《青藏高原雨季变化特征及归因研究》

正申红艳主编该书聚焦在气候变暖背景下,对青藏高原雨季变化的响应特征及归因等关键问题进行系统梳理,详细阐释了雨季起讫期、雨量异常及雨季期内极端降水等的变化特征,从大气内部变率、水汽输送和海温外强迫信号影响的角度揭示雨季来临早晚和雨季降水异常的关键因子和影响机制,为开展青藏高原前瞻性基础研究、引领性原创研究提供重要参考,     

青藏高原雨季起讫的研究

本文利用西藏、青海、宁夏、甘肃、陕西、四川、云南、贵州、广西九个省区1951—1970年的降水资料,讨论了高原及其邻近地区雨季划分的方法、雨季起讫和持续期的特征以及高原雨季与环流、高原季风爆发和长江流域入梅的关系。从而为长期预报提供一些依据。     

中国雨季的一种客观定量划分

从客观分析角度出发,利用有序样本最优分割法对中国610个台站的气候平均（1961—2010年）候降水序列进行有序分割,给出中国不同区域的雨季定量划分。根据中国13个区域候降水量的气候平均值分布特征,并基于有序样本最优分割法的划分结果需同时满足分割段内波动小、段间差异大的要求,确定了各区域的合理分割数,通过制定3种雨季划分方案,对中国区域雨季进行了细致的定量划分。第1种方案将全年降水划分为雨季和旱季,结果表明,雨、旱两季差异明显的地区出现在华南西部沿海和新疆邻近区域;第2种方案将全年降水划分为雨季相对干期、雨季相对湿期和旱季3个降水阶段,这种特征出现的区域为华南大部分地区、江南地区、长江中下游地区、西南地区东部和南部,以及西北地区中东部;第3种方案将全年降水划分为春雨季、主雨季、秋雨季和旱季,出现这种特征的区域为长三角及淮河流域、黄淮和华北地区、东北地区、西北地区中部、内蒙古地区西部、青藏高原中东部及其以东地区。与已有的中国不同区域降水特征研究结果的比较表明,有序样本最优分割法不仅对中国雨季的划分客观有效,且其划分结果合理并具有明确的气象意义。     

高原东南角早春雨的气候特征及其成因研究

使用1998—2013年TRMM格点及GHCN站点降水、1979—2013年CMAP降水和ERA-Interim再分析资料,研究了早春季节青藏高原东南角降水中心的气候特征及其成因。其气候特征为:雨带主要沿布拉马普特拉河谷分布(包括藏东南、滇西北、印度东北部的阿萨姆邦和缅甸北部地区),雨季建立时间在第17候,雨区上游地区(88~94°E,22~27°N)低层的西北风转为西南风是雨季建立的一个标志性环流调整特征。早春雨期间,雨区上游地区的西南风大值中心使得风速及水汽在雨区辐合,同时该西南气流沿着由喜马拉雅山脉-横断山脉-那加山脉组成的向西南方向敞开的喇叭口地形爬坡抬升,在迎风坡出现降水大值中心,这是高原东南角早春雨的直接成因。该西南风大值中心的产生既与青藏高原大地形的动力绕流作用有关,也与春季高原中南部的地表感热加热密切相连,这是高原东南角早春雨形成的根本原因。     

1998年夏季亚洲地区低频大气环流的特征及其与长江中下游降水的关系

利用日本GAME资料、TRMM卫星资料及中国730站降水资料研究了1998年夏季亚洲地区对流层至平流层低频振荡(LFO)的传播特征及该年长江中下游夏季降水变化的LFO型,结果表明:1998年5-8月,在青藏高原经纬度上,对流层LFO的东西向传播特征与季节变化有关.在东西方向上,高原和东亚大陆雨季开始前,LFO以向东传播为主;在雨季开始后,LFO以向西传播为主.南北方向上,LFO的传播在雨季前后基本一致,高原南北两侧均向高原传播.在南北方向上,青藏高原是LFO的汇;而在东西方向上,高原西部只在雨季开始后是LFO加强区,使西传进入高原的LFO继续西传.整个大气层以对流层顶(100 hPa)LFO最强,进入平流层LFO迅速减弱.1998年夏季长江中下游降水存在两次明显的LFO循环,我们根据两次降水LFO各位相合成分析了降水、500和100 hPa LFO环流以及沿30°N LFO垂直环流.结果表明:来自西伯利亚向南传播和来自孟加拉湾及南海向北传播的LFO气旋(降水谷值期)和反气旋(降水峰值期)形成了高原东部上空LFO气旋(降水谷值期)和反气旋(降水峰值期)以及来自中纬度西太平洋南下西移经日本、黄海到达中国大陆东部海洋上空的LFO反气旋(降水谷值期)和气旋(降水峰值期)的共同作用造成了长江中下游地区强烈的下沉(降水谷值期)和上升(降水峰值期),形成长江中下游降水LFO谷值期和峰值期.     

青藏高原雨季的降水特征与东亚夏季风爆发

用小波分析方法研究了1993年和1994年青藏高原雨季降水的多时间尺度变化特征,结果表明,小波变换对高原上降水从活跃期到中断期之间突变的时间有很好的分辨能力,并发现强弱季风年高原降水的变化特征有很大的差异：即高原降水除了其季节变化外,强东亚季风年(1994年)还有明显的30～60天低频变化;弱东亚季风年(1993年)却是准双周的变化明显。另外,还将高原上降水从活跃期到中断期的变化与同期的NcEP资料作了一些对比分析,发现高原雨季的开始与东亚夏季风爆发可能有一定的联系,即高原东部夏季降水的第一次活跃期与东亚夏季风的爆发时间基本一致。     

横断山脉中西部降水的季节演变特征

利用台站观测逐日降水资料,对横断山脉中西部地区的降水季节演变特征进行了分析,发现该地区降水具有独特的季节变化特征:雨季开始早,从第10候前后降水开始迅速增加,至第19候前后就达到第1个峰值;雨季时间长,从第10候前后雨季开始,至第60候雨季结束,雨季持续长达8个月;多峰值特征明显,雨季先后经历3个降水峰值,分别在第19、35、55候前后.通过再分析资料对这一地区风场的季节变化进行分析发现,这些降水的季节演变特征与这一地区独特地形下风场季节演变密不可分.雨季开始早与第10候起低层西风、南风迅速加强,特别是西风加强有关;第2、3个降水峰值则与西南风,特小,降水主要受西风系统影响,与西风系统的季节变化密切相关;而第2、3个降水峰值分别发生在西太平洋副热带高压西伸、东退进程中,位势高度场东高西低,降水主要受西南风控制,并伴有南风辐合,与南风的季节变化相关.别是经向南风增强有关.对3个降水峰值时刻的环流背景进行了分析,第1个降水峰值发生时,位势高度东西方向水平差异     

甘肃雨季的气候特征

根据全省主要气象台站1951—1990年旬降水相对系数,确定了雨季的起讫日期,分析了雨季的稳定程度和变化规律。结果表明:甘肃雨季比较明显,来临较迟,起讫日期不稳定,大部分地方降水变率大,特别是河西东部和中部8月降水变率大于7月,更易出现旱涝。且3年周期振动显著,是个比较重要的气候特征。     

青藏高原雪盖异常对福建雨季旱涝影响的环流诊断

利用19555-1994年多种不同类型青藏高原积雪资料的综合再分析结果，通过分析青藏高原雪盖异常年冬季和初夏北半球大气环流特征，及北半球大气环流与福建雨季降水的遥相关，讨论高原雪盖异常反馈影响大气环流，进而导致福建雨季旱涝的可能途径，为在福建雨季旱涝预测中应用积雪因子提供一定的物理基础。     

云南雨季逐候降水量的低频振荡特征

应用主分量方法分析了云南省84站1991~2000年雨季(5~10月)逐候降水量的主要时空特征,并用非整波技术分析了所提取的第1、第2主分量频谱分布的低频振荡特点,同时分析了低频振荡现象与El Nino(La Nina)事件及云南雨季降水多、少之间的关系。结果表明:①云南地区雨季降水主要低频振荡周期为6候(30天)、10候(50天)的月际振荡和15~17候(75~85天)的季节内振荡;②云南雨季的候降水每年都存在30天振荡周期,30天振荡是云南雨季固有的振荡;③当发生El Nino或La Nina异常气候事件时,云南雨季的候降水存在50天振荡周期;④当云南雨季存在75~85天振荡时,云南主汛期(6~8月)降水距平百分率为正(除2000年为零距平);当云南雨季不存在75~85天振荡时,云南主汛期降水距平百分率为负。     

Spatial and temporal characteristics of wet spells in the Yangtze River Basin from 1961 to 2003

Daily precipitation records of 147 meteorological stations over the Yangtze River Basin have permitted a detailed analysis of the spatio-temporal distribution of wet spells during the period 1961–2003 by distinguishing average daily amount thresholds of 90th and 95th percentiles. The analysis are based on several time series, namely the number of the days in wet spells, the longest wet spell and the precipitation amount in wet spells. Time series trends analyses are compiled for each station by means of the Mann-Kendall test, for four sub-regions. The results show that the annual precipitation in wet spells is higher in the southeast area and the eastern Tibetan Plateau than in the other parts. The longest wet spells are found in the eastern Tibetan Plateau for both the thresholds. The indices in wet spells for most stations have no significant trends. In contrast, only some stations in eastern Tibetan Plateau and the lower Yangtze River Basin increase significantly, while some in the middle reaches show significant decreasing trends. The regional trends analysis presents a noticeable downward trend in the middle Yangtze River Basin and upward trends in the eastern Tibetan Plateau for both 90th and 95th percentiles, however, the upward trend in the lower Yangtze River Basin and downward trends in the upper Jinshajiang River Basin are not significant.     

Simulation and Projection of Changes in Rainy Season Precipitation over China Using the WRF Model

The Weather Research and Forecasting (WRF) model is used in a regional climate model configuration to simulate past precipitation climate of China during the rainy season (May-September) of 1981-2000, and to investigate potential future (2041-2060 and 2081-2100) changes in precipitation over China relative to the reference period 1981-2000. WRF is run with initial conditions from a coupled general circulation model, i.e., the high-resolution version of MIROC (Model for Interdisciplinary Research on Climate). WRF reproduces the observed distribution of rainy season precipitation in 1981-2000 and its interannual variations better than MIROC. MIROC projects increases in rainy season precipitation over most parts of China and decreases of more than 25 mm over parts of Taiwan and central Tibet by the mid-21st century. WRF projects decreases in rainfall over southern Tibetan Plateau, Southwest China, and northwestern part of Northeast China, and increases in rainfall by more than 100 mm along the southeastern margin of the Tibetan Plateau and over the lower reaches of the Yangtze River during 2041-2060. MIROC projects further increases in rainfall over most of China by the end of the 21st century, although simulated rainfall decreases by more than 25 mm over parts of Taiwan, Guangxi, Guizhou, and central Tibet. WRF projects increased rainfall of more than 100 mm along the southeastern margin of the Tibetan Plateau and over the lower reaches of the Yangtze River and decreased rainfall over Southwest China, and southern Tibetan Plateau by the end of the 21st century.     

青藏高原闪电和降水气候特征及时空对应关系

基于1998—2013年的TRMM (tropical rainfall measuring mission) 数据,分析青藏高原闪电活动与降水气候特征及时空对应关系,结果表明:青藏高原 (简称高原) 的闪电活动中心在高原中部和东北部,中部最大闪电密度达到6.2 fl·km-2·a-1;但高原降水最活跃的区域是东南部,年降水量超过800 mm。闪电活动和降水随月份均呈现出先西进再东退的特征,但高原东北部强闪电活动区位置几乎不变化。在固定区域闪电和降水月变化具有一致性,活跃期出现在5—9月,呈单峰结构,除西部和东南部外,闪电与降水峰值月份吻合。结合TRMM降水特征 (简称PFs) 资料研究单个闪电表征降水量 (rainyield per flash,RPF) 的空间分布特征表明,闪电活动可以作为高原深对流的指示因子,而RPF可以有效表征深对流系统在整个降水系统中的比例。高原中西部和东北部深对流系统在整个降水系统中的比例最大,而在高原东南部最小,高原东南部的降水更多由暖云降水系统贡献。     

CHARACTERISTICS OF SEASONAL VARIATION OF RAINFALL OVER THE TIBETAN PLATEAU DURING SUMMER 1998 AND ITS IMPACT ON EAST ASIAN WEATHER

The seasonal variation of rainy season over the Tibetan Plateau in summer 1998 is analyzed byusing daily observational rainfall data for Lhasa from 1955 to 1996,and rainfall data at 70 stationsfrom January to August of 1998 over the Tibetan Plateau (TP) and adjacent regions,as well asTBB data from May to August of 1998.The onset date of rainy season for Lhasa is climatologically6 June.Among the analyzed years,the earliest onset date is 6 May,while the latest may delay to2 July.The obvious inter-decadal variation can be found in the series of onset date.The onset dateof summer 1998 over middle TP (onset date of Lhasa) is 24 June,which is relatively later than thenormal case.The onset for rainy season of 1998 started over southeast and northeast parts of TP and thenpropagated westward and northward.The convection over east and west parts of TP shows thatthere is a quasi 12-15 day oscillation.In June,the convection over middle and lower reaches ofYangtze River is formed by the westward propagation of convection over subtropical westernPacific.while in July.it is formed by the eastward propagation of convection over TP.Besides,it is also found that there exists good negative and obvious advance and lagcorrelation between the convection over the middle and western TP and that over the subtropicalwestern Pacific and southern China.Therefore it can be inferred that a feedback zonal circulationwith a quasi two-three week oscillation exists between the ascending region of TP and descendingregion of subtropical western Pacific,i.e.the convection over TP may affect the subtropical highover western Pacific and vice versa.     

西藏高原汛期降水类型的研究

利用西藏高原２６个测站２６年（１９７３￣１９９８年）汛期（５￣９月）降水量资料,采用主成分分析和旋转主成分分析方法,对高原汛期降水空间分布型进行了分析。结果表明,主成分分解得到的降水空间分布形式较为集中,前３个特征向量场的分布型具有十分明确的物理意义,可表示降水场部方差的６３．１４％。旋转主成分分解生前６个载荷向量的累积方差贡献达７６．６７％,可较好反映西藏高原汛期降水６个异常敏感区：东南部、东北     

南海夏季风爆发前后华南前汛期降水日变化对比分析

利用华南地区248个国家级地面气象站逐小时降水数据和14个探空站数据,分析了2003—2016年4—6月华南前汛期降水日变化特征。据南海夏季风爆发时间,将降水分为爆发前后两个时段。华南地区主要存在两条大雨带,一个位于云贵高原至南岭山脉以南,另一个位于广东沿海地区。偏北雨带集中发生在后半夜至清晨时段,偏南雨带集中发生在中午至下午时段。南海夏季风爆发前后,降水量不存在明显相关性,相关系数较大时次位于中午至下午时段。前后期年降水标准差在0.5附近,变化幅度明显时段主要集中于凌晨至清晨。午后出现3 h多年降水量变化幅度最大值,最小时段为中午12时。降水量、降水频率和降水强度的经向分布特征明显且相似:降水量和降水频率在112 °E附近出现日变化转折,以西多出现不稳定夜雨,以东白天降水波动较大。在南海夏季风爆发前,降水特征主要表现为西部高频、南部高强,在清晨更多作用于对暴雨系统的增长;季风爆发后则表现为西北-东南南的高频率高强度降水形态,在傍晚更多作用于增加降水发生频率。      

CHARACTERISTICS OF SEASONAL VARIATION OF RAINFALL OVER THE TIBETAN PLATEAU DURING SUMMER 1998 AND ITS IMPACT ON EAST ASIAN WEATHER*

The seasonal variation of rainy season over the Tibetan Plateau in summer 1998 is analyzed by using daily observational rainfall data for Lhasa from 1955 to 1996,and rainfall data at 70 stations from January to August of 1998 over the Tibetan Plateau (TP) and adjacent regions,as well as TBB data from May to August of 1998.The onset date of rainy season for Lhasa is climatologically 6 June.Among the analyzed years,the earliest onset date is 6 May,while the latest may delay to 2 July.The obvious inter-decadal variation can be found in the series of onset date.The onset date of summer 1998 over middle TP (onset date of Lhasa) is 24 June,which is relatively later than the normal case.The onset for rainy season of 1998 started over southeast and northeast parts of TP and then propagated westward and northward.The convection over east and west parts of TP shows that there is a quasi 12-15 day oscillation.In June,the convection over middle and lower reaches of Yangtze River is formed by the westward propagation of convection over subtropical western Pacific.while in July.it is formed by the eastward propagation of convection over TP.Besides,it is also found that there exists good negative and obvious advance and lag correlation between the convection over the middle and western TP and that over the subtropical western Pacific and southern China.Therefore it can be inferred that a feedback zonal circulation with a quasi two-three week oscillation exists between the ascending region of TP and descending region of subtropical western Pacific,i.e.the convection over TP may affect the subtropical high over western Pacific and vice versa.     

青藏高原对亚洲夏季风爆发位置及强度的影响

通过数值模拟,研究了青藏高原位于不同经度位置时,亚洲夏季风的爆发和演变情况,从动力和热力学角度分析了青藏高原大地形对亚洲夏季风爆发位置的影响。结果表明,青藏高原的“热力滑轮”作用引起:高原东南面热带陆地上空的偏南气流加强,降水增加,凝结潜热加强;高原西南面热带陆地上空出现偏北气流,降水减弱,陆面的感热加热加强。青藏高原对于亚洲夏季风的爆发地点有锚定的作用,在热带海陆分布的背景下,使亚洲夏季风首先在高原东南面的海洋东岸—陆地西岸爆发,并使亚洲季风降水重新分布。     

亚洲-澳大利亚海陆地形与热力季节演变下的季风槽和季风降水

通过对1999-2007年美国NCEP FNL逐日全球大气分层分析资料和同期美国NASA热带测雨卫星(TRMM)降水产品资料进行气象要素分解,取其海陆差异影响的要素场,对亚洲-澳大利亚季风区的季风槽进行了逐候辨识,分析了亚澳季风区850 hPa各槽线的季节演变与降水的关系.结果发现在亚洲夏季风最强盛的时候青藏高原周边地区一共有五个季风槽,澳大利亚夏季风最强盛的时候在其周边地区存在三个季风槽,这些季风槽都有对应的降水出现并受当地半岛尺度地形的影响.南亚和东南亚的季风槽以及对应的降水持续时间约为半年(24-60候),东亚和澳大利亚季风期要短一些(28-48候和1-17候).东亚和澳大利亚北部地区都存在季风爆发之前的前汛期降水或过渡时期降水.     

Effects of rainfall amount and frequency on vegetation growth in a Tibetan alpine meadow

Over the past decades, rainfall amount and frequency changed considerably on the Tibetan Plateau. However, how altered rainfall pattern affects vegetation growth and phenology in Tibetan alpine grasslands is poorly understood. In this study, we investigated the long-term effects of rainfall amount and frequency on production (i.e., aboveground biomass, AGB) and phenology of three perennial plants in a Tibetan alpine meadow from 1994 to 2005. Growth period (i.e., the dates from greening to senescence) was referred to plant phenology here. Our results showed that annual precipitation and total rainfall from large events (≥ 5 mm per day) were mainly distributed in the growing season, which increased significantly from 1994 to 2005 with more increment in May and July (p?<?0.05). Total AGB and growth periods of three plants were linearly correlated with annual precipitation and total rainfall from large events, but have insignificant correlations with total rainfall from small events (< 5 mm per day) and rainfall frequency (including small, large, and all events). The results suggest that aboveground plant production and phenology are more sensitive to changes in large rainfall events (≥ 5 mm per day) than small events (< 5 mm per day) in the alpine meadow ecosystems.