Connection of the stratospheric QBO with global atmospheric general circulation and tropical SST. Part II: interdecadal variations

The interdecadal variation of the association of the stratospheric quasi-biennial oscillation (QBO) with tropical sea surface temperature (SST) anomalies (SSTA) and with the general circulation in the troposphere and lower stratosphere is examined using the ERA40 and NCEP/NCAR reanalyses, as well as other observation-based analyses. It is found that the relationship between the QBO and tropical SSTA changed once around 1978–1980, and again in 1993–1995. During 1966–1974, negative correlation between the QBO and NINO3.4 indices reached its maximum when the NINO3.4 index lagged the QBO by less than 6?months. Correspondingly, the positive correlations were observed when the NINO3.4 index led the QBO by about 11–13?months or lagged by about 12–18?months. However, maximum negative correlations were shifted from the NINO3.4 index lagging the QBO by about 0–6?months during 1966–1974 to about 3–12?months during 1985–1992. During 1975–1979, both the negative and positive correlations were relatively small and the QBO and ENSO were practically unrelated to each other. The phase-based QBO life cycle composites also confirm that, on average, there are two phase (6–7?months) delay in the evolution of the QBO-associated anomalous Walker circulation, tropical SST, atmospheric stability, and troposphere and lower stratosphere temperature anomalies during 1980–1994 in comparison with those in 1957–1978. The interdecadal variation of the association between the QBO and the troposphere variability may be largely due to the characteristic change of El Ni?o-Southern Oscillation. The irregularity of the QBO may play a secondary role in the interdecadal variation of the association.     

A comparison of reanalyses in the tropical stratosphere. Part 2: the quasi-biennial oscillation

 Reanalysis datasets potentially offer the opportunity to examine the tropical quasi-biennial oscillation (QBO) in greater detail than in the past, including the associated meridional circulation and the links with other parts of the atmosphere. For such studies to be useful, the QBO represented by the reanalyses should be realistic. In this work, the QBO in the ERA and NCEP reanalyses is validated against rawinsonde observations from Singapore. Monthly mean data are used. In the lower stratosphere (at 50 hPa and 30 hPa) the ERA QBO is reasonable, although the wind extrema in both phases are too weak and the vertical shear and the temperature anomalies are too small. The NCEP QBO is weaker still. At 10 hPa neither reanalysis system performs well, both systems failing to reproduce the westerlies, possibly because of the proximity of the upper boundary. The Singapore wind is representative of the zonal means in the reanalyses. The weak wind extrema in the reanalyses would not support a wave-mean flow interaction theory of the QBO, because a large portion of the gravity wave spectrum which would be absorbed in reality would be transmitted beyond 10 hPa. The stronger shear zones captured in the ERA data are associated with larger, more realistic temperature perturbations near 30 hPa. The northward velocities in the NCEP data show a more realistic structure than in the ERA reanalysis, where they are dominated by a vertical “gridpoint wave” structure in the lowermost stratosphere. Despite the shortcomings of the reanalyses, the high correlations of the wind at 30 hPa and 50 hPa with the observations at Singapore mean that the reanalyses could potentially be used to examine the effects of the QBO away from the tropical stratosphere. Future reanalyses need to take full account of the wind shears evident in the rawinsonde observations and use models with an adequate resolution to capture these vertical scales. Received: 23 June 1997/Accepted 17 December 1998     

赤道低平流层纬向风垂直切变与ENSO变率的关系

利用NCEP／NCAR 40a再分析资料研究了赤道低平流层纬向风垂直切变与ENSO变率间的关系。结果得出，赤道低平流层纬向风的垂直切变呈现明显的准两年振荡，SOI和Nino3区SSTA的准两年周期成分与赤道低平流层纬向风垂直切变分别呈现反位相和同位相关系。赤道低平流层西（东）风切变位相时，OLR、1000hPa高度，2000hPa高度和温度、850hPa温度等要素的距平分布与其在El Nino(La Nina)时段的分布相似。     

低平流层准两年变率研究

分析ＮＣＡＲ／ＮＣＥＰ４０年分析资料得出,赤道低平流层纬向风年际变率的平均周期约２８．２个月,最大振幅的２０ｈＰａ,西（东）风距平平垂直下传平均速度１．２１（１．０４）ｋｍ／月。用１０ｈＰａ和７０ｈＰａ月平均纬向风标准化距平之差反映整层准两年变率的相位。低平流层两半球中纬气温有与之配合的振荡,西（东）风切变时,中纬气温偏低（高）。赤道纬向风准两年变率引起的经圈环流异常是联系低续续向风与中纬气温准年     

低平流层准两年变率研究

分析NCAR/NCEP40年再分析资料得出,赤道低平流层纬向风年际变率的平均周期约28.2个月,最大振幅在20hPa,西(东)风距平垂直下传平均速度1.21(1.04)km/月。用10hPa和70hPa月平均纬向风标准化距平之差可反映整层准两年变率的相位,低平流层两半球中纬气温有与之配合的振荡,西(东)风切变时,中纬气温偏低(高)。赤道纬向风准两年变率引起的经圈环流异常是联系低纬纬向风与中纬气温准两年变率的纽带。     

Quasi-periodic imprints in the equatorial troposphere and stratosphere in three decades of reanalysis data

Wavelet analysis is applied to zonal mean zonal wind and temperature fields to represent characteristics of temporal periodic features different from the annual and semi-annual recurrence in the troposphere and stratosphere. A daily database of reanalyses is used for the period 1979–2008, which comprises the era of satellite-based data, as some discontinuities have been observed around 1978 in previous studies. Levels for this study have been chosen at 400 and 10 hPa, respectively in the middle troposphere and middle stratosphere. As representative for diverse latitudinal regions we have respectively selected 0°, ±20°, ±40°, ±60°, ±80°. Significant features were only found at the equator. The period of the quasi-biennial oscillation (QBO) is found to exhibit a decreasing trend in time over the 30 years studied. Potential harmonics of the QBO are found in the tropical stratosphere but also troposphere. However, they do not exhibit the same tendency. This fact supports in particular the idea that the QBO and the tropospheric biennial oscillation may be unrelated phenomena. Some of the observed features lie within the known range of variability of the El Niño Southern Oscillation. Faint effects of the 11-year solar cycle variability may have been observed in the troposphere and stratosphere, but no firm assertion may be made due to the low number of observed cycles for this kind of phenomenon in the used data-set time span. Short-term solar variabilities leave no relevant imprint.     

印度洋海温异常和南海夏季风建立迟早的关系 II.机理分析

通过区分ENSO外部影响和偶极子内部局地作用,探讨了前期春季的印度洋海温异常对南海夏季风建立早晚的可能影响途径。结果表明:在没有去除ENSO信号(外部作用)的情况下,全区一致型的海温分布主要通过影响热带印度洋上空纬向季风环流的强弱来影响南海夏季风建立的早晚。去除ENSO信号后,非ENSO全区一致型的海温分布则主要通过影响低层东西向的气压差异和对流层中上层的南北温度梯度的逆转,进而对南海夏季风建立的早晚产生影响;而南印度洋偶极子(SIODM)型的海温分布则主要通过影响亚洲大陆热低压、西太平洋副热带高压和高低层的辐合辐散运动影响南海夏季风的建立。     

A DIAGNOSIS OF THE INTERANNUAL VARIABILITY OF SEA SURFACE TEMPERATURE AND SURFACE WIND FIELD IN THE TROPICAL OCEANS AND ITS CORRELATIVE CHARACTERS WITH ENSO CYCLE*

Utilizing the NCEP/NCAR reanalysis monthly datasets,and based on the filter and standard deviation calculation,the interannual variability of sea surface temperature (SST) and 1000 hPa wind field for the tropical Pacific,Indian and Atlantic Oceans is investigated for the past 20 years (1979-1998).The characters of space-time evolution in SST anomalies (SSTA) for each ocean and corresponding wind anomaly field are acquired by using rotated principal component (RPC) and linear regression analysis methods.Using the method of correlation analysis.the characters of three tropical oceans correlated with ENSO are investigated.The contemporary correlation between the SSTA in the Indian Ocean and in the equatorial eastern Pacific is positive,and there is a weak negative correlation between the SSTA in the equatorial east Atlantic Ocean and in the equatorial eastern Pacific.The lead-lag correlation analysis indicates that the SSTA in the equatorial Indian Ocean lags the dominant Pacific ENSO mode by 3 months,and the SSTA in the equatorial Atlantic Ocean leads ENSO mode by 6 months.The ENSO-correlated components in tropical Indian Ocean and tropical Atlantic Ocean display much the same amount of total variance in each ocean,i.e..14% in the Indian Ocean and 12% in the Atlantic Ocean and the maximums are all above 40%.     

Manifestation of reanalyzed QBO and SSC signals

Global spatial distribution of oscillations in the period bands linked to the quasi-biennial oscillation (QBO) and to the 11-year sunspot cycle (SSC) was investigated using the pseudo-2D wavelet transform. The results were obtained for the ERA-40, NCEP-DOE 2, NCEP/NCAR, and Twentieth Century Reanalysis V2 datasets. Those included time series of air temperature and zonal and meridional wind velocities were examined for all reanalyzed series from 1,000 up to 10 hPa. Most of the datasets covered the second half of the twentieth century. The results are generally in agreement with other related studies, and they point to the presence of the QBO in the tropical stratosphere along with the regions of induced changes in residual circulation, temperature, or ozone amount across extratropics. The SSC imprint is located mainly over similar locations showing that the cycles’ signals are mutually affected there.     

热带海表温度和低层风场的年际变率及与ENSO循环的相关特征研究

采用 NCEP/NCAR的 1 979～ 1 998年逐月平均的海表温度及 1 0 0 0 h Pa风场资料 ,进行滤波和均方差计算 ,得到了热带太平洋、印度洋、大西洋海表温度 (SST)和风场的年际变化特征。用旋转主分量 (RPC)方法和投影法对热带三大洋海表温度距平 (SSTA)进行分析 ,得到了各大洋 SSTA演变的主要时空特征和相应的距平风场特征 ;并用相关分析研究热带三大洋与ENSO相关的特征 ,得到三大洋间的同期相关关系为 :印度洋 SSTA与赤道东太平洋 SSTA成正相关 ,而赤道东大西洋 SSTA与赤道东太平洋 SSTA成弱的负相关 ;赤道印度洋在落后于赤道东太平洋 3个月左右时正相关达到最大 ,赤道大西洋在超前于赤道东太平洋 6个月左右时负相关达到最大 ;热带印度洋和大西洋与 ENSO相关的分量对各自大洋海表温度年际变化的方差贡献数值相近 ,最大在 40 %以上 ,平均解释方差分别为 1 4%和 1 2 %。     

夏季厄尔尼诺-Modoki和东部型ENSO海表温度异常分布型特征及其与海洋性大陆区域气候异常的联系

2007年,Ashok等揭示了赤道太平洋区域存在一种三极型分布海表温度异常并称之为厄尔尼诺-Modoki,同时定义了相应的海表温度异常指数EMI（记为I_EM）。在此基础上,利用英国哈得来中心逐月海表温度资料、美国NCEP/NCAR月平均再分析数据集、美国国家海洋和大气管理局（NOAA）逐月降水资料（CMAP）,通过在太平洋海表温度异常中扣除厄尔尼诺-Modoki信号后,在Nino1+2区域上定义了东太平洋型海表温度异常指数EPNI（I_EPN）。据此,由I_EPN和I_EM可构成描述热带太平洋海表温度异常变化的一对指数。分析了两个指数相应的海气状态及对海洋性大陆区域气候异常的影响。结果表明,厄尔尼诺-Modoki和东太平洋型海表温度异常及其影响存在显著差异。在北半球夏季,当I_EM处于正位相时,热带太平洋海表温度异常呈现“负-正-负”的结构,海洋性大陆大部分区域海表温度异常为负,此时对流层低层太平洋地区辐合,海洋性大陆地区辐散,对流层高层太平洋地区辐散,海洋性大陆地区辐合。对应于辐合辐散中心,存在着自赤道中太平洋分别向赤道东太平洋和海洋性大陆中东部地区的异常垂直环流圈,同时也存在自海洋性大陆西部向印度洋西部的垂直环流。大气在海洋性大陆区域北部加热,南部冷却;在太平洋地区西部加热而东部冷却;在海洋性大陆区域10°N以南降水偏少,而10°N以北降水偏多。当I_EPN处于正位相时,热带太平洋海表温度异常呈现“西负东正”分布型,海洋性大陆区域海表温度异常呈现“西正东负”分布,对流层低层海洋性大陆地区辐散中心范围偏大、位置偏东、强度偏强,太平洋地区辐合中心范围偏小、位置偏东,热带环流异常在垂直方向上呈斜压结构,海洋性大陆区域北部大气加热而南部冷却,太平洋地区大气均呈加热正异常,海洋性大陆大部分区域降水均偏少,赤道太平洋降水偏多。以上这些结果有利于深刻理解热带太平洋海表温度异常的特征及其对海洋性大陆区域气候的影响。      

Diagnostic study on seasonality and interannual variability of wind field

l.Intr0ductionThoughseasonalvariationoftheatmosphericgeneralcirculationismainlycausedbythatofthesolarradiation,itsdistributionsareinhomogeneousovertheglobe,forinstance,itismoresignificantinmonsoonregionthaninanyotherregions.Inatraditionalsense,mon-soonsummarisesalldrasticseasonalvariationsinthetropicsandsubtropics(e.g.,IndiaandEastAsia).Besidestheclassicmonsoonregions,thereexistsomeotherregionsovertheglobe,wheretheseasonalvariationisclearorevendrastic.Inordertodescribequantitativelysea-sonal…     

热带太平洋SSTA与太平洋北美区500 hPa高度场的非线性关系

利用NOAA的逐月平均SST资料和NCEP/NCAR的逐月平均500 hPa高度场资料,采用非线性典型相关分析(NLCCA)分析了冬季热带太平洋SSTA场和太平洋北美地区500 hPa高度距平场之间的非线性关系,结论得出:NLCCA有能力表示出更一般的低维结构,可以提取资料集中传统CCA所不能提取的特征.NLCCA第一模态的典型相关变量μ从最大值变化到最小值,重建的SSTA场从强El Nino位相变换到强La Nina位相.La Nina位相的负距平中心(100 °W左右)比El Nino位相的正距平中心(150 °W左右)偏西约50个经度.对于500 hPa高度场,其非线性特征主要表现为定常波列(Rossby波)的位置偏差.El Nino时,PNA正位相的四个距平中心比La Nina时PNA负位相距平中心位置向东偏离约20个经度.NLCCA所得结论与合成分析结果一致.     

Interannual variability of total ozone and its relation with the Asia Pacific Wave

Analysis of the NCEP/NCAR reanalysis wind data shows the presence of a stationary Rossby wave in the lower stratosphere during May. This wave is seen prominently below 70 hPa level, confined between 10°N and 50°N latitudes and has a zonal wave number of 6 or 7. It is an extension into the stratosphere of the Asia Pacific Wave (APW) of the troposphere documented by Joseph and Srinivasan (1999) . As in the troposphere, in the lower stratosphere this wave shows a phase shift of 20° longitude between deficient and excess Indian summer monsoon rainfall (ISMR) years. This wave has maximum amplitude at about 200 hPa. The amplitude of the wave decreases both above and below 200 hPa level. The large-amplitude portion of this wave is thus situated in the break region between the tropical and extratropical tropopauses around 30°N latitude. It is suggested that this large-amplitude APW exchanges the tropical and extratropical airmasses through the tropopause break, making the APW signature seen in the satellite monitored total ozone (TOMS data). APW is found to exist in the following monsoon season (June to September) with the same phase as in May and its signature is also seen in that season in total ozone.     

Intercomparison of the Summertime Subtropical High from the ERA-40 and over East Eurasia and the western North Pacific

An intercomparison of summertime (JJA)subtropical geopotential heights from the ERA-40 and NCEP/NCAR reanalysis is specifically conducted over East Eurasia and the western North Pacific. The NCEP/NCAR is obviously lower than the ERA-40 in the mid-to-lower troposphere in most regions of East Eurasia before the mid-1970s, but becomes higher than the ERA-40 after the mid-1970s and thus demonstrates stronger increased trends during the period of 1958-2001. Both reanalyses are lower than the observations in most regions of China. The NCEP/NCAR especially shows tremendously systematic lower values before the mid-1960s and displays abrupt changes before the 1970s. Several indices of the western North Pacific subtropical high (WNPSH), calculated from both reanalyzed summer geopotential heights, also reveal that the variation trend of the NCEP/NCAR is stronger than that of the ERA-40 in the mid-to-lower troposphere from 1958 to 2001. Through singular value decomposition (SVD) analysis, the summer geopotential heights at 500 hPa from the ERA-40 are better than the NCEP/NCAR counterparts at interacting with the precipitation over the East Asian monsoon region. The results indicate that the NCEP/NCAR in the mid-and-lower troposphere may overestimate interdecadal changes and should be used cautiously to study the relationship between the WNPSH and precipitation ove ther East Asia Monsoon region before the mid-1970s.     

Intercomparison of the Summertime Subtropical High from the ERA-40 and NCEP/NCAR Reanalysis over East Eurasia and the western North Pacific

An intercomparison of summertime (JJA) subtropical geopotential heights from the ERA-40 and NCEP/NCAR reanalysis is specifically conducted over East Eurasia and the western North Pacific. The NCEP/NCAR is obviously lower than the ERA-40 in the mid-to-lower troposphere in most regions of East Eurasia before the mid-1970s, but becomes higher than the ERA-40 after the mid-1970s and thus demonstrates stronger increased trends during the period of 1958--2001. Both reanalyses are lower than the observations in most regions of China. The NCEP/NCAR especially shows tremendously systematic lower values before the mid-1960s and displays abrupt changes before the 1970s. Several indices of the western North Pacific subtropical high (WNPSH), calculated from both reanalyzed summer geopotential heights, also reveal that the variation trend of the NCEP/NCAR is stronger than that of the ERA-40 in the mid-to-lower troposphere from 1958 to 2001. Through singular value decomposition (SVD) analysis, the summer geopotential heights at 500 hPa from the ERA-40 are better than the NCEP/NCAR counterparts at interacting with the precipitation over the East Asian monsoon region. The results indicate that the NCEP/NCAR in the mid-and-lower troposphere may overestimate interdecadal changes and should be used cautiously to study the relationship between the WNPSH and precipitation ove ther East Asia Monsoon region before the mid-1970s.     

Uncertainty estimation of the global temperature trends for multiple radiosondes, reanalyses, and CMIP3/IPCC climate model simulations

Based on three groups of datasets that include radiosondes, reanalyses, and climate model simulations (e.g., Coupled Model Intercomparison Project, CMIP3) from 1979 to 2008, the interannual variability, global temperature trends, and their uncertainty using ensemble spread among intra-group and inter-group datasets have been discussed. The results show that the interannual temperature variability increased from the troposphere to stratosphere, and the maximum occurs around 50?hPa. The CMIP3 climate models have the largest discrepancy in the stratosphere. The intra-group correlations at 500?hPa generally show high similarity within each data group while the inter-group correlations between reanalyses and the CMIP3 climate model simulations indicate lesser similarity. In contrast, the inter-group correlation at 50?hPa is improved except with the Japanese 25-year Reanalysis Project (JRA-25) dataset, and the Twentieth Century Reanalysis (20CR) reanalysis shows a weak cross correlation. The global temperature trends are highly dependent on the individual data sources. Compared to the radiosondes, the reanalyses show a large ensemble spread of trends in the stratosphere, and the CMIP3 climate model simulations have a large ensemble spread in the height of the crossover point where tropospheric warming changes into stratospheric cooling. The largest ensemble spread among the reanalyses in the stratosphere is mainly from the large discrepancy in the JRA-25 reanalysis after 1998 and a relatively weak anomaly in the 20CR before 1986. The largest ensemble spread among the CMIP3 climate models in the troposphere is related to the influence of both volcanic eruptions and El Ni?o/La Ni?a–Southern Oscillation events. The strong anomalies corresponding to the volcanic eruptions of El Chichon in 1982 and Mt Pinatubo in 1991 are clearly identified in the stratosphere. These volcanic eruptions reduced the warming in the troposphere and strengthened the cooling in the stratosphere during the most recent 30?years.     

A comparison of reanalyses in the tropical stratosphere. Part 1: thermal structure and the annual cycle

 An intercomparison of the thermal structure and the annual cycle in the tropical lower stratosphere of two reanalysis datasets is presented. These are from the National Centers for Environmental Prediction (NCEP)/National Center for Atmospheric Research (NCAR) and the European Centre for Medium Range Weather Forecasts (ECMWF Re-Analysis: ERA). Generally, the ERA data are coldest and in better agreement with radiosonde observations; this is particularly apparent at 100 hPa where there is also a strong geographic bias, the maximum differences (more than 4 K) occurring over the southern Pacific and the Indian Ocean, with much smaller (sometimes reversed) differences over land. The NCEP temperatures are biased towards satellite-derived values, while the ERA data resolve the low tropopause temperatures much better. The lower ERA temperatures have important implications for the cross-tropopause exchange of water vapor. The meridional-height structure of the annual cycles agree quite well, but the amplitude in the ERA data is about 50% stronger than in NCEP at 70 hPa (in better agreement with previous studies) and weaker at lower pressures. As in previous studies, an anticorrelation is found between the tropical and extratropical temperatures of the reanalyses. The mean meridional flow at the equator is northward all year at all stratospheric levels in the NCEP data, implying a mass transport from the Southern to the Northern Hemisphere; in the ERA data the expected annual cycle (flow from summer to winter) is reproduced with very small annual mean exchange. Received: 17 June 1997/Accepted: 17 December 1997     

热带风场季内振荡强度与海表温度异常关系研究

利用NCEP/NCAR逐日风场及英国气象局逐月海表温度资料,研究了对流层高低层风场季内振荡强度季节变化特征,探讨了其年际及年代际异常特征与海表温度异常的关系。热带印度洋、热带西太平洋是高低层风场季内振荡终年均活跃的区域。对流层高低层风场季内振荡强度异常与海表温度异常均不存在确定的局地关系。风场季内振荡能量异常与海表温度异常在年代际尺度上具有良好对应关系,20世纪70年代中后期以来,赤道东太平洋海温异常升高,Walker环流减弱,导致亚洲区域季风季内振荡强度减弱,赤道太平洋区域200hPa（850hPa）风场季内振荡在赤道东太平洋增强（减弱）,在印度洋东南部—印尼—中西太平洋的暖池区域减弱（增强）,促进了ElNino事件的增强。对流层高低层风场季内振荡强度年际异常与ElNino事件关系密切,这一特征在低层（850hPa）风场表现更显著。在事件发展初期,热带中西太平洋区域850hPa风场季内振荡异常增强并东移,事件发生之后这些区域能量减弱。大气季内振荡可能是ElNino事件的激发因素。