川渝盆地主汛期短时强降水事件日变化特征研究

利用四川盆地和重庆地区1980-2012年主汛期（5-9月）基本站小时降水观测资料,分析了短时强降水事件降水量、频次和强度的日变化特征,研究了短时强降水事件日峰值位相和空间分布特征,事件极值降水日变化和持续时间等分布特征,得出以下主要结论：1）川渝盆地短时强降水事件开始时间的日变化上（01：00-24：00时,北京时间,下同）,表现为“V”型结构下典型夜间峰值位相特征;结束时间的日变化上,表现为多个峰值型结构分布.强降水事件持续时间的日变化上,频次和降水量均呈双峰型结构,频次极大峰值出现在3 h,而强度上随着持续时间的延长,呈现逐渐增加的趋势;2）短时强降水事件极值开始时间空间分布上,极大频次和极大降水量出现在20：00-01：00时内,主要分布在盆地南部和西部大部分地区;日峰值频次结束时间主要发生在20：00-01：00时和08：00-13：00时两个时段内,主要分布于盆地南部、中部和西部大部分地区;3）短时强降水事件极值降水的日变化上,降水量和频次呈现单峰型结构,白天多为短时间（2~4 h）强降水事件出现极值,而傍晚开始至第二天清晨,持续2~10 h强降水事件出现极值均有发生;强降水事件极值降水持续时间日变化,1~24 h内呈单峰型结构,峰值出现在2 h.     

Synoptic-scale variation of δ18O in summer monsoon rainfall at Lijiang, China

Based on the daily δ~(18)O data in June―September 2003 at Lijiang and the daily mean NCEP/ NCAR reanalysis data, synoptic-scale variation of δ~(18)O in summer monsoon rainfall was investigated. The 'precipitation amount effect' is obvious for the daily δ~(18)O variation, whereas the 'temperature effect' is insignificant. Alternate occurrences of active phase and break phase of the southwest monsoon probably influence the synoptic-scale δ~(18)O variation prominently. Moreover, the isotopic composition in precipitation during the late monsoon months is presumably influenced significantly by recycling of monsoon precipitation. Both the above factors disturb the 'amount effect' of isotopic variation in the monsoon region. This study also indicates that the synoptic-scale rainfall δ~(18)O variation at Lijiang in summer is domi-nated by the Indian monsoon depression (low pressure) system at large scale. These results are important for further studying the 'amount effect' and reconstructing paleoclimate in the monsoon region.     

The asymmetry of rainfall process

Using hourly station rain gauge data in the warm season (May-October) during 1961-2006, the climatological features of the evolution of the rainfall process are analyzed by compositing rainfall events centered on the maximum hourly rainfall amount of each event. The results reveal that the rainfall process is asymmetric, which means rainfall events usually reach the maximum in a short period and then experience a relatively longer retreat to the end of the event. The effects of rainfall intensity, duration and peak time, as well as topography, are also considered. It is found that the asymmetry is more obvious in rainfall events with strong intensity and over areas with complex terrain, such as the eastern margin of the Tibetan Plateau, the Hengduan Mountains, and the Yungui Plateau. The asymmetry in short-duration rainfall is more obvious than that in long-duration rainfall, but the regional differences are weaker. The rainfall events that reach the maximum during 14:00-02:00 LST exhibit the strongest asymmetry and those during 08:00-14:00 LST show the weakest asymmetry. The rainfall intensity at the peak time stands out, which means that the rainfall intensity increases and decreases quickly both before and after the peak. These results can improve understanding of the rainfall process and provide metrics for the evaluation of climate models. Moreover, the strong asymmetry of the rainfall process should be highly noted when taking measures to defending against geological hazards, such as collapses, landslides and debris flows throughout southwestern China.     

Statistic characteristics and weather significance of infrared TBB during May―August in Beijing and its vicinity

In order to meet the demand of nowcasting convective storms in Beijing, the climatological characteristics of convective storms in Beijing and its vicinity were analyzed based on the infrared （IR） temperature of black body （TBB） data during May--August of 1997--2004. The climatological probabilities, the diurnal cycle and the spatial distribution of convective storms are given respectively in this paper. The results show that the climatological characteristics of convective storms denoted by TBB≤-52℃ are consistent with those statistic studies based on the surface and lightning observations. Furthermore, the climatological characteristics of May and June are very different from those of July and August, showing that there are two types of convective storms in this region. One occurs in the transient polar air mass on the midlatitude continent during the late spring and early summer. This type of convection arises with thunder, strong wind gust and hail over the mountainous area in the northern part of this region from afternoon to nightfall, the other occurs with heavy rainfall in the warm and moist air mass over the North China Plain and vicinity of Bohai Sea. This study also shows that the long-term data of IR TBB observed by geostationary satellite can complement the temporal and spatial limitation of the weather radar and surface observations.     

1951—2014年淮河流域降水量时空变化特征

以1951—2014年淮河流域29个站点月降水量数据为研究对象,运用线性趋势、累积距平、小波分析及空间分析等方法,分析了降水量时间和空间变化特征.结果表明:(1)1951—2014年,年、春、夏和秋季降水量呈不显著减少趋势,冬季降水量则具有不显著增加趋势.(2)春、秋和冬季易发生旱涝灾害,夏季降水量变化控制年降水量变化.(3)年降水量具有准2a和6a振荡周期.(4)东南部年和四季降水量多于西北部,这与我国年和四季降水量分布模式一致.(5)空间上,年和四季降水量变率中,年和夏季最大,降水量减少区域呈半环状包围降水量增加区域;整个流域冬季降水量几乎没有变化.     

A physically-based statistical forecast model for the middle-lower reaches of the Yangtze River Valley summer rainfall

A new approach to forecast the middle-lower reaches of the Yangtze River Valley summer rainfall in June-August （JJA） is proposed in this paper. The year-to-year increment of the middle-lower reaches of the Yangtze River Valley is forecasted and hence the summer precipitation could be predicted. In this paper, DY is defined as the difference of a variable between the current year and the preceding year （year-to-year increment）. YR denotes the seasonal mean precipitation rate of the middle-lower reaches of the Yangtze River Valley summer rainfall. After analyzing the atmospheric circulation anomalies in winter and spring that were associated with the DY of YR, six key predictors for the DY of YR have been identified. Then the forecast model for the DY of YR is established by using the multi-linear regression method. The predictors for the DY of YR are Antarctic Oscillation, the meridional wind shear between 850hPa and 200hPa over the Indo-Australian region, and so on. The prediction model shows a high skill for the hindcast during 1997-2006, with the average relative root mean square error is at 18%. The model can even reproduce the upward and downward trends of YR during 1984--1998 and 1998--2006. Considering that the current operational forecast models of the summer precipitation over the China region have the average forecast scores at 60%--70% and that the prediction skill for the middle-lower reaches of Yangtze River Valley summer precipitation remains quite limited up to now, thus this new approach to predict the year-to-year increment of the summer precipitation over the Yangtze River Valley （and hence the summer precipitation itself） has the potential to significantly increase the operational forecast skill of the summer precipitation.     

Climatic significance of δ18O records from precipitation on the western Tibetan Plateau

Analysis of daily precipitation samples for stable oxygen isotopes （δ^18O） collected at the Shiquanhe and Gerze （Gaize, Gertse） stations in the Ngari （Ali） region on the western Tibetan Plateau indicates that air temperature affects the δ^18O variations in precipitation at these stations. In summer, Shiquanhe and Gerze show strongly similar trends in precipitation δ^18O, especially in simultaneous precipitation events. Moreover, both stations experienced low δ^18O values in precipitation during the active monsoon period, resulting from the southwest monsoon （the summer phase of the Indian monsoon）. However, during the break monsoon period （during the summer rainy season, when the monsoon circulation is disrupted）, δ^18O values in summer precipitation remain relatively high and local moisture recycling generally controls the moisture sources. Air temperature correlations with δ^18O strengthen during the non-monsoon period （January--June, and October--December） due to continental air masses and the westerlies. In addition, evaporation also influences the δ^18O variations in precipitation. The observed temporal and spatial variations of δ^18O in precipitation on the western Tibetan Plateau and adjacent regions show that the late May and early June-the late August and early September time frame provides an important period for the transportation of moisture from various sources on the Tibetan Plateau, and that the region of the West Kunlun-Tanggula Ranges acts as a significant climatic divide on the Plateau, perhaps for all of western China.     

Climatological distribution and diurnal variation of mesoscale convective systems over China and its vicinity during summer

The climatological distribution of mesoscale convective systems （MCSs） over China and its vicinity during summer is statistically analyzed, based on the 10-year （1996-2006, 2004 excluded） June-August infrared TBB （Temperature of black body） dataset. Comparing the results obtained in this paper with the distribution of thunderstorms from surface meteorological stations over China and the distribution of lightning from low-orbit satellites over China and its vicinity in the previous studies, we find that the statistic characteristics of TBB less than -52℃ can better represent the spatiotemporal distribution of MCSs over China and its vicinity during summer. The spreading pattern of the MCSs over this region shows three transmeridional bands of active MCSs, with obvious fluctuation of active MCSs in the band near 30^oN. It can be explained by the atmospheric circulation that the three bands of active MCSs are associated with each other by the summer monsoon over East Asia. We focus on the diurnal variations of MCSs over different underlying surfaces, and the result shows that there are two types of MCSs over China and its vicinity during summer. One type of MCSs has only one active period all day long （single-peak MCSs）, and the other has multiple active periods （multi-peak MCSs）. Single-peak MCSs occur more often over plateaus or mountains, and multi-peak MCSs are more common over plains or basins. Depending on lifetimes and active periods, single-peak MCSs can be classified as Tibetan Plateau MCSs, general mountain MCSs, Ryukyu MCSs, and so on. The diurnal variation of multi-peak MCSs is very similar to that of MCCs （mesoscale convective complexes）, and it reveals that multi-peak MCSs has longer life cycle and larger horizontal scale, becomes weaker after sunset, and develops again after midnight. Tibetan Plateau MCSs and general mountain MCSs both usually develop in the afternoon, but Tibetan Plateau MCSs have longer life cycle and more active MαCSs. Ryukyu MCSs generally develop after     

雷达估测降水模拟史灌河流域径流

运用雷达联合少量雨量计方法估测流域面雨量,结合GAME/HUBEX国际合作项目1998年加强观测期在史灌河流域获取的水文观测资料和TOPMODEL进行降水径流模拟,并与稠密雨量计站网测量的面雨量进行流域出口流量模拟的对比试验.在1500小时时间序列的比较试验表明,雷达估测面雨量和雨量计测量的面雨量都能较好地模拟每小时流域出口蒋集的出流量,数值试验还表明,雷达估测面雨量在某一时段上的均值误差作为一个指标可以较好地反映其应用于降水径流模拟时的精度;总雨量和强降水的估测精度是雷达估测面雨量能否用于径流模拟的关键.     

郑州市夏季降水的变化特征

利用1955—2011年郑州市夏季降水日逐分钟降水量,对郑州市降水日的降水量及其场次的年内和年际变化进行分析.结果表明:郑州市1981—2010年夏季降水量场次及其降水量平均分别为42.7场和8.4 mm,二者均有显著的变化趋势,气候倾向率分别为-2.2场/10a和0.56 mm/10a.郑州市场次降水平均持续时间和实际维持时间具有显著的线性相关关系.不管用场次降水量最长持续时间与其对应降水量的关系,还是利用场次最大降水量与其对应持续时间的关系,均表明随着时间的延长,降水量的数值会增加,反之依然.     

Interdecadal shift in the western North Pacific Summer SST anomaly in the late 1980s

An interdecadal shift in summer (June―August) sea surface temperature (SST) variations during the period of 1968―2002 was identified in the late 1980s, which is characterized by a phase alternating from negative to positive phases of the leading mode of the empirical orthogonal function (EOF) analysis of the summer monthly mean SST in the Pacific domain 100°―180°E and 0°―40°N, accounting for 30.5% of the total variance. During the period of 1968―1987, the leading mode with a mean negative phase state (mean standard deviation = ?0.586) controlled SST variability in the western North Pacific. Correspondingly, negative SST anomalies occupied the western North Pacific south of Japan and Chinese marginal seas. During the period of 1988―2002, the leading mode shifted to its strong positive polarity (mean standard deviation = 0.781), thus positive SST anomalies appeared in the western North Pacific. Accompanied by the interdecadal shift in summer mean SST, summer mean rainfall increased in southern and southeastern China during the late period, particularly in southeastern China where increase in summer mean rainfall exceeded 40 mm, at the 0.05 significance level.     

中尺度暴雨模式MRM1简介及预报效果检验

介绍了近年来我们所研制的中尺度暴雨模式MRM1的基本情况及特点，以及对1998年，1999年和2001年6月、7月的降水集中时段进行的逐日降水预报试验及效果检验，并和美国著名中尺度模式MM5进行了同一时段降水预报检验的比较。结果表明，它是目前国内较好的中尺度暴雨预报模式，在暴雨预报方面较MM5也有一定的优越性。     

福建省台风降雨的小时尺度响应特征

基于近5 a登陆福建沿海地区的台风最佳路径,采集台风登陆地区在台风登陆前后3 d(总计7 d)1747个气象监测站的降雨时程数据.通过识别提取台风登陆区域的降雨特征,在小时时间尺度上,比较研究各登陆区域台风降雨雨型、累积降雨量时程响应特征、峰值降雨强度以及降雨的时间尺度特征.研究结论可为台风暴雨型滑坡灾变机理的数值模拟...     

前汛期惠州市强降水气候突变及其环流特征分析

 惠州市地处气候年际变化显著的东亚季风区,近几十年来前汛期强降水事件频繁,尤其自20世纪90年代以来有很多暴雨灾害发生。为了客观地分析惠州前汛期强降水事件的异常情况,利用1967-2009年惠州市降水资料和NCEP/NCAR再分析资料,研究了前汛期惠州强降水的气候变化及其环流特征。结果表明：前汛期惠州市总降水量和暴雨量大,暴雨日数多;它们的年际变化一致,无明显趋势变化。但自1990年代中期至今,强降水异常有增多且强化的趋势。进一步对比惠州前汛期强降水异常事件突变前后的环流特征,强降水偏多（少）年,突变前后低纬地区均呈现偏南（东北）气流异常,而引起强降水偏多（少）年突变的环流形势差异,主要表现为突变后冷空气作用明显,低层北风分量增强;突变前后物理量的差异则主要表现为,突变后强降水偏多年高、低层散度梯度加大,垂直上升运动偏强,对流性不稳定加大,强降水偏少年上述物理量的变化相反;以上差异特征均导致突变后强降水偏多年更易引发或加剧强降水异常,强降水偏少年更不易于强降水的发生。     

甘肃陇中安家沟小流域日降水格局

利用1981-2009年生长季日降水资料,对陇中黄土高原安家沟小流域日降水格局及脉动特征进行研究.结果表明:生长季年均降水量为271.56 mm,年际变异系数为29.14%.降水事件以≤5 mm的降水为主,占全年降水事件的44.55%;≥10 mm的降水频率很低,但对年降水的贡献大,占降水总量的64.87%.0～10d降水间隔期(无降水日)所占比例最大,为年无降水期的87.03%;>10d降水间隔期呈增加趋势.近30年来,≤5 mm/d的降水呈下降趋势,而≥10 mm/d的降水略有上升,年内总降水日数与降水量均呈下降趋势.     

Rainfall retrieval over land from satellite remote sensing (SSM/I)

Composite microwave index (CMI) method is used with the satellite SSM/I data to retrieve summer rainfall rate over 96°E–127°E, 17°N–44°N. The results of verification are: the root-of-mean-square error is 0.9 mm/ h in the actual rain rate range from 2 to 2.9 mm/ h; 1.6 mm/h in that from 3 to 5 mm/h and the maximum rms error is 4.2 mm/h in that from 5.1 to 50 mm/h. Case study shows the decision tree and CMI method presented in the note are effective to the rainfall recognition and rain rate retrieval over land of East China.     

Barrier layer in the northeastern South China Sea and its formation mechanism

A VERTICALLY UNIFORM LAYER OF TEMPERATURE(ISOTHERMAL LAYER),SALINITY(ISOHALINE LAYER)AND DENSITY(MIXED LAYER)IS USUALLY FORMED IN THE UPPER OCEAN DUE TO THE WIND STIRRING.UNDERNEATH IS THE LAYER WITH RELATIVELY STRONG VERTICAL GRADIENT AS THE THERMOCLINE,…     

Numerical simulation of topography effects on the "00.7" severe rainfall in Beijing

In an effort to study the severe rainfall event of 4-5th July 2000 in Beijing (with 24h accumulated precipitation of 240 mm), we perform numerical simulations to investigate this event using the MM5v3.6 model. The model is initialized with the MM5/WRF 3DVAR analysis, which incorporates the ground-based GPS precipitable water vapor, automatic and conventional meteorological observations in its assimilation step. For 24 h accumulated precipitation forecast, the threat scores are 0.72, 0.76, 0.67 and 0.63, for thresholds of 1, 5, 10, and 20 mm, respectively. Holding other factors unchanged, sensitivity experiments were conducted with different topographic resolutions of 110, 50 and 3.7 km to investigate the topographic effects on precipitation over the Beijing area. In these sensitivity experiments, we attempt to preserve the realistic orographic distribution in the model topography under the condition of keeping the dynamic-thermodynamic consistency of the initial model atmosphere to the extent possible. Results indicate that the unique topographic distribution and variations in the Beijing area play an important role in determining the location, distribution and intensity of heavy precipitation.     

Meridional seesaw-like distribution of the Meiyu rainfall over the Changjiang-Huaihe River Valley and characteristics in the anomalous climate years

Although Meiyu rainfall has its in-phase spatial variability over the Changjiang-Huaihe River Valley (CHRV) in most years, it is distributed in some years like a seesaw to the north and south of the Changjiang River, when the precipitation tends to be nearly normal throughout the valley, which would inevitably increase difficulties of making short-term prediction of the rainfall. For this reason, EOF analysis is made on 15 related stations’ precipitation from June to July during 1951─2004, revealing that the EOF2 mode shows largely a north-south seesaw-like pattern, and thereby classifying Meiyu patterns into two types: "northern drought and southern flood (NDSF)" and "northern flood and southern drought (NFSD)". Afterwards, the authors investigated ocean-atmospheric characteristics when these two anomalous types occured using the NCEP reanalysis (version 1) and the extended reconstructed SSTs (version 2). The results show that in the NDSF years, the low-level frontal area and moisture convergence center lie more southward, accompanied by weaker subtropical summer mon- soon over East Asia, with the western Pacific subtropical high and 200 hPa South Asia High being more southward. Both the Northern and Southern Hemisphere Annular Modes are stronger than normal in preceding February; SST is higher off China during boreal winter and spring and the opposite happens in the NFSD years. Also, this seesaw-form Meiyu rainfall distribution might be affected to some degree by the previous ENSO event.     

Numerical simulation of topography effects on the “00.7” severe rainfall in Beijing

In an effort to study the severe rainfall event of 4?5th July 2000 in Beijing (with 24h accumulated precipitation of 240 mm), we perform numerical simulations to investigate this event using the MM5v3.6 model. The model is initialized with the MM5/WRF 3DVAR analysis, which incorporates the ground-based GPS precipitable water vapor, automatic and conventional meteorological observations in its assimilation step. For 24 h accumulated precipitation forecast, the threat scores are 0.72, 0.76, 0.67 and 0.63, for thresholds of 1, 5, 10, and 20 mm, respectively. Holding other factors unchanged, sensitivity experiments were conducted with different topographic resolutions of 110, 50 and 3.7 km to investigate the topographic effects on precipitation over the Beijing area. In these sensitivity experiments, we attempt to preserve the realistic orographic distribution in the model topography under the condition of keeping the dynamic-thermodynamic consistency of the initial model atmosphere to the extent possible. Results indicate that the unique topographic distribution and variations in the Beijing area play an important role in determining the location, distribution and intensity of heavy precipitation.