrops after standard curve fitting is underestimated during the observation period.Moreover,conventional radar estimation methods would underestimate the precipitation in the Northeastern Tibetan Plateau.
基金Supported by the National Key Research and Development Program of China(2022YFC3003901)National Natural Science Foundation of China(42305087 and 42105141)+2 种基金Science and Technology Innovation Project for Ecosystem Construction of Zhengzhou Supercomputing Center in Henan Province(201400210800)Meteorological Joint Project of Henan Provincial Science and Technology(222103810094 and 232103810091)Basic Research Fund of Chinese Academy of Meteorological Sciences(451490 and 2023Z008).
文摘In this study,a regional Parsivel OTT disdrometer network covering urban Zhengzhou and adjacent areas is employed to investigate the temporal-spatial variability of raindrop size distributions(DSDs)in the Zhengzhou extreme rainfall event on 20 July 2021.The rain rates observed by disdrometers and rain gauges from six operational sites are in good agreement,despite significant site-to-site variations of 24-h accumulated rainfall ranging from 198.3 to 624.1 mm.The Parsivel OTT observations show prominent temporal-spatial variations of DSDs,and the most drastic change was registered at Zhengzhou Station where the record-breaking hourly rainfall of 201.9 mm over 1500-1600 LST(local standard time)was reported.This hourly rainfall is characterized by fairly high concentrations of large raindrops,and the mass-weighted raindrop diameter generally increases with the rain rate before reaching the equilibrium state of DSDs with the rain rate of about 50 mm h^(−1).Besides,polarimetric radar observations show the highest differential phase shift(K_(dp))and differential reflectivity(Z_(dr))near surface over Zhengzhou Station from 1500 to 1600 LST.In light of the remarkable temporal-spatial variability of DSDs,a reflectivity-grouped fitting approach is proposed to optimize the reflectivity-rain rate(Z-R)parameterization for radar quantitative precipitation estimation(QPE),and the rain gauge measurements are used for validation.The results show an increase of mean bias ratio from 0.57 to 0.79 and a decrease of root-mean-square error from 23.69 to 18.36 for the rainfall intensity above 20.0 mm h^(−1),as compared with the fixed Z-R parameterization.This study reveals the drastic temporal-spatial variations of rain microphysics during the Zhengzhou extreme rainfall event and warrants the promise of using reflectivity-grouped fitting Z-R relationships for radar QPE of such events.
