Observational constraints on the tropospheric and near-surface winter signature of the Northern Hemisphere stratospheric polar vortex

A composite analysis of Northern Hemisphere’s mid-winter tropospheric anomalies under the conditions of strong and weak stratospheric polar vortex was performed on NCEP/NCAR reanalysis data from 1948 to 2013 considering, as additional grouping criteria, the coincidental states of major seasonally relevant climate phenomena, such as El Niño-Southern Oscillation (ENSO), Quasi Biennial Oscillation and strong volcanic eruptions. The analysis reveals that samples of strong polar vortex nearly exclusively occur during cold ENSO states, while a weak polar vortex is observed for both cold and warm ENSO. The strongest tropospheric and near-surface anomalies are found for warm ENSO and weak polar vortex conditions, suggesting that internal tropospheric circulation anomalies related to warm ENSO constructively superpose on dynamical effects from the stratosphere. Additionally, substantial differences are found between the continental winter warming patterns under strong polar vortex conditions in volcanically-disturbed and volcanically-undisturbed winters. However, the small-size samples obtained from the multi-compositing prevent conclusive statements about typical patterns, dominating effects and mechanisms of stratosphere-troposphere interaction on the seasonal time scale based on observational/reanalysis data alone. Hence, our analysis demonstrates that patterns derived from observational/reanalysis time series need to be taken with caution as they not always provide sufficiently robust constraints to the inferred mechanisms implicated with stratospheric polar vortex variability and its tropospheric and near-surface signature. Notwithstanding this argument, we propose a limited set of mechanisms that together may explain a relevant part of observed climate variability. These may serve to define future numerical model experiments minimizing the sample biases and, thus, improving process understanding.     

Observed and simulated multidecadal variability in the Northern Hemisphere

 Analyses of proxy based reconstructions of surface temperatures during the past 330 years show the existence of a distinct oscillatory mode of variability with an approximate time scale of 70 years. This variability is also seen in instrumental records, although the oscillatory nature of the variability is difficult to assess due to the short length of the instrumental record. The spatial pattern of this variability is hemispheric or perhaps even global in scale, but with particular emphasis on the Atlantic region. Independent analyses of multicentury integrations of two versions of the GFDL coupled atmosphere-ocean model also show the existence of distinct multidecadal variability in the North Atlantic region which resembles the observed pattern. The model variability involves fluctuations in the intensity of the thermohaline circulation in the North Atlantic. It is our intent here to provide a direct comparison of the observed variability to that simulated in a coupled ocean-atmosphere model, making use of both existing instrumental analyses and newly available proxy based multi-century surface temperature estimates. The analyses demonstrate a substantial agreement between the simulated and observed patterns of multidecadal variability in sea surface temperature (SST) over the North Atlantic. There is much less agreement between the model and observations for sea level pressure. Seasonal analyses of the variability demonstrate that for both the model and observations SST appears to be the primary carrier of the multidecadal signal. Received: 8 June 1999 / Accepted: 11 February 2000     

Interannual variability of the winter stratospheric polar vortex in the Northern Hemisphere and their relations to QBO and ENSO

We investigated the interannual variations of the winter stratospheric polar vortex in this paper. EOF analysis shows that two modes of variability dominate the stratospheric polar vortex on interannual timescales. The leading mode (EOF1) reflects the intensity variation of the polar vortex and is characterized by a geopotential height seesaw between the polar region and the mid-latitudes. The second one (EOF2) exhibits variation in the zonal asymmetric part of the polar vortex, which mainly describes the stationary planetary wave activity. As the strongest interannual variation signal in the atmosphere, the QBO has been shown to influence mainly the strength of the polar vortex. On the other hand, the ENSO cycle, as the strongest interannual variation signal in the ocean, has been shown to be mainly associated with the variation of stationary planetary wave activity in the stratosphere. Possible influences of the stratospheric polar vortex on the tropospheric circulation are also discussed in this paper.     

Decay of the Northern Hemisphere stratospheric polar vortex and the occurrence of cut-off low systems: An exploratory study

Summary The authors perform an exploratory analysis on the effect of the timing of the stratospheric vortex breakup in the occurrence of cut-off low systems (COLs) in the Northern Hemisphere. The first multidecadal Northern Hemisphere COLs database (Nieto et al, 2005) covering a 41 year-long period (1958–1998) was used in the analysis. The dates of stratospheric vortex breakup were obtained using two different approaches recently purposed in literature based in potential vorticity and zonal winds. An analysis of differences of COLs occurrences for the five earlier (later) breakup years showed that, at latitudes lower than 45° N, COLs are more frequent for earlier vortex years during the following spring and summer. The monthly analysis showed that, in general, the significant differences start in May lasting until September, being especially relevant for the European sector, the area with the highest rates of COLs occurrence in the Northern Hemisphere.     

北半球平流层极涡崩溃早晚的环流特征及其对5月南亚降水的影响

本文采用1979—2014年NCEP/NCAR月平均再分析资料、CMAP和GPCP月平均降水资料,分析了北半球平流层极涡崩溃早晚的环流特征及其与南亚降水的关系。结果表明,北半球平流层极涡崩溃时间存在明显的年际变化特征。极涡崩溃偏早(偏晚)年,自3月开始异常信号从平流层向下传播,之后的4月,从平流层到对流层高层极区温度异常偏高(偏低),极涡异常偏弱(偏强),极夜急流异常偏弱(偏强)。结果还表明,5月南亚降水异常与平流层极涡崩溃时间的早晚存在显著相关,5月南亚降水异常与平流层极涡崩溃早晚年平流层异常信号的下传有关。当平流层极涡崩溃偏晚年,4月平流层极区表现为位势高度异常偏低,而中纬度则位势高度场异常偏高,并伴随位势高度异常场的向下传播,5月该位势高度异常场下传至阿拉伯海北部大陆上空对流层顶,形成有利于降水的环流场,导致南亚降水偏多。反之,则相反。     

北半球冬季极涡异常变化的时空特征

利用NCEP/NCAR再分析月平均高度场资料,计算了1948/1949-2009/2010年北半球冬季500～10 hPa的极涡环流指数,包括面积指数S、强度指数P和中心位置指数(λc,φc).分析了北半球冬季极涡在垂直高度上(共12层)的季、月气候态和异常态变化规律.结果表明:极涡面积和强度在不同高度上的大小变化不同,最大值出现的时间也存在差异,二者相关性不好,为两个相对独立的指数.极涡面积和强度的年代际变化趋势在上下层上也不一样,异常变化规律复杂;极涡中心位置上下层变化规律相同,主要在东半球80°N以北范围变化,在极点附近经度变化大,纬度变化小,纬度指数年代际变化明显,近10 a极涡明显偏南.从整体上看,极涡中心位置从500 hPa到10hPa形态上为逆时针、半径越向上越大的旋转变化.     

平流层极涡振荡与ENSO热带海温异常的时空联系

利用一个在等熵位涡坐标下建立的平流层极涡振荡(Polar Vortex Oscillation)指数,以及NCEP/NCAR再分析资料和NOAA_OISST_V2逐周海温资料,研究了月尺度以上热带海温异常与平流层极涡振荡的时间和空间联系,通过相关、回归以及合成分析发现,两者的显著联系主要发生在3—5年的年际时间尺度上,表现为ENSO型海温异常与极涡振荡年际趋势之间的时空关联。首先,两者的关系并不表现在同期相关上,而是当ENSO海温异常超前极涡振荡年际异常9—11个月时,两者具有最大的负相关关系。当前期热带海温偏暖(冷)时,9—11个月后极涡振荡的年际趋势为负(正)的异常,即极涡偏弱(强)或负(正)振荡事件为主。统计合成结果进一步证实,前期热带ENSO海温暖事件背景下,后期极涡振荡负事件的发生比正事件更多,强度更强,持续时间也更长,反之亦然;另外,前期热带ENSO暖海温背景下,极涡正、负振荡事件的发生均更频繁。研究连接热带ENSO海温异常与平流层极涡振荡的过程发现,热带海温异常不仅可在热带地区引起大气温度的异常响应,而且可以引发从平流层热带到极区的一系列温度异常同时向下和向极区的传播过程,并与9—11个月以后发生在极区的极涡振荡异常相联系。表明与热带海温异常相联系的极涡振荡年际异常,可能存在与季节尺度极涡振荡中类似的全球质量环流的异常变化。     

Observational evidence of the delayed response of stratospheric polar vortex variability to ENSO SST anomalies

The temporal and spatial relationship between ENSO and the extratropical stratospheric variability in the Northern Hemisphere is examined. In general, there exists a negative correlation between ENSO and the strength of the polar vortex, but the maximum correlation is found in the next winter season after the mature phase of ENSO event, rather than in the concurrent winter. Specifically, the stratospheric polar vortex tends to be anomalously warmer and weaker in both the concurrent and the next winter season following a warm ENSO event, and vice versa. However, the polar anomalies in the next winter are much stronger and with a deeper vertical structure than that in the concurrent winter. Our analysis also shows that, the delayed stratospheric response to ENSO is characterized with poleward and downward propagation of temperature anomalies, suggesting an ENSO-induced interannual variability of the global mass circulation in the stratosphere. Particularly, in response to the growing of a warm ENSO event, there exist warm temperature and positive isentropic mass anomalies in the midlatitude stratosphere since the preceding summer. The presence of an anomalous wavenumber-1 in the concurrent winter, associated with an anomalous Aleutian high, results in a poleward extension of warm anomalies into the polar region, and thus a weaker stratospheric polar vortex. However, the midlatitude warm temperature and positive isentropic mass anomalies persist throughout the concurrent winter till the end of the next summer. In comparison with the concurrent winter, the strengthening of poleward heat transport by an anomalous wavenumber-2 in the next winter results in a much warmer and weaker polar vortex accompanied with a colder midlatitude stratosphere.     

Link between Arctic ozone and the stratospheric polar vortex

The stratospheric ozone layer protects life on earth by preventing solar ultraviolet radiation from reaching the surface. Owing to the large population in the Northern Hemisphere and extreme ozone loss in the Arctic, changes in Arctic stratospheric ozone (ASO) and their causes have attracted broad attention recently. Using monthly mean data during the period 1980–2020 from MERRA-2, the relationship between the stratospheric polar vortex (SPV) and ASO, along with the relative contributions of chemical and dynamic processes associated with the SPV to changes in ASO, were examined in this study. Results showed that the ASO in March has a strong out-of-phase link with the strength of the SPV in March, with no obvious lead–lag correlations, i.e., an increase (decrease) in ASO corresponds to a weakened (strengthened) SPV. Further analysis suggested that the strong out-of-phase link between the SPV and ASO is related to changes in Brewer–Dobson circulation (BDC). Strong SPV events, accompanied by a low temperature condition and weakened upward propagation of planetary waves over the Arctic in the stratosphere, result in weakened BDC. The weakened downwelling at high latitudes tends to transport less ozone-rich air in the upper stratosphere at lower latitudes into the lower stratosphere at high latitudes, facilitating a decrease in ASO. The BDC's vertical velocity plays the dominant role in modulating ASO.摘要利用1980–2020年MERRA-2资料, 分析了平流层极涡 (Stratospheric polar vortex, SPV) 和北极臭氧 (Arctic stratospheric ozone, ASO) 的关系, 评估了与SPV相关的化学, 动力过程在其中的相对作用. 结果表明, 3月份ASO与同期SPV强度反相关最大. SPV-ASO二者反相关与平流层剩余环流 (Brewer-Dobson circulation, BDC) 变化密切相关. 强SPV伴随的北极平流层低温条件和行星波向上传播减弱, 导致BDC减弱, 减弱的BDC下沉支将低纬度平流层上层臭氧含量较低的空气输送到北极平流层低层, 从而导致ASO减少. BDC垂直速度在其中起主导作用.     

Climatological variations in the Northern Hemisphere circumpolar vortex in January

Summary Recent secular variations in the January circumpolar vortex over the Northern Hemisphere are examined by digitizing the latitude at which the 546 dam isoheight at 50 kPa crosses every 10° meridian from 1947–90. A statistically significant expansion of the vortex is detected from 1966–90. Most of the expansion occurred over the North Pacific Ocean in the vicinity of the Aleutian Low and a less dramatic but significant expansion also occurred over eastern Canada and northern New England. The only region where the vortex contracted significantly is over the western United States. The trough in the western Pacific expanded eastward across the International Date Line in the past quarter century and, in conjunction with the observed contraction over the western United States, indicates amplification of 50 kPa standing waves in the Western Hemisphere. This change in circulation regimes could account for the increased frequency of warm air masses and the decreased occurrence of the coldest wintertime air masses in Alaska.With 6 Figures     

东北夏季气温变化与北半球温度及极涡的关系

利用1961-2002年中国东北地区80个气象站夏季6-8月逐日气温、美国NCAR/NCEP再分析资料和国家气候中心环流因子资料,采用相关分析、SVD分解等方法,对中国东北夏季气温变化与中高纬主要环流系统的关系进行探讨.结果发现:中国东北位于东西伯利亚变温区南缘,其夏季气温年际变化规律和东西伯利亚一致;北极极涡边缘的形态变化影响东北夏季气温,不同的边缘形态对应东北不同的温度分布特征,主要是极涡边缘70 °N左右的150～180 °E和60～90 °W两个关键区,其高度场的变化决定着东北夏季气温的变化.     

Teleconnection Paterns in the Northern Hemisphere Simulated by IAP GCM

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中部型ENSO和平流层准两年振荡对冬季北半球平流层臭氧的联合调制作用

利用观测和再分析资料通过合成分析方法,研究了中部型ENSO和平流层准两年振荡（QBO）对冬季北半球平流层臭氧的独立影响和联合调制作用。研究表明,北半球平流层臭氧在中部型厄尔尼诺年增加,而在中部型拉尼娜年减少;准两年振荡东风位相年份,北半球平流层臭氧增加,准两年振荡西风位相结果则相反。相比之下,北半球中、高纬度平流层臭氧异常对准两年振荡活动的响应明显小于其对ENSO活动的响应。进一步研究发现,准两年振荡东风位相会加强中部型厄尔尼诺事件引起的北半球平流层臭氧的增加,而减弱中部型拉尼娜事件造成的平流层臭氧的减少。在准两年振荡西风位相下,中部型厄尔尼诺事件仅导致北半球平流层臭氧含量少量升高,而中部型拉尼娜事件期间臭氧会大幅度减少。因此,准两年振荡东风位相会加强中部型厄尔尼诺事件对北半球平流层臭氧的影响,而减弱中部型拉尼娜事件对北半球平流层臭氧的影响。准两年振荡西风位相会减弱中部型厄尔尼诺而加强中部型拉尼娜事件对北半球平流层臭氧的影响。      

太阳准周期变化对北半球夏季平流层加热率的影响

采用1979—2013年6—8月欧洲中期数值预报中心ERA-Interim逐月再分析资料和2004—2010年6—8月美国国家大气和海洋管理局太阳光谱辐照度资料,利用北京气候中心大气辐射模式,计算了北半球平流层夏季臭氧加热率(Ozone Heating Rate,OHR)和净加热率(Net Heating Rate,NHR),分析了太阳准11 a变化中太阳活动强年与弱年纬向平均OHR(NHR)的差异,并讨论了差异形成的原因。结果表明:太阳活动强年比弱年的紫外辐射明显要强,导致OHR、NHR整层增强,且随高度增加而增加;臭氧浓度在平流层下层较小,在平流层上层较大,该变化导致OHR、NHR有类似的变化型,且稍向高处偏移;OHR、NHR在平流层上层的变化,由紫外辐射和臭氧共同作用,其他地区均为臭氧起主要作用。     

2019-2020冬季北半球超强极涡事件

2019-2020冬季北极平流层极涡异常并且持续的偏强,偏冷.利用NCEP再数据和OMI臭氧数据,本文分析了此次强极涡事件中平流层极涡的动力场演变及其对地面暖冬天气和臭氧低值的影响.此次强极涡的形成是由于上传行星波不活跃.持续的强极涡使得2020年春季的最后增温出现时间偏晚.平流层正NAM指数向下传播到地面,与地面AO...     

平流层异常下传对2009年12月北半球大范围降雪过程的影响

2009年12月北半球中纬度出现大范围持续低温、暴风雪等天气。采用NCEP／NCAR再分析资料研究了平流层AO（Arctic Oscillation,北极涛动）异常信号下传的特征及其对本次极端气候事件的影响,并讨论了与平流层异常信号下传相关的行星波活动。结果表明：1）与此次极端气候事件相联系的负位相A0异常11月首先发生在平流层,维持将近1个月后于12月初开始下传,并且迅速传至地面。12月整个对流层的位势高度及温度在极区附近出现强的正异常,而中纬度地区则为负异常。2）平流层AO异常信号下传后,地面出现有利于低温降雪过程的环流异常。12月上旬,亚洲大陆东部及北美大陆西部出现异常偏北风,造成了俄罗斯、北美西部大面积负的温度异常;12月中下旬,欧洲大陆盛行偏西北气流,同时蒙古高压增强,欧亚大陆北部包括中国北方出现大片负的温度异常。3）在此次极端气候事件之前,北半球高纬度地区有异常强的行星波上传至平流层,导致平流层出现负位相的AO异常,并维持了一个月;随后,上传到平流层的行星波减弱,同时平流层负位相的AO异常迅速传至地面,导致了有利于低温降雪的环流异常。     

Northern Hemisphere circulation regimes: observed, simulated and predicted

Nonlinear principal component analysis provides evidence that the Northern Hemisphere extratropical atmosphere supports three distinct circulation regimes with an average residence time of about 7 days. The role of high- and low-frequency dynamics is studied and results indicate that they are both involved in the formation, maintenance and decay of the regimes. A global coupled climate model also supports three distinct circulation regimes with strikingly similar spatial structures, residence times and linked high- and low-frequency dynamics to those observed. The issue related to how long a data record is required to properly resolve the regime structures is addressed by exploiting the model output. Regime residence times and spatial structures are predicted to change over the next century given increasing concentrations of atmospheric greenhouse gases.     

Quantifying the Response Strength of the Southern Stratospheric Polar Vortex to Indian Ocean Warming in Austral Summer简

A previous multiple-AGCM study suggested that Indian Ocean Warming （IOW） tends to warm and weaken the southern polar vortex.Such an impact is robust because of a qualitative consistency among the five AGCMs used.However,a significant difference exists in the modeled strengths,particularly in the stratosphere,with those in three of the AGCMs （CCM3,CAM3,and GFS） being four to five times as strong as those in the two other models （GFDL AM2,ECHAM5）.As to which case reflects reality is an important issue not only for quantifying the role of tropical ocean warming in the recent modest recovery of the ozone hole over the Antarctic,but also for projecting its future trend.This issue is addressed in the present study through comparing the models＇ climatological mean states and intrinsic variability,particularly those influencing tropospheric signals to propagate upward and reach the stratosphere.The results suggest that differences in intrinsic variability of model atmospheres provide implications for the difference.Based on a comparison with observations,it is speculated that the impact in the real world may be closer to the modest one simulated by GFDL AM2 and ECHAM5,rather than the strong one simulated by the three other models （CCM3,CAM3 and GFS）.In particular,IOW during the past 50 years may have dynamically induced a 1.0℃ warming in the polar lower stratosphere （～100 hPa）,which canceled a fraction of radiative cooling due to ozone depletion.