多窗谱分析方法及其在全球变暖研究中的应用

多窗谱分析方法是一种低方差、高分辨的谱分析方法 ,尤其适合于非线性气候系统中高噪声背景下弱信号、时频演变信号的诊断分析。文中简要地介绍了多窗谱分析方法的基本原理 ,并将其用于近 1 5 0 a来全球及南、北半球温度变化的研究。结果表明 :(1 )在温度呈线性变暖的背景趋势下 ,北半球、全球年平均温度还具有显著的 40～ 70 a的准周期低频振荡 ,它们与变暖过程中的波动性密切相关 ;(2 )年代际振荡信号在北半球温度序列中也相当明显 ,南半球则存在多种低于 5 a尺度的显著振荡周期 ,半球或全球 ENSO振荡分量、QBO周期信号的振幅都具有缓变包络的特性 ;(3 )与传统功率谱估计、最大熵谱估计结果的对比表明 ,多窗谱分析方法方法得到的谱估计分辨力高 ,稳定性强。     

全球变暖背景下热带大气季节内振荡的变化特征及数值模拟

利用欧洲中期数值预报中心的ERA40再分析逐日的200 hPa风场资料,选取1958-1977年和1980-1999年各20年,对比分析了在全球变暖背景下前后两个时段热带大气季节内振荡(ISO)的特征及其变化.研究表明: 近20 a来,原来在赤道中太平洋上活跃的ISO减弱,而在中印度洋、孟加拉湾地区ISO变得活跃;全球变暖背景下,ISO的强度变化幅度加大,表明ISO更加活跃,且季节变化明显,冬、春季强,夏、秋季弱;对流层上层的纬向风能量更集中于1-3波,ISO的频率有加大的趋势.还利用中国科学院大气物理研究所LASG发展的耦合气候系统模式FGOALS-1.0g中的控制试验及其二氧化碳浓度加倍试验结果,分别对应实测资料的前后20年进行对比分析.发现模式对ISO的空间结构模拟较好,但低估了ISO的强度;时空谱分析表明模式结果中包含有更多的纬向风的高频成分,由于能量的分散,导致对ISO活动强度的低估.但通过对模式的控制试验和温室气体增加试验结果的对比分析,发现耦合模式还是较好地反映出在全球变暖背景下ISO在中印度洋、孟加拉湾地区变得活跃、频率加大等变化特征.     

THE RESPONSE OF SUMMER DRYNESS/WETNESS PROBABILITY IN NORTH CHINA TO GLOBAL WARMING

Using the data of summer(June—August)precipitation during the period of 1951—1990 in 14 stations over NorthChina,the wetness probability(WP)series based on gamma distribution has been built.Main temporal and spatial char-acteristics for the series of WP in the stations are extracted by using empirical orthogonal functions(EOFs).The spatialpatterns show that the dryness/wetness variations in the stations in the area are consistent with each other and its maincharacteristics can be represented by the WP series in Beijing.Having analysed the WP series of 120 years(1870—1989)in Beijing,the results show that the dry tendency has a re-sponse to the global warming.The variation of the dryness/wetness in the stations is associated with the temperaturevariation in the Northern Hemisphere.Their relation is negative.The degree of the reliance is associated with the centuryvariation of the temperature.     

宁夏气温、降水、蒸发的变化及其对气候变暖的响应

本文对近40多a来宁夏气温、降水、小型蒸发皿蒸发量的变化进行了分析,结果表明:宁夏年平均气温具有明显的年代际变化特征,1986年附近发生了一次明显气候跃变,跃变后增温最明显的是冬季;秋季降水量的年代际变化特征较明显,在1978年发生转折,此前宁夏处于多雨时段,其后处于降水偏少的气候背景之中;宁夏小型蒸发皿蒸发量近40 a来存在下降趋势,下降趋势最明显的季节是夏季,最明显的区域是宁南山区;近年来宁夏蒸发量的减少与太阳辐射的减弱及水汽压的增加有关,宁南山区蒸发明显下降,与低云量的减少有关;宁夏平均气温对中国区域气候变暖响应明显,当中国区域平均气温增加1℃(各季及年),宁夏春季平均气温约升高1.1℃,夏、秋、冬季及年平均气温约升高1.3℃;宁夏春季降水量与中国区域同期降水量有密切联系;在全球气候变暖的大背景下,宁夏秋季降水有下降趋势,冬季降水存在上升趋势;宁夏气候有变干的趋势。     

SPATIAL AND TEMPORAL VARIABILITY OF NORTHWEST PACIFIC TROPICAL CYCLONE ACTIVITY IN A GLOBAL WARMING SCENARIO

Utilizing the Joint Typhoon Warning Center (JTWC) and Tokyo-Typhoon Center of the Japan Meteorological Agency (JMA RSMC TOKYO) best-track tropical cyclone (TC) data for the period 1951–2014, variations in spatial and temporal characteristics of Northwest Pacific TC activity for a global warming scenario are discussed. The results suggest that since the early 1960s, there has been an overall decreasing trend in the frequency of occurrence, intensity, peak intensity, length of movement, and lifetime of TCs. However, global warming has led to a linearly increasing trend in TC activity in eastern Asia, which indicates that Northwest Pacific TC activity decreases, but the frequency of landfalls and intensity are likely strengthened. Therefore, the threat of TCs towards eastern Asia is enhanced. The increase in TC activity in eastern Asia is likely the result of a strengthened Walker circulation due to an increasing temperature gradient between the northwest Pacific Ocean and the central and eastern Pacific Ocean. The strengthening Walker circulation could increase the magnitude of the vertical wind shear, relative vorticity, and meridional wind shear of low-level easterlies near the equator in the tropical Northwest Pacific, which affects the spatial and temporal variations of TC activity in the Northwest Pacific.     

全球变暖对区域极端气温出现概率的影响

在适当的概率分布模式基础上，考察冬夏极端气温出现概率对全球气候变暖的敏感率，以上海、南京、东台、徐州站为试验实例。分析结果表明，无论是冬季逐日最低(极端)或平均最低气温或夏季逐日最高(极端)或平均最高气温的概率分布的敏感率几乎都呈现出气温方差变化的影响大于气温均值变化的影响。     

“全球变暖”背景下的全球温度时空变化特征

通过对各种温度资料所作的统计分析,得到全球变暖背景下的全球温度的时空变化特征.结果表明:二十世纪初以来,总体来讲全球、南半球、北半球均出现了强烈的增温;这种增温过程中存在着很大的地区差异和季节差异,甚至有些区域在某些时段出现了很强的降温;南北半球在这些变化过程中表现出了很大的差异;对流层上层的温度变化要强于对流层下层的温度变化;冬季的增温要明显地高于夏季,冬夏温差有减小的趋势.     

全球变暖背景下我国热带气旋灾害趋势分析

利用热带气旋(TC)灾害等资料,对全球变暖背景下我国TC灾害和防台减灾工作的成效等进行了初步分析.在过去25年中,每年平均有6～7个TC登陆我国沿海省份及海南岛,登陆时的平均强度达到29.9 m/s,平均在陆地上维持15.6个小时,导致505人死亡,造成370亿(2008年人民币水平)的直接经济损失,占GDP的0.4％...     

A POSSIBLE MECHANISM OF ABRUPT GLOBAL WARMING IN THE 1920s

The abrupt warming of Northern Hemisphere in 1920s has been detected,the simplest model is introduced to ex-plain some deterministic and stochastic nature with this interesting phenomenon,and the implications of our approachto the predictability are discussed.     

全球变暖背景下东亚对流层顶高度演变特征的研究

研究了1948～2004年东亚增暖背景下对流层顶高度的演变特征,重点分析对流层温度、平流层中下部温度与对流层顶高度变化之间的关系。结果表明：东亚地区对流层顶高度在1970年代后呈现波动上升趋势,其上升趋势不如南半球显著;东亚对流层温度与对流层顶高度呈显著正相关,特别是对流层中上部温度与对流层顶高度的正相关最显著,这说明对流层中上部的增温对对流层顶高度的抬升贡献较大;东亚平流层中下层温度与对流层顶高度基本呈显著负相关,70hPa层上的负相关最显著;近20年来东亚对流层温度上升了约0．2℃,平流层中下部温度下降了约1．2℃,对流顶高度上升了约86m,对流层的增暖和平流层的冷却作用共同导致了东亚对流层顶高度的变化。     

全球变暖对我国亚热带北界的影响

根据历史气候暖期亚热带北界变迁和划分亚热带北界的热量指标，借助于文献「１」模拟ＣＯ２倍增的全球平均温度状况，采用几种气候指标推估的经验公式，预测未来气候变暖背景下我国亚热带北界的位置。结果表明，ＣＯ２倍增状况下，我国亚热带北界平均约北移３个纬度，其界线将变为西南向东北的波形走向。     

COMPARISON OF GLOBAL CLIMATE CHANGE SIMULATIONS FOR 2 × CO2-INDUCED WARMING

In this article we compile 108 national and international studies on global climate change, each projecting a quantitative impact on global surface-air temperature due to a doubling of the atmospheric CO₂ concentration. These predictions, documented between 1980 and 1995, are based primarily on climate-modeling research, including radiative-convective, energy-balance, and general circulation models. Collectively over the past 15 years, the average (mean) temperature change projection due to doubled CO₂ is +2.62°C, with a range of 0.16–8.7°C. General circulation models tend to estimate slightly higher values (2.98°C), compared with radiative-convective models (1.98°C) and energy-balance models (2.54°C). During the years 1980 through 1995, an increasing trend in predictions is noticed, although the mean temperature change prediction each year has remained fairly consistent near 2–3°C. These findings suggest that the estimated sensitivity of the climate system continues to remain comparable to the range calculated in earlier studies. However, tremendous advancements in the capacity of climate models continue to reveal important uncertainties in the dynamic nature of global atmospheric interactions. The predictions continue to validate the need for a global policy relating to human influence on global climate change.     

SENSITIVITY OF LANDFALLING TYPHOON STRUCTURE AND PRECIPITATION TO VARYING CLOUD MICROPHYSICAL PROCESSES

Typhoon KROSA in 2007 is simulated using GRAPES, a mesoscale numerical model, in which a two-parameter mixed-phase microphysics scheme is implanted. A series of numerical experiments are designed to test the sensitivity of landfalling typhoon structure and precipitation to varying cloud microphysics and latent heat release. It is found that typhoon track is sensitive to different microphysical processes and latent heat release. The cloud structures of simulated cyclones can be quite different with that of varying microphysical processes. Graupel particles play an important role in the formation of local heavy rainfall and the maintenance of spiral rainbands. Analysis reveals that the feedback of latent heat to dynamic fields can significantly change the content and distribution of cloud hydrometeors, thus having an impact on surface precipitation.     

植被和土壤湿度对西南低涡降水影响的敏感性试验

利用含Ｄｅａｒｄｏｒｆｆ植被参数化方案的颜宏等有限区域细网格模式，研究西南低涡降水对青藏高原及其邻近区域植被覆盖和土壤湿度变化的敏感性，着重分析在“８２．７”和“８１．７”两次西南低涡降水过程中的降水、上升运动和地面感热与水汽通量对植被覆盖和土壤湿度的敏感性问题。试验表明，西南低涡降水对青藏高原及其邻近地区的植被覆盖和土壤湿度是非常敏感的，对大气低层上升运动和地面感热、潜热通量也较为敏感。     

气候变暖背景下全球海温对中国东部夏季降水年代际转折的影响

针对1970年代末及1990年代初中国东部夏季降水（ECP）的年代际变化格局,采用EOF分解、相关分析、回归分析等统计方法诊断了全球海表面温度对ECP年代际变化前两个模态（EOF1、EOF2）的影响。发现大西洋多年代际振荡（AMO）序列,印度洋偶极子（DMI）序列,太平洋年代际振荡（PDO）序列与ECP前两个模态时间系数（PC1、PC2）相关性较好,结合各海温指数的年代际变化特征,发现ECP在1970年代末受PDO及DMI的影响在低纬及中纬度地区分别呈现EOF1、EOF2的正位相分布特征;而在1990年代初受AMO及PDO的影响主要呈现EOF1的特征。由各海温指数及PC1、PC2重建的ECP分布特征可知,AMO及DMI与PC1重建的ECP型相近,对ECP的影响范围集中在低纬地区。除去变暖影响的DMI及PC1回归的高度场中发现一个源起大西洋的波列,黄河以北为异常反气旋中心,以南为异常气旋中心,低层南风异常,水汽被输送到北方,导致中国北方降水增加,南方降水减少。PDO与PC2重建的ECP型相近,对ECP的影响集中在中纬度地区。二者回归得到中国东部低层北风异常,水汽在长江流域辐合,长江流域降水增加。      

STUDY ON SENSITIVITY OF WIND FIELD VARIATION TO STRUCTURE AND DEVELOPMENT OF CONVECTIVE STORMS

A numerical experiment was carried out on individual cases of severe convections in the Jianghuai area under cold vortex on April 28, 2015 in order to study the impact of wind field variations at the middle and low troposphere on the development and structure of storms. The results show that the structure and development of convective storm is highly sensitive to the changes of wind fields, and the adjustment of wind field at the middle or low troposphere will lead to significant changes in the development and intensity of storms. When the wind field at the middle or low troposphere is weakened, the convective development suffers different degrees of attenuation compared with the control experiment, and the ways of attenuation of the two levels are different. In the attenuation test of wind field at the middle level, convection is obviously weak at all stages of its development, while for the wind field at the low level, the convective development is weak only in the initial development stage of storm. On the contrary, the enhancement of the wind field at the middle or low troposphere is conducive to the development of convection, especially the enhancement of the wind field at the middle troposphere. In comparison, the convection develops rapidly in this test, as the most intensive one. The wind field variations have a significant impact on the structure and organization of the storm. The enhancement of the wind field at the middle troposphere makes for the intension of the middle-level swirl of convective storm, the reduction of the storm scale, and the organized evolution of convection. The development of the wind field at the low level troposphere is conducive to the development of the low-level secondary circulation of the storm and the cyclonic vorticity at the middle and low levels at the inflowing side.     

全球变化的区域响应和适应

20世纪 90年代以来 ,全球变化研究进入了一个新的时期 ,其研究方向发生了重大调整 :从认识地球系统基本规律的纯基础研究为主 ,扩展到与人类社会可持续发展密切相关的一系列生存环境实际问题的研究 ;从研究人类活动对环境变化的影响 ,扩展到研究人类如何适应全球环境的变化 ;在更高层次上进行地球系统的综合集成研究。文中对日益受到重视的全球变化区域响应和适应研究的背景进行了分析 ,并着重介绍了一些概念和研究进展 :( 1)对全球和区域环境变化的适应同可持续发展之间的关系。两者应存在协调统一的关系。同时 ,适应应是对区域和全球环境系统的整体性和系统性适应 ,不应是局部的和片面的。( 2 )“有序人类活动”的研究框架。介绍了对“有序人类活动”的一些基本认识 ,以及在虚拟试验研究、示范区建设和长期监测研究等方面的进展。( 3 )集成研究。以东亚区域环境系统和北方干旱化的集成研究为例 ,介绍了集成研究的方法和过程     

SENSITIVITY OF THE WEATHER RESEARCH AND FORECASTING MODEL TO RADIATION SCHEMES IN CHINA

Results of one-year simulations using the Weather Research and Forecast (WRF) model, with the use of different radiation schemes (RRTM, RRTMG, CAM, New Goddard and Goddard), are evaluated for China. The observations used in the model assessment include station data from the China Meteorological Administration, 14 flux field sites arranged in a coordinated observation network, and Global Land Data Assimilation System (GLDAS) data. Specifically, based on a Taylor diagram, the temperature differences between the radiation schemes are small, and the best annual mean spatial pattern and average value for China as a whole is produced by RRTMG. For the rainfall and net radiation annual mean simulation, the New Goddard and CAM schemes present better results than the RRTMG scheme. With respect to low cloud cover, all the schemes have similar reproduction without high cover on east of Tibet Plateau. Overall, the New Goddard and CAM schemes are suitable for longtime simulation without nesting and nudging options.     

A CASE STUDY OF FRONTAL CYCLOGENESIS AND ITS SENSITIVITY TO COASTAL INITIAL CONDITIONS

In this study,the predictability and physical processes leading to the rapid frontal cyclogenesis,that took place in the east coast of the U.S.during 3—4 October 1987,are examined using a nested-grid.mesoscale model with a fine-mesh grid size of 25km.It is shown that the model reproducesreasonably well the cyclogenesis in a coastal baroclinic zone.its subsequent deepening and movementas well as the pertinent precipitation.It is found that the frontal cyclogenesis occurs in a favorablelarge-scale environment with pronounced thermal advection in the lower troposphere and markedpotential vorticity(PV)concentration aloft associated with the tropopause depression.The transportof warm and moist air from the marine boundary layer by the low-level in-shore flow provides thenecessary energy source for the observed heavy precipitation and a variety of weather phenomenareported in the cold sector.Several 24-h sensitivity simulations are performed to examine the relative importance of diabaticheating,adiabatic dynamics and various initial conditions in the frontal cyclogenesis.It is found thatlatent heat release,even though quite intense,accounts for only 25% of the cyclone's total deepeningin this case:the weak impact seems due to the occurrence of latent heating in the cold sector and theupward lifting of the dynamical tropopause by diabatic updrafts.Vorticity budgets show that the low-level thermal advection dominates the incipient stage,whereas the vorticity advection determines therapid deepening rate at the mature stage.The results reveal that the predictability of the presentstorm is closely related to the vertical coupling between the surface cyclone and the upper-level PVcore,which is in turn determined by initial offshore perturbations in the lower troposphere.     

赤道东太平洋海温长期变化中的突变现象及其与全球增温的同步性

运用１８５４～１９９０年的冬季海温资料,对赤道东太平洋海温的年际及年代际变化进行分析,并运用滑动ｔ－检验方法对其突变性进行了讨论,发现赤道东太平洋海温具有三次突变增温过程,分别发生在上世纪末、本世纪２０年代和５０年代。另外,通过求滑动相关系数,发现赤道东太平洋海温与全球其他地区海温变化的相关性具有显著的年代际的阶段性。通过对比及相关分析,发现全球增温与赤道东太平洋的增温具有显著的同步性。在年际及年代际尺度场均表现出较强的正相关。