The 2001 Mesoscale Convective Systems over Iberia and the Balearic Islands

Summary This paper characterizes Mesoscale Convective Systems (MCSs) during 2001 over Iberia and the Balearic Islands and their meteorological settings. Enhanced infrared Meteosat imagery has been used to detect their occurrence over the Western Mediterranean region between June and December 2001 according to satellite-defined criteria based on the MCS physical characteristics. Twelve MCSs have been identified. The results show that the occurrence of 2001 MCSs is limited to the August–October period, with September being the most active period. They tend to develop during the late afternoon or early night, with preferred eastern Iberian coast locations and eastward migrations. A cloud shield area of 50.000 km² is rarely exceeded. When our results are compared with previous studies, it is possible to assert that though 2001 MCS activity was moderate, the convective season was substantially less prolonged than usual, with shorter MCS life cycles and higher average speeds. The average MCS precipitation rate was 3.3 mm·h⁻¹ but a wide range of values varying from scarce precipitation to intense events of 130 mm·24 h⁻¹ (6 September) were collected. The results suggest that, during 2001, MCS rainfall was the principal source of precipitation in the Mediterranean region during the convective season, but its impact varied according to the location. Synoptic analysis based on NCEP/NCAR reanalysis show that several common precursors could be identified over the Western Mediterranean Sea when the 2001 MCSs occurred: a low-level tongue of moist air and precipitable water (PW) exceeding 25 mm through the southern portion of the Western Mediterranean area, low-level zonal warm advection over 2 °C·24 h⁻¹ towards eastern Iberia, a modest 1000–850 hPa equivalent potential temperature (θ_e) difference over 20 °C located close to the eastern Iberian coast, a mid level trough (sometimes a cut-off low) over Northern Africa or Southern Spain and high levels geostrophic vorticity advection exceeding 12·10⁻¹⁰ s⁻² over eastern Iberia and Northern Africa. Finally, the results suggest that synoptic, orographic and a warm-air advection were the most relevant forcing mechanisms during 2001.     

Analysis of mesoscale convective systems in Catalonia using meteorological radar for the period 1996–2000

The aim of this paper is to show a climatology of Mesoscale Convective Systems (MCS) in the NE of the Iberian Peninsula, on the basis of meteorological radar observations. Special attention was paid to those cases that have produced heavy rainfalls during the period 1996–2000. Identification of the MCS was undertaken using two procedures. Firstly, the precipitation structures at the lowest level were recognised by means of a 2D algorithm that distinguishes between convective and non-convective contribution. Secondly, the convective cells were identified using a 3D procedure quite similar to the SCIT (Storm Cell Identification and Tracking) algorithm that looks for the reflectivity cores in each radar volume. Finally, the convective cells (3D) were associated with the 2D structures (convective rainfall areas), in order to characterize the complete MCS. Once this methodology was presented the paper offers a proposal for classifying the precipitation systems, and particularly the MCS. 57 MCS structures were classified: 49% of them were identified as linearly well-organised systems, called TS (39%), LS (18%) and NS (43%). In addition to the classification, the following items were analysed for each MCS found: duration, season, time of day, area affected and direction of movement, and main radar parameters related with convection. The average features of those MCS show an area of about 25000 km², Z_max values of 47 dBz, an echotop of 12 km, the maximum frequency at 12 UTC and early afternoon and a displacement towards E-NE. The study was completed by analysing the field at surface, the presence of a mesoscale low near the system and the quasi-stationary features of three cases related with heavy rainfalls. Maximum rainfall (more then 200 mm in 6 h) was related with the presence of a cyclone in combination with the production of a convective train effect.     

Intercomparison and Evaluation of Precipitation Forecasts for MAP Seasons 1995 and 1996

Summary  The precipitation forecasts of four operational numerical weather prediction models over the Alpine region are evaluated and intercompared for two periods of interest to the Mesoscale Alpine Programme (MAP). The new analysis of Alpine rainfall of Frei and Scha?r (1998) is used to validate the models. It is found that the models have a tendency to overestimate the total precipitation and the frequency of intense rain events over high orography. The skill scores show good consistency between models, except for the ability to forecast light rain or heavy rain events. The partition between convective and stratiform rainfall is rather variable between the models. Received March 15, 1999/Revised July 12, 1999     

Mesoscale Convective System over the Yellow Sea – A Numerical Case Study

Summary  A mesoscale convective system (MCS) case that developed over the Yellow Sea (12–13 July 1993) is studied by using a 23-level, 30 km-mesh Penn State/NCAR mesoscale model MM5. This MCS was generated in northern China, south of the Changma front, in a convectively unstable environment, under the influence of a short-wave trough accompanied by a marked cold vortex aloft. The model with all model physics (refereed to as CNTL) captured the major features of this MCS. A mesoscale low-level jet (mLLJ), with a horizontal scale of a few hundred km, developed within the MCS. Available wind data support the realism of this mLLJ. This mLLJ not only transports convectively unstable air directly toward the MCS but is also responsible for a strong low-level convergence in the MCS. At 200 hPa, an anticyclonic northwesterly flow with a relatively high wind speed core on the east of MCS was simulated. This relatively high-speed flow can be regarded as a mesoscale upper level jet (mULJ), acted as an upper outflow over the MCS. Low-level convergence on the left-front of the mLLJ and upper divergence in the right-rear of the mULJ creates a strong upward motion (≅ 40 cm s⁻¹) in the MCS. Heavy precipitation up to 45 mm between 1800–2100 UTC was observed after this MCS landed on the southern Korean Peninsula. The CNTL run captured this heavy rainfall event. A maximum rainfall of 50 mm 3 h⁻¹ was simulated. In another experiment, with surface sensible and moisture fluxes withheld (NOSF), the 3-h simulated rainfall was decreased to 30 mm. Less latent heat released in the NOSF led to a weaker MCS and mLLJ. The concurrent surface fluxes sustained a high low-level moisture field over the Yellow Sea, which helped the development of the MCS and enhanced its precipitation in this case. Received January 8, 1999     

Satellite- and radar-based investigations of heavy precipitation systems on the southern side of the European Alps

Summary In autumn 1999 during the field phase of the Mesoscale Alpine Programme (MAP), the geostationary satellite Meteosat-6 performed 5-minute rapid scan imagery over central Europe. The rapid scan data of 11 heavy precipitation events are investigated by analyzing the spatial and temporal characteristics of cloud top structures. The objectives are to separate convective from stratiform cloud regions by satellite data alone and to gain insight into the life cycle of heavy precipitation systems. For verification of the satellite-based results, radar data from the operational Mt. Lema C-band radar is interpolated on the spatial grid of the infrared and visible Meteosat images. The interpolated radar data of each single grid cell is then classified by a convective-stratiform algorithm and compared to the analysed rapid scan imagery.The satellite- and radar-based approaches do only rarely produce matching classifications concerning the identification of convective areas. Since convection during the field phase of MAP occurred mostly embedded within stratiform cloud regions, no temporal and spatial characteristics of convective activity within clouds can be systematically derived from satellite imagery. This lack of characteristic cloud top structures prevented the unambiguous identification of typical cloudiness associated with stratiform precipitation. It is one of the major findings of this study, that in several cases being classified as stratiform by radar, strong cloud development is observed in satellite imagery. The preferred area of strong cloud development is located ahead of the Alpine barrier in a precipitation-free atmosphere. Two contrasting examples of life cycles of heavy precipitation systems are given based on the complementary information extracted from satellite and radar data.     

雨滴谱垂直演变特征的微雨雷达观测研究

雨滴谱的垂直变化特征对于认识降水过程、改进模式和雷达定量估计降水等具有重要意义。利用2016年6月1日-9月30日雨量筒、微雨雷达（micro rain radar,简称MRR）和PARSIVEL雨滴谱仪连续4个月的观测数据,在对比3种仪器观测结果的基础上,研究了层状云降水不同降水强度下微物理特征量和雨滴谱垂直演变特征。结果表明:MRR与PARSIVEL雨滴谱仪观测降水强度相关性较好,且两种仪器观测的雨滴谱在中等粒子段（0.5~2.5 mm）表现出较好的一致性,而对于小粒子段（雨滴直径小于0.5 mm）PARSIVEL雨滴谱仪观测的数浓度明显低于MRR。对于弱降水（降水强度R ≤ 0.2 mm·h-1）,液水含量和降水强度随高度降低减小,雨滴在下落过程中蒸发明显。对于较强降水（R>2 mm·h-1）,随高度降低,雷达反射率因子增大,小滴数浓度减小的同时大滴数浓度增加明显,雨滴下落过程碰并作用明显。所有高度直径不超过0.5 mm的小滴对数浓度贡献均为最大。高层雨滴直径不小于1 mm的小粒子对降水强度的贡献可达50%,小粒子对降水强度贡献随高度降低减小。     

Rainfall regionalization on the basis of the precipitation convective features using a raingauge network and weather radar observations

The main objective of the present paper is to show a methodology for undertaking rainfall regionalization of a region taking into account the convective features of the precipitation, and useful for establishing homogeneous zones for improving the alert system. This methodology has been applied to a hydrographic region located in northeast Spain, with an area of 16000 km² and characterized by a highly contrasted topography. Information provided by meteorological radar and 5-min precipitation data for 126 automatic raingauges has been used for the period 1996–2002. The previous analysis done on the basis of the 1927–1981 rainfall rate series for the Jardí raingauge, located in Barcelona, has also been considered. To that end, the first step was to draw up a proposal for classification of the pluviometric episodes. Recourse was had for this purpose to definition of the β parameter, related with the greater or lesser convective character of the event and calculated on the basis of the rainfall intensity at the surface (Llasat, 2001) and, when data are available, on the basis of radar reflectivity. Results show that the threshold of 35 mm/h to characterize convective episodes from raingauge data can be corroborated from the radar point of view when convective precipitation is identified using 2-D algorithms with a reflectivity threshold of 43 dBZ. Once the soundness of the β parameter had been corroborated, it was applied to more than 2900 precipitation episodes recorded in the region, in order to discriminate the features of the different subregions and their time and space distribution throughout the entire series of the samples. Using this definition, 92% of the precipitation events recorded in this region, with accumulated rainfall above 35 mm, are classified as convective ones, representing 95% of the precipitation amount. Application of the β parameter combined with monthly rainfall data allows differentiation of 8 regions with different convective precipitation features.     

Characterization of tropical precipitation using drop size distribution and rain rate-radar reflectivity relation

Characterization of precipitation is important for proper interpretation of rain information from remotely sensed data. Rain attenuation and radar reflectivity (Z) depend directly on the drop size distribution (DSD). The relation between radar reflectivity/rain attenuation and rain rate (R) varies widely depending upon the origin, topography, and drop evolution mechanism and needs further understanding of the precipitation characteristics. The present work utilizes 2 years of concurrent measurements of DSD using a ground-based disdrometer at five diverse climatic conditions in Indian subcontinent and explores the possibility of rain classification based on microphysical characteristics of precipitation. It is observed that both gamma and lognormal distributions are performing almost similar for Indian region with a marginally better performance by one model than other depending upon the locations. It has also been found that shape-slope relationship of gamma distribution can be a good indicator of rain type. The Z-R relation, Z = AR^b, is found to vary widely for different precipitation systems, with convective rain that has higher values of A than the stratiform rain for two locations, whereas the reverse is observed for the rest of the three locations. Further, the results indicate that the majority of rainfall (>50%) in Indian region is due to the convective rain although the occurrence time of convective rain is low (<10%).     

Assessment of mesoscale convective systems using IR brightness temperature in the southwest of Iran

In this research, the spatial and temporal distribution of Mesoscale Convective Systems was assessed in the southwest of Iran using Global merged satellite IR brightness temperature (acquired from Meteosat, GOES, and GMS geostationary satellites) and synoptic station data. Event days were selected using a set of storm reports and precipitation criteria. The following criteria are used to determine the days with occurrence of convective systems: (1) at least one station reported 6-h precipitation exceeding 10 mm and (2) at least three stations reported phenomena related to convection (thunderstorm, lightning, and shower). MCSs were detected based on brightness temperature, maximum areal extent, and duration thresholds (228 K, 10,000 km², and 3 h, respectively). An MCS occurrence classification system is developed based on mean sea level, 850 and 500 hPa pressure patterns.

The results indicated that the highest frequency of MCSs occurred in December and April. Assessment of MCSs spatial frequency showed that MCS occurrence is strongly correlated with topography in April and May unlike the cold months. In other words, the role of Zagros Mountains in developing MCSs varies based on the season so that its impact increases with enhancement of mean monthly temperature. In addition, the occurrence of MCSs depends closely on the configuration of the Sudan Low in the southwest of Iran.

     

内蒙古典型暴雨过程的中尺度雨团观测分析

利用FY-2E逐时云顶黑体亮温资料 (TBB)、闪电定位资料、自动气象站资料和逐时降水资料,对2009—2013年6—8月内蒙古7例暴雨天气过程的中尺度雨团特征进行分析。结果表明:内蒙古暴雨的降水强度在1~3 h即可达到暴雨或大暴雨量级,中尺度雨团活动是内蒙古暴雨过程形成原因,而80%雨团活动是中尺度对流系统 (MCS) 造成的。MCS内TBB不超过-52℃冷云区和地闪密度大值中心对雨团强度和发展具有重要的指示作用,冷锋云系中MCS造成的雨团多原地生成和消亡,TBB不超过-52℃冷云区面积小,维持时间为2~8 h,地闪密度增长缓慢而且发生频次低;冷涡云系中雨团跳跃式出现在MCS冷云区或冷空气流入一侧,出现TBB不超过-62℃冷云区,雨团出现频次高,持续出现时间可长达24 h,地闪密度增长迅速且发生频次高。7次暴雨过程中约有60%雨团伴有地闪活动,地闪密度达到最大值时刻预示未来1~3 h最强雨团出现和MCS发展到成熟。地面加密风场中尺度辐合线先于MCS和雨团出现,中尺度辐合线造成的局地辐合可作为MCS发展的启动机制。     

沿海地区一次中尺度对流系统闪电活动及降水结构

利用TRMM卫星的测雨雷达,微波成像仪,闪电成像仪等探测数据,研究了2010年8月5日发生在江苏北部一次中尺度对流系统(MCS)的降水结构和闪电活动之间的关系.结果表明:MCS在发展阶段,对流云降水面积与层状云降水区相当;在减弱阶段,层状云降水区面积远大于对流云降水区.MCS的生命史中,大部分闪电发生在对流云区,仅有少数闪电发生在层状云区,在减弱阶段闪电多发生在对流云和层云的过渡区中.发生闪电的层云和对流云降水垂直廓线表明:在MCS的发展成熟和减弱中在4 km高度,层云降水率都达到最大值;在对流云降水区中发生闪电主要与对流云上空含丰富的冰相粒子和对流云发展厚度(顶高达17 km)有关.研究还表明闪电数目最大值一般回波强度在35～45 dBz之间,并非回波越强闪电越多.闪电主要发生在40～50 dBz之间,且明显向强回波区趋近,这对我们利用雷达回波预警闪电落区具有一定的参考意义.     

A MASCOTTE-based characterization of MCSs over Spain, 2000–2002

A 3-year Mesoscale Convective Systems (MCSs) database, which extends from 2000 to 2002, has been built for the Iberian Peninsula and the Balearic Islands using the objective method MASCOTTE (MAximum Spatial COrrelation Technique). It was originally developed to track the evolution of convective systems over the Amazon region; after modifications, it is able to track MCS evolution even with an hour and a half of missed images and provides essential information of both dynamical and morphological characteristics of MCSs. MASCOTTE is tested against a visual and subjective method, and is found to offer advantages such as automation and a simple and efficient operation that make it very useful for building large MCS databases.Thirty-five MCSs were found between June and October, most of them originated along the Mediterranean coast and near the Pyrenees, showing an increasing occurrence from June to September, when the maximum is found. The regions most influenced by MCS occurrences are Balearic Islands, Valencia, Catalonia, Murcia and the Basque Country. The MCSs tend to be small, short-lived and linear, usually moving eastward or northeastward with low velocities.The MCSs-associated precipitation presents high variability, ranging from 80 to 0 mm h⁻¹ as maximum hourly records. Two different convective regions are identified based on MCS behavior in extreme precipitation events: Northern Spain (the Basque Country) with abundant and continuous precipitation regime but little MCS influence, and the Mediterranean coast, where precipitation is sporadic but much more intense.     

雷达与雨量计联合估测降水的相关性分析

在对比分析质量控制前后雷达估测降水量与自动雨量计降水量之间相关性的基础上,采用雷达-雨量计联合校准方法,对14种不同密度雨量计校准雷达估测降水的效果进行分析。结果表明:在使用雷达资料和雨量计资料前有必要对资料的质量进行分析与控制。联合雨量计校准雷达能明显提高雷达对降水的估测能力;采用不同密度雨量计校准雷达,随着校准雨量计密度的加大,雷达估测降水的精度不断提高并趋于稳定。校准雷达的效果及所需雨量计密度与降水类型有关,当校准效果相同时,积云强降水过程需要的雨量计密度最大,积混对流性降水过程次之,层云稳定性降水过程需要的雨量计密度最小。不同方法的校准效果不同,卡尔曼滤波方法适合于对稳定性降水的校准,或在雨量计密度低的地区对雷达进行校准;变分校准法和最优插值法的校准效果相当,适合对积混对流性降水的校准,或在雨量计密度高的地区对雷达进行校准。     

海河流域切变线类暴雨成因分析

应用常规观测资料、FY2C卫星TBB资料、多普勒雷达资料、风廓线雷达、加密自动站以及NCEP1°×1°再分析资料分析海河流域切变线类暴雨成因。结果表明：暴雨过程是低空切变线与高低空急流构成有利配置条件下发生的, 系统空间结构和冷空气移动路径的不同,造成了暴雨落区和强度的不同;沿切变线有带状中-α尺度对流云团形成和发展,并有中-β尺度MCS沿带状有组织的发展、移动、合并、加强,沿低空切变线如有低涡形成,带状对流云系内将有MCC形成,强降雨在MCS或MCC移动方向的前侧、TBB等值线梯度最大处;强降雨之前都有水汽辐合从地面向高层伸展,伸展高度越高,降雨强度越大,强降雨中心对应西南与偏东两个大水汽通量造成的辐合且等值线密集处;VAD风廓线和风廓线雷达资料都显示出对流层低空急流和超低空急流的先后形成,造成雨强也两度加强。     

中国区域高分辨率多源降水观测产品的融合方法试验

高质量、高分辨率降水产品研制对于数值天气模式检验、水文陆面模拟、山洪地质灾害监测有着重要意义。利用中国近4万自动气象站逐时降水资料、中国雷达定量降水估计和CMORPH卫星反演降水产品,开展0.05°×0.05°和0.01°×0.01°两种高分辨率下的三源降水融合方法研究试验,探讨如何有效引入雷达高分辨率信息来提高降水产品质量。一方面,在0.05°分辨率上,先以自动气象站观测降水数据为基准,采用概率密度函数（PDF）匹配法订正雷达和卫星估测降水产品的系统偏差,将雷达降水产品的偏差从-0.05 mm/h降至-0.008 mm/h;再采用贝叶斯模型平均（BMA）方法融合雷达和卫星降水产品,形成0.05°分辨率的中国区域覆盖完整且最优的联合降水背景场。此外,在0.01°分辨率上,以0.05°分辨率的卫星-雷达贝叶斯模型平均联合降水产品为背景,采用1 km雷达估测降水的空间结构信息进行降尺度,亦能有效提高0.01°分辨率背景场的质量。然后,分别以不同分辨率的卫星-雷达联合降水产品为背景,采用统计方法量化误差估计,再采用最优插值方法融入地面观测。通过2419个中国国家级气象台站的独立样本检验,评估了多种类型的降水资料及融合试验产品在中国地区的质量。结果表明,两种分辨率的三源融合试验产品的精度均优于任何单一来源的降水产品,特别是在站点稀疏地区,降水精度均较融合前有显著提高,达到了较好的融合效果,其中在0.05°分辨率上采用“概率密度函数+贝叶斯模型平均+最优插值”方法的三源融合降水产品整体质量最好,而0.01°分辨率上基于“概率密度函数+贝叶斯模型平均+降尺度+最优插值”方法的三源融合降水产品在强降水监测上更有优势。      

Ice Storm ’98 in Southcentral Canada and Northeastern United States: A Climatological Perspective

Summary Dubbed Ice Storm ’98, an extreme weather event characterized by two synoptic systems in succession dropped about 70–100 mm (in terms of water equivalent) of freezing precipitation over southeastern Ontario, southwestern Quebec and northeastern New York during a 6-day period from January 5 to 10 in 1998. Individually, the two synoptic systems were not dramatically more extreme in freezing precipitation than other major freezing rain events (4 since 1961) which occurred in the past over the affected area. Some regions in the target area, however, were impacted more by the second system. Based on an analysis of the 500 hPa vorticity field during the ’98 event, we suggest that the 1997/98 El Ni?o had a role in creating a flow environment conducive to the rapid formation of the second synoptic system. In contrast, other major freezing rain events in the last 30 years involved only one synoptic system per event lasting no more than 3 days, and producing 20–50 mm of precipitation. We have also found that, 3 out of 4 past major freezing rain events since 1958 were associated with the positive phase of the North Atlantic Oscillation (NAO). Consistent with this usual past association between the NAO and a major freezing rain event, Ice Storm ’98 also occurred when the phase of the NAO was positive. Analysis of these 3 past and the ’98 events also indicates an apparent connection between the positive phase of the NAO and the northern Quebec high pressure system, which is an essential synoptic feature of a major freezing rain occurrence over the southcentral region of Canada. As measured by their respective indices, the maximum positive NAO state leads the maximum northern Quebec high by about 2 days (5 days in the ’98 event). There is some suggestive evidence to indicate that the persistence of the northern Quebec high pressure system is connected to the persistence of the positive phase of the NAO. Received January 17, 2000     

一次飞机冷云增雨作业效果检验

最近60多年,全球范围内广泛开展了人工增雨作业,但人工增雨效果检验一直是个难题。传统上,利用雨量计和目标/对比区统计数据评估人工增雨效果,结果大多不确定。对一次人工增雨作业而言,从科学上给出令人信服的效果检验更是没有好的解决方案。2017年3月19日,陕西省实施业务飞机冷云增雨作业播撒含有750 g碘化银（AgI）的催化剂,播撒线长125 km。作业后卫星、雷达观测到一条与播云线对应的清晰的云迹线,地面雨滴谱仪观测到相应的雨强、雨滴数浓度、雨滴直径增大,表明播云使云体产生了增雨响应。针对这次增雨过程,从连片雷达回波中分离增雨作用造成的回波增强带（增雨影响回波）和确定了自然降水回波强度,建立增雨影响回波强度（Z）与地面雨强（I）的拟合关系（Z-I关系）,定量研究人工增雨的时、空演变。结果表明:（1）增雨影响时间约4 h,增雨影响回波区域（增雨影响区）面积为5448 km2。该区累计降雨总量和增雨总量分别为1.518×106 m3和8.04×105 m3,增雨影响区内增雨率达53%。（2）总降雨量、增雨量、自然降雨量随时间先增后减,总降雨量与增雨量的峰值同步,两者峰值都早于自然降雨峰值;催化后146 min （04时47分,世界时,下同）,每6 min增雨量达到最大,为4.9×104 m3;催化后174 min （05时15分）,增雨雷达回波面积达到最大（1711 km2）,面积峰值滞后增雨量峰值出现。（3）增雨影响区位于播撒线下游,呈条带状;区域内总降雨量空间分布为中间大边缘小,与增雨量空间分布一致。（4）此次增雨作业改变了降雨时、空分布,促进降雨形成,增加了地面降雨量。      

Diurnal phase of late-night against late-afternoon of stratiform and convective precipitation in summer southern contiguous China

Using the tropical rainfall measuring mission (TRMM) Precipitation Radar (PR) observations combined with the surface rain gauge data during 1998–2006, the robust diurnal features of summer stratiform and convective precipitation over the southern contiguous China are revealed by exploring the diurnal variations of rain rate and precipitation profile. The precipitation over the southern contiguous China exhibits two distinguishing diurnal phases: late-night (2200–0600 LST) and late-afternoon (1400–2200 LST), dependent on the location, precipitation type and duration time. Generally, the maximum rain rate and the highest profile of stratiform precipitation occur in the late-afternoon (late-night) over the southeastern (southwestern) China, while most of the stratiform short-duration rain rate tends to present late-afternoon peaks over the southern China. For convective precipitation, the maximum rain rate and the highest profile occur in the late-afternoon over most of the southern contiguous China, while the convective long-duration rain rate exhibits late-night peaks over the southwestern China. Without regional dependence, the convective precipitation exhibits much larger amplitude of diurnal variations in both near surface rain rate and vertical extension compared with stratiform precipitation and the convective rain top rises most rapidly between noon and afternoon. However, there are two distinctive sub-regions. The diurnal phases of precipitation there are very weakly dependent on precipitation type and duration time. Over the eastern periphery of the Tibetan Plateau, the maximum rain rate and the highest profile of either convective or stratiform precipitation occur in the late-night. Over the southeastern coastal regions, both the near surface rain rate and rain top of convective and stratiform precipitation peak in the late-afternoon.     

Forecasting weather radar propagation conditions

Summary The increasing use of weather radar quantitative precipitation estimates, particularly in automatic applications such as operational hydrometeorological modelling or assimilation in numerical weather prediction (NWP) models, has promoted the development of quality control procedures on radar data. Anomalous propagation (AP) of the radar beam due to deviation from the standard refractivity vertical profile, is one of the factors that may affect seriously the quality of radar observations because of the increase in quantity and intensity of non-precipitating clutter echoes and consequent contamination of the estimated rainfall field. Another undesired effect of AP is the change in the expected radar echo height, which may be relevant when correcting for beam blockage in radar rainfall estimation in complex terrain. The aim of this paper is to study the use of NWP mesoscale forecasts to predict and monitor AP events. A nested 15-km grid resolution version of the MASS model has been used to retrieve refractivity profiles in the coastal area of Barcelona, near a weather radar and a radiosonde station. Using the refractivity profiles two different magnitudes were computed: the vertical refractivity profile of the lowest 1000 m layer and a ducting index which describes the existence and intensity of the most super-refractive layer contained in the lowest 3-km layer. A comparison between model forecasts and radiosonde diagnostics during a six-month period showed that the model tended to underestimate the degree of super-refraction, with a bias of 4 km⁻¹ and RMSE of 11 km⁻¹ in the 1-km vertical refractivity gradient. Further analysis of the data showed that a combination of previous observations and forecasts allowed to produce modified forecasts improving the original direct model output, decreasing substantially the bias, reducing the RMSE by 20% and improving the skill by 40%, beating also radiosonde observations persistence.     

Passive microwave and infrared structure of mesoscale convective systems

Summary The precipitation structure of mature Mesoscale Convective Systems (MCS) is examined in both the midlatitudes and the tropics using SSM/I microwave measurements, geostationary satellite observations, and ground-based radar observations. Discussion includes qualitative comparisons between midlatitude and tropical MCS cases, with particular emphasis on the delineation of convective and stratiform regions and the characterization of microwave polarization difference temperatures in the MCSs. Implications are given regarding the importance of the vertical precipitation structure on top of the atmosphere (TOA) microwave temperatures and for rain retrieval algorithms using measurements from space.Some of the principle findings include the ability of passive microwave brightness temperature measurements to distinguish stratiform and convective regions of MCSs for both tropical and midlatitude cases and over land and ocean backgrounds. Convective regions typically had low differences between the vertical and horizontal brightness temperatures while the stratiform regions have larger differences, and these differences are likely related to the spatial microphysical variations in the upper levels of the precipitation region. Several cases were found in midlatitudes and one case in the tropics where the lowest infrared (IR) brightness temperatures were displaced into the anvil region and were not colocated with the coldest microwave temperatures. Life cycle dependence of the displacement is suggested, but the SSM/I measurements with a maximum of twice daily coverage over the same location were inadequate to answer this question.With 10 Figures