Variability of Raindrop Size Distribution during a Regional Freezing Rain Event in the Jianghan Plain of Central China

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.

Statistical Characteristics of Raindrop Size Distribution in the South China Monsoon Region(Guangdong Province)

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.)

Raindrop Size Distribution Measurements at High Altitudes in the Northeastern Tibetan Plateau during Summer

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.

Seasonal Variations of Observed Raindrop Size Distribution in East China

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.

Statistical Characteristics of Raindrop Size Distribution in the Tibetan Plateau and Southern China

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.

MICROPHYSICAL CHARACTERISTICS OF THE RAINDROP SIZE DISTRIBUTION IN TYPHOON MORAKOT(2009)

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.

Raindrop Size Distribution Parameters Retrieved from Xinfeng C-Band Polarimetric Radar Observations

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.

Comparative Analysis of the Characteristics of Rainy Season Raindrop Size Distributions in Two Typical Regions of the Tibetan Plateau

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.

Comparison of FDA safety and efficacy data for KAMRA and Raindrop corneal inlays

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.

Comparison of two double-moment microphysics schemes in aspects of warm-rain droplet spectra and raindrop budget

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.

Diurnal Variation in the Vertical Profile of the Raindrop Size Distribution for Stratiform Rain as Inferred from Micro Rain Radar Observations in Sumatra

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.

Understanding the Variability of Z-R Relationships Caused by Natural Variations in Raindrop Size Distributions(DSD):Implication of Drop Size and Number

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.

Raindrop Size Distributions in the Zhengzhou Extreme Rainfall Event on 20 July 2021:Temporal-Spatial Variability and Implications for Radar QPE

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.

Roles of raindrop impact in detachment and transport processes of interrill soil erosion

To date the roles of raindrop impact in sediment entrainment and transport processes of interrill soil erosion are not yet fully quantified.The objectives are to 1)evaluate the effects of raindrop impact on sediment entrainment,2)systematically quantify the relative importance of raindrop-driven and flow-driven transport,and 3)characterize sediment size distributions in different sediment transport re-gimes.A loam soil with 48.4%sand and 23%clay was packed into flumes(L × W × H:1.8 × 0.5 × 0.1 m)and subjected to intensities of 60,90,120 mm h^(-1) at gradients of 5,10,and 16°.Air filter and tarp covers were used to vary impact energy and flow length.Results show that sediment is largely entrained by raindrop impact and transported by raindrop-impacted flow.Interrill erosion consists of two composite processes:raindrop-induced detachment/entrainment and raindrop-impacted flow transport.The former includes direct detachment by raindrop impact and'flow detachment'.The latter includes raindrop-driven and flow-driven transports.The proportions between the two transports vary with slope steepness,slope length,flow depth(or flow discharge),rainfall intensity,and sediment characteristics.Raindrop-driven transport is competent but inefficient,while the opposite is true for flow-driven transport.Because raindrop impact plays dual roles in detaching soil(and/or entraining sediment)and enhancing sediment transport,a drop energy factor must be included in interrill erosion models to adequately simulate the dual roles.More studies are required to derive a drop energy function that takes into consideration the rainfall energy dissipation by canopies of various plants under natural conditions.

大型风力机叶片前缘的雨滴冲击动力学响应机制

随着近年海上风力机设计的大型化,叶片前缘的雨蚀失效问题变得愈发突出,不仅影响机组的风能转化效率,对结构的稳定运行也构成潜在威胁。采用光滑粒子流体动力学(smooth particle hydrodynamics,SPH)法研究雨滴内部的本构关系,以有限元法(finite element method,FEM)建立叶片前缘的代表性体积单元(representative volume element,RVE)模型,两者相互耦合,研究雨滴在叶片表面形成的冲击响应过程。考虑自然降雨的实际工况,建立与降雨强度相关联的雨滴尺寸模型,以及雨滴的空间分布模型;通过单雨滴的冲击仿真,研究叶片表面冲击载荷以及雨滴内部的速度分布,从而解构雨滴冲击的物理过程,并通过冲击的应力、应变场分析,为潜在损伤区提供评价;建立多雨滴冲击的仿真模型,研究冲击应力场之间的耦合作用以及涂层表面的塑性应变累积效果。研究结果表明,水锤冲击是造成塑性应变累积的关键因素,虽然横向喷射阶段的应力响应幅值小并呈现一定的无序特征,但如果存在多雨滴耦合冲击的情况,则会在耦合区内出现应力峰值,并对叶片变形和失效存在潜在影响。

2024年2月湖北省一次大范围冻雨过程的宏微观特征及形成机制初探

2024年2月长江中下游地区先后出现两次低温雨雪冰冻天气,其中第一次过程(2月1-6日)冻雨表现出量大、范围广、持续时间长、危害性强等特征。为此,基于湖北省80个国家气象站激光雨滴谱仪观测数据,结合气象要素观测资料,对此次冻雨过程进行定量判断,并对其宏微观特征进行定量分析,结果表明:(1)此次过程冻雨区主要集中在江汉平原和武汉城市圈等地,表现为液态降水维持时间长。(2)冻雨时数和冻雨量分布具有较好的一致性,其高值区均呈现西北-东南走向,冻雨时数一般在15h以上,冻雨量超过24mm;冻雨集中期在2月2-3日,此时段各区间其数浓度、液水含量、雨强和粒径站时数占比均显著高于该过程其他时段。(3)各地区平均冻雨滴谱分布呈单峰型,其峰值数密度在200mm^(-3)·mm^(-1)左右。(4)构建的Z-R关系不同于短历时、区域性冻雨过程,能较好地实现对此类冻雨定量估测降水(Quantitative Precipitation Estimation QPE)的估算。整个过程中质量加权平均直径(D_(m))和归一化截距参数(log_(10)N_(w))的平均值分别为1.07mm和3.03。(5)在水汽凝华、丛集和凇附机制的共同影响下,致密霰粒和冰晶聚合物融化形成此次冻雨过程。

Microphysical Characteristics of Rainfall Based on Long-Term Observations with a 2DVD in Yangbajain,Tibet

Raindrop size distribution(DSD)plays a crucial role in enhancing the accuracy of radar quantitative precipitation estimates in the Tibetan Plateau(TP).However,there is a notable scarcity of long-term,high-resolution observations in this region.To address this issue,long-term observations from a two-dimensional video disdrometer(2DVD)were leveraged to refine the radar and satellite-based algorithms for quantifying precipitation in the hinterland of the TP.It was observed that weak precipitation(R<1,mm h-1)accounts for 86%of the total precipitation time,while small raindrops(D<2 mm)comprise 99%of the total raindrop count.Furthermore,the average spectral width of the DSD increases with increasing rain rate.The DSD characteristics of convective and stratiform precipitation were discussed across five different rain rates,revealing that convective precipitation in Yangbajain(YBJ)exhibits characteristics similar to maritime-like precipitation.The constrained relationships between the slopeΛand shapeμ,D_(m)and N_(w)of gamma DSDs were derived.Additionally,we established a correlation between the equivalent diameter and drop axis ratio and found that raindrops on the TP attain a nearly spherical shape.Consequently,the application of the rainfall retrieval algorithms of the dual-frequency precipitation radar in the TP is improved based on the statistical results of the DSD.

伊犁河谷流域山区和平原雨滴谱特征统计研究

雨滴谱是理解降水微物理特性和定量降水估测的基础,尤其是在降水机制复杂、时空变异性大的复杂地形中。本文利用Parsivel2激光雨滴谱仪对2020-2022年夏季伊犁河谷流域山区和平原不同降水强度和不同降水类型的雨滴谱特征进行了研究。结果表明:山区和平原降水主要以小雨滴为主,对降水强度R贡献最大的主要是中雨滴。山区降水和平原降水主要出现在午后至傍晚,山区降水大中型雨滴数浓度在各时间段均高于平原。随着雨强增大,雨滴谱的谱宽和各直径档的雨滴数浓度也随之增加,山区降水的大中型粒子数浓度在小雨和大雨时明显大于平原。在相同降水强度和降水类型的情况下,山区降水具有较大的质量加权平均直径(D_(m))和较小的标准化截断参数(log_(10)N_(w))。此外,伊犁河谷流域山区和平原的对流云滴谱均倾向于“大陆性对流簇”。研究发现,两地区降水的μ-Λ关系和Z-R关系也存在显著差异,Z=300R^(1.40)的经验关系显然高估了降水量。研究结果揭示了伊犁河谷流域不同地形条件下的降水微物理特征,为后续利用雷达资料反演降水提供可靠的事实依据。

工频下导线单雨滴电晕全过程分析

输电线路电磁环境问题主要由电晕放电引起,而降雨等环境变化会加剧这一现象。该研究通过高速摄像与电晕电流测量同步测量技术,详细分析工频下导线单雨滴电晕全过程。结果表明,导线单雨滴电晕全过程可分为4个阶段,尖端放电与振动破碎放电为主要放电类型,且两种放电的上升时间及半波时间概率密度分布均服从正态分布。随电压升高,尖端放电次数占比先减小后增大,电流脉冲幅值、上升时间、半波时间呈上升趋势;振动破碎放电次数占比先增大后减小,电流脉冲幅值、上升时间呈上升趋势,半波时间呈先上升后下降趋势。雨滴半径的增大对不同放电类型的放电次数和电流脉冲特性也产生一定的影响。该研究为理解雨天输电线路的电晕损耗和可听噪声变化提供新的视角。

四川盆地降水对PM_(2.5)和PM_(10)的清除作用分析

四川盆地是中国空气污染最严重的区域之一,为研究降水对四川盆地PM_(2.5)、PM_(10)的清除作用,利用2016—2021年四川盆地90个环境监测站PM_(2.5)、PM_(10)质量浓度观测资料和17个地面气象站观测资料,首先分析了降水对四川盆地PM_(2.5)、PM_(10)空间分布的影响;然后基于描述降水前后气溶胶粒子质量浓度变化的清除率,揭示了降水强度、时长对PM_(2.5)、PM_(10)清除效果的影响;最后,利用雨滴谱分布、雨滴大小、下降末速度等雨滴谱参量计算污染物的清除系数,分析了四川盆地4次污染事件中降水对PM_(2.5)、PM_(10)的清除效果。结果表明:(1)四川盆地降水影响PM_(2.5)、PM_(10)空间分布,降水量越大、降水持续时间越长,清除率越大,清除效果越明显;(2)大雨个例中,降水持续时间大于6 h后,清除率对降水持续时间增加不敏感;(3)当雨滴直径、雨滴总个数和分钟雨强出现峰值,雨滴谱加宽变强后,PM_(2.5)、PM_(10)质量浓度快速降低;(4)清除系数对PM_(2.5)和PM_(10)质量浓度变化具有指示意义,当清除系数峰值达10 h^(-1)以上,降水对PM_(2.5)和PM_(10)清除效果显著。