不同类型大尺度环流背景下强对流天气的短时临近预报预警研究

利用乌鲁木齐多普勒天气雷达、风廓线雷达、GPS/MET水汽探测仪以及FY—2E/G卫星、区域加密自动气象站资料和GFS/NCEP 0.5°×0.5°逐6 h再分析资料,对2015年6月9日18:30—20:00出现在乌鲁木齐的短时强降水过程进行分析,重点分析了强降水过程的环境场和中小尺度特征。结果表明：该短时强降水过程有4个降水集中时段,每个时段约为10~15 min。降水发生在高压脊前低槽后部的西北气流控制之下,700 hPa β中尺度西北急流上γ尺度对流单体是短时强降水直接影响系统。该降水过程水汽来自于乌鲁木齐周围并在2~3 h内快速集中。对流不稳定潜势从午后14 h开始发展,到降水开始仅4.5 h。沿西北低空急流出现多个γ中尺度对流单体以“列车效应”形式依次影响乌鲁木齐造成短时强降水,对流单体组合反射率最强达45~50 dBz,生命史仅15~20 min。降水发生在局地新生中尺度对流云团西南侧云顶亮温TBB梯度最大处,TBB最低达-44 ℃,对流云团生命史2~3 h。

     

Comparison of classification and clustering methods in spatial rainfall pattern recognition at Northern Iran

Pattern recognition is the science of data structure and its classification. There are many classification and clustering methods prevalent in pattern recognition area. In this research, rainfall data in a region in Northern Iran are classified with natural breaks classification method and with a revised fuzzy c-means (FCM) algorithm as a clustering approach. To compare these two methods, the results of the FCM method are hardened. Comparison proved overall coincidence of natural breaks classification and FCM clustering methods. The differences arise from nature of these two methods. In the FCM, the boundaries between adjacent clusters are not sharp while they are abrupt in natural breaks method. The sensitivity of both methods with respect to rain gauge density was also analyzed. For each rain gauge density, percentage of boundary region and hardening error are at a minimum in the first cluster while the second cluster has the maximum error. Moreover, the number of clusters was sensitive to the number of stations. Since the optimum number of classes is not apparent in the classification methods and the boundary between adjacent classes is abrupt, use of clustering methods such as the FCM method, overcome such deficiencies. The methods were also applied for mapping an aridity index in the study region where the results revealed good coincidence between the FCM clustering and natural breaks classification methods.     

Developing a climate model for Iran using GIS

Summary In order to develop a climate model for Iran, monthly mean climatic variables from 117 synoptic stations were obtained from the Iranian Meteorological Organisation. These variables were reduced to six orthogonal factors using factor analysis. The stations were then divided into six groups using cluster analysis. Within each climatic group, the lowest and highest thresholds for each factor were identified. The factor scores of the stations within each factor were interpolated across the country applying Inverse Squared Distance Weight in the ArcGIS environment. Based on the factor scores, six conditional functions were defined to allocate each pixel to a region. In order to simplify the models, one index variable was substituted for each factor. Then, through Discriminant Analysis, the constants and coefficients of the models were determined. The final models were evaluated against some examples, one of which, Yazd, was demonstrated fully. Authors’ address: Bohloul Alijani, Manijeh Ghohroudi, Nahid Arabi, Department of Geography, Teacher Training University, Mofetteh Avenue, Tehran, Iran.     

Surface radar-derived convective rainfall associations with Midwest US land surface conditions in summer seasons 1999 and 2000

Previous research has suggested that spatial heterogeneities in soil moisture and/or vegetation cover promote the development of convective clouds. We examine the intensity of convective precipitation for the Midwest US Corn Belt in the summers of 1999 and 2000, which had contrasting synoptic circulation, atmospheric humidity, and soil moisture conditions. For days when synoptic scale atmospheric forcing is weak, we calculate a convective severity index (CSI) based on radar reflectivity composite values. Our results suggest that boundaries between soil types, and cropland and forest vegetation types in the western portion of the Corn Belt, enhance the development of convective precipitation. In the eastern part of the Corn Belt, less convection occurs, but we find a positive correlation between the intensity of convection and soil moisture conditions. Our results also demonstrate that the CSI is a simple yet effective technique for identifying where deep convection occurs relative to lighter precipitation.     

Synoptic and dynamic analysis of a flash flood-inducing heavy rainfall event in arid and semi-arid central-northern Iran and its simulation using the WRF model

The synoptic and dynamic aspects of heavy rainfall occurred on 5th May 2017 and caused flash flooding in arid and semi-arid central-northern Iran is analyzed by the Weather Research and Forecasting (WRF) model. This system synoptically is attributed to a surface low-pressure centered over southern Iran extended to the central parts, linking to a mid-tropospheric tilted-trough over western Iran, and advecting significant moisture from the Mediterranean Sea and the Red Sea to the studied area. The dynamical analysis revealed that the penetration of the upper-tropospheric potential vorticity streamer up to 300 hPa level was not related to such heavy rainfall. Contrarily, the low-level factors such as extensive moisture advection, mid-tropospheric diabatic processes such as the latent heat release, daytime deep convection, and topographical impact of Zagros Mountains were found as the key factors leading to this system. This study also examines 11 different convection schemes simulated by the WRF model and verified against rainfall observation. The forecast skills of the output simulations suggest the Grell-Devenyi scheme as the superior configuration in simulating observed precipitation of the event over the area.     

Evaluating rainfall patterns using physics scheme ensembles from a regional atmospheric model

This study evaluated the ability of Weather Research and Forecasting (WRF) multi-physics ensembles to simulate storm systems known as East Coast Lows (ECLs). ECLs are intense low-pressure systems that develop off the eastern coast of Australia. These systems can cause significant damage to the region. On the other hand, the systems are also beneficial as they generate the majority of high inflow to coastal reservoirs. It is the common interest of both hazard control and water management to correctly capture the ECL features in modeling, in particular, to reproduce the observed spatial rainfall patterns. We simulated eight ECL events using WRF with 36 model configurations, each comprising physics scheme combinations of two planetary boundary layer (pbl), two cumulus (cu), three microphysics (mp), and three radiation (ra) schemes. The performance of each physics scheme combination and the ensembles of multiple physics scheme combinations were evaluated separately. Results show that using the ensemble average gives higher skill than the median performer within the ensemble. More importantly, choosing a composite average of the better performing pbl and cu schemes can substantially improve the representation of high rainfall both spatially and quantitatively.     

湖北宜昌市暴雨雨型的演变特征

基于1980—2018年武汉国家基本气象观测站逐分钟降雨数据,分别利用同频率分析法和Huff雨型分析法确定武汉主城区历时1 440 min设计暴雨雨型,并采用InfoWorks ICM水力模型软件对雨水管网进行模拟计算,分析两种设计暴雨雨型的雨峰、降雨量时间分布和积水情况,研究结果表明：（1）基于同频率分析法和Huff雨型分析法确定的武汉主城区历时1 440 min设计暴雨雨型均为单峰型,两者雨峰位置均略微超前整场降雨过程的前2/3分位,在降雨时程的60%~70%阶段,前者降雨强度迅速增加,大于后者。（2）在同频率分析法确定的武汉主城区历时1 440 min设计暴雨雨型下,武汉汉口中心城区的淹没面积均大于Huff雨型分析法的确定结果,且水深、流量、流速等峰值均较大。（3）同频率分析法确定的设计暴雨雨型结果使得武汉主城区系统内达标管网比例更低,积水情况更严重。

     

The spatial distribution of annual rainfall in Israel — a review

Summary This paper summarizes relevant studies dealing with the analysis of the annual rainfall map of Israel. With the aid of multiple regression analysis it was possible to quantify the contribution of each of the five geographical factors determining the annual rainfall map. Although the variance of the north-south component on the rainfall map looks most impressive, the orographic factor seems to be the more important contributor. The contribution of the spatially discrete urban factor has to be isolated from the deliberated cloud seeding augmentation. The statistical tools, spatial regression model and distance correlation matrix technique, were applied for the Central Coastal Plain and the Haifa area downwind, respectively. By applying sophisticated remote sensing methods, it was possible to classify and determine the rainfall yields of the variety of cloud formations appearing in the cold air mass following the cold front.With 8 Figures     

2020年6-7月长江中下游极端梅雨天气特征分析

利用逐小时地面、风廓线和天气雷达观测资料,对局地分析与预报系统的再分析产品（Local Analysis and Prediction System-Live Products,Laps_Live）和欧洲中期天气预报中心的第五代再分析产品（The fifth Generation ECMWF Reanalysis,ERA5）在2020年梅雨期的日变化特征进行检验和分析。结果表明：LAPS_LIVE地面要素日变化与实况的相关性普遍比ERA5高。LAPS_LIVE对武陵山区地面温、湿度日变化再现能力不如ERA5,对大别山区海平面气压和地面温、湿度的日变化再现能力明显优于ERA5。两种再分析资料在江汉平原区的海平面气压和地面温、湿度的日变化均与实况误差很小。LAPS_LIVE地面平均风场的误差比ERA5小,但风场日变化幅度明显偏小、风速偏低;ERA5地面风场的日变化幅度和风速则比实况显著偏强。LAPS_LIVE低空风廓线的惯性振荡特征与观测一致,对上午时段低层风场的时间演变和垂直切变的再现能力强于ERA5,但对夜间低空急流的再现能力不足。ERA5低空风场高估上午时段的偏北风和凌晨时段的西南低空急流,但ERA5的低空风廓线平均场比LAPS_LIVE更接近探测值。

     

Improvement of model forecast on the Asian summer rainfall anomaly with the application of a spatial filtering scheme

Summary A revised 25-point Shuman-Shapiro Spatial Filter (RSSSF) has been applied to six atmospheric circulation models and multi-model ensemble (MME) predictions, and its effect on the improvement of model forecast skill scores of the Asian summer precipitation anomaly is discussed in this paper. On the basis of 21-yr model ensemble predictions, the RSSSF can remove the unpredictable ‘noise’ with respect to the 2-grid wavelength in the model precipitation anomaly fields and maintain the large-scale counterpart, which is related to the response of the model to large-scale boundary forcing. Therefore, this could possibly enhance the forecast skill of the Asian summer rainfall anomaly in the models and the MME. The potential improvement of model forecasting skill is found in the Asian summer monsoon region, where the anomaly correlation coefficient (ACC) has been improved by 7–40%, corresponding to the decreased root mean square error (RMSE) in the model and the MME precipitation anomaly forecasts.     

Spatial interpolation of monthly and annual rainfall in northeast of Iran

Precipitation maps are the key input to many hydrological models. In this paper different univariate (inverse distance weighing and ordinary kriging) and multivariate (linear regression, ordinary cokriging, simple kriging with varying local mean and kriging with an external drift) interpolation methods are used to map monthly and annual rainfall from sparse data measurements. The study area is Golestan Province, located in northeast of Iran. A digital elevation model is used as complementary information for multivariate approaches. The prediction performance of each method is evaluated through cross-validation and visual examination of the precipitation maps produced. Results indicate that geostatistical algorithms clearly outperform inverse distance weighting and linear regression. Among multivariate techniques, ordinary cokriging or kriging with an external drift yields the smallest error of prediction for months April to October (autumn and winter) for which the correlation between rainfall and elevation is greater than 0.54. For all other months and annual rainfall, ordinary kriging provides the most accurate estimates.     

Forced response of the East Asian summer rainfall over the past millennium: results from a coupled model simulation

The centennial?Cmillennial variation of the East Asian summer monsoon (EASM) precipitation over the past 1000?years was investigated through the analysis of a millennium simulation of the coupled ECHO-G model. The model results indicate that the centennial?Cmillennial variation of the EASM is essentially a forced response to the external radiative forcing (insolation, volcanic aerosol, and green house gases). The strength of the response depends on latitude; and the spatial structure of the centennial?Cmillennial variation differs from the interannual variability that arises primarily from the internal feedback processes within the climate system. On millennial time scale, the extratropical and subtropical precipitation was generally strong during Medieval Warm Period (MWP) and weak during Little Ice Age (LIA). The tropical rainfall is insensitive to the effective solar radiation forcing (insolation plus radiative effect of volcanic aerosols) but significantly responds to the modern anthropogenic radiative forcing. On centennial time scale, the variation of the extratropical and subtropical rainfall also tends to follow the effective solar radiation forcing closely. The forced response features in-phase rainfall variability between the extratropics and subtropics, which is in contrast to the anti-correlation on the interannual time scale. Further, the behavior of the interannual?Cdecadal variation in the extratropics is effectively modulated by change of the mean states on the millennial time scale, suggesting that the structure of the internal mode may vary with significant changes in the external forcing. These findings imply that on the millennial time scale, (a) the proxy data in the extratropical EA may more sensitively reflect the EASM rainfall variations, and (b) the Meiyu and the northern China rainfall provide a consistent measure for the EASM strength.     

Modelling Indonesian rainfall with a coupled regional model

Long-term high-resolution coupled climate model simulations using the Max Planck Institute Regional Climate Model and the Max Planck Institute Ocean Model have been performed with boundary forcings from two reanalyses: firstly from the European Centre for Medium-Range Weather Forecasts, and secondly from the joint reanalysis of the National Centers for Environmental Prediction and the National Center for Atmospheric Research. This study employs a special coupling setup using a regional atmospheric model and a global ocean model. The latter model applies a special conformal grid from a bipolar orthogonal spherical coordinate system, which allows irregular positions of the poles and focuses on the detail over the Maritime Continent. The coupled model was able to simulate stable and realistic rainfall variabilities without flux correction and at two different ocean resolutions. The coupled system is integrated for a period between 1979 and 1993 and the results are then compared to those from uncoupled runs and from observation. The results show improved performance after coupling: a remarkable reduction of overestimated rainfall over the sea for the atmospheric model and of warm SST biases for the ocean model. There is no significant change in rainfall variability at higher ocean model resolution, but the ocean circulation shows less transport variability within the Makassar Strait in comparison to observations. This paper has not been published or considered by any other journal in any language.     

Time-lagged impact of spring sensible heat over the Tibetan Plateau on the summer rainfall anomaly in East China: case studies using the WRF model

This study explores the time-lagged impact of the spring sensible heat (SH) source over the Tibetan Plateau (TP) on the summer rainfall anomaly in East China using the Weather Research and Forecasting model. Numerical experiments for 2003 indicate that a spring SH anomaly over the TP can maintain its impact until summer and lead to a strong atmospheric heat source, characterized both by the enhanced SH over the western TP and enhanced latent heat of condensation to the east. Wave activity diagnosis reveals that the enhanced TP heating forces a Rossby wave train over the downstream regions. A cyclonic response over the northeast TP brings about a low-level northerly anomaly over northern China, while an anticyclonic response over the western Pacific enhances the subtropical high and the low-level southerly on its western flank. As a result, cold and dry airflow from mid-high latitudes, and warm and wet airflow from tropical oceans converge around the Huaihe River basin. In addition, warm advection originating from the TP induces vigorous ascending motion over the convergence belt. Under these favorable circulation conditions the eastward-propagating vortexes initiated over the TP intensify the torrential rainfall processes over the Huaihe River basin. In contrast, additional experiments considering the year 2001 with weak spring SH over the TP and an overall southward retreat of the summer rainfall belt in East China further demonstrate the role of spring SH over the TP in regulating the interannual variability of EASM in terms of wave activity and synoptic disturbances.     

Recent spatial and temporal variations in mean sea level pressure over Europe and the Middle East,and their influence on the rainfall regime in the Galilee,Israel

Summary A comparison of maps of mean sea level pressure (MSLP) for two normal peridos enabled the detection of variations in MSLP over Europe and the Middle East. Even though a general pattern is evident on the maps for each month in both periods, differences in the magnitude of the values were detected. Plotting these differences permitted the identification of regions with the greatest variations and determination of the anomaly flow between the two periods. A polynomial curve fitted to the seasonal record of the MSLP at 35 selected points for each period allowed identification of temporal variations in MSLP. The main temporal change between the period 1931–60 and the period 1951–80 was a delay in the development of a high pressure over Siberia in the latter period. Changes in horizontal pressure differences (CHPD) between Byelorussia in the Soviet Union and the Sahara Desert related previously described rainfall variations to those pressure variations.The present paper is based on data analyzed by the author as part of his dissertation completed at the University of Utah in 1988 under the supervision of Professor Paul A. Kay.With 11 Figures     

基于贝叶斯模型的器测、古气候重建与气候模拟数据的融合试验

气象部门馆藏的西部最早的器测气象资料始于20世纪30年代,不能满足建立20世纪以来中国气候变化序列的需求,而古气候重建或气候模拟资料则可以延伸到器测时代以前。为了探讨长序列多源气候资料序列融合方法,采用贝叶斯方法对中国北疆地区8条树轮气温重建资料、器测资料与国际耦合模式比较计划第5阶段（CMIP5）模式模拟资料进行了融合试验。首先利用器测资料对气温代用资料进行校验与网格重建,并以此作为贝叶斯模型的先验分布,然后,用泰勒图选出了该区域气候模拟效果最佳的几个模式;最后将网格重建和气候模拟序列用贝叶斯模型进行了融合试验。结果表明,贝叶斯融合模型能有效提取各种数据来源的有用信息进行融合,融合结果的长期变化（线性）趋势更接近器测气候序列,并在一定程度上提高了序列的精度,减小了结果的不确定性;并且,融合结果能够纠正先验分布及气候模拟数据的明显偏差,为长年代气候序列重建提供了一个可行的思路。