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1.
The research on climate change in polar regions, especially on the role of polar in the global climate system, has gain unprecedented level of interest. It has been the key scientific issue of the International Polar Year program (IPY, 2007―2008). In this paper, we dealt with the debate upon the breakup time of the stratospheric polar vortex in boreal spring. An observational study of the relation between strato- spheric polar vortex breakup and the extra-tropical circulation was performed. The mean breakup date―when the winter westerly at the core of polar jet turns to summer easterly―is about April 10. The breakup time has large interannual variation with a time span of about 2 months. It also has a long-term trend with the 1990s and 2000s witnessing more and more late breakups of polar vortex. Composite of wind speed at the core of polar jet for the extremely early and late breakup years shows that late years have two periods of westerly weakening while early breakup years have only one. The first weakening in the late years happens in middle January with wind speed dropping sharply from more than 40 m s?1 to about 15 m s?1. This is accompanied with anomalous activities of planetary waves in both strato- sphere and troposphere; while the second weakening in the late breaking years is mainly the results of diabatic heating with very weak wave activities. In early breakup years, the transition from westerly to easterly is rapid with wind speed dropping from more than 30 m s?1 to less than ?10 m s?1 within a month. This evolution is associated with a strong bidirectional dynamical coupling of the stratosphere and troposphere. The circulation anomalies at low troposphere are also analyzed in the extremely early and late breakup years. It shows that there are significant differences between the two kinds of extreme years in the geopotential height and temperature composite analysis, indicating the dynamical cou- pling of stratosphere and troposphere with the evolution of stratospheric polar vortex.  相似文献   

2.
Scattering ratios of stratospheric aerosol obtained by lidar at McMurdo Station, Antarctica (78°S, 167°E), during February–December 1993, have been analysed in relation to the stratospheric polar vortex. Seasonal changes in their properties are used to infer dynamic processes occurring in the Antarctic stratosphere during the year. Descent rates are calculated and compared to values obtained with different studies. Our analysis suggests that the apparent springtime cleansing of the Antarctic stratosphere is the result of subsidence of air masses inside the vortex and of sedimentation of larger particles. Below 20 km of height, an enhancement of the aerosol descent rates during July was associated with high occurrence of Polar Stratospheric Cloud events above McMurdo Station in that period. A synoptic approach using potential vorticity values at 425 K above the station has been employed to figure out the behaviour of the aerosol across the vortex boundary during its early formation.  相似文献   

3.
This paper reports the study data on variations in the ozone content in the middle stratosphere over Moscow based on millimeter wavelength observations during a range of midwinter sudden stratospheric warmings that occurred in the past two decades. The relation of ozone with planetary waves and the intensity of the polar stratospheric vortex has been established. The ozone vertical distribution has been monitored with a highly sensitive spectrometer with a two-millimeter wave band. The discovered phenomena of a relatively long-term lower ozone content in December in the considered cold half-year periods are related to the higher amplitude of the planetary wave with n = 1. Such phenomena preceded the development of strong midwinter stratospheric warmings, which, in turn, were accompanied by a significant increase in the ozone content in January. This ozone enrichment was related to the lower amplitude of the wave with n = 1 and higher amplitude of the wave with n = 2 and was accompanied by geopotential H c.v. growth in the polar vortex center. Specific features of variations in the ozone content under the influence of the major atmospheric processes are observed not only in certain cold half-year periods but are also well seen in the general averaged pattern for winters with strong stratospheric warmings.  相似文献   

4.
毕云 《地球物理学报》2011,54(10):2468-2476
北极地区(60°N～90°N)平流层纬向风和气压场有明显的季节变化,不同高度层季节变化的时间有差异.北极平流层从冬至夏,季节转换从上向下推进,从夏至冬,季节转换从下向上推进.以20 hPa为例,平均而言,4月上旬以前,北极被极涡控制;4月中旬北极地区高压的势力开始超过低压,5月上旬,北极高压正式建立;7月份达到最强,8...  相似文献   

5.
Analyses of evolutions of the kinetic and thermal energy associated with the major and minor stratospheric warmings in the winters of 1976–77 and 1975–76 respectively indicate that the predominant ultra-long waves in the stratosphere oscillated at periods of 10–20 days, whereas in the troposphere the predominant long waves oscillated at periods of 8 to 12 days. These tropospheric long waves are almost out-of-phase with the stratospheric ultra-long waves for the minor warming, but in-phase for the major warming. The kinetic energy of the zonal mean flow in the stratosphere for the minor warming is much greater than that for the major warming, indicating that the occurrence of a major warming depends on the magnitude of the kinetic energy of the zonal mean flow relative to that of the meridional convergence of the poleward flux of sensible heat. In both the major and minor warmings, most of the stratospheric eddy kinetic energy is contained in waves of wavenumbers 1 and 2, whereas the stratospheric available potential energy is primarily contained in waves of wavenumber 1. The kinetic energy associated with waves of wavenumber 1 appeared to be 180° out-of-phase with those of wavenumber 2, indicating that nonlinear transfer of kinetic energy occurred between waves of wavenumbers 1 and 2. The occurrences of wind reversals were accompanied by decouplings of the stratospheric and tropospheric motions, and blockings in the troposphere.  相似文献   

6.
Using the monthly mean NCEP/NCAR reanalysis and NOAA Extended Reconstructed sea surface temperature (SST) datasets, strong correlations between the SST anomalies in the North Pacific and calculated three-dimensional Eliassen–Palm vertical fluxes are indicated in December 1958–1976 and 1992–2006. These correlations between the interannual variations of the SST anomalies and the penetration of planetary waves into the stratosphere are much less during the decadal sub-period 1976–1992 in the positive phase of the Pacific Decadal Oscillation (PDO) and the decadal cold SST anomalies in the North Pacific. Interannual variations of the polar jet in the lower stratosphere in January are strongly associated with SST anomalies in the Aleutian Low region in December for the years with positive PDO index. This sub-period corresponds well with that of the violation of the Holton–Tan relationship between the equatorial Quasi-Beinnial Oscillation (QBO) and the stratospheric circulation in the extra-tropics. It is shown that interannual and interdecadal variations of stratospheric dynamics, including stratospheric warming occurrences in January, depend strongly on changes of the upward propagation of planetary waves from the troposphere to the stratosphere over North Eurasia in preceding December. These findings give evidences of a large impact of the decadal SST variations in the North Pacific on wave activity in early winter due to changes of thermal excitation of planetary waves during distinct decadal periods. Possible causes of the decadal violation of the Holton–Tan relationship, its relation to the PDO and an influence of the 11-year solar cycle on the stratosphere are discussed.  相似文献   

7.
The planetary wave impact on the polar vortex stability, polar stratosphere temperature, and content of ozone and other gases was simulated with the global chemical–climatic model of the lower and middle atmosphere. It was found that the planetary waves propagating from the troposphere into the stratosphere differently affect the gas content of the Arctic and Antarctic stratosphere. In the Arctic region, the degree of wave activity critically affects the polar vortex formation, the appearance of polar stratospheric clouds, the halogen activation on their surface, and ozone anomaly formation. Ozone anomalies in the Arctic region as a rule are not formed at high wave activity and can be registered at low activity. In the Antarctic Regions, wave activity affects the stability of polar vortex and the depth of ozone holes, which are formed at almost any wave activity, and the minimal ozone values depend on the strong or weak wave activity that is registered in specific years.  相似文献   

8.
The North Atlantic Oscillation (NAO) is the prominent pattern of winter climate variability that has a strong effect on weather in the North Atlantic region and the adjacent continents. At present, uncertainty prevails as to the mechanisms controlling the variability of the NAO. It is also difficult to explain why the positive phase of the NAO has prevailed over the past 37 years (1972–2008). We found high positive correlation coefficients between geomagnetic activity (used as a measure of solar wind intensity) and the NAO indices that equal 0.76 for 1962–1994 and 0.63 for 1961–2011. Positive correlations of the distribution of surface air temperature with the NAO and similarly with geomagnetic activity occur in the Northern Hemisphere. These results encourage our search for possible causes controlling the NAO. We have found that at times of high geomagnetic activity the NAO index is positive and magnetic reconnection may enable the solar wind to initiate downward winds in the magnetosphere. Wind anomalies originate at the edge of the stratospheric polar vortex and propagate downward through the troposphere taking part in the intensification of the vortex and of the westerlies. Stronger northerly winds over Greenland carry cold air southward and, together with the enhanced westerlies, advect the warm air from the Atlantic along the deep Icelandic low into Eurasia increasing temperatures there. On the other hand, at times of low geomagnetic activity, the NAO index is negative and the stratospheric polar vortex is weak. Warm air from the subtropics is carried into the Arctic and a rapid amplification of planetary waves propagating upward may cause displacement or even splitting of the weak vortex and sudden stratospheric warming. During this negative NAO phase the weakened westerlies allow more cold air to build up over North America and Eurasia.  相似文献   

9.
van Loon et al. [2007. Coupled air–sea response to solar forcing in the Pacific region during northern winter. Journal of Geophysical Research 112, D02108, doi:10.1029/2006JD007378] showed that the Pacific Ocean in northern winter is sensitive to the influence of the sun in its decadal peaks. We extend this study by three solar peaks to a total of 14, examine the response in the stratosphere, and contrast the response to solar forcing to that of cold events (CEs) in the Southern Oscillation. The addition of three solar peak years confirms the earlier results. That is, in solar peak years the sea level pressure (SLP) is, on average, above normal in the Gulf of Alaska and south of the equator, stronger southeast trades blow across the Pacific equator and cause increased upwelling and thus anomalously lower sea surface temperatures (SSTs). Since the effect on the Pacific climate system of solar forcing resembles CEs in the Southern Oscillation, we compare the two and note that, even though their patterns appear similar in some ways, they are particularly different in the stratosphere and are thus due to separate processes. That is, in July–August (JA) of the year leading into January–February (JF) of the solar peak years, the Walker cell expands in the Pacific troposphere, and the stratospheric wind anomalies are westerly below 25 hPa and easterly above, whereas this signal in the stratosphere is absent in CEs. Thus the large-scale east–west tropical atmospheric (Walker) circulation is enhanced, though not to the extent that it is in CEs in the Southern Oscillation, and the solar influence thus appears as a strengthening of the climatological mean regional precipitation maxima in the tropical Pacific. Additionally, CEs have a 1-year evolution, while the response to solar peaks extends across 3 years such that the signal in the Pacific SLP of the solar peaks is similar but weaker in the year leading into the peak and in the year after the peak. The concurrent negative SST anomalies develop during the year before the solar peak, and after the peak the anomalies are still present but are waning. In the stratosphere in solar peaks, the equatorial quasi-biennial oscillation (QBO) is amplified when it is in its westerly phase in the lower stratosphere and easterly phase above; and the QBO is suppressed when in its easterly phase below–westerly phase above. Such an association is not evident in CEs.  相似文献   

10.
The transport mechanisms responsible for the seasonal behavior of total ozone are deduced from the comparison of model results to stratospheric data. The seasonal transport is dominated by a combination of the diabatic circulation and transient planetary wave activity acting on a diffusively and photochemically determined background state. The seasonal variation is not correctly modeled as a diffusive process. The buildup of total ozone at high latitudes during winter is dependent upon transient planetary wave activity of sufficient strength to cause the breakdown of the polar vortex. While midwinter warmings are responsible for enhanced ozone transport to high latitudes, the final warming marking the transition from zonal mean westerlies to zonal mean easterlies is the most important event leading to the spring maximum. The final warming is not followed by reacceleration of the mean flow; so that the ozone transport associated with this event is more pronounced than that associated with midwinter warmings.  相似文献   

11.
Stratospheric sudden warming events in the Northern Hemisphere of the Berlin TSM GCM are investigated. In about 50% of the simulated years (13 out of 28), major midwinter warmings occur. This agrees well with observations but, whereas real events tend to occur approximately every second season, those in the model are clustered, most of them occur in the period between years 15/16 and years 24/25. In most other years, minor warming events take place. The warming events are found earlier in the winter than in reality. Many of the observed characteristics of warming events are well captured by the model: pulses of wave activity propagate out of the troposphere; these transient events force the zonal-mean zonal wind in the stratosphere and coincide with increases of the temperature at the North Pole and cooling at low levels in the tropics; temperature changes of opposite sign are modelled at higher levels. Synoptically, the modelled stratosphere evolves quite realistically before the warmings: the cyclonic vortex is displaced from the Pole by an amplifying anticyclone. After minor warmings, the stratosphere remains too disturbed as the cyclonic centre does not return to the North Pole as quickly as in reality. In the aftermath of major warmings the cyclonic vortex is not fully eroded and the anticyclonic circulation does not develop properly over the Pole; furthermore, the wintertime circulation is not properly restored after the event.  相似文献   

12.
Continuous wind observations allow detailed investigations of the upper mesosphere circulation in winter and its coupling with the lower atmosphere. During winter the mesospheric/lower thermospheric wind field is characterized by a strong variability. Causes of this behaviour are planetary wave activity and related stratospheric warming events. Reversals of the dominating eastward directed mean zonal winds in winter to summerly westward directed winds are often observed in connection with stratospheric warmings. In particular, the amplitude and duration of these wind reversals are closely related to disturbances of the dynamical regime of the upper stratosphere.The occurrence of long-period wind oscillations and wind reversals in the mesosphere and lower thermosphere in relation to planetary wave activity and circulation disturbances in the stratosphere has been studied for 12 winters covering the years 1989–2000 on the basis of MF radar wind observations at Juliusruh (55°N, since 1989) and Andenes (69°N, since 1998). Mesospheric wind oscillations with long-periods between 10 and 18 days are observed during the presence of enhanced planetary wave activity in the stratosphere and are combined with a reversal of the meridional temperature gradient of the stratosphere or with upper stratospheric warmings.  相似文献   

13.
Based on the daily NCEP/DOE reanalysis II data,dates of the boreal spring Stratospheric Final Warming(SFW) events during 1979–2010 are defined as the time when the zonal-mean zonal wind at the central latitudes(65°–75°N) of the westerly polar jet drops below zero and never recovers until the subsequent autumn.It is found that the SFW events occur successively from the mid to the lower stratosphere and averagely from the mid to late April with a temporal lag of about 13 days from 10 to 50 hPa.Over the past 32 years,the earliest SFW occurs in mid March whereas the latest SFW happens in late May,showing a clear interannual variability of the time of SFW.Accompanying the SFW onset,the stratospheric circulation transits from a winter dynamical regime to a summertime state,and the maximum negative tendency of zonal wind and the strongest convergence of planetary-wave are observed.Composite results show that the early/late SFW events in boreal spring correspond to a quicker/slower transition of the stratospheric circulation,with the zonal-mean zonal wind reducing about 20/5 m s-1 at 30 hPa within 10 days around the onset date.Meanwhile,the planetary wave activities are relatively strong/weak associating with an out-of-/in-phase circumpolar circulation anomaly before and after the SFW events in the stratosphere.All these results indicate that,the earlier breakdown of the stratospheric polar vortex(SPV),as for the winter stratospheric sudden warming(SSW) events is driven mainly by wave forcing;and in contrast,the later breakdown of the SPV exhibits more characteristics of its seasonal evolution.Nevertheless,after the breakdown of SPV,the polar temperature anomalies always exhibit an out-of-phase relationship between the stratosphere and the troposphere for both the early and late SFW events,which implies an intimate stratosphere–troposphere dynamical coupling in spring.In addition,there exists a remarkable interdecadal change of the onset time of SFW in the mid 1990s.On average,the SFW onset time before the mid 1990s is 11 days earlier than that afterwards,corresponding to the increased/decreased planetary wave activities in late winter-early spring before/after the 1990s.  相似文献   

14.
Quasi-biennial oscillation (QBO) is a predominant phenomenon in the tropical stratosphere and troposphere. The possible interactions between the stratospheric QBO and tropospheric biennial oscillation (TBO) over the Indian monsoon region as well as the equatorial region is investigated using the zonal wind data of 23 vertical levels (1000–1 hpa) from 1960–2002. The structure of lower stratosphere and troposphere are entirely different over the equator and India. In biennial scales, both the stratosphere and troposphere over the Indian region are closely related and winter season QBO is a good predictor of Indian summer monsoon rainfall.  相似文献   

15.
Stratospheric warmings are attributed to an enhanced planetary wave activity, occurring nearly each winter – at least in the northern hemisphere – with different strengths. The generation of stratospheric warmings is not totally understood. One of the most promising explanations is the interaction of planetary waves: in many cases, the amplitude of the quasi-stationary planetary wave 1 builds up, until it transmits its momentum and energy to the background wind field. The role of wave 2 is usually considered to be less important.Based on ERA-40 and DYANA temperature data (January–February 1990), we found evidence that a resonant wave–wave interaction between a travelling and a stationary wave 2 was responsible for a minor stratospheric warming in February 1990. The interaction being observed during four weeks can eventually be used as an indication for an upcoming stratospheric warming.  相似文献   

16.
本文通过分析1957~2002年平流层爆发性增温(SSW)的环流特征,研究平流层爆发性增温可能对我国天气气候的影响.平流层爆发性增温发生后平流层高纬地区有异常的环流变化,但是这种变化并不仅局限于平流层内部,其产生的环流异常能够向下传播,并对对流层的天气和气候产生影响.研究发现,平流层出现强爆发性增温后,平流层异常温度场和位势高度场在中、高纬度形成AO型振荡并向下传播,使得对流层低层西伯利亚高压增强、阿留申低压加深,500 hPa东亚大槽加深且偏西,导致东亚冬季风增强,我国北部大部分地区气温偏低.而在爆发性增温前,强行星波扰动使得东亚大槽加深,西伯利亚高压和阿留申低压同时增强,也可能导致东亚冬季风偏强.El Nio可能激发出强行星波,有利于强SSW事件的发生.通过上述的两个过程可能造成东亚冬季风的加强,这将会对"El Nio事件通过对流层过程而引起东亚冬季风减弱"的结论有一定影响. 因此,ENSO事件影响东亚冬季风及中国的天气气候存在不止一种途径,具体影响情况应该是几种途径的综合结果.  相似文献   

17.
The heavy rain event of 30 January to 4 February 1993 in the Segura Basin in SE Iberia is investigated. The study emphasizes the atmospheric processes that led to thunderstorm development. The meteorological scenario has been separated into preconvective and convective periods and into large-scale and subsynoptic settings. The warm, moist air now from the Mediterranean Sea, channelled by a high-over-low blocking pattern with a cold front over southeastern Iberia appears to be the main reason that helped trigger a severe weather occurrence. The study of the mesoscale environment parameters showed an enhanced conditional unstability through a deep troposphere layer with a moderate to strong vertical wind shear that promoted conditions to allow organization of long-lived convective structures.  相似文献   

18.
A new two-dimensional zonal model of the stratosphere, based on a formulation in an isentropic framework, with complete chemistry has been coupled with a high resolution detailed microphysical model for polar stratospheric clouds (PSCs). The 2D model chemistry includes all presently known heterogeneous processes on sulfate aerosols and PSCs. The coupling of these two models, with inherently different time scales, is discussed. It is demonstrated that in order to obtain a realistic interrelationship between NOy and N2O an accurate simulation of the sedimentation by PSC particles is necessary. A good agreement of model PSC presence and observations is found for the Antarctic polar winter without the need to impose additional artificial temperature variations in the model. The calculated occurrence of polar stratospheric clouds and resulting heterogeneous chemistry during the Antarctic winter are discussed. Sensitivity of the polar stratospheric chemical composition and cloud formation for different perturbations is investigated by studying the effects of transport across the polar vortex boundary and heterogeneous processing by an enhanced sulfate aerosol load. The importance of including sedimentation for all cases is also discussed.  相似文献   

19.
Regular measurements of the velocity and direction of the horizontal wind in the mesosphere/lower thermosphere (MLT) region at a height of ∼95 km have been conducted since 1975 over Eastern Siberia (Badary observatory near Irkutsk), using the spaced-diversity reception method in the LF range. The accumulated database of measurement results (for more than 20 years, from 1974 to 1996) makes it possible to get information on the impact on wind in the MLT region from both below (stratospheric warmings) and above (geomagnetic storms as a consequence of magnetospheric disturbances) with sufficient statistical reliability. Effects of stratospheric warmings and strong geomagnetic storms in the prevailing wind and amplitude of the semidiurnal tide are evaluated by the superposed epoch method. It is shown that the effects of stratospheric warmings depend on the type (intensity) of stratospheric warming and on the phase of quasi-biennial oscillations of the wind in the equatorial stratosphere at the 30 hPa level. The response of MLT winds to external impacts is different for the 21st and 22nd cycles of solar activity. Effects of geomagnetic storms (A p > 100) are manifested in the decrease in the eastward prevailing wind and increase in the semidiurnal tide amplitude.  相似文献   

20.
梅雨与北极涛动及平流层环流异常的关联   总被引：11，自引：4，他引：7       下载免费PDF全文
李崇银  顾薇  潘静 《地球物理学报》2008,51(6):1632-1641
平流层过程如何影响气候变化是一个大家关注的科学问题,在WCRP中专门设置了一个研究子计划SPARC.本文的分析研究表明,中国的梅雨异常可能受到平流层大气环流异常的影响,而这种影响是通过北极涛动（AO）的变化来实现的.从分析和计算结果可以看到,二月份北半球30 hPa位势高度的EOF第一主分量对应着副热带和高纬度地区的显著下传异常波作用量,其第三主分量对应着极地地区的显著下传异常波作用量,这些下传的异常波作用量都对三月份AO形势的形成有明显的贡献.三月份的AO则会通过影响东亚地区夏季对流层大气的冷暖状况和环流,在长江中下游地区导致异常垂直运动和辐散辐合形势,从而影响夏季的梅雨降水.  相似文献   

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