中国西北春季降水与太平洋海温相关特征的研究

应用奇异值分解对中国西北3-5月的降水资料与太平洋海温进行了相关分析。结果表明：北太平洋与中国西北春季降水有较好的相关,在太平洋海温3-5月呈El Nino峰值位相时,除青海高原外,中国西北地区降水偏水;而当12-2月的海温呈El Nino成熟位相型时,次年西北地区3-5月的降水偏多;而当北太平洋海温12-2月呈La Nina型时,次年青海高原区3-5月的降水偏少。太平洋海温的西风漂流区、黑潮区、加利福尼亚海流区和北赤道海流区的海温的变化与中国西北地区3-5月的降水之间有明显的相关关系。其中黑潮区12-2月的海温与新疆北部的降水呈反相变化,即当黑潮区的海温低时,西北地区的新疆北部降水偏多。中国西北地区3-5月的降水对太平洋温变化的响应区主要的新疆北部、青海高原及其东北侧、沙漠盆地、河西西部等地。     

北太平洋海温异常对中国东北地区旱涝的影响

文中利用 196 1～ 2 0 0 0年中国东北地区 80个测站 4 0a的月降水和同一时期的北太平洋海温资料以及奇异值分解 (SVD)技术 ,分析了北太平洋海温异常对中国东北地区夏季旱涝的影响。结果表明 :东北地区夏季降水与北太平洋海温异常之间存在着较为密切的联系 ,当前期冬季和春季甚至是前一年夏季赤道中东太平洋海温如果处于异常偏暖 (或偏冷 )状态 ,并且西风漂流区具有较明显的SST负 (或正 )距平分布时 ,则东北大部分地区夏季降水具有整体偏多 (或偏少 )的倾向。当然 ,东北地区降水与北太平洋海温异常之间的这种联系也并非是简单的一一对应的关系     

THE RELATIONSHIP BETWEEN TROPICAL PACIFIC SEA SURFACE TEMPERATURE AND SUMMER RAINFALL OVER NORTHWEST CHINA

In this paper,the data of summer precipitation in Northwest China were expanded by means of EOF.According tomajor eigenvectors in expansion the area of Northwest China was divided into four natural rainfall regions.Amongthem the region of greatest precipitation variability is found over the East Qinghai-North Shaanxi region,includingEast Qinghai,Central and East Gansu,Ningxia and North Shaanxi.There is apparent teleconnection between the firstand second time-dependent coefficients in EOF expansion and the tropical Pacific SST in the corresponding period andearlier months.The variation of the east tropical Pacific SST in winter and spring is able to predict precipitation trend ofNorthwest China next summer.Moreover,in the El Nino years precipitation trend is opposite to the following year,andthe region from East Qinghai to North Shaanxi is most sensitive.     

南海地区OLR变化与华南汛期降水的联系

用奇异值分解的方法逐月分析了华南汛期（4-9月）降水与南海地区OLR变化的关系，并用合成分析的方法对OLR异常年份的降水进行对比分析，结果表明两者确实有一定的相关关系，后汛期（特别是7、8月）两者的相关程度比前汛期大，但每个月的情况各有不同。     

NUMERICAL EXPERIMENTS OF THE EFFECTS OF SEA SURFACE TEMPERATURE ANOMALIES OVER THE PACIFIC ON PRECIPITATION IN 1991

A zonal domain,primitive equation model is used in this paper to study the influences of the main sea surface tem-perature anomaly(SSTA)areas over the Pacific on precipitation in 1991.Some numerical experiments are made and themechanisms of the influences are discussed.The results show that the influences of the SSTA are mainly confined withinthe tropical and the subtropical regions.The direct effect of the SSTA is to change the exchanges of the sensible heat andthe water vapour between the air and the sea,through the consequent changes of temperature and the flow fields and thefeedback process of condensation,the SSTA finally affects precipitation.     

夏季赤道太平洋,北极及高原地区热状况对西北太平洋副高及我国降水的影响

本文利用一个全球大气环流说模式，对七月份赤道太平洋海温异常，北极海冰异常及高原积雪对西北太平洋副高和我国降水的影响进行数值试验，得出一些有铁结果。例如，当赤道东或西太平洋海表温度出现负距平时，副高较趋近负ＳＳＴＡ区，当出现正距平时，副高则远离正ＳＳＴＡ区；北区海冰覆盖面积较大时副高位置偏南，覆盖面积较小时副高位置偏北等等。     

CHARACTERISTICS OF MEI-YU PRECIPITATION AND SVD ANALYSIS OF PRECIPITATION OVER THE YANGTZE-HUAIHE RIVERS VALLEYS AND THE SEA SURFACE TEMPERATURE IN THE NORTHERN PACIFIC OCEAN

Based on the precipitation data of Meiyu at 37 stations in the valleys of Yangtze and Huaihe Rivers from 1954 to 2001, the temporal-spatial characteristics of Meiyu precipitation and their relationships with the sea surface temperature in northern Pacific are investigated using such methods as harmonic analysis, empirical orthogonal function (EOF), composite analysis and singular value decomposition (SVD). The results show that the temporal evolution and spatial distribution of Meiyu precipitation are not homogeneous in the Yangtze-Huaihe Rivers basins but with prominent inter-annual and inter-decadal variabilities. The key region between the anomalies of Meiyu precipitation and the monthly sea surface temperature anomalies (SSTA) lies in the west wind drift of North Pacific, which influences the precipitation anomaly of Meiyu precipitation over a key period of time from January to March in the same year. When the SST in the North Pacific west wind drift is warmer (colder) than average during these months, Meiyu precipitation anomalously increases (decreases) in the concurrent year. Results of SVD are consistent with those of composite analysis which pass the significance test of Monte-Carlo at 0.05.     

江淮梅雨特征及其与北太平洋海温的SVD分析

利用江淮地区1954～2001年48年梅雨量资料,采用谐波分析、EOF、合成分析和SVD分解等方法讨论了江淮梅雨的时空变化特征以及与北太平洋海温的关系.结果表明:江淮梅雨量时空分布不均,存在显著的年际和年代际变化特征.影响江淮梅雨的海温关键区是北太平洋西风飘流区,关键影响时段是当年的1～3月;当年1～3月北太平洋西风飘流区海温异常偏高,同年江淮大部地区梅雨量异常偏多,反之亦然.SVD分解结果与合成分析的结果相吻合,通过0.05的Monte-Carlo显著性检验.     

NUMERICAL EXPERIMENTS OF THE EFFECTS OF SEA SURFACE TEMPERATURE ANOMALIES OVER THE PACIFIC ON PRECIPITATION IN 1991*

A zonal domain,primitive equation model is used in this paper to study the influences of the main sea surface temperature anomaly(SSTA) areas over the Pacific on precipitation in 1991.Some numerical experiments are made and the mechanisms of the influences are discussed.The results show that the influences of the SSTA are mainly confined within the tropical and the subtropical regions.The direct effect of the SSTA is to change the exchanges of the sensible heat and the water vapour between the air and the sea,through the consequent changes of temperature and the flow fields and the feedback process of condensation,the SSTA finally affects precipitation.     

NUMERICAL EXPERIMENT OF IMPACT OF SEA SURFACE TEMPERATURE IN SOUTH CHINA SEA AND WARM POOL/WEST PACIFIC ON EAST ASIAN SUMMER MONSOON

By using the NCAR CCM1 model, we have designed six sensitive experiments, which areincreased and decreased SST (sea surface temperature) by 1℃ each in the SCS (South China Sea)and in the West Pacific warm pool, increased and decreased SST by 1℃ in the warm pool withincreased SST by 1℃ in the SCS. All experiments are integrated from April to July. Comparingwith the control experiment, we have analyzed the anomalies of the wind field at the upper andlower layers, the anomalies of the seasonal variability of the monsoon and precipitation for eachexperiment. In the result, we have found that the SST anomaly (SSTA) in the SCS greatly affectsthe seasonal variability of the SCS monsoon and precipitation in China, especially during the coldperiod of SST in the SCS. The impact of SSTA in the warm pool on SCS monsoon is also found.but is weak as compared to the effect of SST anomaly in the SCS. Besides, its impact on rainfall inChina is uncertain.     

POSSIBLE RELATIONSHIP BETWEEN THE INTERANNUAL ANOMALY OF THE TROPICAL PACIFIC SEA SURFACE HEIGHT AND SUMMER PRECIPITATION IN CHINA

By using NCEP GODAS monthly sea surface height(SSH) and 160-station monthly precipitation data in China,the seasonal and interannual characteristics of SSH are analyzed over the tropical Pacific,and correlations between SSH and summer rainfall are discussed.The results are shown as follows:(1) The tropical Pacific SSH takes on a "V" pattern in the climatic field with an eastward opening,and it is higher in the western part(in the northwestern part) than in the eastern part(in the southwestern part).The high-value areas are more stable in the northwest,and the value range(greater than 0.8 m) is larger in spring and summer than in autumn and winter.The high-value area in the southwestern part is the largest(smallest) and more northerly(southerly) in spring(summer).SSH is higher in spring and autumn than in summer and winter over the equatorial zone.(2) The interannual anomalies of the SSH are the strongest over the tropical western and southwestern Pacific and are stronger in winter and spring than in summer and autumn.The interannual anomalies are also strong over the equatorial middle and eastern Pacific.The distribution ranges are larger and the intensities are stronger in the autumn and winter.There is a close relationship between the SSH interannual anomalies and ENSO events in autumn,winter and spring.(3) When ENSO events take place in winter,according to the simultaneous relationship among the tropic Pacific SSH,850 hPa wind fields and the summer precipitation of China,it can be predicted that the precipitation will be significantly more than normal over the south of the Yangtze River,especially over Dongting Lake and Poyang Lake region,eastern Qinghai-Tibet Plateau,Yangtze-Huai River Valley,eastern part of Inner Mongolia and less than normal over the area of Great Band of Yellow River,North China and South China in successive summers.     

广西前汛期降水变化特征及其与东南太平洋海温变化的因果联系

利用1979—2019年全国160站逐月降水资料、国家气候中心的西太平洋副热带高压特征指数逐月资料、英国Hadley中心逐月海表面温度资料以及NCEP/NCAR逐月再分析资料,结合小波分析、相关分析、信息流以及合成分析方法,分析了广西前汛期降水的变化特征及其与东南太平洋海温变化的因果联系。结果表明：近40 a来广西前汛期降水呈弱增多趋势,在1980年代末至21世纪初存在显著的3～5 a周期。在1980年代至1990年代初为少雨期,而在20世纪末至21世纪初期转为多雨期。东南太平洋是海温影响广西前汛期降水的关键区,同年春季以及同期该区域海温变化是造成广西前汛期降水变化的原因之一,海温升高（降低）能够部分导致降水的减少（增多）。同年春季海温偏冷年,关键区西侧为对流抑制,南太平洋出现异常反气旋环流响应,通过垂直环流引起澳大利亚西北侧上升运动异常,减弱了局地Hadley环流。该异常通过大气桥一方面使得副高增强增大,位置偏西偏南,有利于副高西侧的西南气流向广西输送水汽;另一方面使得广西地区上空局地Hadley下沉支减弱,受异常上升运动控制,对流增强,导致降水正异常。反之亦然。     

NUMERICAL EXPERIMENT OF IMPACT OF SEA SURFACE TEMPERATURE IN SOUTH CHINA SEA AND WARM POOL/WEST PACIFIC ON EAST ASIAN SUMMER MONSOON*

By using the NCAR CCM1 model, we have designed six sensitive experiments, which are increased and decreased SST(sea surface temperature) by 1℃ each in the SCS(South China Sea) and in the West Pacific warm pool, increased and decreased SST by 1℃ in the warm pool with increased SST by 1℃ in the SCS. All experiments are integrated from April to July. Comparing with the control experiment, we have analyzed the anomalies of the wind field at the upper and lower layers, the anomalies of the seasonal variability of the monsoon and precipitation for each experiment. In the result, we have found that the SST anomaly(SSTA) in the SCS greatly affects the seasonal variability of the SCS monsoon and precipitation in China, especially during the cold period of SST in the SCS. The impact of SSTA in the warm pool on SCS monsoon is also found.but is weak as compared to the effect of SST anomaly in the SCS. Besides, its impact on rainfall in China is uncertain.     

北极海冰与赤道东太平洋海温的相互影响及其与El Nino的联系

对北极海冰面积与赤道东太平洋海温作了交叉相关分析，揭示了北极海冰与赤道东太平洋海温间相互影响的关系及其时空特点，并讨论了Ｅｌ Ｎｉｎｏ与北极海冰间的联系。结果表明，北极Ⅴ－Ⅵ区冬季海冰面积能够对以后冬季的赤道东太平洋海温产生持续的影响，而北极Ⅶ区夏秋季的海冰面积能够影响来年夏秋季的海温；赤道东太平洋海温对海冰的影响表现为前期海温能够影响北极Ｉ区春季海冰的消融。此外，前期北极海冰状况对Ｅｌ Ｎｉｎｏ     

VARIATIONS OF SEA SURFACE TEMPERATURE AND SEA LEVEL PRESSURE OVER PACIFIC AND INDIAN OCEANS AND THEIR INFLUENCE ON COLD SUMMER IN EAST ASIA

An EOF analysis was performed to investigate the variations of sea surface temperature (SST) of Pacific and Indian Oceans.Result shows that the distribution of SST anomaly exhibits a distinct anticorrelation pattern between Northwest and Southeast Pacific,as well as between Northwest Pacific and the Arabian Sea.It also shows that the sea level pressure (SLP) anomaly between North Pacific and North Indian Oceans is of a seesaw pattern,which we named the North Paci-fic and North Indian Ocean Oscillation (PIO).Such a phenomenon is closely correlated with the cold summer in East Asia.     

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。      

SENSITIVITY OF SEA SURFACE TEMPERATURE RETRIEVAL TO SEA SURFACE EMISSIVITY

To estimate sea surface temperature(SST)with high accuracy from radiometrie measure-ments,it is no longer acceptable to assume that sea surface emissivity is unity or any other con-stant.This note presents an investigation of the desirable emissivity accuracy in relation to re-trieval.It was found that 1% error in surface emissivity can cause up to 0.7 K error in the re-trieved SST,although this sensitivity is often reduced to about 0.5 K on average because of thedownward atmospheric radiation at surface partially compensates for the emissivity error.Since thedownward atmospheric radiation ratio is controlled to a large extent by the integrated water vaporin the atmosphere and,secondarily,by view angle,the sensitivity of SST retrieval to surface emis-sivity has been computed as a function of these two parameters.     

SENSITIVITY OF PRECIPITATION TO SEA SURFACE TEMPERATURE AND ITS DIURNAL VARIATION: A PARTITIONING ANALYSIS BASED ON SURFACE RAINFALL BUDGET

The sensitivity of precipitation to sea surface temperature(SST) and its diurnal variation is investigated through a rainfall partitioning analysis of two-dimensional cloud-resolving model experiments based on surface rainfall budget.For all experiments,the model is set up using zero vertical velocity and a constant zonal wind and is integrated over 40 days to reach quasi-equilibrium states.The 10-day equilibrium grid-scale simulation data and a time-invariant SST of 29°C are used in the control experiment.In the sensitivity experiments,time-invariant SSTs are 27°C and 31°C with an average value of 29°C when the minimum and maximum values of diurnal SST differences are 1°C and 2°C,respectively.The results show that the largest contribution to total rainfall is from the rainfall with water vapor convergence and local atmospheric drying and hydrometeor gain/divergence(~30%) in all experiments.When SST increases from 27°C to 29°C,the contribution from water vapor convergence decreases.The increase of SST reduces the contribution of the rainfall with water vapor convergence primarily through the decreased contribution of the rainfall with local atmospheric drying and hydrometeor gain/divergence and the rainfall with local atmospheric moistening and hydrometeor loss/convergence.The inclusion of diurnal variation of SST with the diurnal difference of 1°C decreases the rainfall contribution from water vapor convergence primarily through the decreased contribution of the rainfall with local atmospheric moistening and hydrometeor loss/convergence.The contribution of the rainfall from water vapor convergence is barely changed as the diurnal difference of SST increases from 1°C to 2°C.     

VARIABILITY IN THE WESTERN PACIFIC SUBTROPICAL HIGH AND ITS RELATIONSHIP WITH SEA TEMPERATURE VARIATION CONSIDERING THE BACKGROUND OF CLIMATE WARMING OVER THE PAST 60 YEARS

By adopting characteristic index data for the Western Pacific Subtropical High (WPSH) from the National Climate Center of China, U.S. National Centers for Environmental Prediction-National Center for Atmospheric Research (NCEP/NCAR) reanalysis data, and the National Oceanic and Atmospheric Administration (NOAA) sea surface temperature (SST) data, we studied the WPSH variability considering the background of climate warming by using a Gaussian filter, moving averages, correlation analysis, and synthetic analysis. Our results show that with climate warming over the past 60 years, significant changes in the WPSH include its enlarged area, strengthened intensity, westward extended ridge point and southward expanded southern boundary, as well as enhanced interannual fluctuations in all these indices. The western ridge point of the WPSH consistently varies with temperature changes in the Northern Hemisphere, but the location of the ridgeline varies independently. The intensity and area of the WPSH were both significantly increased in the late 1980s. Specifically, the western ridge point started to significantly extend westward in the early 1990s, and the associated interannual variability had a significant increase in the late 1990s; in addition, the ridgeline was swaying along the north-south-north direction, and the corresponding variability was also greatly enhanced in the late 1990s. With climate warming, the SST increase becomes more weakly correlated with the WPSH intensity enhancement but more strongly correlated with the westward extension of the ridge point in the equatorial central and eastern Pacific Ocean in winter, corresponding to an expanding WPSH in space. In the northern Pacific in winter, the SST decrease has a weaker correlation with the southerly location of the ridgeline but also a stronger correlation with the westward extension of the ridge point. In the tropical western Pacific in winter, the correlations of the SST decrease with the WPSH intensity enhancement, and the westward extension of the ridge point is strengthened. These observations can be explained by strengthened Hadley circulations, the dominant effects of the southward shift, and additional effects of the weakened ascending branch of the Walker circulation during warm climatological periods, which consequently lead to strengthened intensities, increased areas, and southward expansions of the WPSH in summer.     

我国夏半年降水距平与北太平洋海温异常的奇异值分解法分析

利用奇异值分解法分析了我国夏半年各月降水距平与北太平洋海温异常的相互关系，指出：（１）平均意义上，秋冬季海温与我国春末至盛夏各月降水存在显著相互关系；（２）秋冬季赤道东太平洋海温对次年４－５月江南东部和７月高原东侧，黄河中下游地区的降水有显著的影响；（３）盛夏至冬季的赤道中东太平洋海温与前一年６月黄淮地区及７月长江流域降水关系密切。