基于标准化降水指数的内蒙古地区干旱时空变化特征

利用内蒙古及周边地区70个气象站1951~2014年降水数据,采用标准化降水指数等方法,对内蒙古近64年气候干旱时空变化进行分析。结果表明:研究区近64年来除西部年际、春、秋、冬季,中部春、秋季及东部春、冬季气候趋于湿润外,其他均趋于干旱。中、东部年际、植(作)物生长期SPI在2001年和1990年左右发生突变,东部突变后趋于干旱并在2006年左右又发生明显转折后趋于湿润。西部在1960s干旱严重,中、东部在1990s至2000s干旱严重。西部年际SPI由西北向东南、东部由南向北干旱趋势速率呈阶梯状下降,中部干旱趋势速率较西、东部快;植(作)物生长期SPI空间变化与年际一致,但西、中部干旱趋势明显的区域有所扩大。     

天山北坡中部一次罕见局地强降水中小尺度系统分析

利用Doppler雷达产品,结合高时空分辨率的T639再分析资料,对2010年6月22日发生在天山北坡中部石河子南部山区罕见局地强降水的中小尺度系统特征和强降水发生时间与落区进行分析。结果表明：西伯利亚至巴尔喀什湖的冷低压东南象限分裂出的中尺度短波,是造成“2010622”罕见局地强降水的直接影响系统。近低层至地面的中尺度切变线、辐合线以及冷锋是局地强降水发生的触发机制。近低层存在着强盛的西南及东南暖湿气流的输送及其在山前的强烈辐合,为南部山区罕见局地强降水的发生提供了有效的水汽和不稳定能量条件。多个中-γ对流单体沿特殊地形滚动更迭是局地强降水天气落区形成的直接原因。中气旋的出现对局地强降水的发生有很好的先兆性和指示意义。强降水发生在回波强度大于50 dBz、回波顶高度大于5 km和垂直累积液态水含量大于45kg·m^-2以及中气旋的重合区域内。可用中气旋提前20 min预警短时局地强降水的发生。     

石笋氧同位素和微量元素记录的陕南地区4200～2000a B.P.高分辨率季风降雨变化

基于陕南祥龙洞石笋XL2的19个230Th年龄、218个氧同位素分析以及896个Sr/Ca分析数据,高分辨率重建了4200～1972a B.P.期间陕南地区季风降雨变化.重建结果显示陕南地区这一时期季风降雨有显著的127～105a和57a周期,可能分别受控于太阳活动、PDO和/或AMO的变化.重建时段有3次百年尺度的干旱事件,分别发生于2200～2100a B.P.,2900～2700a B.P.和3600～3400a B.P.,其中2900～2700a B.P.干旱事件对应于北大西洋地区2.8ka冷事件.对比研究显示,尽管祥龙洞石笋和董哥洞石笋δ18O记录整体一致,但除了2900～ 2700aB.P.干旱事件之外,其他两次干旱事件在董哥洞石笋记录中并不明显.而尽管总体上祥龙洞和和尚洞石笋δ18O记录的差异要大,但XL2的3次干旱事件在和尚洞记录都有明显体现.有精确年代控制的祥龙洞、董哥洞及和尚洞石笋氧同位素记录的差异,揭示晚全新世我国季风降雨在十一百年尺度存在区域差异.     

Likely effects of climate change on groundwater availability in a Mediterranean region of Southeastern Spain

Groundwater resources are typically the main fresh water source in arid and semi‐arid regions. Natural recharge of aquifers is mainly based on precipitation; however, only heavy precipitation events (HPEs) are expected to produce appreciable aquifer recharge in these environments. In this work, we used daily precipitation and monthly water level time series from different locations over a Mediterranean region of Southeastern Spain to identify the critical threshold value to define HPEs that lead to appreciable aquifer recharge in this region. Wavelet and trend analyses were used to study the changes in the temporal distribution of the chosen HPEs (≥20 mm day^?1) over the observed period 1953–2012 and its projected evolution by using 18 downscaled climate projections over the projected period 2040–2099. The used precipitation time series were grouped in 10 clusters according to similarities between them assessed by using Pearson correlations. Results showed that the critical HPE threshold for the study area is 20 mm day^?1. Wavelet analysis showed that observed significant seasonal and annual peaks in global wavelet spectrum in the first sub‐period (1953–1982) are no longer significant in the second sub‐period (1983–2012) in the major part of the ten clusters. This change is because of the reduction of the mean HPEs number, which showed a negative trend over the observed period in nine clusters and was significant in five of them. However, the mean size of HPEs showed a positive trend in six clusters. A similar tendency of change is expected over the projected period. The expected reduction of the mean HPEs number is two times higher under the high climate scenario (RCP8.5) than under the moderate scenario (RCP4.5). The mean size of these events is expected to increase under the two scenarios. The groundwater availability will be affected by the reduction of HPE number which will increase the length of no aquifer recharge periods (NARP) accentuating the groundwater drought in the region. Copyright © 2016 John Wiley & Sons, Ltd.     

物理过程参数化方案对中国夏季降水日变化模拟的影响

国际耦合模式比较计划第六阶段(CMIP6)新增的高分辨率模式比较计划(HighResMIP)首次提供全球高分辨率(25—50 km)多模式集合的气候模拟试验结果。利用8个CMIP6 HighResMIP模式评估了高分辨率全球气候模式对青藏高原夏季小时降水与极端降水的模拟能力,结果表明：CMIP6高分辨率模式高(低)估了青藏高原地区的降水量和频率(强度),过多的降水量主要来自模式对降水频率的高估,尤其是弱降水(< 2 mm·h^-1)的发生频率。模拟偏差与地形海拔密切相关,偏差大值区主要位于高原南坡和东坡陡峭地形区。模式不能准确再现降水量与海拔之间的关系,高(低)估了高(低)海拔地区的降水量。模式低估了降水强度随海拔升高而降低的变化速率。在日变化方面,模式能够模拟出青藏高原降水傍晚至午夜的峰值特征,但明显低估了降水的日变化振幅。在小时极端降水方面,模式低估了高原区域平均极端降水第95百分位数阈值,仅为观测值的57%。

     

COMPARATIVE ANALYSIS OF THE INTENSITY AND DISTRIBUTION OF HEAVY RAINS IN ZHEJIANG PROVINCE CAUSED BY TYPHOONS HAITANG AND MATSA

Study was carried out on two landfall typhoons Haitang and Matsa, which affected Zhejiang province seriously in 2005. Firstly, the similarity and difference between the two typhoon-induced heavy rains were compared and it was pointed out that both of them brought strong large-scale precipitation and the maximum centers of rainfall were located on the north side of the landfall site. Making landfall on Fujian, Haitang was weaker than Matsa in intensity but surpassed it in rainfall. Then with focus on intensity, moving speed, structure of typhoon, circulation and terrain, the two typhoon-related heavy rains were compared and analyzed. Results show that the asymmetrical distribution of rainfall was closely related to the structure of typhoons themselves, moisture transportation and mesoscale terrain. In contrast to the south side, the north side was hotter and wetter and water vapor was also more abundant. The phenomenon of more rainfall induced by Haitang was in connection with the following reasons. Invading cold air led to rainfall increases, weakened dynamic field and slower movement both benefited precipitation. For the last part, the cold characteristic of air mass over Zhejiang was also a favorable factor for the rain.     

全球增暖1.5/2℃下中国区域极端降水的风险变化及其影响因子

利用24个CMIP6全球气候模式的逐日降水模拟资料,基于广义极值分布(GEV)模型,研究了全球增暖1.5/2℃下我国20、50和100 a重现期极端降水的未来风险变化。可以发现,相对于历史时期(1995—2014年),全球升温1.5和2℃下极端降水发生概率风险空间分布相近,总体上呈现增加趋势,但额外增暖0.5℃将导致更高的风险。如50 a重现期极端降水,在增暖1.5/2℃下其重现期将分别变为17/14 a,极端降水将变得更加频繁。不同区域对气候变暖的响应存在区域差异,其中中国西部长江黄河中上游和青藏高原地区、中国东部长江黄河中下游及其以南地区,极端降水发生概率比达到3以上,局部更是达到5以上,为我国极端降水气候变化响应高敏感区域。进一步,基于概率分布函数从理论角度探讨了位置和尺度参数对发生概率风险的影响与贡献度量,并用于探讨极端降水气候平均态和变率变化对极端降水发生风险的影响,结果显示：位置和尺度参数的增量变化、风险变化率存在着显著的东西部差异,从而导致极端降水发生风险的影响因素存在差异。如中国西部尽管极端降水气候平均态和变率变化幅度不大,但因风险变化率较高,从而导致该区域的发生风险大...     

IMERG卫星降水数据在嘉陵江流域的干旱监测效用评估

针对嘉陵江流域存在雨热同期,水旱灾害频发的现象,为快速且准确地把握流域内降水与干旱情况,利用覆盖范围广且分辨率高的网格化IMERG卫星降水数据对嘉陵江流域进行多时空尺度反演,并基于卫星降水数据采用标准化降水指数(SPI)对流域实行干旱监测。结果表明：1)根据分类指标与统计指标的计算结果,三种卫星降水数据中的IMERG-F能更准确地反映流域内的日降水量,与地面降水数据CC达0.737,整体高估地面降水2.6%,具有在干旱监测方面的应用潜力。2)三种卫星降水数据驱动的SPI指数在干旱监测方面存在一定的差异,IMERG-F驱动的SPI指数与地面降水数据驱动的SPI指数保持较高的一致性(CC>0.9),较近实时产品IMERG-F更能准确地呈现出流域的干湿特征。3)卫星识别降水与干旱监测的能力受地形地貌的影响,IMERG卫星降水数据在平原丘陵地带具有较好的适用性。     

Atmospheric forcing of the eastern tropical Pacific: A review

The increase in marine, land surface, atmospheric and satellite data during recent decades has led to an improved understanding of the air–sea interaction processes in the eastern tropical Pacific. This is also thanks to extensive diagnoses from conceptual and coupled ocean–atmosphere numerical models. In this paper, mean fields of atmospheric variables, such as incoming solar radiation, sea level pressure, winds, wind stress curl, precipitation, evaporation, and surface energy fluxes, are derived from global atmospheric data sets in order to examine the dominant features of the low level atmospheric circulations of the region. The seasonal march of the atmospheric circulations is presented to depict the role of radiative forcing on atmospheric perturbations, especially those dominating the atmosphere at low levels.In the tropics, the trade winds constitute an important north–south energy and moisture exchange mechanism (as part of the low level branch of the Hadley circulation), that determines to a large extent the precipitation distribution in the region, i.e., that associated with the Inter-Tropical Convergence Zone (ITCZ). Monsoonal circulations also play an important role in determining the warm season precipitation distribution over the eastern tropical Pacific through a large variety of air–sea–land interaction mechanisms. Westward traveling waves, tropical cyclones, low latitude cold air intrusions, and other synoptic and mesoscale perturbations associated with the ITCZ are also important elements that modulate the annual rainfall cycle. The low-level jets of the Gulf of California, the Intra-Americas Sea (Gulf of Mexico and Caribbean Sea) and Chocó, Colombia are prominent features of the eastern tropical Pacific low-level circulations related to sub-regional and regional scale precipitation patterns. Observations show that the Intra-Americas Low-Level Jet intensity varies with El Niño/Southern Oscillation (ENSO) phases, however its origin and role in the westward propagation and development of disturbances that may hit the eastern tropical Pacific, such as easterly waves and tropical cyclones, are still unclear. Changes in the intensity of the trade winds in the Caribbean Sea and the Gulf of Mexico (associated with eastern tropical Pacific wind jets) exert an important control on precipitation by means of wind–topography interactions. Gaps in the mountains of southern Mexico and Central America allow strong wind jets to pass over the continent imprinting a unique signal in sea surface temperatures and ocean dynamics of the eastern tropical Pacific.The warm pools of the Americas constitute an important source of moisture for the North American Monsoon System. The northeastern tropical Pacific is a region of intense cyclogenetic activity, just west of the coast of Mesoamerica. Over the oceanic regions, large-scale properties of key variables such as precipitation, moisture, surface energy fluxes and wind stress curl are still uncertain, which inhibits a more comprehensive view of the region and stresses the importance of regional field experiments. Progress has been substantial in the understanding of the ocean and atmospheric dynamics of the eastern tropical Pacific, however, recent observational evidence such as that of a shallow meridional circulation cell in that region, in contrast to the classic concept of the Hadley-type deep meridional circulation, suggests that more in situ observations to validate theories are still necessary.This paper is part of a comprehensive review of the oceanography of the eastern tropical Pacific Ocean.     

近45年华中地区不同级别强降水事件变化趋势

利用华中五省84个测站1961—2005年逐日降水资料,通过分位值法、趋势系数法、蒙特卡洛统计检验法、曼肯德尔法、小波分析等现代统计诊断方法,分析了华中地区不同级别强降水的时空变化趋势、突变和周期特征。结果表明:随着分位值减小,降水量、日数的平均值和均方差逐渐减小,变差系数逐渐增大;而强度的3项指标均逐渐增大;在空间分布上,降水量自河南向湖南和江西逐渐增大;日数自北向南逐渐增大;强度以湖北东部至江西北部的长江中下游一线以及湖南西北部局部地区为高值区;区域平均的降水量、日数和强度均呈增加趋势,但不同测站表现不同;降水量一致在1993年发生突变,呈增多趋势;日数在20世纪80年代末、90年代初发生突变;强度自1994年开始增强,21世纪后加强、减弱现象交替出现;降水量、日数和强度有12~14年的年代际变化和6~9年的短期变化。