Stratospheric Polar Vortex Splitting in December 2009

Abstract

The 2009–10 Arctic stratospheric winter, in comparison with other recent winters, is mainly characterized by a major Sudden Stratospheric Warming (SSW) in late January associated with planetary wavenumber 1. This event led to a large increase in the temperature of the polar stratosphere and to the reversal of the zonal wind. Unlike other major SSW events in recent winters, after the major SSW in January 2010 the westerlies and polar vortex did not recover to their pre-SSW strength until the springtime transition. As a result, the depletion of the ozone layer inside the polar vortex over the entire winter was relatively small over the past 20 years. The other distinguishing feature of the 2010 winter was the splitting of the stratospheric polar vortex into two lobes in December. The vortex splitting was accompanied by an increase in the temperature of the polar stratosphere and a weakening of the westerlies but with no reversal. The splitting occurred when, in addition to the high-pressure system over northeastern Eurasia and the northern Pacific Ocean, the tropospheric anticyclone over Europe amplified and extended to the lower stratosphere. Analysis of wave activity in the extratropical troposphere revealed that two Rossby wave trains propagated eastward to the North Atlantic several days prior to the vortex splitting. The first wave train propagated from the subtropics and mid-latitudes of the eastern Pacific Ocean over North America and the second one propagated from the northern Pacific Ocean. These wave trains contributed to an intensification of the tropospheric anticyclone over Europe and to the splitting of the stratospheric polar vortex.     

Forecast of Polar Stratospheric Vortex Dynamics Using the SL-AV Global Atmosphere Model

The quality of Arctic winter stratospheric dynamics forecast using the SL-AV atmospheric global circulation model is studied. The series of numerical experiments show that forecasts with the lead time up to 7 days are successful. Zonal wind reversal during minor sudden stratospheric warmings is predicted 10–11 days ahead. Overall, the situations of strong polar jet disturbances are beneficial for the forecast accuracy.     

平流层极涡偏移对我国冬季降水的影响

利用1970—2010年NCEP/NCAR再分析资料、我国160站月平均降水资料分析了平流层极涡向欧亚大陆偏移与我国冬季降水的关系。结果表明:1月极涡偏欧亚大陆强度指数与同期1月降水的显著正相关区域主要分布在我国中部大面积地区及新疆西南部的少数地区,显著负相关区域主要分布在新疆中部;相对1月而言,与后期2月显著正相关区域仍然主要分布在我国的中部地区但向西北方向延伸,使得华中北部、华北南部相对减少,而华北西部、西北东部等地区增大。对流层环流形势显示出在欧亚型强极涡年的1月,东亚冬季风和东亚大槽异常减弱,我国内陆中东部东南风距平显著,而贝加尔湖北部北风距平显著,南下的冷空气与暖湿气流交汇地区较常年偏北,同时我国中部地区低层水汽向上传播也明显增强,存在显著的水汽强辐合中心。     

Northern Hemisphere Stratospheric Polar Vortex Extremes in February under the Control of Downward Wave Flux in the Lower Stratosphere

Using ECWMF ERA-40 and Interim reanalysis data, the planetary wave fluxes associated with the February extreme stratospheric polar vortex were studied. Using the three-dimensional Eliassen-Palm (EP) flux as a measure of the wave activity propagation, the authors show that the unusual warm years in the Arctic feature an anomalous weak stratosphere-troposphere coupling and weak downward wave flux at the lower stratosphere, especially over the North America and North Atlantic (NANA) region. The extremely cold years are characterized by strong stratosphere-troposphere coupling and strong downward wave flux in this region. The refractive index is used to examine the conception of planetary wave reflection, which shows a large refractive index (low reflection) for the extremely warm years and a small refractive index (high reflection) for the extremely cold years. This study reveals the importance of the downward planetary wave propagation from the stratosphere to the troposphere for explaining the unusual state of the stratospheric polar vortex in February.     

平流层极涡变化与我国冬季气温、降水的关系

利用国家气候中心提供的1951-2010年逐月环流指数资料,分析了北半球极涡强度指数、面积指数和中心强度指数的相关关系,并通过极涡强度指数的变化讨论了冬季北半球极涡强度的时间变化特征。结果表明,冬季极涡强度指数与面积指数和中心强度指数有较好的相关性,能够更好地反映冬季极涡强度的变化特征;冬季极涡存在准13年的年代际振荡周期,准5年的年际振荡周期在20世纪90年代后期较为明显。结合气温、降水观测资料和NCEP/NCAR月平均再分析资料,探讨了极涡强、弱不同年份我国冬季气温、降水和大气环流形势的变化。相对极涡弱值年而言,极涡强值年我国北方地区、东部地区特别是东北地区的气温偏高,西南大部分地区的气温偏低,长江流域和华南地区的气温变化不明显;我国南方地区降水偏多,长江中下游和华南地区的降水偏多最为明显,北方地区的降水略有减少;500hPa高度场上高纬度地区的位势高度降低,中高纬度的位势高度升高,冷空气向极地聚集,东亚大槽减弱,我国东北和东部地区的气温偏高;同时东亚冬季风减弱,湿空气向我国内陆输送,长江流域和我国南方地区的降水偏多。     

On the Differences and Climate Impacts of Early and Late Stratospheric Polar Vortex Breakup

The stratospheric polar vortex breakup (SPVB) is an important phenomenon closely related to the seasonal transition of stratospheric circulation. In this paper, 62-year NCEP/NCAR reanalysis data were employed to investigate the distinction between early and late SPVB. The results showed that the anomalous circulation signals extending from the stratosphere to the troposphere were reversed before and after early SPVB, while the stratospheric signals were consistent before and after the onset of late SPVB. Arctic Oscillation (AO) evolution during the life cycle of SPVB also demonstrated that the negative AO signal can propagate downward after early SPVB. Such downward AO signals could be identified in both geopotential height and temperature anomalies. After the AO signal reached the lower troposphere, it influenced the Aleutian Low and Siberian High in the troposphere, leading to a weak winter monsoon and large-scale warming at mid latitudes in Asia. Compared to early SPVB, downward propagation was not evident in late SPVB. The high-latitude tropospheric circulation in the Northern Hemisphere was affected by early SPVB, causing it to enter a summer circulation pattern earlier than in late SPVB years.     

亚洲东部冬季地面温度变化与平流层弱极涡的关系

利用NCEP资料计算NAM指数和标准化温度距平,对17次平流层弱极涡事件时亚洲东部温度变化进行了研究。结果表明:平流层环流异常比对流层温度变化超前约15天,地面温度变化的最大距平出现在平流层弱极涡后期,大约以40°N为界,北部比正常年份偏冷而南部偏暖。文中通过位势涡度的分布和变化以及500 hPa东亚大槽的变化讨论了其影响过程和机理,在弱极涡初期和中期,自平流层向下,高位涡冷空气主要局限于60°N以北。从弱极涡的后期开始,在45°N以北地区,高位涡冷空气向南扩张,在对流层中上层,极地附近的高位涡冷空气扩张到45°N附近。同时,500 hPa东亚大槽虽有加强,但低压区向东延伸,而贝加尔湖附近的高压脊显著减弱,致使槽后的偏北气流减弱,槽后冷空气主要影响中国华北、东北及其以北地区,造成这些地区偏冷。而40°N以南地区,从弱极涡的后期开始有南方低位涡偏暖空气向北运动,同时冷空气活动减少,地面显著偏暖。     

近年平流层气溶胶模式研究综述

平流层气溶胶在全球大气的辐射与化学平衡中起着重要作用,对全球气候变化有着重要的影响。数值模拟研究是研究平流层气溶胶浓度、粒径分布及其化学组成的重要手段之一。回顾了平流层气溶胶模式的发展历程,并对现今研究中较有代表性的5种模式进行了比较,着重考察了模拟结果在OCS、SO2分布情况等方面与实测数据的相符程度。结果发现5种模式均可再现平流层气溶胶和它的主要前体气体分布的大部分特征,但同时也都存在各自的局限。最后展望了平流层气溶胶模式未来的发展方向以及需要改进的问题。     

Middle Stratospheric Polar Vortex Ozone Budget during the Warming Arctic Winter, 2002--2003

The ozone budget inside the middle stratospheric polar vortex(24-36 km) during the 2002-2003 Arctic winter is studied by analyzing Michelson Interferometer for Passive Atmospheric Sounding(MIPAS) satellite data.A comprehensive global chemical transport model(Model for Ozone and Related Chemical Tracers,MOZART-3) is used to analyze the observed variation in polar vortex ozone during the stratospheric sudden warming(SSW) events.Both MIPAS measurement and MOZART-3 calculation show that a pronounced increase(26-28 DU) in the polar vortex ozone due to the SSW events.Due to the weakening of the polar vortex,the exchange of ozone mass across the edge of the polar vortex increases substantially and amounts to about 3.0× 107 kg according to MOZART-3 calculation.The enhanced downward transport offsets about 80% of polar vortex ozone mass increase by horizontal transport.A "passive ozone" experiment shows that only ～55% of the vertical ozone mass flux in February and March can be attributed to the variation in vertical transport.It is also shown that the enhanced downward ozone above ～32 km should be attributed to the springtime photochemical ozone production.Due to the increase of air temperature,the NOx reaction rate increases by 40%-80% during the SSW events.As a result,NOx catalytic cycle causes another 44% decrease in polar vortex ozone compared to the net ozone changes due to dynamical transport.It is also shown that the largest change in polar vortex ozone is due to horizontal advection by planetary waves in January 2003.     

平流层强、弱极涡事件的演变过程及其对我国冬季天气的影响

本文利用1979～2010年的NCEP再分析资料,通过北半球环状模NAM指数挑选出的强、弱极涡个例,分析了北半球平流层异常变化过程中行星波的演变以及与之相联系的我国天气的变化特征。结果表明,在强极涡事件前,行星波1波会被反射回对流层,极地波导减弱,低纬波导增强,中高纬地区的E-P通量矢量有着从平流层传播到对流层的趋势;强极涡事件后,极地波导增强,低纬波导减弱。在弱极涡事件前,中、高纬度行星波1波沿着极地波导的传播明显增强;弱极涡事件后,极地波导明显减弱。与此对应的我国天气也有明显变化,在强极涡事件前,我国大部分地区温度偏低,南方地区偏湿而新疆西北部和云南西部地区偏干;在强极涡事件后,东亚冬季风进一步增强,冷空气加强南下,南方地区可降水量减少,新疆西北部仍然偏干,而云南大部分地区可将水量增加。在弱极涡事件前,东亚冬季风显著增强,使我国气温偏冷,降水减少,而弱极涡事件后,我国气温明显回升,中、东部地区和新疆西北部地区降水明显增加。     

The Influence of Meridional Variation in North Pacific Sea Surface Temperature Anomalies on the Arctic Stratospheric Polar Vortex

This study examines the dependence of Arctic stratospheric polar vortex(SPV) variations on the meridional positions of the sea surface temperature(SST) anomalies associated with the first leading mode of North Pacific SST. The principal component 1(PC1) of the first leading mode is obtained by empirical orthogonal function decomposition. Reanalysis data,numerical experiments, and CMIP5 model outputs all suggest that the PC1 events(positive-minus-negative PC1 events),located relatively northward(...     

热带加热异常影响冬季平流层极涡强度的数值模拟

本文利用大气环流模式SAMIL/LASG,通过选择两种对流参数化方案,研究了热带加热异常对热带外平流层模拟的影响。结果表明,因不同对流参数化方案引起的热带对流加热状况的差异,可显著影响模式对北半球冬季平流层极涡强度的模拟偏差。与采用Manabe对流参数化方案相比,采用Tiedtke参数化方案可以显著改善对平流层极涡强度的模拟,使平流层极涡“过强”及极区“过冷”的模拟偏差得到明显改善。研究其中的影响过程发现,由于Manabe方案最大凝结潜热加热高度过低,在对流层中低层;而Tiedtke方案的最大凝结潜热加热位置在对流层中上层,因而Tiedtke(Manabe)方案时热带大气温度在对流层中上层较为偏暖(偏冷),在平流层低层较为偏冷(偏暖)。自秋季开始,与热带对流层高层温度的暖偏差相联系,热带外对流层高层以及热带平流层低层出现伴随的温度冷偏差;与之对应,平流层中纬度从秋季开始也出现持续的温度暖偏差。另外,随着秋冬季节平流层行星波活动的出现,Tiedtke方案时热带外地区行星波1波的强度也明显强于Manabe方案,使得秋冬季节涡动引起的向极热通量在Tiedtke方案时明显偏强,从而造成了冬季平流层极区温度偏暖、极涡强度偏弱。     

加拿大极地通信和气象卫星计划分析

北极是全球气候敏感区域之一,长期以来极地气象观测资料比较缺乏.为了提高北美及全球天气预报的准确性,加拿大航天局联合加拿大环境、气象、国防等部门多个单位共同启动了极地通信和气象卫星(PCW:Polar Communication and Weather)计划,持续提供50°N以北地区的通信服务和气象遥感观测.在气象方面,PCW将提供北极极地附近地区每隔15/30min的多光谱遥感信息,重点用于高纬度风场反演、海/湖冰、积雪和植被监测,云、气溶胶和火山灰信息反演,这些遥感信息在气候变化研究中将发挥重要作用.简要介绍了PCW计划的进展、卫星观测系统设计、轨道设计、遥感仪器、气象和空间天气的监测产品及应用.     

2008年中国南方雪灾与平流层极涡异常的等熵位涡分析

2008年1月中国南方遭遇罕见的大范围冰冻雨雪灾害, 本文利用NCEP/NCAR逐日再分析资料和等熵位涡分析方法, 分析了这次冰雪灾害期间平流层极涡的变化及其对对流层的影响。结果表明： 平流层极涡在2007年12月已经开始增强, 到1月中旬亚洲北部极地平流层极涡变得异常强大。高位涡冷空气向南扩展时, 沿着倾斜的等熵面运动, 从极地平流层上层一直延伸到中低纬度对流层。低层高位涡冷空气主体比较靠北, 华北一带为低位涡区; 南方为高位涡区, 呈东北—西南向伸展, 引导北方高位涡主体冷空气和西南暖湿气流在此汇合, 引起大范围降温和降雪。     

The Role of Stationary and Transient Planetary Waves in the Maintenance of Stratospheric Polar Vortex Regimes in Northern Hemisphere Winter

Using 1958-2002 NCEPNCAR reanalysis data, we investigate stationary and transient planetary wave propagation and its role in wave-mean flow interaction which influences the state of the polar vortex (PV) in the stratosphere in Northern Hemisphere (NH) winter. This is done by analyzing the Eliassen-Palm (E-P) flux and its divergence. We find that the stationary and transient waves propagate upward and equatorward in NH winter, with stronger upward propagation of stationary waves from the troposphere to the stratosphere, and stronger equatorward propagation of transient waves from mid-latitudes to the subtropics in the troposphere. Stationary waves exhibit more upward propagation in the polar stratosphere during the weak polar vortex regime (WVR) than during the strong polar vortex regime (SVR). On the other hand, transient waves have more upward propagation during SVR than during WVR in the subpolar stratosphere, with a domain of low frequency waves. With different paths of upward propagation, both stationary and transient waves contribute to the maintenance of the observed stratospheric PV regimes in NH winter.     

极涡研究进展

极涡是北极地区的一个深厚系统,它以极地为活动中心,最能体现高纬大气活动特征,属大气环流最主要的系统之一,通常与副热带高压、阻塞高压、季风等环流系统相互配合,在全球天气气候变化中起着至关重要的作用。本文就极涡的气候特征、对天气气候的影响、变化机理及数值模拟等几方面的研究进展进行综述。在行星波破碎、平流层爆发性增温、平流层对流层的动力耦合等过程中,极涡也扮演着重要角色;极涡对HNO3、臭氧等大气化学成分渗吸和输送过程的影响显著,而这些化学成分的再分布对极涡有较强的反馈作用;极涡还受到海温、冰雪、植被甚至太阳活动等的影响。前人已经关于极涡做了不少研究,但在气候动力学方面,还存在一些问题,有待进一步加强研究。     

涡动在南北半球平流层极涡崩溃过程中作用的比较

比较了南北半球春季平流层极涡的崩溃过程以及涡动在此崩溃过程中的作用。极涡的崩溃时间以平流层极夜急流核区最后一次西风转换为东风的时间来确定。结果表明南北半球平流层极涡的崩溃过程有着共同的特点,涡动和非绝热加热过程都对极涡的崩溃起着重要的作用,在极涡崩溃前平流层行星尺度波动活动明显,极涡崩溃以后,这种波动活动便迅速减弱。其中从对流层上传的行星波决定着极涡的具体崩溃时间。两个半球的差别主要表现在南半球极涡崩溃过程一般始于平流层高层,然后逐渐下传,而北半球这种下传不是很明显。其次,北半球平流层极涡崩溃偏晚年,极涡的减弱有两次过程,第一次为快速变化过程,第二次变化比较缓慢,而南半球平流层极涡崩溃无论早晚年只有一次减弱过程。长期的变化趋势分析表明南北半球平流层极涡的崩溃时间逐渐推迟,特别是20世纪90年代中后期以来,这种推迟更加明显。进一步的研究还发现,伴随着平流层极涡的崩溃过程平流层和对流层存在强烈的动力耦合,南北半球极涡迅速减弱前,各自半球的环状模指数也由负指数增加为正指数,表明低层环流对于平流层极涡的崩溃起到重要的作用;同时极涡不同强度所对应的低层环状模指数也不同,这可能与不同强度平流层极涡对于上传的行星波的反射有关。     

Ground Based FTIR Measurements of Stratospheric Species from Harestua, Norway During Sesame and Comparison with Models

Vertical columns of HF, HCl, HNO3, ClONO2, N2O, ClO and COF2 were measured at Harestua, Norway (60.22° N, 10.75° E, Elevation 600 a.s.l.) beginning on 24 November 1994 and concluding on 1 May 1995 during Phase-III of the SESAME (Second European Stratospheric Arctic and Mid-latitude Experiment) measurement campaign. The vertical columns of HCl, HNO3 and ClONO2 measured on 81 days were compared with columns calculated by the 3-D Cambridge model SLIMCAT. In addition the results were also interpreted by comparison with a photochemical trajectory model. Good agreement was seen for HCl while the nitrogen compounds showed larger discrepancies, especially for ClONO2. Evidence for chlorine activation was seen with 65% reduction of the chlorine reservoirs (HCl + ClONO2) while the levels of ClO were greatly enhanced. Interpretation of the loss with the trajectory model indicated condensation of chlorine on PSCs. The vertical column ratio of COF2 and HF was measured to 0.21 outside the vortex and a factor of two lower inside. The recovery of ClONO2 was seen to be much faster than that of HCl in the early spring.     

Intercomparison of Secondary Inorganic Aerosol Concentrations in the UK with Predictions of the Unified Danish Eulerian Model

Nitrate and sulphate concentrations were measured over the period January 2002–December 2003 on daily basis at two stations in the UK: a rural site (Harwell) and an urban site (Belfast). The measurements were compared with model results obtained by using the Unified Danish Eulerian Model (UNI-DEM), which was run using both a coarse resolution grid (50 km × 50 km surface cells) and a fine resolution grid (10 km × 10 km surface cells). The results from the comparison show reasonably good agreement between concentrations measured at the two stations and calculated by the model. This is achieved despite the absence of aqueous phase sulphur oxidation chemistry in the model. The model results were also used to predict the spatial distributions of nitrate and sulphate concentrations in the UK which agree well with observations. The contribution of mainland European emission sources and that of UK sources to pollution levels in the UK was estimated. The relative proportions differ substantially across the UK with the imported contribution to UK sulphate and nitrate typically in the range 20–45% and 35–65% respectively.     

Validation of the Polar MM5 for use in the simulation of the Arctic river basins

The simulations were performed using a modified mesoscale model,the Polar MM5,which was adapted for use within polar regions.The objective of the study was to illustrate the skill of the Polar MM5 in simulating atmospheric behavior over the Arctic river basins.Automatic weather station data,global atmospheric analyses,as well as near-surface and upper-air observations were used to verify the simulation. Parallel simulations of the Polar MM5 and the original MM5 within the period 19-29 April 1997 simula- tions revealed that Polar MM5 reproduced better near-surface variables forecasts than the original MM5 for the region located over the North American Arctic regions.The well predicted near-surface temperature and mixing ratio by the Polar MM5 confirmed the modified physical parameterization schemes that were used in this model are appropriate for the Arctic river regions.Then the extended evaluations of the Polar MM5 simulations over both the North American and Eurasian domains during 15 December 2002 to 15 May 2003 were then carried out.The time series plots and statistical analyses from the observations and the Polar MM5 simulations at 16 stations for the near-surface and vertical profiles at 850 hPa and 500 hPa variables were analyzed.The model was found to reproduce the observed atmospheric state both at magnitude and variability with a high degree of accuracy,especially for temperature and near-surface winds,although there was a slight cold bias that existed near the surface.