Idealized numerical simulation experiment of ice seeding in convective clouds using a bin microphysics scheme

A 2D axisymmetric bin model is used to conduct idealized numerical experiments of cloud seeding. The simulations are performed for two clouds that differ in their initial wind shear. Results show that, although cloud seeding with an ice concentration of 1000 L^?1 in a regime that has relatively high supercooled liquid water can obtain a positive effect, the rainfall enhancement seems more pronounced when the cloud develops in a wind shear environment. In no-shear environment, the change in the microphysical thermodynamic field after seeding shows that, although more graupel is produced via riming and this can increase the surface rainfall intensity, the larger drag force and cooling of melting graupel is unfavorable for the development of cloud. On the contrary, when the cloud develops in a wind shear environment, since the main downdraft is behind the direction of movement of the cloud, its negative effect on precipitation is much weaker.摘要本文采用二维轴对称分档云模式开展了人工催化数值试验, 对两种不同初始风切变的对流云进行了模拟. 结果表明, 尽管在过冷水相对较高的区域播撒 1000 L^?1 的冰晶可以增加地面降水, 但当云在风切变环境中发展时, 人工播撒对降雨增强的作用似乎更加明显. 在无切变环境下, 微物理量, 热力场的变化表明播撒后大量的霰所产生的拖曳力和融化冷却有可能切断主上升气流, 从而不利于云的发展. 相反, 当云在风切变环境中发展时, 由于播撒产生的主下沉气流位于云的运动方向之后, 其对降水的负面影响要弱得多.     

An aerosol climatology of Samoa

An atmospheric monitoring station is operated at Cape Matatula, American Samoa, by the Geophysical Monitoring for Climatic Change program under the National Oceanic and Atmospheric Administration. A nearly continuous record of condensation nucleus (CN) concentration and multiwavelength aerosol scattering extinction coefficient (_sp) is available from mid-1977 to the present. This report presents the 1977–1983 data. The long-term mean of CN concentration is 274 cm^-3 the long-term mean of _sp (550 nm) is 1.54×10^-5, and no significant long-term, annual, or diurnal trend is apparent in either data record.     

2013年6月26—29日江西暴雨过程的中尺度数值模拟分析

利用NCEP再分析资料和WRF模式,对2013年6月26—29日江西大范围暴雨过程进行了数值模拟分析。结果表明,西太平洋副热带高压脊线稳定维持在21°N附近,副高北侧强盛西南气流将水汽向江南北部地区输送是暴雨产生和稳定维持的主要原因。超低空偏南急流的建立、发展和维持是这次连续暴雨过程产生的一个重要因素,同时低空低涡南侧出现一串近似东西向排列的30～60km更小尺度的强对流系统,它们与大暴雨区相吻合;整层水汽通量密集区的南北界位置和暴雨区南北界位置基本吻合,整层水汽的大值中心的范围和大暴雨中心的范围具有明显的正相关关系;水汽通量散度最大辐合中心为暴雨的产生输送了大量的水汽,水汽辐合中心与暴雨的落区有很好的一致性;强降水落区与假相当位温最大值区相对应。     

An analysis of precipitation climatology in Jordan

Summary ?One of the most important features in analysing the climatology of any region is to study the precipitation and its periodicity of different harmonics in order to study the behavior of the observed data. In this study the amplitude of frequencies, phase angle and basic statistical parameters are calculated in order to depict spatial characteristics of precipitation over Jordan. Precipitation records of 17 stations were chosen according to climatic regions of Jordan. The first and second harmonic analyses explain more than 90% of the precipitation variation in Jordan effectively. The amplitudes of the first and second harmonic were calculated in order to describe the climatic regions in the country. The maximum amplitudes were found in the northern mountainous region. The phase angle representing the time of maximum rainfall is also used in the form of a contour chart. It is found that Jordan has its main rainfall season in winter with maximum around January. The coefficient of variation shows the high variability of rainfall of the country. Received February 4, 2002; revised August 1, 2002; accepted August 6, 2002     

Future changes in cyclone climatology over Europe as inferred from a regional climate simulation

This study analyzes the cyclone climatology in regional climate model simulations of present day (1961–1990) and future (2071–2100, A2 and B2 emission scenarios) european climate conditions. The model domain covers the area from Scandinavia to Northern Africa and from the Eastern Atlantic to Russia at a horizontal grid spacing of 50 km. Compared to present day, in the A2 and B2 scenario conditions the annual average storm track intensity increases over the North-East Atlantic and decreases over Russia and the Eastern Mediterranean region. This overall change pattern is larger in the A2 than in the B2 simulations. However, the cyclone climatology change signal shows a large intermonthly variability and important differences across European regions. The largest changes are found over the North-East Atlantic, where the storm track intensity increases in winter and decreases in summer. A significant reduction of storm track intensity is found during late summer and autumn over the Mediterranean region, and from October to January over Russia. The number of cyclones decreases in future conditions throughout Europe, except over the Central Europe and Mediterranean regions in summer (where it increases). The frequency of intense cyclones and the depth of extreme cyclones increase over the North-East Atlantic, decrease over Russia and show an irregular response over the rest of the domain.

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慕尼黑一次混合型雹暴的数值模拟与成雹机制

利用三维冰雹云模式,对2013年4月29日四川西昌的一次降雹过程进行了数值模拟。模拟结果显示：该例冰雹云存在过冷雨水累积带;霰是冰雹的主要胚胎,雹块主要通过撞冻云水增长,其次是撞冻霰增长;模拟区域内液态降水量和固态降水量分别占地面总降水量的52%和48%,冰雹占固态降水94%;通过对该例雹云中冰晶、雪、霰、冻滴的微物理过程分析发现,在雹云发展的不同阶段,冰雹的形成机制不同。

     

Impact of precipitating ice on the simulation of a heavy rainfall event with advanced research WRF using two bulk microphysical schemes

In this study, the Weather Research and Forecasting (WRF) model version 3.2 is used to examine the impact of precipitating ice and especially snow-graupel partitioning in the simulation of a heavy rainfall event over Chalkidiki peninsula in Northern Greece. This major precipitation event, associated with a case of cyclogenesis over the Aegean Sea, occurred on the 8th of October 2006 causing severe flooding and damage. Two widely used microphysical parameterizations, the Purdue Lin (PLIN) and WRF Single-Moment 6-class scheme (WSM6) are compared with available raingauge measurements over the complex topography of Chalkidiki. To further investigate the importance of snow and graupel relative mass content and the treatment of precipitating ice sedimentation velocity, two older versions of the WSM6 scheme were compiled and run with the current model. The verification results indicate that all simulations were found to match raingauge data more closely over the eastern mountainous Chalkidiki peninsula where maximum accumulations were observed. In other stations all schemes overestimate 24h accumulated rainfall except a station situated at the western part of the peninsula, where none of the simulations was able to reproduce observed rainfall. Graupel dominance in PLIN generates rapid precipitation fallout at the point of maximum predicted 24h accumulation. Similar behavior is shown in WSM6 from WRF version 2, but with significant less rainfall. Increasing snow amounts aloft, due to the unified treatment of precipitating ice in WSM6 from WRF version 3, modifies rain dynamics which decrease rainfall rates, but increases 24h accumulations. A sensitivity experiment where PLIN is used with snow accretion by graupel turned off, indicated that this process seems to be the most important factor controlling the differences in surface precipitation between PLIN and WSM6 from WRF version 3, determining the spatial and temporal distribution of this heavy precipitation event. The results also revealed that snow overestimation can lead to high rainfall accumulations, even though rain is more evenly distributed over the 24h period, deteriorating precipitation forecast.     

全球多源海冰密集度融合资料研制试验

为了发展一套全球多源海冰密集度逐日融合资料,以欧洲气象卫星应用组织(EUMETSAT)海洋海冰应用中心(OSI SAF)海冰密集度数据、中国国家卫星气象中心(NSMC)的MWRI和VIRR全球海冰密集度数据、美国国家冰雪数据中心(NSIDC)的NISE海冰密集度数据、美国国家冰中心(NIC)的IMS北半球海冰数据为观测...     

南京及周边地区雷达气候学分析

为了研究南京及周边地区暖季（6-9月）对流风暴的活动分布规律,利用2009-2013年6-9月长时间序列的南京多普勒天气雷达数据识别对流回波并格点化,统计并分析了南京及周边地区对流风暴的气候学分布特征,结果表明:（1）在暖季,南京及周边地区对流风暴具有明显的区域分布特征,其中7与8月为对流风暴活动高峰期,对流风暴频数分布大值中心位于南京东部沿江地区;（2）不同尺度和伸展高度对流风暴的分布特征各不相同,较大较深对流的分布大值中心更加明显;（3）对流风暴的垂直结构因月份不同而有所差异,7与8月对流风暴强度最大;（4）不同尺度和伸展高度对流风暴频数存在明显的日变化特征,呈多峰分布,主峰值区位于午后,同样,各月份对流风暴频数的日变化特征也非常明显,呈单峰或者多峰分布。      

An analysis of precipitation climatology over Indian urban agglomeration

Theoretical and Applied Climatology - While urban areas in India are rapidly expanding, the analysis of how the precipitation regimes are changing is very limited. In the present study, an attempt...     

2009年春季一次黄海海雾的观测分析及数值模拟

利用5种观测资料和RAMS（regional atmospheric modeling system）模式对2009年5月2_5日发生在黄海海域的一次海雾过程进行了观测分析和数值模拟研究。结果表明：1）所取个例的整个生命过程受同一高压系统影响,该高压在海雾过程后期的形变促使海雾消散,这在以往的黄海海雾中较为罕见。2）黄海北部形似“7”的雾区形态的出现和演化与1～3℃气海温差的变化吻合,气海温差对海雾形成和演变的重要作用得到再次验证。3）RAMS模式具有一定的海雾数值模拟能力,得到的雾顶高度分布与卫星云图所显示的雾区形态吻合良好。     

Numerical simulation of a heavy rainfall event in China during July 1998

Summary A detailed analysis associated with this case has been carried out (Zhao et al., 2001). In order to conduct further research on the meso-β scale system, which is the directly influencing system, the heavy rainfall that occurred in Wuhan (Station no.: 57494) and Huangshi (Station no.: 58407), Hubei Province during July 1998 are simulated using higher resolution and more complete initial data, after the large scale fields and rainfall areas have been simulated successfully. The simulation results indicate that there are meso-β scale weather systems which developed and dissipated near Wuhan and Huangshi during 1800 UTC 20 July to 0600 UTC 21 July and 1800 UTC 21 July to 0600 UTC 22 July in 1998, respectively. The life cycle of the meso-scale system is about 12 hours and its horizontal scale is from 100 to 200 km. These are characteristic of a typical meso-β scale system. By analyzing the vertical section of wind field and other physical variables during the mentioned-above two periods, it is found that horizontal convergence, ascending motion and positive vorticity of the middle and lower troposphere are strengthened during the heavy rainfall periods near the above mentioned two places. In addition, the wind disturbance in middle and lower troposphere may be a possible triggering mechanism for the occurrence of the meso-β weather system. A budget analysis of the meso-scale system indicates that the sources of moisture and positive vorticity are different during the different stages of the meso-scale systems. Finally, a three dimensional conceptual model of the meso-β scale systems causing the sudden heavy rainfall in Wuhan and Huangshi is suggested. Received November 4, 2001 Revised December 28, 2001     

The climatology of tornadoes and waterspouts in Italy

In this work 10 years of reports collected by weather amateurs are used to define a preliminary climatology of tornadoes and waterspouts in Italy. The results show behaviors different from those observed in other countries. Generally, tornadoes and waterspouts are more frequent in late summer and autumn than in the other seasons. The seasonality of tornadoes and waterspouts appears different for different Italian zones, in particular in the Po Valley and Friulian plain and coast (south to the Alps) tornadoes and waterspouts are more frequent in spring and early summer while in the Tirrenian and Ionian coasts (western and southern Italy), tornadoes and waterspouts are more frequent in late summer and autumn. As observed in other studies (Brooks, H., E. and Doswell, C. A. III, 2001. Some aspects of the international climatology of tornadoes by damage classification. Atmos. Res., 56, 191–201.) Italian tornadoes and waterspouts are statistically weaker than in other countries but this difference cannot be completely ascribed to the presence of waterspouts. The “CAPE Storm-Relative-Helicity diagrams” and “Shear Magnitude diagrams” obtained for Italian tornadoes and waterspouts show different characteristics than those obtained for US. The cause of these differences is still unknown, it can rely in the sample selection (problems with the concept of proximity sounding) or in a real climatic effect.     

The changing rainy season climatology of mid-Ghana

Daily rainfall data are examined through the temporal analysis of various definitions of variable temporal units (VTUs) consisting of combinations of various starting dates and durations over mid-Ghana. These VTUs are independent of, yet encompass, the starting dates and durations of the major and minor rainy seasons. Within each VTU, total rainfall and number of rainy days are calculated to describe the rainfall characteristics of the unit. Means and variances of each variable are calculated for each unit over two 20-year periods, 1951–1970 (P1) and 1981–2000 (P2). In P2, the major and minor rainy seasons have undergone varying degrees of desiccation. This reduction in rainfall is, however, not temporally or spatially uniform. The widespread decline of mean rainfall totals and number of rainy days during the minor rainy season, often associated with greater inter-annual variability, is particularly threatening to the production of a second crop.