Calibration of radar reflectivity measurements from the KMA operational radar network

A systematic procedure for calibrating system gain bias (so-called “calibration error”) of radar reflectivity measurements from the Korea Meteorological Administration (KMA) operational radar network is presented. First, the RJNI radar located at Jindo Island is calibrated by comparing with radar reflectivities simulated theoretically by a scattering algorithm using drop spectra collected by a disdrometer from June 19 to 29, 2009. Once the RJNI radar is calibrated, the reflectivity measurements from nearby radars are compared with the RJNI radar reflectivities to determine existing gain biases of nearby radars. This radar-radar calibration procedure was repeated with the other radars within the network. For isolating a system gain bias, echoes affected by partial beam blockage due to ground clutter and by attenuation due to precipitation were removed. The system gain biases of the RJNI and RPSN radars were ?3 and ?4.2 dB, respectively, during the experimental period. The RBRI and RDNH radars revealed relatively large biases, above ?8 dB. The other radars (RKSN, RGSN, RSSP, RKWK, RGDK, RIIA, and RMYN) revealed biases from ?6 to ?7 dB. Thus, the reflectivity measurements from all of the KMA radars were severely biased. New R-Z relations of R = 3.350 × 10^?2Z^0.624 (Z = 231.1R ^1.6) for stratiform and R=1.546 × 10^?2 Z ^0.714 (Z = 342.4R ^1.4) for convective precipitations were derived using disdrometer data. Using these R-Z relations, the radar-derived total rainfall amounts from the reflectivity measurements without calibration produced significant underestimations, compared to gauge measurements at about 80 sites, with a normalized bias of about ?56%. On the other hand, after calibrating the above system biases, the radar-derived rainfall amounts corresponded well with the gauge measurements, with a normalized bias of about ?3%. In conclusions, the radar reflectivity measurements from the KMA radar network are severely biased and the procedure presented in this study can be used to resolve the system gain biases.     

对非球形冰晶94 GHz云雷达后向散射和衰减的研究

针对94 GHz毫米波云雷达的数据处理,基于离散偶极子近似法(DDA)计算了几种非球形冰晶的后向散射及衰减效率,探讨了不同冰云模型下冰云的雷达反射率因子(Z_e)和衰减系数(k)及冰水含量(IWC,记作W)的关系。结果表明:(1)形状对冰晶的散射及衰减效率与粒子大小有关。(2)在实际的冰云中,将六角形冰晶和椭圆冰晶看做同体积的球形粒子将低估其衰减和后向散射。将聚合物冰晶看做等体积球形,将高估其后向散射及衰减,子弹花冰晶的后向散射与同体积的球形相比有减小也有增大,但是衰减比同体积球形的小。(3)冰云模型对Z_e-k、Z_e-W关系具有较大影响,假设滴谱相同的条件下,得到了具体冰云模型下对应Z_e-k、Z_e-W关系的系数。这些探讨为我国W波段云雷达的数据处理提供了参考。     

青藏高原对流云的偏振雷达观测研究

利用可移动式C波段双偏振雷达（C-POL）,以及那曲新一代天气雷达（CINRAD/CD）于2014年7月30日和8月5日在西藏那曲地区的观测资料,并通过双多普勒雷达风场反演、偏振雷达相态识别,清晰展示了这两次高原冰雹云发生发展的动力、微物理、热力结构特征。结果表明:青藏高原地区的对流云多在午后出现,水平及垂直尺度不大,但是对流云发生频繁、生消快,一般持续几十分钟。从RHI扫描的水平偏振反射率因子（Z_H）、差分反射率因子（Z_DR）,以及反演的相态（Class）分布上可以明显看出,粒子跟随"0线"抬高,不断增长,回波强度也越来越大,并最终超过主上升气流从另一侧降落,形成冰雹墙的整个动力与微物理过程。从连续时次的RHI上还观测到一次对流单体发生、发展过程中相态从湿雪到冰雹的变化,单体刚刚触发时,回波高度不高,强度还很弱,但是却出现成片的湿雪区域,说明上升气流非常旺盛,将本来落到0℃层以下的未完全融化的湿雪重新带到0℃层以上,通过凝华、凇附、攀附等物理过程,仅仅10多分钟,这些湿雪就能够迅速增长成为冰雹。这些湿雪重新凝结过程中,释放潜热,进一步促进了不稳定结构,加强了上升气流和下沉气流。因此,如果某个刚刚生成的弱回波区域内,在融化层以上出现大量的湿雪,往往预示着该区域上升气流强劲,会迅速发展成强回波单体。      

深圳S波段与X波段双偏振雷达在定量降水估计中的应用

双偏振多普勒天气雷达的一个重要应用是进行定量降水估计（QPE）,它可以获得反射率（Z_H）、差分反射率（Z_DR）和差传播相移率（K_dp）这些与降水粒子有关的信息,常用的双偏振雷达降水估计方法有基于Z_H的R（Z_H）、基于Z_H和Z_DR的R（Z_H,Z_DR）、基于K_dp的R（K_dp）和基于K_dp与Z_DR的R（K_dp,Z_DR）这4种。文中利用深圳市S波段和X波段双偏振多普勒雷达探测资料,结合高精度地形数据和雨滴谱仪观测数据,设计了基于双偏振量的定量降水估计方法:首先利用地形数据和雷达地理信息,分析了雷达的遮挡状况,形成了这两部雷达的复合平面扫描仰角信息;随后利用雨滴谱仪观测资料,使用T矩阵方法统计得到了深圳地区的上述4种降水反演方法的参数;最后设计了混合降水反演方法,基于双偏振信号（即K_dp和Z_DR）的强弱,使用不同的降水反演方法进行定量降水估计。基于12个降水个例,利用各反演方法产生的定量降水估计结果与雨量计观测资料比较。结果表明,混合降水反演方法在降水反演的准确度和稳定性上均优于任何一种单一定量降水估计反演方法。基于文中介绍的定量降水估计方法,使用深圳S波段和X波段雷达产生了定量降水估计产品,并与深圳目前业务定量降水估计产品进行对比评估。结果表明,使用本方法产生的定量降水估计产品在准确度和稳定性上要优于目前的业务产品。此外,X波段雷达的定量降水估计产品性能要略高于S波段雷达的定量降水估计产品,这说明高时、空分辨率的X波段雷达可以提高定量降水估计精度。但由于雷达扫描平面内双偏振雷达对融化层和冰区的偏振量观测与降水的关系尚未明确,因此,本方法仅适用于雷达扫描平面内液态降水区。      

毫米波测云雷达在降雪观测中的应用初步分析

本文利用毫米波云雷达联合称重式雨量计、气球探空和S波段天气雷达在北京对2015年11月三次降雪进行了观测,以2015年11月22~23日降雪过程为例,主要从降雪系统的宏观结构特征、微物理变化以及毫米波雷达在降雪探测中电磁波衰减情况、雪粒子含水量和地面降雪量估测几方面进行初步分析。结果表明:（1）毫米波云雷达具有高时空分辨率,能对降雪系统进行精细化探测,在降雪系统发展最旺盛的阶段能够通过反射率（Z）、退极化比（LDR）和径向速度（V）初步判断出云中是否含有过冷液滴;（2）降雪回波强度最大值能反映整层云系中含水量最大的区域,当最大值Z大于20 dBZ时,最大值的大小、最大值持续时间、最大值出现的高度与地面降水量成正相关,速度最大值表示云中粒子上升最大速度（速度为正时）或者粒子下落的最小速度（速度为负时）,主要分布在－0.5~2 m s?1,速度最小值表示粒子下落的最大速度,主要在－3~－1 m s?1;（3）随着高度增加反射率的垂直廓线会出现多个峰值,这是由于不同高度层风速分布不均造成的,降雪回波这种特点比降雨回波更明显;（4）对比Ka与S波段雷达反射率可知,两雷达反射率平均差值小于2.5 dBZ,Ka波段反射率略大S波段雷达反射率;（5）降雪量反演与地面降雪量仪数据对比,逐小时降雪量反演精度为20.38%,累计降雪量反演误差为6.58%,24小时累计降雪量绝对误差为1.9 mm,说明云雷达估算累计降雪量具有较高的可行性,能够很准确的反映地面实际降雪情况,当降雪系统发展旺盛时,雪粒子含水量分布在0.05~0.15 g m?3,在降雪初期或者降雪系统消散期,雪粒子含水量一般小于0.04 g m?3,能够很好地反映出整层降雪回波的雪粒子含水量。这些云雷达在降雪观测中的应用和初步分析结果可以更好的地了解降雪系统宏微观结构,为云模式的发展和人工影响天气中增雪潜力评估提供一些参考。     

河北冬季一次冷锋降雪云系微物理演变特征综合观测分析研究

利用河北省中南部地区皇寺国家观测站布设的毫米波云雷达、微雨雷达结合飞机等联合观测数据，对2019年2 月14日河北中南部地区一次冷锋降雪云系微物理演变特征进行分析，探讨雷达回波与冰雪晶粒子微结构的关系，以便更好地认识该地区自然降雪的宏微观结构特征。研究结果表明：降雪初生阶段表现为双层云结构，中云云顶高约4100 m，云底高约3600 m，低云云顶高约3100 m，云底高约200 m，中间存在一干层，3000 m以下高度粒子增长以凇附过程为主。降雪发展阶段上下两层云相接，雷达回波强度较强的时段地面降水量也较大，该时段降雪过程主要以凝华〖CD*2〗聚并增长为主。降雪后期回波强度最大值减小，云顶高降低，3000 m以下高度范围内回波强度、多普勒速度、谱宽随高度降低呈增大趋势；飞机观测结果显示，降雪消散阶段逆温层底部由于水云云层较薄，催化潜力较小,冰雪晶粒子主要位于云的中上部，随着高度降低，冰雪晶粒子在下落过程中增大，与雷达观测结果一致，毫米波云雷达和微雨雷达反射率因子随高度变化与降水粒子有效粒径之间相关系数分别为0.89和0.83, 雷达反射率因子主要受冰雪晶等大尺度粒子主导。     

A study of the microphysical processes in a numerically simulated heavy snowfall event in North China: the sensitivity of different snow intercept parameters

We performed a modeling study of the cloud processes in a heavy snowfall event occurring in North China on 20–22 December 2004. The nonhydrostatic Mesoscale Model (MM5) was used to carry out experiments with the Reisner-2 explicit microphysical parameterizations in four nested domains to test the sensitivity of simulated heavy snowfall to different snow intercept parameters. Results show that while the different intercept parameters do not significantly affect the accumulated snowfall amounts at the surface in either total amount or location, some microphysical characteristics of the modeled heavy snowfall event are impacted. The budget of cloud microphysics is analyzed to determine the dominant cloud processes. In the control experiment (CTL) with the snow intercept (N _os) specified as a function of temperature, the primary simulated hydrometeor is snow, and its mixing ratio is an order of magnitude larger than that of the other cloud species. Relative to CTL, the experiment with a fixed intercept (CON3E6) produced lower snow mixing ratios, more cloud water and graupel mixing ratios. Among the two experiments, while snowfall is slightly smaller in CON3E6, other processes like the rate of graupel fall, condensation and evaporation of cloud water, deposition and sublimation of graupel are all larger in CON3E6 than in CTL. Among CTL, CON3E6, and two more experiments (CON2E7: with a smaller fixed intercept; and NOSQS: N _os a function of snow mass mixing ratio), the budget shows that CON3E6 produces the smallest deposition and sublimation of snow, the largest deposition of cloud ice, and the largest conversion from cloud ice to snow.     

Influence of drizzle on Z–M relationships in warm clouds

This paper addresses the sensitivity of the relationships between radar reflectivity (Z) and liquid water content (M) for liquid water clouds to microphysical drizzle parameters by means of simulated radar observation at a frequency of 3 GHz of modeled cumulus clouds. A power law relationship for non drizzling clouds with water content as high as 3 gm^− 3: Z_c = 0.026 M_c^1.61 is numerically derived and agreed with previous empirical relationships relative to cumulus and stratocumulus. This relationship is then used to explore the influence of drizzle on the correlation between radar reflectively and water content. Due to their large diameters with respect to cloud droplets, drizzle sized drops dominate radar reflectivity but do not carry the cloud water content so that reflectivity and liquid water content are expected to be not correlated in clouds containing drizzle. It is shown that for congestus or extreme congestus cumuli, microphysical conditions for which the Z_c–M_c relationship can be used with a tolerance of 5 and 10% are provided whereas for humilis or mediocris cumuli, the presence of drizzle breaks down the Z_c–M_c relationship whatever the situations.     

微降水雷达测量精度分析

利用数值模拟的方法,讨论了利用微降水雷达MRR(Micro Rain Radar)雷达功率谱密度反演降水参数时,MIE散射(米散射)效应、垂直气流(包括上升气流、下沉气流)对数浓度N、雷达反射率Z、雨强I、液态含水量LWC等参数的影响。MIE散射主要影响直径为1.20~4.00 mm的粒子,MIE散射效应影响的N、Z、I、LWC偏差的平均值分别为2.74 m-3 mm-1、1.47 d BZ、0.0061 mm h~(-1)、0.0004 g m-3。下沉气流使反演液滴直径偏大,上升气流使得反演的液滴直径偏小,下沉气流的影响更大,尤其是对低层影响大于高层。例如,在300 m高度上,当液滴直径为2.67 mm时,下沉气流为2.00 m s-1时,理论上反演的直径为8.07 mm,超出了MRR探测的阈值,其相对误差值能接近200%。下沉气流使得反射率谱向大粒子方向平移,且谱型展宽;上升气流则相反。将MRR资料与同步观测的THIES雨滴谱仪数据进行比对,分析MRR资料的可靠性。选取2015年4月1日01~12时(协调世界时)山东济南的一次降水过程,将MRR在300 m高度上反演的雷达反射率因子、雨强、数浓度、中值体积直径与雨滴谱仪资料进行对比。结果表明:两种仪器探测的Z、I、N、中值体积直径D0在时间序列上都有较好的吻合度,变化趋势和幅度相近,Z、I、D0的平均偏差分别为1.19 d BZ、0.34 mm h~(-1)、0.36 mm。MRR反演的I值偏大,而粒子直径偏小,分析了产生偏差的主要原因,除了探测系统偏差、分析方法本身存在的偏差外,上升气流导致的偏差不容忽视。这些结果初步验证了微降水雷达观测的功率谱密度及其反演方法的可靠性。     

X波段双线偏振雷达回波强度衰减和地物回波识别订正

与常规雷达相比,双线偏振天气雷达在降水系统的准确探测、资料质量的提高等方面具有明显的优势,但X波段双线偏振雷达资料受衰减和地物的影响较大,需要进行必要的衰减和地物订正。本文以2010年7月中国气象局在广东阳江开展的遥感数据比对试验得到数据为例,用ZH和ZDR结合的方法对ZH进行衰减订正,用ZH和ZDR的方差识别地物回波,并利用反射率因子垂直廓线订正受地物影响的底层回波。将订正后的ZH与S波段雷达探测的ZH相比较,将订正后的ZH与KDP的散点图和拟合的KDP与ZH曲线关系对比验证。结果表明经过订正的ZH与S波段雷达探测的ZH一致性较好,与拟合曲线也更为吻合,说明方法能有效提高雷达资料的质量。     

双线偏振雷达资料在数值模式中的应用: 模拟器的构建

基于Rayleigh-Gans散射原理构造一个S波段双线偏振雷达模拟器。模拟器考虑了云冰、雪、雨和雹4种水凝物,以水凝物的混合比和数浓度以及水凝物粒子的轴比、相对介电常数、下落倾角为输入量,计算得到水平/垂直偏振反射率因子、差分反射率、比差分相位等偏振量。通过二维理想飑线模拟的试验结果表明,模拟器合理地再现了二维理想飑线系统成熟期的主要偏振特征:雹的反射率较高,差分反射率较低(又称Zdr洞);对流云区的Zdr柱;层云区的反射率和比差分相位的0℃层亮带特征;雨滴反射率与差分反射率因子的“雨线”统计特征。利用该模拟器建立了模式变量和偏振雷达观测的联系,有助于未来将偏振雷达观测资料应用于模式预报效果评估及对流尺度资料同化等方面的研究和应用。      

Statistics of the <Emphasis Type="Italic">Z</Emphasis>–<Emphasis Type="Italic">R</Emphasis> Relationship for Strong Convective Weather over the Yangtze–Huaihe River Basin and Its Application to Radar Reflectivity Data Assimilation for a Heavy Rain Event

The relationship between the radar reflectivity factor (Z) and the rainfall rate (R) is recalculated based on radar observations from 10 Doppler radars and hourly rainfall measurements at 6529 automatic weather stations over the Yangtze–Huaihe River basin. The data were collected by the National 973 Project from June to July 2013 for severe convective weather events. The Z–R relationship is combined with an empirical q_r–R relationship to obtain a new Z–q_r relationship, which is then used to correct the observational operator for radar reflectivity in the three-dimensional variational (3DVar) data assimilation system of the Weather Research and Forecasting (WRF) model to improve the analysis and prediction of severe convective weather over the Yangtze–Huaihe River basin. The performance of the corrected reflectivity operator used in the WRF 3DVar data assimilation system is tested with a heavy rain event that occurred over Jiangsu and Anhui provinces and the surrounding regions on 23 June 2013. It is noted that the observations for this event are not included in the calculation of the Z–R relationship. Three experiments are conducted with the WRF model and its 3DVar system, including a control run without the assimilation of reflectivity data and two assimilation experiments with the original and corrected reflectivity operators. The experimental results show that the assimilation of radar reflectivity data has a positive impact on the rainfall forecast within a few hours with either the original or corrected reflectivity operators, but the corrected reflectivity operator achieves a better performance on the rainfall forecast than the original operator. The corrected reflectivity operator extends the effective time of radar data assimilation for the prediction of strong reflectivity. The physical variables analyzed with the corrected reflectivity operator present more reasonable mesoscale structures than those obtained with the original reflectivity operator. This suggests that the new statistical Z–R relationship is more suitable for predicting severe convective weather over the Yangtze–Huaihe River basin than the Z–R relationships currently in use.     

THE DESIGN AND CORRECTION OF A QUANTITATIVE METHOD OF SNOW ESTIMATE BY RADAR

An optimization method is based to design a snowfall estimate method by radar for operational snow warning, and error estimation is analyzed through a case of heavy snow on March 4, 2007. Three modified schemes are developed for errors caused by temperature changes, snowflake terminal velocity, the distance from the radar and calculation methods. Due to the improvements, the correlation coefficient between the estimated snowfall and the observation is 0.66(exceeding the 99% confidence level), the average relative error is reduced to 48.74%, and the method is able to estimate weak snowfall of 0.3 mm/h and heavy snowfall above 5 mm/h. The correlation coefficient is0.82 between the estimated snowfall from the stations 50 to 100 km from the radar and the observation. The improved effect is weak when the influence of the snowflake terminal velocity is considered in those three improvement programs, which may be related to the uniform echo. The radar estimate of snow, which is classified by the distance between the sample and the radar, has the most obvious effect: it can not only increase the degree of similarity, but also reduce the overestimate and the undervaluation of the error caused by the distance between the sample and the radar.The improved algorithm further improves the accuracy of the estimate. The average relative errors are 31% and 27% for the heavy snowfall of 1.6 to 2.5 mm/h and above 2.6 mm/h, respectively, but the radar overestimates the snowfall under1.5 mm/h and underestimates the snowfall above 2.6 mm/h. Radar echo may not be sensitive to the intensity of snowfall, and the consistency shown by the error can be exploited to revise and improve the estimation accuracy of snow forecast in the operational work.     

94GHz云雷达回波及测云能力分析

重点利用英国的94 GHz Galileo测云雷达,结合35 GHz云雷达、地面雨滴谱仪、雨量计和探空资料等,分析了94 GHz 雷达的回波特征及测云能力。结果表明：（1）94 GHz云雷达能清楚反映出云及弱降水过程的云系结构变化和云内小尺度变化,可以探测到雾,雾的多普勒速度杂乱;（2）94 GHz云雷达区别于厘米波雷达的较显著的回波特征是层状云降水的0℃层亮带下面雷达反射率因子降低不明显或没有降低及0℃层亮带上面存在0℃层暗带,分别是因为雨滴较大及冰晶较大产生非瑞利散射引起的,暗带区域的宽度一般在600 m以下,暗带区域的许多冰晶聚合物最大尺度可超过3 mm,有些暗带区域的许多冰晶聚合物最大尺度可超过6.8 mm,多普勒速度及谱宽显著增大的地方是融化层顶;（3）与35 GHz测云雷达相比,由于衰减和非瑞利散射,降水时的94 GHz雷达反射率因子远小于35 GHz雷达反射率因子,使探测到的高云云顶高度偏低,但94 GHz云雷达抑制地物杂波的能力更高,在晴空低云探测方面具有优势。这些结果为中国正在研制的94 GHz云雷达回波可靠性分析提供了参考。94 GHz云雷达与其他探测手段结合,可揭示各种天气形成的物理机制,对天气预报、云物理的发展、人工影响天气、气候变化的研究均有重要意义。     

Fuzzy logic based melting layer recognition from 3 GHz dual polarization radar: appraisal with NWP model and radio sounding observations

The advent of polarimetry makes it possible to categorize hydrometeor inferences more accurately by providing detailed information of the scattering properties. In light of this, the authors have developed a fuzzy logic based system for the recognition of melting layer in the atmosphere. The fuzzy system is based on characterizing melting layer scatterers from non-melting scatterers using five crisp inputs, namely, horizontal reflectivity (Z _H), differential reflectivity (Z _DR), co-polar correlation coefficient (ρ _HV), linear depolarization ratio (LDR) and height of radar measurements (H). For the implementation of melting layer recognition, the study employs the dual polarized signatures from the 3 GHz Chilbolton Advanced Meteorological Radar (CAMRA). Furthermore, a simple but effective averaging procedure for melting level estimation from a volume RHI scan is proposed. The proposed scheme has been evaluated with Weather Research and Forecasting (WRF) model simulated and radio soundings retrieved melting level height over a total of 84 RHI scan-based bright band cases. The results confirm that the estimated melting level heights from the proposed method are in good agreement with the WRF model and radio sounding observations. The 3 GHz radar melting level height estimates correspond with the R ² and RMSE values of 0.92 and 0.24 km, respectively, when compared to the radio soundings, and 0.93 and 0.21 km, respectively, when compared to the WRF model results. Moreover, the related R ² and RMSE values are reported as 0.93 and 0.22 km respectively between the WRF and radio soundings retrievals. This implies that the downscaled WRF modelled melting level height may also be used for operational or research needs.     

张家口市崇礼的雪季与冬奥会赛期的降雪特征分析

利用张家口市崇礼1960-2014年逐日降水和天气现象资料,分析了雪季与冬奥会赛期(2月4-20日)的降雪特征。结果显示：崇礼最早降雪初日为10月13日,最迟降雪终日为4月30日,初、终雪日多年平均为11月2日和4月6日;雪季长度最长和最短分别为190 d和123 d,多年平均为156 d。雪季间最长连续无降雪时段多出现在12月末到1月下旬。冬奥会赛期前的11月上旬降雪日数少,但降雪量较大;此后各旬降雪日数、雪量差异不大。2月4-20日间平均4~5 d出现一次降雪,且主要为中小雪,出现大雪的概率极低。这些结果为冬奥会赛场充分利用降雪资源、制定赛事计划和赛事期间的气象条件预测及预报等保障提供参考依据。     

Twenty-Seven Years of Manual Fresh Snowfall Density Measurements on Whistler Mountain,British Columbia

Snow density is important information for a wide range of activities including avalanche control, marketing, building-code development, weather forecasting, and water supply forecasting. Extended recent high-quality datasets from the mountainous regions of the Pacific Northwest coastal area are rare. This paper presents a study of an unusually long and continuous (January 1990 to April 2016) manually collected dataset of fresh snowfall measurements for Whistler Mountain, British Columbia, Canada. The dataset consists of snowboard core measurements that were collected by Whistler–Blackcomb ski patrol staff twice daily for avalanche control and resort-marketing purposes. These records were collated, transcribed, quality controlled, and made computer accessible in this study. A discussion of the characteristics of the data collection site and an assessment of data reliability are presented. Two examples of the many purposes to which this high-quality dataset might be put were studied. Climatic teleconnections to winter (December–February) mean snow density were examined, which revealed a positive relationship to the quadratic form of the Pacific Decadal Oscillation pattern (i.e., PDO²). In addition, an analysis of daily snow density relationships to air mass types was performed, which suggested that higher (lower) densities are associated with maritime inflow (arctic outflow) conditions. Both of these relationships appear to be mediated by the positive correlation between snow density and air temperature.

Based on the full dataset (N?=?1275 individual snow density measurements) for all months with measured snowfall, annual snowfall season (November to May) mean snow densities ranged from 77?kg?m^?3 to 109?kg?m^?3 with an overall mean of 91?kg?m^?3, giving an overall snow-depth to water-depth ratio of 11:1.     

Characteristics of easterly-induced snowfall in Yeongdong and its relationship to air-sea temperature difference

Characteristics of snowfall episodes have been investigated for the past ten years in order to study its association with lowlevel stability and air-sea temperature difference over the East Sea. In general, the selected snowfall episodes have similar synoptic setting such as the Siberian High extended to northern Japan along with the Low passing by the southern Korean Peninsula, eventually resulting in the easterly flow in the Yeongdong region. Especially in the heavy snowfall episodes, convective unstable layers have been identified over the East sea due to relatively warm sea surface temperature (SST) about 8～10°C and specifically cold pool around 1～2 km above the surface level (ASL), which can be derived from Regional Data Assimilation and Prediction System (RDAPS), but that have not been clearly exhibited in the weak snowfall episodes. The basic mechanism to initiate snowfall around Yeongdong seems to be similar to that of lake-effect snowstorms around Great Lakes in the United States (Kristovich et al., 2003). Difference of equivalent potential temperature (θ _e ) between 850 hPa and surface as well as difference between air and sea temperatures altogether gradually began to increase in the pre-snowfall period and reached their maximum values in the course of the period, whose air (850 hPa) — sea temperature difference and snowfall intensity in case of the heavy snowfall episodes are almost larger than 20°C and 6 tims greater than the weak snowfall episodes, respectively. Interestingly, snowfall appeared to begin in case of an air-sea temperature difference exceeding over 15°C. The current analysis is overall consistent with the previous finding (Lee et al., 2012) that an instabilityinduced moisture supply to the lower atmosphere from the East sea, being cooled and saturated in the lower layer, so to speak, East Sea-Effect Snowfall (SES), would make a low-level ice cloud which eventually moves inland by the easterly flow. In addition, a longlasting synoptic characteristics and convergence-induced invigoration also appear to play the important roles in the severe snowstorms. Improvements in our understanding of mesoscale sea-effect snowstorms require detailed in-situ and remote sensing observations over and around East Sea since observations of the concurrent thermodynamic and microphysical characteristics have not been available there and this study emphasizes the importance of low level stability as quantitative estimation of moist static energy generation over the East Sea.     

近30年来我国雪量变化的初步探讨

本文根据2300多个地面气象台站资料,对近30年来我国雪量波动进行了监测与诊断研究。发现全国尺度的雪量变化趋势与全球平均气温成正相关,其年际波动与火山活动相位相反,多雪冬季与厄尼诺-南方涛动相同步。CO_2增温将加剧雪量分布的区域差异,导致北方平原、盆地积雪日数减少,青藏高原、高山地区和长江中下游降雪量增加。     

X波段双线偏振气象雷达反射率的衰减订正

X波段天气雷达的强衰减是影响其探测精度与应用推广的主要问题.本文旨在寻求适用于降水过程中对X波段双偏振雷达进行衰减订正的一种方法.在订正前先对雷达数据进行了质量控制和预处理;在分析了国内外已有订正方法的基础上,选择并改进了自适应约束算法作为雷达反射率进行衰减订正的方法;最后进行方法的效果验证.既对衰减订正前后反射率与同...