冬季北极涛动异常对北太平洋风暴轴的可能影响

基于美国国家海洋和大气局气候预测中心公报的北极涛动（Arctic Oscillation,AO）指数逐月数据以及美国国家环境预报中心和大气研究中心的1986—2017年逐日再分析资料等,运用回归和合成分析等方法,分析了北极涛动与北太平洋地区风暴轴的时间演变特征、两者之间的联系及AO异常影响风暴轴的可能机制。结果表明：1）风暴轴经度指数与纬度指数有显著正相关性,两者具有同步变化的特征,而这两者与风暴轴强度指数都呈负相关,但不显著。AO指数与北太平洋风暴轴强度呈显著正相关,且AO指数与风暴轴经度、纬度指数也呈正相关,但并不显著。2）在北极涛动强正（负）位相年份,风暴轴区域天气尺度滤波方差强（弱）、500 hPa高度场上东亚大槽减弱（加深）、急流偏北偏强（偏南偏弱）、扰动动能增强（减弱）、斜压性增强（减弱）。可能影响机制是,异常变化的AO影响东亚大槽,改变急流强度,使斜压性发生变化,进而对风暴轴产生影响。     

The influence of tropical Pacific forcing on the Arctic Oscillation

The potential role of tropical Pacific forcing in driving the seasonal variability of the Arctic Oscillation (AO) is explored using both observational data and a simple general circulation model (SGCM). A lead–lag regression technique is first applied to the monthly averaged sea surface temperature (SST) and the AO index. The AO maximum is found to be related to a negative SST anomaly over the tropical Pacific three months earlier. A singular value decomposition (SVD) analysis is then performed on the tropical Pacific SST and the sea level pressure (SLP) over the Northern Hemisphere. An AO-like atmospheric pattern and its associated SST appear as the second pair of SVD modes. Ensemble integrations are carried out with the SGCM to test the atmospheric response to different tropical Pacific forcings. The atmospheric response to the linear fit of the model’s empirical forcing associated with the SST variability in the second SVD modes strongly projects onto the AO. Idealized thermal forcings are then designed based on the regression of the seasonally averaged tropical Pacific precipitation against the AO index. Results indicate that forcing anomalies over the western tropical Pacific are more effective in generating an AO-like response while those over the eastern tropical Pacific tend to produce a Pacific-North American (PNA)-like response. The physical mechanisms responsible for the energy transport from the tropical Pacific to the extratropical North Atlantic are investigated using wave activity flux and vorticity forcing formalisms. The energy from the western tropical Pacific forcing tends to propagate zonally to the North Atlantic because of the jet stream waveguide effect while the transport of the energy from the eastern tropical Pacific forcing mostly concentrates over the PNA area. The linearized SGCM results show that nonlinear processes are involved in the generation of the forced AO-like pattern.     

The nonlinear association between the Arctic Oscillation and North American winter climate

Nonlinear projections of the Arctic Oscillation (AO) index onto North American winter (December–March) 500-mb geopotential height (Z500) and surface air temperature (SAT) anomalies reveal a pronounced asymmetry in the atmospheric patterns associated with positive and negative phases of the AO. In a linear view, the Z500 anomaly field associated with positive AO resembles a positive North Atlantic Oscillation pattern with statistically significant positive and negative anomalies stretching zonally into central-eastern USA and Canada, respectively, resulting in a cold climate anomaly over northeastern and eastern Canada, Alaska and the west coast of USA, and a warm climate anomaly over the rest of the continent. By contrast, the nonlinear behavior, mainly a quadratic association with AO, which is most apparent when the amplitude of the AO index is large, has the same spatial pattern and sign for both positive and negative values of the index. The nonlinear pattern reveals negative Z500 anomalies over the west coast of USA and the North Atlantic and positive Z500 anomalies at higher latitudes centered over the Gulf of Alaska and northeastern Canada accompanied by cooler than normal climate over the USA and southwestern Canada and warmer than normal climate over other regions of the continent. A similar analysis is conducted on the data from the Canadian Center for Climate Modelling and Analysis second generation coupled general circulation model. The nonlinear patterns of North American Z500 and SAT anomalies associated with the AO in the model simulation are generally consistent with the observational results, thereby confirming the robustness of the nonlinear behavior of North American winter climate with respect to the AO in a climate simulation that is completely independent of the observations.     

The effect of the North Sea-Caspian pattern (NCP) on winter temperatures in Iran

Summary This study attempts to find possible linkages between the NCP index and the winter temperature variability over Iran. The investigation is based on statistical analysis of simple, partial and multiple correlations and also evaluation of composite maps of the extreme NCP index and maps of correlation between atmospheric variables and the temperature time series. Our results show that the NCP has a strong negative correlation with the winter temperature in Iran. Furthermore, combination of both the NCP and the AO (Arctic Oscillation) indices improve the correlations in all stations, implying both NCP and AO can be considered as major patterns for explaining the Iranian winter temperature variability. The results show that the positive NCP is associated with enhanced precipitation and cloudy conditions, consequently causing below normal temperature over Iran. The anomalies of OLR in this phase are also negative, implying a cloudy sky. For the negative NCP phase these results are completely reversed. The correlation maps indicate that the NCP is negatively/positively correlated with winter Outgoing Long-wave Radiation/precipitation over Iran. The results also show that the SLP and GPH patterns are quite different for the positive and negative NCP phases over Iran. During the negative NCP a small cyclone is formed over the Arabian Sea causing a strong easterly towards Iran. During the positive NCP this cyclone is removed. Our results show that for the positive NCP years an upper-level trough is formed over northern Iran and the eastern Mediterranean. For the negative NCP years this trough becomes weak and is located over central European regions. This trough is closely linked with the winter temperature over Iran. This is expressed by a high correlation between 500-hPa geopotential height at this region and Iranian winter temperature. Authors’ addresses: A. R. Ghasemi, Climate Research Center, Water Engineering Department, Agricultural Faculty, Shiraz University, Shiraz, Iran; D. Khalili, Water Engineering Department, Agricultural Faculty, Shiraz University, Shiraz, Iran.     

ENSO和北极涛动对东亚冬季气候异常的综合影响

基于1901-2000年多种海-气资料,分析了厄尔尼诺成熟年冬季-初夏西北太平洋异常反气旋（WNPAC）的年际变化特征及其对东亚气候的影响。结果表明,无论是厄尔尼诺事件成熟期的冬季还是次年的春季和初夏,WNPAC的年际变化主要存在两个空间变化型,即反映其强度变化的经验正交函数分解第1模态和反映其位置变化的第2模态。厄尔尼诺成熟年冬季WNPAC强度不仅与赤道中东太平洋海温异常有关,而且与太平洋西部（WP）型遥相关的强度有关,而其位置的变化则主要与西北太平洋局地海温异常以及北极涛动（AO）有关;次年春季,WNPAC的强度除了与赤道中东太平洋海温异常和太平洋西部型遥相关存在显著相关外,还与赤道大西洋海温异常有关,而其位置的变化则主要与西北太平洋局地海温异常和太平洋西部型遥相关有关;次年初夏,WNPAC强度主要与西北印度洋和西南印度洋的海温异常以及东亚-太平洋（EAP）型遥相关的强度有关。进一步分析表明,成熟年冬季-初夏WNPAC的强度和位置的变化均可对东亚地区降水异常分布产生影响,这对预测厄尔尼诺事件发生后冬季及后期春、夏季节东亚地区降水异常分布具有一定的指示意义。此外,次年初夏,WNPAC强度变化与西北太平洋台风发生频数存在显著负相关,即WNPAC越强,台风发生的频数越少,反之亦然。     

青藏高原东部冬季降水对北极涛动异常的响应

基于1979—2015年中国区域CN05.1格点降水以及全球降水气候中心(GPCC)降水等数据资料,采用回归、合成分析等方法,分析了青藏高原东部(简称高原)冬季降水的南、北区域性差异及其年际变化对北极涛动(AO)异常的响应.结果表明:(1)高原北部和南部冬季降水都与AO异常存在密切关系,但降水的年际变化并不一致,对AO...     

北极涛动的年代际变化及其气候影响

北极涛动(Arctic Oscillation,AO)是北半球热带外地区大气环流变率的主导模态,对北半球以及区域尺度气温变化具有重要影响.AO可在没有外强迫条件下通过d波流相互作用形成,因此它被认为是全球气候系统内部变率的重要组成部分.研究年代际尺度上AO的变化及其气候影响,可加深对当前北半球气候变化规律的物理理解,也...     

秋季北极海冰对中国冬季气温的影响

利用海冰资料、中国地面气候资料、环流特征量资料及NCEP/NCAR再分析资料,研究了秋季北极海冰变化对中国冬季平均气温、日气温变率以及异常低温天气的影响。分析结果表明,秋季北极海冰异常偏多年中国冬季常为暖冬;异常偏少年中国冬季常为冷冬,且异常低温天气出现频率更高,常发生低温灾害事件。秋季北极海冰通过影响后期的北半球极涡、东亚冬季风和西伯利亚高压进而影响中国冬季的平均气温,且通过影响冬季异常强西伯利亚高压的出现频次,影响中国冬季异常低温天气的发生频次。合成分析结果表明,秋季北极海冰异常偏少年的冬季,中国以北亚欧大陆高纬度的偏北风较强,且中国及其以北的中高纬度地区空气异常偏冷,导致极地和高纬度的冷空气易向南爆发,造成中国冬季气温偏低,异常低温天气频发。     

中国东部地区冬季气温与北极涛动的关系

利用NCEP/NCAR再分析资料、北极涛动（AO）指数序列及中国160个台站月温度资料,分析1951-2007年中国冬季气温与AO指数的变化特征及其相互关系。结果表明：1951-2007年AO与中国东部地区冬季气温基本呈正相关关系。中国东部地区冬季气温指数（IWT）与北极涛动指数（IAO）均逐渐增强,并有显著的年际和年代际变化,均存在准18 a的周期变化特征。从偏相关系数来看,在年际尺度上,西伯利亚高压对中国东部地区冬季气温的年际变化影响较大,而AO与冬季气温无显著相关关系;在年代际尺度上,AO对中国东部地区冬季气温的影响较显著,比西伯利亚高压影响大。东亚大槽偏弱时,中国冬季气温偏高,AO指数也偏高,反之则相反。在年际尺度上,东亚大槽对中国东部地区冬季气温的年际变化影响较大,而AO与冬季气温无显著相关关系;在年代际尺度上,AO和东亚大槽对中国冬季气温的变化影响均较显著。     

The hindcast of winter and spring Arctic and Antarctic Oscillation with the coupied climate models

研究评估了耦合气候模式对冬、春季北极涛动(AO)和南极涛动(AAO)的预测效能.结果表明,模式对于北极涛动和南极涛动的模拟能力都是比较强的,其中,对冬季的模拟能力要强于春季.冬季,几乎所有的模式都能很好地模拟出对流层内北极涛动的空间分布形态特点,空间相关系数很高.春季,大部分模式的模拟结果仍然是比较好,与再分析资料结果的空间相关性比较高.对于南极涛动,模式在全年对流层各个层次上都能比较好地刻画其空间分布,且模式在850 hPa等压面上的空间模拟效能要稍强于海平面.相对来说,冬季的模拟效果也稍强于其他季节,但是,差异不显著,模式与模式的差别也比较小.另外,模式对于北极涛动和南极涛动的时间序列模拟能力有限,时间序列相关系数只有少数几个模式达到显著性水平.     

耦合模式对冬春季节南、北极涛动的季节气候预测能力研究

研究评估了耦合气候模式对冬、春季北极涛动(AO)和南极涛动(AAO)的预测效能。结果表明,模式对于北极涛动和南极涛动的模拟能力都是比较强的,其中,对冬季的模拟能力要强于春季。冬季,几乎所有的模式都能很好地模拟出对流层内北极涛动的空间分布形态特点,空间相关系数很高。春季,大部分模式的模拟结果仍然是比较好,与再分析资料结果的空间相关性比较高。对于南极涛动,模式在全年对流层各个层次上都能比较好地刻画其空间分布,且模式在850hPa等压面上的空间模拟效能要稍强于海平面。相对来说,冬季的模拟效果也稍强于其他季节,但是,差异不显著,模式与模式的差别也比较小。另外,模式对于北极涛动和南极涛动的时间序列模拟能力有限,时间序列相关系数只有少数几个模式达到显著性水平。     

Monthly Changes in the Influence of the Arctic Oscillation on Surface Air Temperature over China

Partial Least Squares Regression （PLSR） is used to study monthly changes in the influence of the Arctic Oscillation （AO） on spring, summer and autumn air temperature over China with the January 500 hPa geopotential height data from 1951 to 2004 and monthly temperature data from January to November at 160 stations in China. Several AO indices have been defined with the 500-hPa geopotential data and the index defined as the first principal component of the normalized geopotential data is best to be used to study the influence of the AO on SAT （surface air temperature） in China. There are three modes through which the AO in winter influences SAT in China. The influence of the AO on SAT in China changes monthly and is stronger in spring and summer than in autumn. The main influenced regions are Northeast China and the Changjiang River drainage area.     

冬季北极涛动对西伯利亚高压、东亚冬季风以及海冰范围的可能影响

利用NCEP／NCAR月平均再分析资料（1958－1997），月平均海表面温度资料（1950－1992）以及月的海冰密集度资料（1953－1995），研究了冬季北极涛动与西伯利亚高压、东亚冬季风以及巴伦支海海冰范围之间的联系。研究结果表明，冬季北极涛动不仅影响北极和北大西洋区域气候变化，并且可能影响冬季西伯利亚高压，进而影响东亚冬季风。当冬季北极涛动处于正位相时，冬季西伯利亚高压和东亚冬季风都偏弱，在西伯利亚南部和东亚沿岸，包括中国东部、韩国和日本，从地表面到对流层中部气温偏高0.5-2℃。当冬季北极涛动处于负位相时，结果正相反。研究结果还表明，冬季西伯利亚高压对北极以及北大西洋区域气候变化没有显的影响，与北极涛动的影响相比，西伯利亚的影响强度和范围明显偏弱。研究进一步揭示了冬季北极涛动可能影响西伯利亚高压的可能机理。冬季西伯利亚高压与动力过程以及从地表面到对流层中部的气温变化有密切的关系。西伯利亚高压的西部变化主要依赖于动力过程，而其东部与气温变化更为密切。冬季西伯利亚高压的维持主要依赖于对流层中的下沉气流，这种下沉气流源于北大西洋区域，其变化受到北极涛动的影响。当冬季北极涛动处于正（负）位相时，气流的下沉运动明显减弱（增强），进而影响冬季西伯利亚高压。此处，冬季北极涛动对同时期的巴伦支海海冰范围有显的影响。     

“拉尼娜”非典型影响下的新疆2021/2022年冬季气温

2021/2022年冬季新疆大部气温偏高,影响新疆冷空气活动频次少,并非拉尼娜事件对新疆冬季气温的典型影响特征。成因分析表明：2021/2022年冬季北极涛动（AO）为正位相,欧亚中高纬度500 h Pa位势高度西高东低,新疆上空700 hPa南风距平优势明显。2021/2022年冬季“拉尼娜”非典型影响新疆气温的原因主要来自于东部型弱拉尼娜事件对北大西洋涛动（NAO）和亚洲极涡面积的非典型影响,而对亚洲极涡面积的非典型影响是来自东部型拉尼娜事件对冬季AO的不确定性影响,冬季AO正位相有利于新疆气温正距平。2月300 hPa区域纬向风异常偏弱,削弱了NAO正位相对新疆气温的影响;70°E以东中纬度高度场负距平是冬季气温阶段性变化的原因之一。     

2010年冬季江苏省雷暴异常活动与北极涛动的相关分析

运用江苏省冬季雷暴日数统计数据和NCEP/NCAR再分析数据,在结合30 a江苏冬季雷暴异常变化可能机理的基础上,分析了2010年冬季雷暴异常变化的原因。结果表明:2010年冬季江苏省雷暴活动异常偏多,其异常变化与同期北极涛动环流异常有密切的负相关关系。AO(Arctic Oscillation)指数偏弱时江苏雷暴增多的天气原因主要是:1)中西伯利亚和西西伯利亚地区气压异常偏高,中纬度地区气压异常偏低,乌拉尔山以西有阻塞高压与之配合,因此东亚冬季风偏强,冷空气南下频繁。对流层低层30°N附近表现为异常暖中心,低层孟加拉湾水汽输送强盛,江苏处于水汽辐合中心,这样"上冷下暖"和"上干下湿"的配置不仅有利于引起大气异常上升运动,也易于不稳定层结的形成,利于雷暴天气的发生。2)30~50°N北太平洋中东部海温异常偏低,引起低层风场异常辐散,对应上空为异常的下沉运动,通过类似于沃克环流圈形式使得东亚同纬度地区低层辐合异常,有利于该地区异常气旋性环流的加强。