ISSN 1000-0526
CN 11-2282/P

Volume 39,Issue 7,2013 Table of Contents

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  • 1  Using Self Organizing Maps to Investigate Summer Synoptic Climatology in North China Area
    DAI Kan JIN Ronghua HU Ting
    2013, 39(7):801-812. DOI: 10.7519/j.issn.1000-0526.2013.07.001
    [Abstract](1114) [HTML](55) [PDF 8.54 M](1116)
    Analysis of the synoptic climatology over the North China Area promotes a better understanding of the relationships between atmospheric circulation and surface elements. Therefore, investigation on synoptic climatology features is conducted based on the classified synoptic types of North China using the summer ERA 40 MSLP data from 1958 to 2002 which are treated by self organizing maps (SOMs) algorithm. 36 different synoptic patterns are identified, which can be divided into 4 kinds of extreme types such as strong north high and south low, strong west high and east trough, strong northwest low and southeast high and westward extension of strong eastern high, as well as transitional types between them. Study of spatial characteristics indicates that the symmetry of synoptic types in 2D self organizing maps reflects the general characteristics of synoptic climatology over the North China Area, whereas the asymmetry represents the unique features. Study of temporal characteristics shows that synoptic situation of the study area is relatively more stable with stronger high and low systems, or with dominant high system, and vice versa. By referring to the interannual analysis, it is apparent that 6 patterns are dominated by remarkable linear trends. Finally, analysis is performed on precipitation distribution characteristics of the corresponding synoptic patterns. It shows that the rainfall in different parts of North China is contributed by distinct synoptic types, and slight changes in surface circulation can produce drastically different locations of precipitation center, while the topographic effect will further amplify the difference. This study uses a more comprehensive dataset and higher temporal resolution data than most of the past studies to quantitatively investigate the summer synoptic types in North China, resulting in the expansion of synoptic climatology research over the study area. Therefore, results here can be applied to develop the identification technology of the typical weather process in numerical weather predication, and to be the basis of regional climate scenarios research.
    2  Analysis on the Spatial Temporal Characteristics of Freezing Rain in Recent Decades
    ZONG Zhiping MA Jie ZHANG Hengde HUA Cong
    2013, 39(7):813-820. DOI: 10.7519/j.issn.1000-0526.2013.07.002
    [Abstract](1233) [HTML](61) [PDF 3.80 M](969)
    Using EC reanalysis data and the data from observation stations in China, this study analyzes the 53 freezing rain processes which occurred during the period 1978-2002, defines the incidental region and discusses the variability of their spatial temporal features in recent decades. The result shows that the intensity of the freezing rain events these years has a significant decreasing trend, whose break point happened in 1990. Then, two kinds of norms that measure the intensity of freezing rain: the number of stations that experienced the freezing rains and the durations are compared, finding close connections in them. The effects of the two methods used for describing the variability of freezing rain are similar. In addition, through the methods of composite analysis and empirical orthogonal function (EOF), it is revealed that the reverse layer is not only the essential requirement for producing freezing rains, but also acts as an intensity adjustor of the change of freezing rain intensity.
    3  Observation and Analysis of a Southwest Vortex Rainstorm in Southern China Using FY-2 Satellite Data
    DU Qian QIN Danyu ZHANG Peng
    2013, 39(7):821-831. DOI: 10.7519/j.issn.1000-0526.2013.07.003
    [Abstract](1530) [HTML](60) [PDF 2.19 M](2107)
    During 11-13 June 2008, one south vortex (SV) rainstorm occurred in South China, in which the 24 h precipitation from 6 stations in Guangxi broke the historical record of daily precipitation in June, and they are: Donglan (306 mm), Huanjiang (218 mm), Lingchuan (270 mm), Guilin (251 mm), Liucheng (177 mm) and Tianlin (163 mm). Based on the FY 2C Infrared (IR) cloud imagery, NCEP reanalysis data, the conventional observation data and surface precipitation data, this paper analyzes the rainstorm cloud cluster, the impact system and ambient fields of this severe rainfall process. The results show that: (1) the infrared and water vapor images can reflect the different effects of the cloud system in mid and low level convergence zone, the upper air disturbed cloud system and weak cold airs when the SV moves eastward. The evolution process of the images depicts the flow pattern of the low level convergence and high level divergence when the rainstorm occurs; (2) This SV rainstorm in Guangxi has two stages in its life cycle. In the 1st stage, the rainfall forms in the warm side of the SV and the convection cloud clusters spread widely with rotation structures; in the 2nd stage, when the weak cloud airs move down from the north, the mesoscale convective system (MCS) of the SV becomes band shaped and dissipates. During the process, both the temporal evolutions of the infrared brightness temperature (TBB) and the TBB difference between the infrared and water vapor images are well corresponding to the evolution of the severe precipitation. By monitoring the rapid drop of multi spectral TBB, the severe rainfall warning could be issued 2-3 h in advance; (3) the rainstorm cloud cluster appears in the areas in the southeast and the south side of the SV, where the southerly wind prevails. Meanwhile, the developing of the cloud cluster is accompanied by the intensification of low level jet and the contribution of the positive vorticity advection at500 hPa.
    4  Fine Analysis on the Rainfall Distribution of Meridional Shear Line Heavy Rain
    SUN Xingchi WU Wei ZHOU Xuesong GUO Junjian JIANG Peng
    2013, 39(7):832-841. DOI: 10.7519/j.issn.1000-0526.2013.07.004
    [Abstract](1421) [HTML](67) [PDF 8.29 M](1177)
    Based on the conventional observational data and NCEP 1°×1° reanalysis data, two types of heavy rains in relation to the surrounding longitudinal shear lines with or without concomitant stationary front are investigated. The surface, high and low level synoptic configuration and interaction between cold and warm airs are carefully analyzed to supply the general conceptual model for the torrential rains in the southeast quadrant of the low vortex and to meet the requirement for refined forecasting. The results indicate that these types of shear lines with or without concomitant front are obviously different in the spatial structure. Because of the existing frontal structure in the shear line system that is accompanied by stationary front, the effect of front lifting is significant. And then, one of the favorable heavy rainfall zones is located in the surface inverted trough or the northerly airflow behind the surface low; another one is in the warm zone of the stationary front, resulting from the dry incursion above the warm conveyor belt during the phase of the interaction between cold and warm air, especially during the mature phase of the extratropical cyclone. On the other hand, during the meridional shear line heavy rain process without the accompanying of the stationary front, there is not the frontal system jointly affected by south winds and north winds so the extremly heavy rainfall appears in the southeast quadrant of the low level vortex. Another likely zone of so heavy rainfall is the overlap zone of the high θe tongue at 850 hPa, high specific humidity tongue and weak water vapor convergence that produce potential convective instability, without the infulence of the low level jet.
    5  Synoptic Analysis on Forecast Error of Super Typhoon Muifa and Severe Typhoon Roke
    ZHANG Ling HUANG Yiwu
    2013, 39(7):842-847. DOI: 10.7519/j.issn.1000-0526.2013.07.005
    [Abstract](975) [HTML](47) [PDF 1.89 M](1204)
    The track and intensity forecast errors of super Typhoon Muifa (No.1109) and the rapid intensification of severe typhoon Roke (No.1115) over south of Japan are analyzed in this paper and some practical forecasting points are obtained. The results show that the combination of NW Pacific Ocean subtropical high and equatorial high located between the two typhoons which row from east to west is an obvious signal for the typhoon in the west to move northward. The high over China mainland at the west of the typhoon and the equatorial high located southeastward of the typhoon should also be focused on in the forecasting process. In terms of the typhoon intensity forecast, upper level trough to its northwest approaching typhoon with southwesterly jet which is at the speed of more than 40 m·s-1 is a favorable condition for the intensifying process. In addition, in the synoptic situation unfavorable for the intensification of typhoon, the mutual effect between thermal status of tropical ocean and the typhoon is another key point in the operational intensity forecasting.
    6  Characteristics of Mesoscale Convective System and Its Effects on Short-Time Severe Rainfall in Sichuan Basin During 21-22 July 2012
    CHEN Yongren LI Yueqing
    2013, 39(7):848-860. DOI: 10.7519/j.issn.1000-0526.2013.07.006
    [Abstract](1497) [HTML](142) [PDF 6.67 M](1431)
    Using FY2D TBB data, radar echo data, routine meteorological data, precipitation data of automatic weather stations, NCEP 1°×1° reanalysis data etc. are analyzed characteristics of mesoscale convective system (MCS) and its effects on short time extremely heavy precipitation in Sichuan Basin during 21-22 July 2012. The results show that: (1) This precipitation process has two significant 6 h short time severe rainfall stages. The first stage is from 00:00 to 06:00 BT 21 July 2012, and the second is from 21:00 BT 21 to 03:00 BT 22 July 2012. In the first stage, the short time severe rainfall in western Sichuan Basin is caused by MCS, which is affected by 500 hPa plateau vortex and 700 hPa low vortex shear line. In the second stage, the extremely heavy rain is caused by the 500 hPa plateau vortex and 700 hPa southwest low vortex. (2) Short time severe rainfalls are usually caused by deep convections in MCS. In its developing process, MCS is in meso βscale or meso γ scale, having the features of low TBB values, big radar reflectivity factors and high VIL values. (3) The analysis of sounding data shows that unstable energy of atmosphere is high, CAPE value is large and vertical wind shear is dramatic during the early stage of MCS. The interaction areas of low level cold and warm temperature advections are beneficial to induce MCS, and the temperature gradient is high in these areas. Also during different developing periods, the structure of MCS shows positive vorticity and negative divergence in low level, while negative vorticity and positive divergence exist in high level. Such physical structure is an important factor for MCS to develop and maintain, and it is also one physical mechanism for short time severe precipitation.
    7  Mesoscale Ambient Field Analysis of Torrential Rains and the Forecast Key Points in Guizhou in 2012
    DU Xiaoling
    2013, 39(7):861-873. DOI: 10.7519/j.issn.1000-0526.2013.07.007
    [Abstract](1137) [HTML](39) [PDF 5.21 M](1136)
    Based on NCEP reanalysis data, FY 2E black body temperature TBB data, MICAPS types data, and the automatic station data in Guizhou, 15 torrential rains are classified into three types mainly. They are the convergence line frontogenesis type, the convergence line frontogenesis and cold air type, and the western Meiyu front type. Mesosclae ambient field analysis is used in each type of torrential rains to hold main influence systems. At the same time, the ingredients based forecasting methodology is used to analyze the water vapor and stability conditions as well as the uplift conditions in the extremely heavy rains. By means of analysis, we find the key points in different types of heavy rains. Those points are useful reference for the forecasting of heavy rains in Guizhou in future.
    8  Analysis on Elevated Thunderstorm Hail in Guangxi in Early Spring of 2012
    NONG Mengsong LAI Zhenquan LIANG Juncong DONG Liangmiao LIU Guozhong
    2013, 39(7):874-882. DOI: 10.7519/j.issn.1000-0526.2013.07.008
    [Abstract](3833) [HTML](91) [PDF 2.97 M](2133)
    Based on conventional observational data and radar data, the elevated thunderstorm hail process in Guangxi in early spring of 2012 is analyzed. The results show that: (1) Hail accompanied by thunderstorm occurs on the surface about 1000 km away from the front, and boundary layer is controlled by cold high pressure. The smaller winds at 850 hPa, strong jet stream at 700 hPa and above layer, strong vertical wind shear between 700 hPa and 850 hPa and eastward move of cold trough at 500 hPa provide the trigger condition for the occurrence of the convection. (2) Hail occurs in the range of approximately 200 km away from the shear line at 850 hPa, where there is strong intensity of the pressure surface frontal zone. The negative variable temperature in front of the upper trough increases the temperature difference in vertical direction between 700 hPa and 500 hPa, resulting in the increase of stratification convective instability. When the trough at 500 hPa moves up to the air above the frontal zone, the frontal slope becomes steep, and the upward movement strengthens while the instability increases. All of these make the ice embryo grow in the troposphere and form hail. (3) The storm tracking information displays that storms are generated in high altitudes, and the centroids are 5-6 km high. After the storm is generated, the centroids gradually develop to lower layer with time going. The maximum reflectivity and liquid water content are not large, showing the significant characteristics of the elevated thunderstorms.
    9  Application of Mesoscale Synoptic Analysis Techniques in Four Heavy Rainfall Processes in South China in 2011
    XU Aihua CHEN Yun
    2013, 39(7):883-893. DOI: 10.7519/j.issn.1000-0526.2013.07.009
    [Abstract](1130) [HTML](54) [PDF 3.16 M](1156)
    The precipitation data from model is a significant forecast basis for the severe precipitation of more than 50 mm in 12 h, but sometimes the deviation can be 100-200 km in forecasting. Based on Mesoscale Synoptic Analysis Technics Regulation (provisional) and sounding data this paper tries to analyze the mesoscale weather chart of 4 severe rainfall processes in South China during the Meiyu season of 2011, getting the key point of forecasting the heavy rainfall near Meiyu front and presenting some evidences for estimating the precipitation regions. Convergence zones of southwest or southern jet under 700 hPa have strong power, moisture convergence and certain vertical wind shear. Surface pressure trough lower than the minimum of 3 h daily variation is prone to form convergence flow field of isallobaric wind. And it is also the heavy rainfall areas (center). In most circumstances, the front can be regarded as southern boundary of the heavy rainfall, but when the 925 hPa warm shear is in (or near) the south of surface front, heavy rainfall occurs in the warm sector ahead of fronts. And, southwest jet above 10 m·s-1which reaches the latitude areas can act as the southern boundary. More than 18 ·s -1 southwest jet in front of trough at 500 hPa can act as the northern boundary of the heavy rainfall area. When the position of 925 hPa shear line overlaps the southwest jet or in the north of it, the 700 hPa shear line can be regarded as the northern boundary. Comparing these criterions with the output of Japanese model, it is found that the results can rectify the southern and northern boundaries of strong rainfall belt as well as rainfall center. Therefore, mesoscale Synoptic Analysis Technics and its forecasting ideas is an effective means for the revised model of heavy rain location forecasting.
    10  Advances of Mesoscale Convective Weather Analysis in NMC Ⅰ: Convective Weather Environment Analysis and Supporting Techniques
    ZHANG Tao LAN Yu MAO Dongyan ZHENG Yongguang TANG Wenyuan CAO Li ZHANG Xiaoling CHEN Yun FANG Chong ZHOU Xiaoxia ZHAO Surong LIU Xinhua TIAN Fuyou
    2013, 39(7):894-900. DOI: 10.7519/j.issn.1000-0526.2013.07.010
    [Abstract](1457) [HTML](82) [PDF 1.55 M](1437)
    The mesoscale convective weather analysis plays an important role in operational forecasting. Progresses have been made in both the mesoscale analysis technique and its operation since 2011, which have significantly promoted the development of severe weather forecasting in the National Meteorological Centre (NMC). The updated Mesoscale Analysis Technical Specification consists of two parts. The mesoscale convective weather environment analysis is presented in this paper while the contents of the mesoscale nowcasting analysis are to be introduced in another paper. Based on ingredient method, the analysis content of the specification was simplified and reconstructed; meanwhile the refinements and the manipulation of analyzing products were given fully consideration. Moreover, a new part of sounding analysis and the quantitative standards for convective parameters were added into the specification. In the aspect of supporting technology, the subjective analyzing toolbox for mesoscale convective weather (in MICAPS 3) was improved, and a product integration system, including data and graphic products of severe convective weather monitoring, subjective and objective mesoscale analysis, diagnostic products of convective parameters and so on, was developed and has been being used in NMC.
    11  Advances of Mesoscale Convective Weather Analysis in NMC Ⅱ: Mesoscale Nowcasting Analysis and Supporting Techniques
    LAN Yu ZHANG Tao ZHENG Yongguang MAO Dongyan ZHU Wenjian LIN Yinjing ZHANG Xiaoling
    2013, 39(7):901-910. DOI: 10.7519/j.issn.1000-0526.2013.07.011
    [Abstract](1347) [HTML](150) [PDF 1.20 M](1314)
    Mesoscale convective analysis plays an important role in short term severe convective weather forecasting. In this paper, the mesoscale nowcasting analysis and its related techniques being used in the National Meteorological Centre (NMC) are presented. The mesoscale nowcasting analysis is the second part of Mesoscale Analysed Technical Specification. A comprehensive analysis method combined with subjective nowcasting techniques and objective algorithm based on CMA Severe Weather Automatic Nowcasting system (SWAN) is used. The techniques of severe convective weather monitoring, and objective analyzing method of automatic observation station are also introduced. Taking the convective weather that occurred on 17 April 2011 as an example, we show how to quickly identify and acquire the actual severe convective weather events such as short time severe precipitation, wind gusts, thunderstorm, hail and tornadoes, analyze the types and structural characteristics of the ongoing mesoscale convective system, judge the favorable mesoscale environments for the future development of the convective system and apply the objective identification, tracking and extrapolation products based on radar and satellite data, so as to guide the convective nowcasting in 0-6 h period. Tests in NMC show that the mesoscale nowcasting analysis can provide reliable references for severe convective weather nowcasting.
    12  Analysis on Sand Entrainment and Deposition and Transportation Pathways of One Sand Dust Process in Beijing
    ZHANG Yani ZHANG Bihui ZONG Zhiping WU Ying
    2013, 39(7):911-922. DOI: 10.7519/j.issn.1000-0526.2013.07.012
    [Abstract](851) [HTML](58) [PDF 6.32 M](1238)
    The sand and dust weather that affected Beijing on 27-28 April 2012 is studied. The finding suggests that the sandstorm in sand source area happens mainly behind the cold front and the 500-hPa trough, where, because of the strong surface sensible heating and the cold advection in middle and lower troposphere, the deep mixed layer or even the unstable stratification forms and can reach up to 600 hPa, and such instability of stratification is an important condition for the sandstorm to affect the downstream area. Moreover, based on the analysis of the variation of the mixed layer thickness and its advective process we also study the transportation pathways and locate the deposition area of the sandstorm. It is found that there are two transportation pathways. One extends eastwards along the northern part of Liaoning Province and then turns to northeast with a higher height. Dust particles move downstream with the advection of the mixed layer. Afterwards, with the decreasing height of the mixed layer, the deposition occurs and sand particles reach the surface. The other extends southeastwards along the south of Liaoning Province. At the stage of transportation, the advection of the mixed layer is clear, but the mechanism of the deposition is different from the former one. The deposition occurs due to the descent in lower troposphereand the surface divergence. Afterwards, along the easterlies on the south side of the cold anticyclone behind the cold front, the sand particles are transported westwards to Beijing. In addition, the latter path is lower than the former because the stable layer which lies above the mixed layer descends obviously. Based on HYSPLIT model the backward and forward trajectories are computed. It proves the above two transportation pathways, showing that it is the easterly return flow that results in the sand dust event in Beijing.
    13  Comparison and Application of Different Adjustment Methods for Quantitative Precipitation Estimate by Weather Radar
    ZHANG Yaping ZHANG Yong LIAO Jun DENG Chengzhi LI Jing
    2013, 39(7):923-929. DOI: 10.7519/j.issn.1000-0526.2013.07.013
    [Abstract](1051) [HTML](73) [PDF 2.29 M](1297)
    Distribution estimates of hourly intense precipitation derived from radar and rain gauges by the local classified average bias adjusted and local average bias adjusted algorithms are examined for an extreme rainfall event that occurred in 21-22 July 2012 in Rongchang, Chongqing. The results show that the local classified average bias adjusted algorithm is better in estimating hourly intense rainfall than the local average bias adjusted algorithm. The accuracy of rainfall estimation is related to the local adjusted radius. The analyses of rainfall distribution and disaster situation show that the combination of intense rainfall distribution and river networks is significant for meteorological flood risk forecast of intermediate rivers.
    14  Features and Possible Causes for East Asian Winter Monsoon in 2012/2013
    WANG Dongqian ZHOU Bing SUN Chenghu YUAN Yuan LIU Yanju WANG Pengling
    2013, 39(7):930-937. DOI: 10.7519/j.issn.1000-0526.2013.07.014
    [Abstract](1164) [HTML](40) [PDF 4.14 M](1040)
    The East Asian winter monsoon (EAWM) was in the phase stronger than normal in the inter decadal variation, and the EAWM index was 0.83 in winter 2012/2013, which was the 6th consecutive year with strong intensity. During the winter from December 2012 to February 2013, the daily Arctic Oscillation index was negative, leading to a colder than normal situation over China. While the Siberian High (SH) exhibited strong intra seasonal variations, the temperature over China had two stage variations last winter, warmer in the early winter and colder in the late winter. Further research indicated that the reduced Arctic sea ice extent in the last autumn was responsible for the positive sea level pressure (SLP) in the Northern Eurasia in winter, resulting in the strengthening of Siberian High which was favorable for cold front to move southward into China. The intra seasonal variation of the SH and EAWM was mainly affected by the downward propagation of positive geopotential height anomalies in stratosphere.The positive stratospheric anomalies over the high latitude areas in Northern Hemisphere in mid January had an evident influence on the mid and low levels of troposphere, causing the periodical weakening of SH and EAWM.
    15  Analysis of the April 2013 Atmosphere Circulation and Weather
    ZHANG Xiaowen SUN Jun
    2013, 39(7):938-944. DOI: 10.7519/j.issn.1000-0526.2013.07.015
    [Abstract](914) [HTML](40) [PDF 2.43 M](997)
    The following are the main characteristics of the general circulation of atmosphere in April 2013. There is one polar vortex center in the Northern Hemisphere, and the strength is similar to normal years. The circulation presents a four wave pattern in middle high latitudes. Both of the south branch trough and the Northwestern Pacific subtropical high (NPSH) are slightly weaker, unfavourable for the drought relief in southwestern China. The monthly mean temperature is 11.0℃, equal to the value in the normal years except the unusual low temperature in northeast. The average precipitation of China is 43.2 mm, 1.5 mm less than the normal. There are 2 cold surge processes accompanied by sand dust events in April. The southern part of China has 3 severe precipitation events, of which the process in 29-30 April covers the largest area and has the strongest intensity, especially in South China and Jiangnan region, severe convections happen at the same time.

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