近50年长江中下游地区夏季气温变化与东半球环流异常

采用中国气象局整编的气温资料以及NCEP/NCAR再分析资料,分析了1960-2005年中国长江中下游地区夏季气温变化与东半球环流异常的联系.结果表明:近50年来,中国长江中下游地区夏季气温呈现出明显的非对称趋势变化特征,夏季气温的上升趋势在很大程度上是日最低气温上升带来的结果;典型高、低温年,在环流场的垂直分布均呈准正压结构的情况下,从对流层低层一直到高层,东半球大部分区域的异常值符号相反.此外,出现在江淮流域上空的异常环流的形成和维持可能与三支不同源头的波列有关;地面长波辐射对气温的影响在夜间超过白天,气温分别与感热通量和潜热通量呈负相关以及正相关关系;典型高(低)温年,垂直温度平流引起的异常动力增(降)温和非绝热加热引起的异常增(降)温可以作为解释高(低)温年气温异常维持的原因.     

1990年代长江中下游地区多雨的机制分析

对长江中下游地区３２个测站１９５１以来的降水记录以及上海、南京等６个站１２０年降水序列的分析表明,１９９０年代是长江中下游地区百年来降水最多的１０年。降水的偏多导致洪涝发生的频率及强度都加强。最近１２０年中１２次异常多雨的年份,出现在１９９０年代的就有４次。１９５１年以来的６个异常多雨夏季个例的合成分析表明,与洪涝直接相联系的大气环流形式是在江南有偏强的向北经向风及水汽输送异常,而在华北及偏北地区     

新疆近40年来的冬春气温变化和环流特征

本文利用1951-1989年近40年的气象资料,采用等级气温方法,对新疆冬春季气温异常时空变化和冬暖环流特征进行分析,结果表明:新疆冬、春季气温变化有明显的阶段性,主要表现为50年代偏冷;60年代前期偏暖;后期偏冷;70年代偏暖;近十年整个时期温度偏高.南疆的分布趋势和北疆近似,其振幅并不显著.     

近46年来中国东部季风区夏季气温变化特征分析

利用中国东部季风区375个测站夏季平均气温资料,分析季风区夏季气温的变化特征.结果表明:(1)近46 a东部季风区夏季气温年平均呈缓慢上升趋势,但淮河流域出现下降趋势;(2)夏季气温稳定性随纬度增加而减小;(3)季风区夏季气温年均增温率0.104℃/10 a,全区平均状况看,1970年代中期后开始表现明显上升趋势;(4)季风区夏季气温变化首先表现为全区一致的变化型,然后为南北反相变化型;(5)根据REOF分析将季风区夏季气温异常分6个气候空间类型,东北、华北、江南及华南均呈现上升增温趋势,西南地区增温缓慢,淮河流域则呈现与全球变暖不一致的降温趋势.     

黄河中上游流域夏季异常降水的变化特征及环流分析

 从中国气象局信息中心提供的全国地面台站逐日观测资料中选取黄河中上游流域66 个台站资料,结合NCEP/NCAR再分析资料,运用小波分析等统计方法,对黄河中上游流域夏季降水异常的变化特征、周期分布及影响降水的因子进行分析,研究结果表明：（1）流域旱涝年夏季降水空间分布上差异显著,易涝区位于河套平原,易旱区位于黄土高原东北部;（2）1960-2008年,流域夏季降水量线性趋势变化不明显,但年际间波动较大,多雨年少雨年相间出现,近50 a中降水整体呈现平稳—少雨—多雨—平稳—多雨—少雨的过程;（3）黄河中上游流域降水变化周期复杂多样,总体以2 a周期振荡为主,异常少雨年多表现为9 a周期振荡,异常多雨年多表现为15 a周期振荡,且流域主周期的空间分布可能与地形地貌、海拔高度及流域分布等地理因素有关;（4）丰、枯雨年环流形式差异显著,影响流域降水的环流系统有季风,西太平洋副高,温带气旋及贝加尔湖低压。     

甘肃省夏季异常高温及其环流特征分析

利用甘肃省62个气象观测站1960—2003年6—8月逐日最高气温、高度场和温度场格点资料,分析了高温极值、高温范围、高温持续时间的变化,并对历史上出现的四次极端高温天气过程的环流形势特征进行了分析。结果表明：甘肃河西地区极端最高气温各月之间的差异大,6月极端值最小,7月极端值最大,7月极端最高气温线性变化略呈上升趋势,6月、8月线性变化呈下降趋势,20世纪90年代极端最高气温增温不明显。河东地区极端最高气温各月之间的差异小,7月、8月的变化呈上升趋势,1995—2002年的增温明显。6月全省最大范围的高温天气出现在60年代;7月,90年代后期出现大范围高温天气的年份明显比以前增多。7月持续高温时间在90年代明显增长。100 hPa南亚高压,300 hPa暖中心、500 hPa副热带高压闭合单体控制西北地区上空,对流层上下层暖高压中心相对应,中心位置基本一致时,将出现大范围、持续性的异常高温天气。     

川西高原夏季降水变化特征及其异常年环流形势

利用川西高原9个观测站的1960—2006年夏季降水资料分析了川西高原夏季降水的气候变化特征及其与大尺度环流的关系。得到如下主要结论:①1960—2006年,川西高原的夏季降水有微弱增加的趋势。20世纪60年代、80年代和近几年,川西高原夏季降水偏多,70年代和90年代川西高原夏季降水明显偏少。②川西高原夏季降水多雨年和少雨年的环流形势存着明显的差异。高原夏季降水与500 hPa乌拉尔山高压脊、亚洲东北部高压脊、巴尔喀什湖至贝加尔湖之间的低压槽密切相关,还与100 hPa南亚高压的强弱有关。③川西高原多雨年前期春季OLR距平场上,印度洋中部对流偏强,印尼-南海南部地区对流减弱。OLR的变化可以为川西高原夏季降水的预测提供参考依据。     

天水地区近50年气温与降水变化特征

根据1961-2006年天水7个站每月温度和降水资料,分析了近50a天水温度和降水的突变事实。在此基础上给出了气候变暖前后气温、降水的概率分布,比较了变暖前后时段天水气温、降水空间分布的差异。结果表明:1)20世纪90年代初期天水气温、降水发生了明显突变,进入温度显著增暖和降水偏少时段;2)增暖后天水气温和降水的概率分布发生了明显变化,气温偏冷的概率显著减小,偏暖的概率显著增大;降水偏少的概率明显增多,偏多的概率明显减少;3)气候变暖后天水地区和各气候分区气温上升幅度均较显著;降水距平百分率渭北区下降幅度相对突出。进而,讨论了温度增加和降水减少对该地区农业生产的影响。     

中国干旱区与季风区夏季气温变化特征对比

利用1961-2006年西北干旱区139站和东部季风区378站夏季平均气温资料,采用趋势系数、相关性检验等方法,对比分析了两个区域夏季气温的时间和空间变化特征、气温变幅分布,并对产生变化的原因进行了初步探讨。结果表明:受气候变暖大背景的影响,西北干旱区和东部季风区夏季气温变化均为波动式上升趋势,但由于地理位置的差异,受夏季风影响不同,导致西北干旱区(0.24℃/10 a)的升温趋明显高于季风区(0.11℃/10 a),同时明显高于相同纬度区域的季风区(0.15℃/10 a)气温变化趋势。两个区域气温变幅空间变化分布上都存在明显的升温区域和气温变化相对较弱的区域,季风区在黄河中下游以南地区到长江中下游以北的广大地区变化不明显,黄河中下游以北的华北、东北地区有相对较明显的升温趋势;西北干旱区以明显的升温为主,尤其是以青海西部至蒙古高原西部形成的一带状区域为主要明显升温区,其最大升温率达到0.93℃/10 a,变化相对较弱的区域主要位于吐鲁番盆地和塔里木盆地。     

Summertime temperature variations in the middle and lower reaches of Yangtze River and their related circulation anomalies in the past five decades

Using the daily data of temperature from China Meteorological Administration and the NCEP/NCAR reanalysis from 1960 to 2005, we have analyzed the relationships between the summertime high/low temperature events in the middle and lower reaches of the Yangtze River (MLRYR) and the related circulation anomalies in the Eastern Hemisphere. Our results have demonstrated that a significantly increasing trend is observed in daily minimum temperature in the past 50 years. And in some regions in the Northern Hemisphere, the opposite scenarios are observed in circulation anomalies in lower and upper parts of the troposphere in the years when the temperatures are higher than normal, as compared to those in the years when the temperatures are lower than normal in the middle and lower reaches of the Yangtze River (MLRYR). Additionally, the anomalous circulation structure in vertical direction in both the high and lower temperature years are barotropic. It is found that the emergence and maintenance of the aforementioned anomalous circulations are related to three kinds of wave train teleconnection patterns. Further more, influences of the long wave surface radiation on the air temperature are stronger in the nighttime than that in the daytime. While both the maximum and minimum temperatures have negative relationships with the sensible heat flux but positive relationships with the latent heat flux. To some extent, the anomalous dynamic heating (cooling) caused by the vertical thermal advection as well as the diabatic heating (cooling) caused by diabatic processes can explain the formation of the high (low) temperature events in the middle and lower reaches of the Yangtze River (MLRYR) in boreal summer.     

长江中下游阻隔性河段作用机理

阻隔性河段能够阻隔上游河势调整向下游的传递,对稳定河势起到关键性作用。本文以长江中下游34个单一河段为研究对象,在系统总结长江中下游河道演变规律的基础上,归纳出阻隔性河段控制要素包括：单一微弯的河道平面形态、河段中上部无挑流节点;河相系数小于4;河道纵比降大于1.2?;凹岸黏粒含量高于9.5%;床沙中值粒径大于0.158 mm等。从Navier-Stokes方程出发,推导出河湾水流动力轴线弯曲半径的表达式,进而分析了各控制要素对水流动力轴线摆动及阻隔性河段形成的作用。阻隔性河段的判别条件为：不同流量级下水流动力轴线摆动力与河道边界条件约束力的比值始终小于1;阻隔性河段作用机理在于：即便上游河势发生调整,本河段的河道边界始终能约束主流摆动幅度,归顺上游不同河势条件下的主流平面位置,为下游河道提供了相对稳定的入流条件,从而阻隔上游河势调整向下游传递。     

Assessment and exploitation of the waterfront resources in the middle and lower reaches of the Yangtze River

Waterfront resources are important and special kind of natural resources in the marginal area between land and water. The Yangtze River, the longest river in China, is not only rich in waterfront resources, but also has favorable development conditions with great potentiality. Aided by large-scale underwater topographic map, the major factors of the waterfront resources in the middle and lower reaches of the Yangtze River, such as the stability, the water depth and the natural conditions for port construction, are assessed in this paper respectively on the basis of the overall investigations. The results show that: (1) the waterfront resources are abundant in the middle and lower reaches of the Yangtze River, but lack of perfectly combined high grade waterfront; (2) there exists an obvious regional difference in the natural quality of the waterfront along the Yangtze; (3) the fore-bank water depth and waterfront stability are the main natural factors related to the waterfront quality in the middle and lower reaches of the Yangtze River; (4) the waterfronts along the Yangtze are mainly used for port, warehouse and industrial purposes; and (5) the waterfronts near important cities are highly used, especially the high-quality waterfronts. In addition, some suggestions for the development and utilization of the waterfront resources are presented in this paper.     

The mechanism of barrier river reaches in the middle and lower Yangtze River

Alluvial channel has always adjusted itself to the equilibrium state of sediment transport after it was artificially or naturally disturbed. How to maintain the equilibrium state of sediment transport and keep the river regime stable has always been the concerns of fluvial geomorphologists. The channel in the middle and lower reaches of the Yangtze River is characterized by the staggered distribution of the bifurcated river and the single-thread river. The change of river regime is more violently in the bifurcated river than in the single-thread river. Whether the adjustment of the river regime in the bifurcated river can pass through the single-thread river and propagate to the downstream reaches affects the stabilities of the overall river regime. Studies show that the barrier river reach can block the upstream channel adjustment from propagating to the downstream reaches; therefore, it plays a key role in stabilizing the river regime. This study investigates 34 single-thread river reaches in the middle and lower reaches of the Yangtze River. On the basis of the systematic summarization of the fluvial process of the middle and lower reaches of the Yangtze River, the control factors of barrier river reach are summarized and extracted: the planar morphology of single-thread and meandering; with no flow deflecting node distributed in the upper or middle part of the river reach; the hydraulic geometric coefficient is less than 4; the longitudinal gradient is greater than 12‰, the clay content of the concave bank is greater than 9.5%, and the median diameter of the bed sediment is greater than 0.158 mm. From the Navier-Stokes equation, the calculation formula of the bending radius of flow dynamic axis is deduced, and then the roles of these control factors on restricting the migration of the flow dynamic axis and the formation of the barrier river reach are analyzed. The barrier river reach is considered as such when the ratio of the migration force of the flow dynamic axis to the constraint force of the channel boundary is less than 1 under different flow levels. The mechanism of the barrier river reach is such that even when the upstream river regime adjusts, the channel boundary of this reach can always constrain the migration amplitude of the flow dynamic axis and centralize the planar position of the main stream line under different upstream river regime conditions, providing a relatively stable incoming flow conditions for the downstream reaches, thereby blocking the upstream river regime adjustment from propagating to the downstream reaches.     

1961-2010年长江中下游地区农业洪涝灾害时空变化

为揭示长江中下游地区农业洪涝灾害的发生、分布及时空演变特征,基于1961-2010年研究区内426个气象站点的逐日降水数据,以湖北省单站洪涝等级标准为初始指标,对该指标临界值在-50~100 mm范围内进行同步增减,结合该区7省（市）的洪涝历史灾情记载和农业洪涝受灾面积,采用逐步剔除的方法筛选指标,构建分省农业洪涝等级指标并验证指标的合理性,分析该区近50年农业洪涝灾害的时空变化。结果表明：① 近50年长江中下游地区的农业洪涝灾害发生总体呈增加的趋势,但不同区域和不同年代际差异明显;② 20世纪60年代至80年代农业洪涝发生次数相对平稳,90年代洪涝明显增多,21世纪初洪涝又相对减少;③ 区域农业洪涝灾害明显呈现出江南多、江北少的分布特征。农业洪涝多发区主要集中在江西中北部、江汉平原、浙江沿海,以及安徽、江西和浙江三省交界地带。     

长江中下游流域旱涝急转事件特征分析及其与ENSO的关系

基于长江中下游流域75个雨量站1960-2015年的日降水资料,通过对原有的旱涝急转指数加以改进,定义了日尺度旱涝急转指数（Dry-Wet Abrupt Alternation Index, DWAAI）,全面分析长江中下游流域夏季（5-8月）旱涝急转事件的时空演变特征,并讨论了旱涝急转事件与事件发生前太平洋海表温度的关系。结果表明：① 改进的DWAAI综合考虑了事件前后期旱涝差异与急转快慢程度,筛选事件更加全面。② 总体来说,自20世纪60年以来,流域内发生旱涝急转事件的区域范围越来越广,事件频率和强度均具有逐年增长趋势。旱涝急转事件主要发生在5月和6月,且汉江水系、中游干流区间、洞庭湖水系北部和鄱阳湖水系西北部地区为事件高发区。③ 旱涝急转事件与事件发生前Nino 3.4区域海温持续异常偏低存在一定关系。在发生时间上,La Ni?a现象具有一定的先兆作用,41.04%的事件发生在La Ni?a现象衰亡期或现象结束后8个月内;在事件强度上,流域内站点的DWAAI与事件发生前第1~6个月的Nino 3.4区域海温异常值存在显著的负相关性,尤其是在鄱阳湖水系和中游干流区间,二者负相关性最强。研究结果可以为长江中下游流域防洪抗旱工作提供一定的依据。     

Study on the extremely cold winter of 1670 over the middle and lower reaches of the Yangtze River

The snow-cover days over the middle and lower reaches of the Yangtze River （MLRYR） in the winter of 1670 were extracted from Chinese historical documents. By these records, the winter temperature anomalies （compared to the mean of 1961-1990） recorded at seven meteorological stations and the regional mean winter temperature were estimated. The results show that： （1） There was an average of about 30 snow-cover days over the MLRYR region in 1670, ranging from 11-20 days in Shanghai and eastern Zhejiang to 5140 days in eastern Hunan Province. The snow-cover days averaged about 40 days in Anqing and Nan- cheng, and ranged from 30 to 40 days in Quzhou, Jingdezhen, and Nanchang; and （2） the regional mean winter temperature in 1670 was estimated to be approximately 4.0 ℃ lower than that of 1961-1990. The maximum negative anomaly of 5.6℃ occurred in Nanchang and the minimum anomaly of-2.8 ℃ was detected in Quzhou. Both of these were lower than that of the coldest winter during the instrumental observation period of 1951-2010. This research could not only provide a method to es- timate historical climate extremes, but also provide a background to understand the recent instrumentally climate extremes.     

基于Google Earth和MODIS陆地数据的农林地转换对地表温度的影响——以长江中下游及毗邻地区为例

揭示耕地与林地转换对地表温度的影响对于认识人类活动的气候与环境效应具有重要意义。基于卫星遥感数据的统计分析是揭示土地利用/覆盖变化对地表温度影响的重要手段。但是,在景观破碎度较高地区,混合像元问题成为使用这一技术手段的主要限制性因素,中国南方长江流域尤为典型。为突破这一限制,论文基于Google Earth高清影像,在1 km尺度上辨识了200对耕地与林地纯像元,进而利用MODIS陆地数据产品,对比分析了耕地与林地的地表温度(LST)、叶面积指数(LAI)、地表反照率(Albedo)之差。结果表明：耕地的LST高于林地,白天和夜间温度分别约偏高2.75 ℃和1.15 ℃,并且温差因季节而异,白昼温差呈双峰(分别是5月和10月,温差约3.18 ℃和3.33 ℃),夜间温差为单峰(7月,约2.46 ℃)。同时,温差因地而异,总体表现为西高东低,陕甘交界处的白昼温差最大,年平均约为3.83 ℃;安徽中南部温差最小,约为1.1 ℃。耕地与林地的LST之差主要由蒸散发的差异所致。林地的LAI较大,蒸散发较强,地表向大气的潜热通量较大,用于直接加热地表的感热相对偏少,因而LST相对偏低。上述结果表明近年来长江流域及毗邻地区的耕地转为林地通过增加蒸发产生了一定的致冷效应。     

长江中下游流域自然保护地空间分布及其与人类活动强度关系研究

以2015年土地利用类型数据为基础,计算长江中下游流域人类活动强度,采用最邻近指数、地理集中指数和不均衡指数分析研究区自然保护区、风景名胜区等六类国家级自然保护地分布特征,并定量揭示保护地空间分布与人类活动强度的关系,旨在为长江中下游流域建立基于人类活动强度的各类自然保护地管控策略提供科学依据。结果表明：1）人类活动高、较高、中、较低和低强度带在研究区的占比分别为3.74%、9.83%、14.98%、30.81%和40.63%;高等级强度带主要分布在长江三角洲平原、江汉平原等平原区,低等级强度带主要分布在秦岭山区、武陵山区等山地丘陵区。2）湿地公园、森林公园、风景名胜区和地质公园的空间分布类型为均匀型,水利风景区和自然保护区为凝聚型;六类保护地在各人类活动强度带空间分布不均衡。3）湿地公园、森林公园、水利风景区、自然保护区、风景名胜区和地质公园分别在中、较高、高、低、较低和低强度带密度最大;在高等级强度带“人地”矛盾更突出,应加强对自然保护地的保护力度和人类活动管控,尤其针对湿地公园、森林公园和水利风景区。