共查询到19条相似文献，搜索用时 187 毫秒
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采用平流层准地转－β通道近似下的波流相互作用模型，考虑大气行星波１和波２与流的相互作用，以平流层底部边界强迫波波１和波２的振幅作为参数，对该模型的分岔特性进行了研究．结果表明，系统具有稳态解支Ａ，Ｂ，Ｃ，在某些参数范围内，多种稳态解同时存在．解支Ａ对应于平流层冷冬状态，解支Ｃ对应于平流层增温状态．由于参数变化系统在稳态解Ａ和Ｃ之间发生灾变是冬季平流层暴发性增温的原因．文中给出了二维参数空间中的分岔集，它表明了对流层顶的波动对平流层暴发性增温的控制作用，能很好地解释观测事实． 相似文献
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对大气重力波触发的赤道电离层Ｒａｙｌｅｉｇｈ－Ｔａｙｌｏｒ不稳定性的时空演变进行了数值模拟．结果表明，重力波能在Ｆ区底部触发Ｒａｙｌｅｉｇｈ－Ｔａｙｌｏｒ不稳定性，这种等离子体不稳定扰动穿过Ｆ峰，到达Ｆ区顶部，形成等离子体泡结构．等离子体泡出现向西倾斜和分岔等特征．当夜Ｆ区较高时，产生等离子体泡的时间仅１９００ｓ．数值模拟结果证实了重力波触发．Ｒａｙｌｅｉｇｈ－Ｔａｙｌｏｒ不稳定性的理论，解释了大量电离层观测现象． 相似文献
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根据实际观测资料反演获得描述大气环流演变的空间谱函数后,从改进的高截断谱模式途径出发研究了夏季东北亚阻塞高压年际变化的物理机制.结果表明,前期外部热源强迫的空间分布大致为El Nio型分布时,外部热力强迫导致大气环流演变中波波相互作用主要表现为纬向2波的相互作用;波流相互作用主要表现为经向2波和3波与反映基本流中的经向1波的相互作用.这样使得500 hPa高度场上东北亚地区为一相对正异常区,为夏季东北亚阻塞的频繁发生提供了有利的大气环流背景.而前期外部热源强迫大致为La Nia型分布时,外部热力强迫则导致大气环流演变中波波相互作用主要表现为纬向1波的相互作用;波流相互作用主要表现为经向2波和4波与反映基本流中的经向2波的相互作用.从而使得500 hPa高度场上帆北亚地区出现相对负异常,抑制了夏季东北亚阻塞的发生. 相似文献
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本文利用f-平面浅水模型讨论了二维情况下快速惯性重力波与平衡涡旋之间的相互作用问题.当快速的惯性重力波传入涡旋区域后，波－涡之间发生了相互作用，涡旋可被加深，涡旋区域的风场等可以出现非对称分布，当惯性重力波全部传出涡旋区域并远离之后，涡旋恢复到其初始状态，但此时惯性重力波可以出现非对称结构，这与一维情况不同.在波－涡发生相互作用过程中，其物理量变化的最大区域分布基本与波动传播方向一致，在波动进入或移出涡旋时，相对应存在两个最大物理量变化区域，此外，相互作用导致的物理量的最大变化与波动结构、强度、传播方向以及涡旋特性有关.非线性条件下的波－涡相互作用要强于线性过程. 相似文献
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板块构造理论关键在于相对坚硬的岩石层在松软的软流层上方运动的概念，但是目前人们对岩石层与软流层边界的性质还知之甚少。在这一边界中地震波速的梯度变化主要反映了造成这两层岩石强度不同的物理和化学特性。比如，如果岩石层仅仅是热边界层，由于其较低温度而比较坚硬，那么地幔对流模型（King et al，2000；Zaranek et al，2004）揭示在其底部的波速梯度可能持续数十千米。相反，如果软流层由于内部挥发物富集（Hirth and Kohlstedt，1996；Gaherty et al，1999；Karato and Jung，1998；Hirth et al，2000）或存在部分熔融（Anderson，1989）而变弱，那么岩石层与软流层之间的边界带可能会出现在小得多的深度范围。这里，我们用北美东部地区地震转换波对岩石层底部（或小于90～110km深度）非常急剧的地震波速梯度进行了成像——S波的速度在11km深度范围内下降了3％～11％。这样巨大、急剧的边界带不能仅仅用热梯度来解释，但可以用软流层内包含百分之几的部分熔融体（Anderson，1989）或比岩石层有更富集挥发物（Hirth and Kohlstedt，1996；Gaherty et al，1999；Karato and Jung，1998；Hirth et al，2000）来解释这一现象。 相似文献
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端承桩在层状地基波动与辐射阻尼影响下的横向地震反应分析 总被引：1，自引：0，他引：1
通过对层状地层中端承桩的分析,建立了合理的几何,数学及力学模型。考虑层状地基ＳＨ与ＳＶ波波动及非线性辐射阻尼影响,应用Ｄｉｒａｃ广义函数及Ｗｉｎｋｌｅｒ地基理论计入各种动力,抗力,地震力及内力等,建立地基波动方程,桩振动方程,地基与桩耦合振动方程。给出了柯西型函数的自由振动解。利用非经典理论正交条件和卷积定理给出了强迫振动地震反应解析解,算例结果充分表明了动力特性及振动规律非常正确,充分体现了本文 相似文献
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《Journal of Atmospheric and Solar》2002,64(8-11):1229-1240
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
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利用气象场的再分析资料和太阳辐射活动资料,对太阳11年周期活动影响北半球冬季(11月~3月)大气环流的过程进行了统计分析和动力学诊断.根据赤道平流层纬向风准两年振荡(QBO)的东、西风状态对太阳活动效应进行了分类讨论,结果表明：东风态QBO时,太阳活动效应主要集中在赤道平流层中、高层和南半球平流层,强太阳活动时增强的紫外辐射加热了赤道地区的臭氧层,造成平流层低纬明显增温,同时加强了南半球的Brewer-Dobson(B-D)环流,引起南极高纬平流层温度增加;而北半球中高纬的环流主要受行星波的影响,太阳活动影响很小.西风态QBO时,太阳活动效应在北半球更为重要,初冬时强太阳活动除了加热赤道地区臭氧层外,还抑制了北半球的B-D环流,造成赤道平流层温度增加和纬向风梯度在垂直方向的变化,从而改变了对流层两支行星波波导的强度;冬末时在太阳活动调制下,行星波向极波导增强,B-D环流逐渐恢复,造成北半球极地平流层明显增温,同时伴随着赤道区域温度的下降. 相似文献
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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
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Gregory M. Zhikharev 《地球物理与天体物理流体动力学》2013,107(3-4):259-279
Abstract A spectral low-order model is proposed in order to investigate some effects of bottom corrugation on the dynamics of forced and free Rossby waves. The analysis of the interaction between the waves and the topographic modes in the linear version of the model shows that the natural frequencies lie between the corresponding Rossby wave frequencies for a flat bottom and those applying in the “topographic limit” when the beta-effect is zero. There is a possibility of standing or eastward-travelling free waves when the integrated topograhic effect exceeds the planetary beta-effect. The nonlinear interactions between forced waves in the presence of topography and the beta-effect give rise to a steady dynamical mode correlated to the topographic mode. The periodic solution that includes this steady wave is stable when the forcing field moves to the West with relatively large phase speed. The energy of this solution may be transferred to the steady zonal shear flow if the spatial scale of this zonal mode exceeds the scale of the directly forced large-scale dynamical mode. 相似文献
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Observations from the Nimbus 6 pressure modulator radiometer (PMR) have been used to estimate monthly mean planetary wave fluxes of heat and momentum in the stratosphere and mesosphere. While the eddy heat fluxes play an important role in the mean meridional circulation of the winter stratosphere they are shown to be less important in the upper mesosphere. Incorporation of the observed momentum fluxes into the Oxford two-dimensional circulation model has shown that they are incapable of providing the momentum transport necessary to balance the zonal flow accelerations induced by the mean meridional motion. Other unspecified transfer processes represented by Rayleigh frictional damping of the zonal fow are shown to dominate. In contrast the observed fluxes in the stratosphere achieve the necessary redistribution of momentum. Moreover their interannual variability profoundly influences the stratospheric circulation, as demonstrated in the model by the use of two different annual sets of observed momentum fluxes. The desirability of calculating the planetary wave behaviour within the model is indicated. 相似文献
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On the basis of calculations using the general circulation model of the middle and upper atmosphere, the relative role of
sources of nonmigrating tides distributed in atmosphere has been investigated. It is shown that in winter, when planetary
waves in stratosphere are well developed, the main contribution to the generation of nonmigrating tides is caused by nonlinear
interaction between migrating tides and a quasi-stationary planetary wave with zonal wave number 1 (SPW1). Taking into account
the longitudinal ozone inhomogeneities in the model leads to the occurrence of additional sources of nonmigrating tides caused
by longitudinally inhomogeneous heating of the atmosphere, the contribution of which can be comparable to that from nonlinear
interaction under an attenuating amplitude of SPW1 in the stratosphere. 相似文献
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Pl. Mukhtarov B. Andonov C. Borries D. Pancheva N. Jakowski 《Journal of Atmospheric and Solar》2010,72(2-3):193-205
The present paper focuses on planetary wave type responses of the thermosphere/ionosphere system to forcing from above and below during the Arctic winter of 2005/2006. The forcing from above is described by the sunspot numbers, the solar wind speed, the Bz-component of the IMF and the geomagnetic Kp-index, while the forcing from below, i.e. by upward propagating atmospheric waves, is represented by the SABER/TIMED temperatures. The observed global ionospheric zonally symmetric oscillations with periods of ～9, ～14 and ～24–27 days were approved to be of solar origin. The most persistent ～9-day oscillation is linked to a triad of solar coronal holes distributed roughly 120° apart in solar longitude. The ～18-day westward propagating wave with zonal wavenumber 1, observed in the ionospheric currents (detected by magnetometer data), and in the F-region plasma (foF2 and TEC) could be allocated to a simultaneous 18-day westward propagating planetary wave observed in the stratosphere/mesosphere/lower thermosphere region with large (～70 km) vertical wavelength. 相似文献
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Michiya Uryu 《Pure and Applied Geophysics》1980,118(1):661-693
The mechanism of acceleration of the mean zonal flow by a planetary wave is explained intuitively by considering the wave drag which a corrugated bottom feels when it excites the wave. The explanation is justified by solving the problem of vertical propagation of a planetary wave packet and the second order mean motion induced around it. The discussion is slightly extended to the case of small damping, to illustrate in a compact form the fact that the mean zonal acceleration is determined by a forcing due to wave transience plus that due to wave dissipation.The mean flow induced by a steady, dissipating planetary wave is discussed, and it is shown that it depends largely on the dissipation scale-height of the wave whether the northern region is heated or cooled. For example, if the wave velocity-amplitude increases upward in spite of dissipation, the induced easterly flow increases with height and the temperature of the northern region increases relative to that in the southern region. A similar point has been made byDunkerton (1979) in connection with westerly flows induced by Kelvin waves.The Lagrangian-mean motion induced by a planetary wave is briefly discussed in connection with the mechanism of acceleration of the mean zonal flow, in the case of a slowly varying wave packet. Further, in order el elucidate the effects of wave dissipation and time dependence of wave amplitude, the results obtained for a steady, dissipating wave and for a growing baroclinic wave are mentioned. 相似文献
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《Journal of Atmospheric and Solar》2003,65(6):765-777
Planetary wave activity at quasi 16-, 10- and 5-day periods has been compared at various altitudes through the middle and upper atmosphere over Halley (76°S, 27°W), Antarctica, during the austral winters of 1997–1999. Observational data from the mesosphere, E-region ionosphere and F-region ionosphere have been combined with stratospheric data from the ECMWF assimilative operational analysis. Fourier and wavelet techniques have shown that the relationship between planetary wave activity at different altitudes is complex and during the winter eastward wind regime does not conform to a simple combination of vertical planetary wave propagation and critical filtering. Strong planetary wave activity in the stratosphere can coincide with a complete lack of wave activity at higher altitudes; conversely, there are also times when planetary wave activity in the mesosphere, E-region or F-region has no apparent link to activity in the stratosphere. The latitudinal activity pattern of stratospheric data tentatively suggests that when the stratospheric signatures are intense over a wide range of latitudes, propagation of planetary waves into the mesosphere is less likely than when the stratospheric activity is more latitudinally restricted. It is possible that, on at least one occasion, 16-day planetary wave activity in the mesosphere may have been ducted to high latitudes from the lower latitude stratosphere. The most consistent feature is that planetary wave activity in the mesosphere is almost always anti-correlated to planetary wave activity in the E-region even though the two are in close physical proximity. The oscillatory critical filtering of vertical gravity wave propagation by planetary waves and the re-generation of the planetary wave component at higher altitudes through subsequent critical filtering or breaking of the gravity waves may provide an explanation for some of these characteristics. Alternatively the nonlinear interaction between planetary waves and tides, indicated in the E-region data, may play a role. 相似文献