西南地区气候季节划分及特征分析

本文运用聚类分析方法对西南地区进行分区讨论,研究了各区域的气候季节及其变化特征。我国西南地区5个区域夏季和秋季的分配基本一致,而冬春两季差异明显;而降水场和温度场四季划分也有一定相关和相异性,均按照云南区-川西高原区-贵州区-四川盆地区-川东区的顺序逐级递减。      

西南地区夏半年降水的多时空尺度特征

根据国家气象中心提供的西南地区夏半年月降水资料,利用旋转经验正交函数(REOF)展开方法,将西南地区划分为川西北、川渝区、云川区和贵州区4个区域,并在此基础上,利用多项式拟合趋势线、小波变换等方法,对各区域降水的变化特征进行了分析。结果表明,西南地区各区域降水的长期变化趋势不尽相同,川西北没有显著的趋势变化,川渝区表现为缓慢上升的趋势,而云川区和贵州区则均表现为先下降后上升的趋势。西南地区各区域降水的周期特征也不尽相同,较短时间尺度的周期变化在西南地区各区域普遍存在;而较长时间尺度的周期,各个区域则有较大的差别,不仅表现在长时间尺度周期的显著性上,还表现在具有相同时间尺度周期,不同区域的干湿期配置等方面。     

中国西南复杂地形区降水观测年际变化代表性问题初步分析

在中国西南地区,受到复杂地形、台站分布等因素的影响,台站的代表性问题较为突出,文章主要利用降水的年际变率来研究该地区降水资料的代表性问题。首先以大理国家气候观象台为例,定量评估单站的代表性区域,发现受周边南北走向高大山地的影响,大理站降水的代表性区域主要集中在以该站为中心南-北向的狭长带状范围内,面积大致5000 km~2。在对单站代表性有一定认识的基础上,结合台站资料及APHRODITE资料开展西南地区的站网覆盖度分析,结果表明台站的覆盖度在台站绝对密度较高及地形平坦的地区呈现高值,覆盖度可达40个站点以上,而在高原主体上,台站的覆盖度低,观测空白区占整个西南地区的15.90%,主要分布于高原主体北侧及西南侧。考虑到降水年际变率的空间差异对台站的代表性有重要影响,最后基于CMORPH卫星资料针对西南地区降水年际变率的空间差异进行研究,发现降水在盆地和高原河谷地区空间差异较小而山脉盆地的过渡区空间差异较大,建议在降水变率空间差异较大的观测空白区设立更多站点。     

基于CRA空间检验技术的西南地区东部强降水EC模式预报误差分析

CRA(contiguous rain area)空间检验技术是将连续雨区作为目标进行检验。通过设定降水量阈值,识别、分离及平移降水目标,将预报偏差分解为落区、强度和形态误差,该方法可避免传统TS评分的双惩罚效应。利用CRA空间检验技术对2011—2014年5—9月西南地区东部EC细网格模式36 h预报时效119个降水目标的预报误差进行分析,并按照环流形势和影响系统对强降水个例进行分型,分为西南地区东部低涡切变型、西南地区东部-江淮切变型、南风型,分别对上述三类不同类型强降水个例的落区和强度误差进行了对比。得到如下结论:西南地区东部降水预报形态误差占比最大,为60%左右,其次是落区误差,为30%左右,强度误差最小,约为10%;落区平均偏西0.7°,经向偏差不明显;模式对于水平尺度较小的降水目标漏报可能性较大,而对于天气尺度降水目标模式预报面积偏大,总降水量偏大,雨强偏小;西南地区东部低涡切变型和西南地区东部-江淮切变型降水强度预报误差类似,模式预报雨区面积均偏大,降水尺度越大,偏大的概率越大,实况平均降水强度越强,模式预报强度越偏弱;南风型预报强降水面积和平均强度均偏弱,出现漏报的概率较大;而对于最大降水量,三种类型模式预报的最强降水均较实况偏弱;西南地区东部低涡切变型模式预报落区偏西,江淮至西南地区东部切变型模式预报落区偏西偏北,南风型模式预报落区偏西偏南。     

西南地区春季降水时空变化特征

根据1961~2012年西南地区(四川、重庆、贵州、云南)116个气象台站逐月降水资料,利用REOF、Morlet小波分析、Mann-Kendall突变检验等方法分析了西南地区春季降水的年代际变化、空间分布特征、周期变化、突变年份等。结果表明,近52 a来,西南地区春季降水有明显的地域性,从20世纪60年代到21世纪初,几乎每个年代降水都呈现东西部反相趋势。据此把西南地区春季降水进行REOF分区,可分为4个区域:Ⅰ区(云南地区和四川西南部)和Ⅳ区(川西高原和攀西高原部分地区)春季降水呈增加趋势,Ⅱ区(贵州地区和四川东南部个别地区)和Ⅲ区(四川东北部和重庆地区)呈减少趋势。4个区域春季降水都是长周期中包含着短周期,24~28 a的周期和10 a以下的周期较为普遍。4个区域春季降水突变都普遍发生在1980年代后,降水变化显著时期基本集中在21世纪初期。     

西南地区不同地质灾害影响区的降水阈值研究

根据1961~2010年西南地区(四川省、云南省、贵州省、重庆市)重大地质灾害资料和全国重大地质灾害年鉴资料统计不同地质灾害(滑坡、坍塌、泥石流)事例,确定其影响区域。利用西南地区77个气象观测站逐日降水资料,根据降水阈值的定义和计算方法,运用线性回归法研究西南地区各灾害影响区的降水阈值。结果表明:我国西南地区是地质灾害多发的地区;1961~2010年西南地区重大滑坡、泥石流灾害具有密集成群、成片或成带的规律,有明显的稀疏区和密集区;且主要发生在6~9月,其中7月份发生最多,与降水的时空分布具有很好的一致性,降水是诱发地质灾害的主要因素。西南地区不同区域内诱发重大滑坡、泥石流灾害的降水阈值存在差异。西南地区的重大滑坡灾害主要是持续性强降雨型的。      

我国西南地区夏季降水异常的区域特征

采用旋转经验正交展开（REOF）方法，对我国西南地区49a夏季降水标准化距平场进行客观分区，并分析了各区夏季降水异常的长期变化趋势。结果表明，西南地区夏季降水量场可以分为5个区域，该5区均具有显著的年代际变化特征，且近50a来它们的旱涝变化存在着显著差异，其中川西、川东和贵州降水的长期变化趋势不明显，而四川盆地和云南显著变干。     

青藏高原冬、春季植被特征及其对西南地区夏季降水的影响

本文利用西南地区96个气象台站1982-2001年夏季(6-8月)月平均降水资料和归一化植被指数(GIMMS NDVI)资料,分析了青藏高原冬、春季植被特征及其对西南地区夏季降水的影响,得到以下几点认识:青藏高原冬、春季植被呈现东南部覆盖较好,逐渐向西北部减少的特征.近20 a来,高原冬、春季植被总体呈增加趋势,其高原中西部、南部、北部增加明显,而南部侧边界和中东部呈减少趋势.相关分析和奇异值分解表明:高原冬、春季植被对西南地区夏季降水有较明显影响,且这种影响也存在一定的区域差异.高原前期植被变化可以作为西南地区夏季降水长期预报综合考虑的一个参考因子.     

西南地区区域洪涝的概念模型

通过对1991 2001年5～9月寸滩(寸滩位于重庆市区以东,长江干流北岸)逐日08时流量分析和区域洪涝暴雨的成因分析,得到几点认识(1)西南地区区域洪涝主要发生在四川盆地,造成区域洪涝的主要因素是流域底水条件和由暴雨造成的面雨量,两者缺一不可.(2)西南地区区域洪涝的概念模型可以以不同的寸滩流量条件与不同的间隔天数、不同的流域性降水条件表示,也可以以第一次区域洪涝出现前、后,不同的间隔天数与不同的流域性降水条件表示.     

西南地区东部夏季旱涝的水汽输送特征

利用1959-2006年两南地区东部20个测站逐日降水量资料和NCEP/NCAR再分析月平均资料,分析了西南地区东部夏季旱涝年的水汽输送特征.结果表明,西南地区东部水汽来源主要有两个:第1条主要来自青藏高原转向孟加拉湾经缅甸和云南进入西南地区东部,第2条水汽经由孟加拉湾南部,强大的水汽输送带继续向东输送至中南半岛及南海,与南海越赤道气流所携带的水汽汇合后转向至西南地区东部,而由四太平洋副热带高压西侧转向的偏南水汽对向西南地区东部水汽输送也有影响.与西南地区东部夏季降水相联系的水汽通道中,印度洋水汽通道强度最强,太平洋水汽通道强度最弱.在印度季风区,偏北的高原南侧水汽通道(经向)强度远小于偏南的印度洋水汽通道.东亚季风区夏季水汽输送经向输送大于纬向输送,而印度季风区夏季水汽输送则是纬向输送大于经向输送.西南地区东部夏季降水与纬向通道的强度变化关系密切,而与经向通道的水汽输送强度变化关系不明显.当印度季风区南支水汽输送偏弱时,印度季风区北支(高原南侧)和东亚季风区向西的水汽输送偏强,使得以纬向输送为主的印度季风区经向水汽输送加大,而以经向输送为主的东亚季风区纬向水汽输送加大,从而使东亚地区的水汽输送带偏西,西南地区东部夏季降水偏多,可能出现洪涝,反之则可能出现干旱.西南地区东部夏季水汽有弱的净流出,是一个弱的水汽源区,南边界流入水汽量最多,干旱年整个区域水汽流出较常年明显,而洪涝年则有弱的净流入.夏季水汽通道水汽输送强弱变化与同期500 hPa高度场和SST场的分布形势密切相关.     

中国东部冬季降水的动力结合统计预测方法研究

针对中国东部6个气候关键区,首先,通过相关分析指出,冬季降水既与前期气候因子有关,又受同期大气环流的影响。因此,有必要采用动力与统计相结合的方法进行气候预测研究。然后,从实时预测的角度出发,综合考虑前期预测因子的观测信息和具有数值可预测性的同期气候因子的数值模式结果,使用多元线性回归分析方法就各区域平均冬季降水逐一建立了短期气候预测模型,并在预测模型中考虑了模型结果中系统误差的订正。交叉检验分析结果表明,所建立的各区域预测模型普遍具有较好的预测效果,预测优势主要表现在对冬季降水的变化趋势、年际变化、以及异常符号的预测准确率上。就6个区域平均而言,1982—2008年交叉检验结果与实况间的相关系数和距平同号率分别为0.69和78%,表明该预测思想具有可行性。     

A Hybrid Dynamical-Statistical Approach for Predicting Winter Precipitation over Eastern China

Correlation analysis revealed that winter precipitation in six regions of eastern China is closely related not only to preceding climate signals but also to synchronous atmospheric general circulation fields.It is therefore necessary to use a method that combines both dynamical and statistical predictions of winter precipitation over eastern China(herein after called the hybrid approach).In this connection,seasonal real-time prediction models for winter precipitation were established for the six regions.The models use both the preceding observations and synchronous numerical predictions through a multivariate linear regression analysis.To improve the prediction accuracy,the systematic error between the original regression model result and the corresponding observation was corrected.Cross-validation analysis and real-time prediction experiments indicate that the prediction models using the hybrid approach can reliably predict the trend,sign,and interannual variation of regionally averaged winter precipitation in the six regions of concern.Averaged over the six target regions,the anomaly correlation coefficient and the rate with the same sign of anomaly between the cross-validation analysis and observation during 1982-2008 are 0.69 and 78%,respectively.This indicates that the hybrid prediction approach adopted in this study is applicable in operational practice.     

ON THE KEY REGIONS OF 500 hPa GEOPOTENTIAL HEIGHTS OVER NORTHERN HEMISPHERE IN WINTER

Variance analysis, correlation analysis and regression analysis methods are applied to analyze the variation of circulation at 500 hPa. In winter, there are three regions (180°E – 150°W, 45°N – 60°N, 70°W – 100 °W，45°N – 75°N, 60°E – 100°E, 65°N – 80°N) whose variations are strong. Those regions are the key regions in which atmospheric circulation can change. Those regions are correlated to some teleconnections and can present a part of variations of 500 hPa to some degree. The linear contemporary correlation between those regions and the height at 500 hPa is significant. Those regions can account for 88 % of variations of concurrent height at 500 hPa. Those regions can present and forecast some variations to some degree in March and April. The longer the time interval, the worse the forecast effect will be. The interannual variations of Q1, Q2 and the SST are weak in the western Pacific.     

A cloud-resolving modeling study of short-term surface rainfall processes

The short-term tropical surface rainfall processes in rainfall regions (raining stratiform and convective regions) and rainfall-free regions (non-raining stratiform and clear-sky regions) are investigated based on the hourly data from a two-dimensional cloud-resolving model simulation. The model is integrated over a 21-day period with imposed zonally uniform vertical velocity, zonal wind, horizontal temperature and vapor advection, and sea surface temperature from the Tropical Ocean Global Atmosphere Coupled Ocean Atmosphere Response Experiment (TOGA COARE). The analysis of the model domain-mean surface rainfall budget reveals that surface rainfall is mainly associated with water vapor convergence and local atmospheric drying. The mean surface rainfall lags the mean water vapor convergence by 3?h. The convective?Cstratiform rainfall separation analysis shows that convective rainfall is associated with water vapor convergence, whereas stratiform rainfall is related to the local atmospheric drying and hydrometeor loss/convergence. The transport of water vapor from rainfall-free regions to rainfall regions creates the main water vapor source for rainfall while it balances local atmospheric drying in rainfall-free regions. Surface evaporation plays a minor role in short-term surface rainfall processes.     

An Analysis of Thermally-Related Surface Rainfall Budgets Associated with Convective and Stratiform Rainfall

Both water vapor and heat processes play key roles in producing surface rainfall.While the water vapor effects of sea surface temperature and cloud radiative and microphysical processes on surface rainfall have been investigated in previous studies,the thermal effects on rainfall are analyzed in this study using a series of two-dimensional equilibrium cloud-resolving model experiments forced by zonally-uniform,constant,large-scale zonal wind and zero large-scale vertical velocity.The analysis of thermally-related surface rainfall budget reveals that the model domain mean surface rain rate is primarily associated with the mean infrared cooling rate.Convective rainfall and transport of hydrometeor concentration from convective regions to raining stratiform regions corresponds to the heat divergence over convective regions,whereas stratiform rainfall corresponds to the transport of hydrometeor concentration from convective regions and heat divergence over raining stratiform regions.The heat divergence over convective regions is mainly balanced by the heat convergence over rainfall-free regions,which is,in turn,offset by the radiative cooling over rainfall-free regions.The sensitivity experiments of rainfall to the effects of sea surface temperature and cloud radiative and microphysical processes show that the sea surface temperature and cloud processes affect convective rainfall through the changes in infrared cooling rate over rainfall-free regions and transport rate of heat from convective regions to rainfall-free regions.     

热带气旋的内、外区结构──Ⅰ.正压模式

将热带气旋分为内外两区，两区的空间、时间及物理量有不同的尺度，应用尺度分析和摄动法到热带气旋的两个区域，分别在正压模式和斜压模式中求得了这两个区域的控制方程，在两个模式中，还解析地求得了两个区域的流场和气压场，得到的结果与实际热带气旋的结构较为接近。研究表明，热带气旋内区和外区有不同的控制方程，内区受旋转风和一个演化方程制约，而外区受梯度风和另一个演化方程制约。     

A climatological perspective of water vapor at the UTLS region over different global monsoon regions: observations inferred from the Aura-MLS and reanalysis data

The Aura-MLS observations of eight years from 2004 to 2011 have been utilized to understand the hydration and the dehydration mechanism over the northern and the southern hemispheric monsoon (NH and SH) regions. The monsoon regions considered are the Asian Summer Monsoon, East Asian Summer Monsoon, Arizona Monsoon (AM), North African Monsoon, South American Monsoon and the Australian Monsoon. The annual cycle of water vapor as expected shows maxima over the NH during June–August and during December–February over the SH. The time taken by the air parcels over the NH monsoon regions is found to be different compared to that over the SH monsoon regions. The analysis shows the concentration of water vapor in the upper troposphere and the lower stratosphere (UTLS) has not changed over these eight years in both the hemispheres during their respective monsoon seasons. The present analysis show different processes viz., direct overshooting convection, horizontal advection, temperature and cirrus clouds in influencing the distribution of water vapor to the UTLS over these different monsoon regions. Analysis of the UTLS water vapor with temperature and ice water content shows that the AM is hydrating the stratosphere compared to all the other monsoon regions where the water vapor is getting dehydrated. Thus it is envisaged that the present results will have important implications in understanding the exchange processes across the tropopause over the different monsoon regions and its role in stratosphere chemistry.     

DOMINANT PHYSICAL PROCESSES ASSOCIATED WITH PHASE DIFFERENCES BETWEEN SURFACE RAINFALL AND CONVECTIVE AVAILABLE POTENTIAL ENERGY

A lag correlation analysis is conducted with a 21-day TOGA COARE cloud-resolving model simulation data to identify the phase relation between surface rainfall and convective available potential energy (CAPE) and associated physical processes. The analysis shows that the maximum negative lag correlations between the model domain mean CAPE and rainfall occurs around lag hour 6. The minimum mean CAPE lags mean and convective rainfall through the vapor condensation and depositions, water vapor convergence, and heat divergence whereas it lags stratiform rainfall via the transport of hydrometeor concentration from convective regions to raining stratiform regions, vapor condensation and depositions, water vapor storage, and heat divergence over raining stratiform regions.     

马尼拉海湾和莱城港湾的辐射状况

本文利用在马尼拉海湾和莱城港湾考察所获得的少量辐射资料,分析了该两地区辐射各量值的日变化特征和地区差异。揭示了海(港)湾水面及其紧邻海岛陆面的辐射特征差异。这些信息很可能有助于上述地区海洋大气间热量交换的分析计算。