台风登陆衰减后造成降水加强的概况

对1965-2008年101例登陆台风衰减后3d内仍存在较强降水的天气过程,运用客观分离方法及其改进方案,分离提取了台风降水(Tropical Cyclone Precipitation;TCP),结果表明:即使登陆台风衰减为热带低压或停编后,因台风系统的存在而产生高强度降水是一种普遍现象,仍旧是预报服务中需要高度关注的问题.采用气候趋势系数和功率谱等方法得到TCP及台风的气候特征:台风衰减点的位置分布具有很强的区域性,与南岭、武夷山脉的走势大致吻合;台风衰减后降水并非单纯性减少,随着时间的推移,空间分布具有向北、向西扩散的特点,特别是中纬度地区的江汉一江淮一带,仍然是防灾减灾的重点.对于衰减后降水反而加强的台风,防御重点可以有针对性地对登陆华南类和登陆华东类两类路径的台风展开.     

1949～2005年海南岛登陆热带气旋的若干变化特征

利用热带气旋(TC)年鉴资料和海南岛逐日降水量资料,对海南岛57a登陆TC年频数、强度、登陆位置、活动时间、登陆维持时间、登陆TC降水量的变化特征进行了分析。结果表明:在全球气候变暖背景下,海南岛登陆TC年频数有显著减少趋势,但登陆时TC的平均强度和极端强度都有增强趋势,这主要归功于南海登陆海南岛的热带低压年频数的显著减少和强热带风暴的弱增加;登陆TC具有准3a的周期,而南海登陆海南岛的TC具有准3a、准5a的周期,西太平洋登陆海南岛的TC具有准13a和准3a的周期;海南岛登陆TC的登陆点位置有南移趋势,80年代中期以来在海南岛最南端地区登陆的TC频数明显增多;登陆TC的活动时间和登陆维持时间均有弱的缩短趋势;登陆TC暴雨与登陆时TC强度成显著负相关关系而和登陆维持时间有显著正相关关系,但登陆时TC强度对暴雨的影响强于登陆维持时间;登陆TC年降水量呈减少变化趋势,其中登陆风暴和强风暴的年降水量有增多趋势,登陆热带低压和登陆台风年降水量均有减少趋势。     

近50 a华东地区雨日及降水量的变化特征

利用1961-2010年华东地区88个气象站逐日降水资料,采用趋势分析和突变检测等方法,研究了华东地区年、季、月雨日和降水量的时空变化特征.结果表明,华东地区年雨日和年降水量的长期趋势变化几乎相反,年雨日普遍减少(区域平均气候倾向率为-2.3d/(10a)),而年降水量除山东省外却普遍增加,反映年平均的日降水强度增加.季雨日与季降水量的长期变化较一致,秋季最相似;春季、秋季雨日和降水量都是大范围负趋势,但雨日的负趋势比降水量的范围更广、强度更大;夏季、冬季降水量在山东省呈减少趋势,在其他地区呈增加趋势,其中长三角地区夏季及江淮流域冬季的降水增加显著,而雨日在山东和福建是负趋势,其他地区为正趋势.年雨日在山东中东部、福建北部减少最多,这些地区一年四季雨日都是减少趋势,平均每10a减少3～5d.山东半岛年雨日在20世纪70年代末期发生突变,此后年雨日明显减少.     

峨眉山及其周边地区降水气候特征研究

基于1959-2016年峨眉山、峨眉市、乐山市及夹江县气象站逐日降水数据和1964-2016年6-9月逐时降水数据,应用统计诊断分析方法,研究了峨眉山及其周边地区降水量、雨日和降水频次的多时间尺度变化特征。结果表明,峨眉山及其周边地区年代降水变化趋势基本一致,但随海拔具有一定差异性,高海拔峨眉山趋势更明显。峨眉山与其周边地区年降水量和年雨日均在20世纪90年代后显著减少,且峨眉山年雨日比其周边地区减少更快。汛期峨眉山及其周边地区降水量、雨日变化均强于其年代和年降水量、雨日变化,较其他时段更突出;高海拔峨眉山冬季、秋季和夏季降水量减少趋势显著,而周边地区夏季和秋季降水量减少趋势明显;峨眉山及其周边地区四季雨日都呈减少趋势,但峨眉山减少程度大于其周边地区。峨眉山及其周边地区月降水量和雨日都呈减少趋势,但峨眉山更明显。峨眉山降水量日变化呈单峰单谷结构,而峨眉市则在清晨出现次峰值,两地夜雨特征突出,夜间降水量远大于白天,且两地降水量峰值出现时间都存在提前的变化特征;峨眉山小时降水频次最大值出现时间存在提前的变化特征,但峨眉市相反,具有延后的变化特征。在全球气候变暖下,峨眉山及其周边地区气候响应主要为降水减少,高海拔地区降水减少的趋势大于低海拔地区。峨眉山及其周边地区这种区域气候响应的一致性与差异性,可能与区域温度响应与水汽状况差异有关。     

海南热带气旋降水的气候特征

整理出海南1962-2004年的热带气旋的降水资料,我们分析了海南省热带气旋降在海南省总降水中的地位及其变化特征,结果表明:海南热带气旋降水平均占年总降水量30%,但呈每10 a 3%的显著线性下降趋势;海南热带气旋降水与年总降水相关显著,年总降水显著偏少的年份,热带气旋降水偏少;热带气旋降水显著偏多的年份,年总降水量偏多;海南热带气旋降水变化的空间特征表现为明显的一致型,时间特征表现明显的周期性:高频的年际变化周期70年代前期以前为3 a周期为主,80年代中期以后以2 a的周期为主;低频的年际变化周期80年代以前以8—9 a为主,80年代以后以准6 a为主;年代际变化则以准17 a的周期为主。     

丽水汛期降水多时间尺度演变特征

根据1953—2008年丽水汛期逐月降水量资料,在利用趋势分析和Morlet连续小波变化对汛期降水时频变化特征进行分析的基础上,利用功率谱及Mann-Kendall检验等方法对丽水汛期降水的周期性特征及突变性进行检验。结果表明:20世纪90年代前,汛期旱涝交替周期为16～20a,90年代后,交替周期缩短为4～6a。近56a来,丽水汛期总降水量呈下降趋势,5月和9月降水量减少较显著,但夏季降水量则有所增加,其中以8月最为明显;丽水汛期降水量存在不同尺度的周期分量,并且各周期强度有所不同,其中5a和18a的周期振荡通过功率谱检验。Mann-Kendall检验显示丽水汛期降水在20世纪80年代减少最为显著,1962年是降水减少的突变点。     

西南地区极端降水变化趋势

利用西南地区90个气象台站1970-2010年逐日降水量资料,依据世界气象组织(WMO)定义的连续5d最大降水量、总降水量、强降水比等6种极端降水指数,采用F检验、11a滑动平均等统计方法,研究了西南地区极端强降水变化趋势的时空变化特征。在时间上,西南地区近41年来冬、春、夏季连续5d最大降水量缓慢波动上升,秋季连续5d最大降水量呈下降趋势;强降水、降水强度及强降水比呈上升趋势,但总降水量和最长持续无降水日数呈减少趋势;另外,各极端降水指数还存在明显的年际、年代际变化。在空间上,西南地区极端降水变化趋势具有显著的地域差异,呈东西或西北东南向梯度变化特征。其中冬季连续5d最大降水量、降水强度、强降水比及最长持续无降水日数,在西南大部分地区呈增加趋势。秋季连续5d最大降水量与总降水量在西南大部分地区呈减少趋势。而春、夏季连续5d最大降水量和强降水的增减区域大致相当。     

毕节市气候变化特征分析

利用毕节市气象站1951-2008年的气温和降水量资料,采用滑动平均、趋势分析、小波分析等方法,分析了毕节市气温和降水量的变化特征。结果表明：①毕节市年平均气温的年代际变化为20世纪70-80年代为偏冷期,其余年代为偏暖期,其中1998年之后气温明显升高,21世纪头8a是58a来最暖的时期;年及各季平均气温均呈上升趋势,秋季增温明显,冬季次之。②降水量的年代际变化为20世纪80年代最少,21世纪头8a次少,其余年代为多雨期,其中以20世纪50年代降水最多,20世纪70年代次多;年及各季降水量均呈减少趋势,夏季减少明显,春季次少。③毕节市气候从20世纪90年代到21世纪呈现冷湿、暖干交替变化的趋势,未来几年气候存在冷湿的变化。     

紫金县汛期降水量的多时间尺度特征

利用紫金县1965-2009年逐日降水资料,统计分析汛期降水气候特征,应用小波分析方法对比分析了前、后汛期降水量的多时间尺度特征,结果表明:前汛期降水量呈总体减少的趋势,对全年雨量的贡献在下降,而后汛期则相反,前、后汛期降水量都具有年代际特征;前汛期主要存在1.7和18.4年的时间尺度变化特征,尤其以1.7a最为显著;后汛期降水量主要存在2.6和21.1a时间尺度变化特征,其中2.6a较为显著.     

近50 a南京夏季降水的气候特征

利用南京6站近50 a(1960—2009年)的夏季逐日降水资料,应用累积距平、趋势系数、小波分析等方法,分析了南京地区夏季降水和旱、涝年的时空特征。结果表明,南京地区夏季降水量、雨日、暴雨日和暴雨日降水强度均有明显的年代际变化特征,其中降水量和暴雨日数的年代际变化基本一致;各站夏季降水量、雨日和暴雨日均呈增加趋势,总降水量的增加趋势主要是大雨及以上量级降水的贡献;夏季降水量存在2～8 a的周期变化;南京地区旱、涝年的夏季降水量与长江中下游地区有较好的一致性,与华南地区呈相反关系。     

Validating a regional climate model’s downscaling ability for East Asian summer monsoonal interannual variability

Performance of a regional climate model (RCM), WRF, for downscaling East Asian summer season climate is investigated based on 11-summer integrations associated with different climate conditions with reanalysis data as the lateral boundary conditions. It is found that while the RCM is essentially unable to improve large-scale circulation patterns in the upper troposphere for most years, it is able to simulate better lower-level meridional moisture transport in the East Asian summer monsoon. For precipitation downscaling, the RCM produces more realistic magnitude of the interannual variation in most areas of East Asia than that in the reanalysis. Furthermore, the RCM significantly improves the spatial pattern of summer rainfall over dry inland areas and mountainous areas, such as Mongolia and the Tibetan Plateau. Meanwhile, it reduces the wet bias over southeast China. Over Mongolia, however, the performance of precipitation downscaling strongly depends on the year: the WRF is skillful for normal and wet years, but not for dry years, which suggests that land surface processes play an important role in downscaling ability. Over the dry area of North China, the WRF shows the worst performance. Additional sensitivity experiments testing land effects in downscaling suggest the initial soil moisture condition and representation of land surface processes with different schemes are sources of uncertainty for precipitation downscaling. Correction of initial soil moisture using the climatology dataset from GSWP-2 is a useful approach to robustly reducing wet bias in inland areas as well as to improve spatial distribution of precipitation. Despite the improvement on RCM downscaling, regional analyses reveal that accurate simulation of precipitation over East China, where the precipitation pattern is strongly influenced by the activity of the Meiyu/Baiu rainfall band, is difficult. Since the location of the rainfall band is closely associated with both lower-level meridional moisture transport and upper-level circulation structures, it is necessary to have realistic upper-air circulation patterns in the RCM as well as lower-level moisture transport in order to improve the circulation-associated convective rainfall band in East Asia.     

THE EAST ASIAN SUBTROPICAL SUMMER MONSOON INDEX AND ITS RELATION WITH THE CLIMATE ANOMALIES IN CHINA

A new East Asian subtropical summer monsoon circulation index is defined, where the barotropic and baroclinic components of circulation are included. Results show that this index can well indicate the interannual variability of summer precipitation and temperature anomalies in China. A strong monsoon is characterized by more rainfall in the Yellow River basin and northern China, less rainfall in the Yangtze River basin, and more rainfall in south and southeast China, in association with higher temperature in most areas of China. Furthermore, comparison is made between the index proposed in this paper and other monsoon indexes in representing climate anomalies in China.     

EFFECT OF TROPICAL CYCLONE PRECIPITATION ON ALLEVIATING THE DROUGHT SITUATION IN THE SOUTHEAST COASTAL REGIONS OF CHINA DURING SUMMER AND AUTUMN: USING THE IMPROVED OBJECTIVE SYNOPTIC ANALYSIS TECHNIQUE

To quantitatively study the role of tropical cyclone precipitation (TCP) on alleviating the drought in the southeast coastal region of China (SCR) during summer and autumn, the objective synoptic analysis technique (OSAT), improved for consistency and rationality, was used to separate the TCP data on the summers and autumns of 1963–2005 on the basis of daily precipitation data from stations and tropical cyclone best track data. After defining the season drought index, the actual drought distribution and the assumed drought distribution without TCP were acquired. The results showed that within 1 000 km from the southeast coastline of China, TCP accounted for 11.3% of natural precipitation (NP). Without TCP, the drought index in the SCR during summer would have increased from 0.2 to 0.6 or even above 1.0 in some regions whereas the drought index during autumn would have increased from 0.4 to 0.6 or above 1.2 in some regions. The impact of TCP on drought decreases progressively from the southeast coastline to the inland regions. The TCP proportion (TCPP) showed a significant negative correlation with the drought index in many regions of the southeast, and the significant region is wider in autumn than in summer. TCP relieved the drought most significantly within a range of 0–500 km from the southeast coastline. This drought relief showed different characteristics for the interannual variability in summer and autumn, and the cross wavelet transform indicated that the impact of TCP on drought mainly lies in 2–4-year time scales. In particular, there was a significant effect during the summers of 1977–1985 and in the autumns following that of 1985. Therefore, TCP has indeed largely alleviated drought in the SCR during summer and autumn.     

1951—2009年中国地表湿润状况变化趋势研究

利用1951—2009年中国160站的月降水和月平均温度资料,通过计算地表湿润指数,在分析其与降水及气温联系的基础上,探讨了中国区域平均地表湿润指数的年代际变化特征差异,给出了地表湿润指数年趋势的地理分布。结果表明：1951—2009年,中国北方的西北地区东部、华北和东北地区长江中下游地区及东南部分地区以干旱化趋势为主,这些地区干旱化趋势的产生与降水年际变差大、年内分配不均,降水持续减少和气温升高密切相关。东南、西南地区及西藏地区于20世纪90年代初期有湿向干的趋势转换,虽然长江中下游地区在70年代初期有明显的干向湿的趋势变换,但于90年代同样出现湿向干的趋势转换,并一直持续显著的干旱化。     

1965-2010年7-9月影响中国的热带气旋降水变化趋势分析

利用中国气象局逐日台站降水和上海台风研究所最佳台风路径等资料,对1965—2010年夏季(7—9月)影响中国热带气旋降水的变化趋势及影响机制进行了分析。热带气旋降水主要影响中国东部和南部,夏季平均的热带气旋降水由沿海向内陆,由东南向西北递减。自1965年以来,夏季影响中国的热带气旋降水呈现华东及东南沿海增多,华南沿海、海南岛以及西南地区减少的变化趋势。分析发现,一方面夏季西北太平洋副热带高压加强西伸,导致同期中国东部地区上空水汽辐合增强;另一方面热带气旋的引导气流发生变化,使夏季热带气旋盛行路径由南海向东亚沿岸偏移,这两个因子的共同作用致使影响中国的热带气旋降水发生变化。     

THE DIRECT EFFECTS OF AEROSOLS AND DECADAL VARIATION OF GLOBAL SEA SURFACE TEMPERATURE ON THE EAST ASIAN SUMMER PRECIPITATION IN CAM3.0

Using the CAM3.0 model, we investigated the respective effects of aerosol concentration increasing and decadal variation of global sea surface temperature(SST) around year 1976/77 on the East Asian precipitation in boreal summer. By doubling the concentration of the sulfate aerosol and black carbon aerosol separately and synchronously in East Asia(100-150 °E, 20-50 °N), the climate effects of these aerosols are specifically investigated. The results show that both the decadal SST changing and aerosol concentration increasing could lead to rainfall decreasing in the center of East Asia, but increasing in the regions along southeast coast areas of China. However, the different patterns of rainfall over ocean and lower wind field over Asian continent between aerosol experiments and SST experiments in CAM3.0 indicate the presence of different mechanisms. In the increased aerosol concentration experiments, scattering effect is the main climate effect for both sulfate and black carbon aerosols in the Eastern Asian summer. Especially in the increased sulfate aerosol concentration experiment, the climate scattering effect of aerosol leads to the most significant temperature decreasing, sinking convection anomalies and decreased rainfall in the troposphere over the central part of East Asia. However, in an increased black carbon aerosol concentration experiment, weakened sinking convection anomalies exist at the southerly position. This weakened sinking and its compensating rising convection anomalies in the south lead to the heavy rainfall over southeast coast areas of China. When concentrations of both sulfate and black carbon aerosols increase synchronously, the anomalous rainfall distribution is somewhat like that in the increased black carbon concentration aerosol experiment but with less intensity.     

近44年来我国西北地区干湿特征分析

利用我国西北地区1960—2003年131个测站降水和小型蒸发皿蒸发量资料, 综合考虑降水和蒸发这两个水分平衡最关键的分量构造了降水蒸发均一化干湿指数, 进而研究了西北地区干湿的时空演变特征。结果表明:一致性异常是西北地区近44年干湿特征的最主要空间分布模态; 西北地区干湿异常特征主要分为西风带气候区型, 高原气候区型和季风气候区型; 整个西北地区及其西风带气候区、高原气候区年干湿特征呈较为显著的变湿趋势, 大约在20世纪70年代中期均发生了由干向湿的突变, 而季风气候区表现为变干趋势, 并且在90年代前期发生了由湿向干的突变; 整个西北地区及各分区近44年来主要以年代际周期振荡为主。     

Regional trends in recent precipitation indices in China

Summary Regional characteristics of recent precipitation indices in China were analyzed from a daily rainfall dataset based on 494 stations during 1961 to 2000. Some indices such as precipitation percentiles, precipitation intensity, and precipitation persistence were used and their inter-decadal differences were shown in this study. Over the last 40 years, precipitation indices in China showed increasing and decreasing trends separated into three main regions. A decreasing trend of annual precipitation and summer precipitation was observed from the southern part of northeast China to the mid-low Yellow River valley and the upper Yangtze River valley. This region also showed a decreasing trend in precipitation intensity and a decreasing trend in the frequency of persistent wet days. On the other hand, increasing trends in precipitation intensity were found in the Xinjiang region (northwest China), the northern part of northeast China, and southeast China, mainly to the south of the mid-low Yangtze River. The indices of persistent wet days and strong rainfall have contributed to the increasing frequency of floods in southeast China and the Xinjiang region in the last two decades. Persistent dry days and weakening rainfall have resulted in the increasing frequency of drought along the Yellow River valley including North China. Regional precipitation characteristics and trends in precipitation indices indicate the climate state variations in the last four decades. A warm-wet climate state was found in northwest China and in the northern part of northeast China. A warm-dry climate state extends from the southern part of northeast China to the Yellow River valley, while a cool-wet summer was found in southeast China, particularly in the mid-low Yangtze River valley over the last two decades.     

中国东部夏季降水年际变化与东中国海及邻近海域海温异常的关系

本文首先利用1979～2008年中国756个站点和GPCP2.1的降水资料与Hadley中心的HadISST再分析海温资料以及应用合成和相关分析方法, 分析了中国东部夏季降水年际变化及其与东中国海及邻近海域海温异常的关系。分析结果表明: 当东中国海及邻近海域为暖 (冷) 异常时, 长江中下游、 江淮地区夏季降水减少 (偏多), 而东北南部的降水偏多 (减少)。并且, 本文应用RegCM3区域气候模式对上述关系进行数值试验, 结果表明了东中国海及邻近海域的暖 (冷) 异常, 将使得我国长江、 黄淮流域和华北大部分地区夏季降水的减少 (增加), 而华南地区、 东北南部和朝鲜半岛等地夏季降水的增加 (减少)。此外, 本文还利用NCEP/NCAR再分析资料和数值模拟对上述关系的大气环流变异过程进行了分析, 分析结果揭示了上述海域的升温或降温对东亚地区上空的纬向和经向环流有较明显的影响。当东中国海及邻近海域升温时, 除了在该海域东部引起低空辐合, 高空辐散, 产生上升运动外, 还在其西部的长江、 黄淮流域和华北地区引起低空辐散, 高空辐合, 产生下沉运动, 这将引起长江、 黄淮流域和华北等地夏季降水的减少; 并在华南、 东北南部和朝鲜半岛地区引起低空辐合, 高空辐散, 从而产生上升运动, 这使得华南地区、 东北南部和朝鲜半岛夏季降水的增加。反之, 当东中国海及邻近海域降温时, 上述区域出现相反的现象。这些都说明东中国海及邻近海域的热力状态可能是影响我国东部夏季降水的重要因子之一。     

冬季NPO突变前后大气环流和我国天气气候的变化

用Mann-Kendall突变检验方法对北太平洋涛动10a际气候突变进行的研究指出，在1976年左右存在着一次明显的气候突变，而突变前后大气环流场及遥相关型均发生了显著的变化。进而研究了北太平洋涛动突变前后我国冬季天气气候的变化特征。结果表明，突变前(后)，我国冬季气温一致性偏低(高)，且北方地区的变化明显大于南方；而降水则呈现出长江中下游地区偏多(少)和华南偏少(多)的反相特征。此外，冬季NPO突变前，北太平洋涛动以3a和6～7a的周期为主；突变后，3a周期仍然存在，但5a和10a左右的周期开始占主导地位。