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1.
It is generally accepted that small-scale gravity waves (GW) produce the observed reversals in the zonal circulation and temperature variations of the upper mesosphere (e.g., Lindzen, 1981). There is evidence that GW also play an important role in the quasi-biennial oscillation (QBO) of the lower stratosphere, which can be generated by planetary waves (Lindzen and Holton, 1968). In the present paper, we summarize the modeling studies with the mechanistic numerical spectral model (NSM), which incorporates the Doppler spread parameterization for GW (Hines, 1997a, Hines, 1997b). Our studies illuminate the importance of GW filtering and momentum deposition associated with critical level absorption and wave braking. Numerical results from the 2D and 3D versions of the NSM show how these wave interactions generate in the zonal-mean: (a) annual and semi-annual oscillations, (b) QBO with related semi-decadal oscillation and solar cycle effects, and (c) monthly intra-seasonal oscillations.  相似文献   

2.
In this paper we present an extension for the 2D (zonal mean) version of our numerical spectral mode (NSM) that incorporates Hines’ Doppler spread parameterization (DSP) for small-scale gravity waves (GW). This model is applied to describe the seasonal variations and the semi-annual and quasi-biennial oscillations (SAO and QBO). Our earlier model reproduced the salient features of the mean zonal circulation in the middle atmosphere, including the QBO extension into the upper mesosphere inferred from UARS measurements. The model is extended to reproduce the upwelling at equatorial latitudes that is associated with the Brewer–Dobson circulation — which affects significantly the dynamics of the stratosphere as Dunkerton had pointed out. In the presence of GW, this upwelling is produced in our model with tropospheric heating, which generates also zonal jets outside the tropics similar to those observed. The resulting upward vertical winds increase the period of the QBO. To compensate for that, one needs to increase the eddy diffusivity and the GW momentum flux, bringing the latter closer to values recommended in the DSP. The QBO period in the model is 30 months (mo), which is conducive to synchronize this oscillation with the seasonal cycle of solar forcing. Associated with this QBO are interannual and interseasonal variations that become increasingly more important at higher altitudes — and this variability is interpreted in terms of GW filtering that effectively couples the dynamical components of the mesosphere. The computed temperature amplitudes for the SAO and QBO are in substantial agreement with observations at equatorial and extra-tropical latitudes. At high latitudes, however, the observed QBO amplitudes are significantly larger, which may be a signature of propagating planetary waves not included in the present model. The assumption of hydrostatic equilibrium not being imposed, we find that the effects from the vertical Coriolis force associated with the equatorial oscillations are large for the vertical winds and significant for the temperature variations even outside the tropics, but the effects are small for the zonal winds.  相似文献   

3.
Based on 5 years of OH imager data between September 2003 and September 2008 over Yucca Ridge Field Station, CO (40.7ºN, 104.9ºW), we presented the variation of gravity wave (GW) occurrence frequency and propagation direction in the upper mesosphere. In summer the GW occurrence frequency was extremely high at above 95% compared to other seasons (around 85%). The GW propagation direction showed a strong northward (poleward) preference in summer and a southward (equatorward) preference in winter. This could be possibly due to ducting of waves in the mesopause thermal structure and wave generation by the strong deep convection located at south side in summer and possible storms located at north side in winter. Westward traveling waves were rare, but eastward were frequent. In addition to seasonal variability, significant interannual variability was also observed.  相似文献   

4.
AIRS观测的东亚夏季平流层重力波特征   总被引：7，自引：4，他引：3       下载免费PDF全文
对流性重力波对中层大气环境有显著影响.重力波活动及重力波源的地理和季节性变化等信息是理解和模拟重力波效应的基础.卫星高光谱红外大气垂直探测器AIRS的4μm和15μm波段可用于识别30~40km高度范围和41km高度附近的重力波,其11μm通道可同步观测对流层深对流.观测个例表明,海面和陆面上空的平流层扰动影响范围均可达1000km,不同高度的扰动强度分布也存在差异.基于2007年6月至8月的AIRS观测资料,分析了东亚区域的对流层深对流活动和平流层的重力波,得到了深对流和重力波发生频率的水平分布.统计结果表明,东亚区域夏季夜间的深对流活动明显少于白天,但AIRS观测到的平流层重力波发生频率和扰动强度均显著大于白天,揭示了夜间对流层深对流诱发的平流层重力波在强度、范围等方面可能与白天存在显著差异.进一步对比分析表明,AIRS观测的平流层扰动高值区与深对流高值区明显不同.平流层重力波与对流层深对流之间的相关分析表明,在36°N以南的区域,41km高度上AIRS观测的重力波中,深对流云诱发的重力波的比例约为30%~100%.在10°N至36°N区间,90%的深对流均可诱发平流层重力波.分析得到的30~40km高度区间和41km高度附近的重力波水平分布对比表明,后一高度上的扰动强度明显大于前一高度,且前一高度在东南亚区域存在强扰动中心而在后一高度则没有.最后,给出了AIRS观测的几种典型形态的东亚区域平流层波动,表明了该区域平流层环境波动形态的复杂性和多样性.  相似文献   

5.
The correlation between atmospheric gravity waves(GWs) and Transient Luminous Events(TLEs) has been poorly studied using both synchronous observations and numerical simulations. To investigate the modulation effects of GWs on TLEs,a troposphere-mesosphere quasi-electrostatic field model is developed in three-dimensional Cartesian coordinates, and the effects of GW perturbations on the initiation and optical emissions of sprite halos are simulated using the model. Simulation results indicate that the atmospheric density at lower ionosphere altitudes becomes inhomogeneous due to GW perturbations, and sprite halos tend to initiate in the GW troughs due to the lower electric breakdown threshold. GW perturbations cause the deformation of sprite halos, strong luminous regions distribute mainly along the GW troughs while optical intensities along the GW peaks is relatively weak. Larger GW perturbations lead to more pronounced deformation of sprite halos, however, stronger lightning discharges in the troposphere result in less optical perturbations of sprite halos. The observed luminous intensities and optical morphology of sprite halos are also affected by the observing orientations and the lightning polarities.  相似文献   

6.
本文利用2006年5月至2013年4月COSMIC干温廓线数据,提取了青藏高原地区大气重力波势能,以此研究了青藏高原大气重力波势能的分布频率模型和大气重力波活动的时空变化特征,并进一步分析了高原大气重力波活动与高原地形、风速和高原大陆热辐射之间的相关性.青藏高原地区大气重力波势能的分布频率服从对数生长分布;青藏高原地区大气重力波在16~18km和28~31km高度较活跃,而在20~26km高度较平静;高原大陆边缘各季节重力波活动均较活跃,而高原大陆上空大气重力波活动呈明显季节性变化,其在冬春季节较活跃,在夏秋季节较平静;2010年冬季青藏高原大气重力波活动异常平静;各季节整个高原上空大气重力波活跃度有随大气高度升高而降低的趋势,高原上低层大气重力波向高层传播会发生耗散作用.地形与风速是影响青藏高原大气重力波活动的重要因素.地形主要影响平流层底部的重力波活动;纬向风比经向风对该地区平流层大气重力波活动的影响大,纬向风总体上会促进高原大气重力波活动.青藏高原大陆热辐射对高原大气的加热作用是导致青藏高原大气重力波活动呈季节性变化的重要因素.  相似文献   

7.
Five years of global temperatures retrieved from radio occultations measured by Champ (Challenging Minisatellite Payload) and SAC-C (Satelite de Aplicaciones Cientificas-C) are analyzed for gravity waves (GWs). In order to separate GWs from other atmospheric variations, a high-pass filter was applied on the vertical profile. Resulting temperature fluctuations correspond to vertical wavelengths between 400 m (instrumental resolution) and 10 km (limit of the high-pass filter). The temperature fluctuations can be converted into GW potential energy, but for comparison with parameterization schemes GW momentum flux is required. We therefore used representative values for the vertical and horizontal wavelength to infer GW momentum flux from the GPS measurements. The vertical wavelength value is determined by high-pass filtering, the horizontal wavelength is adopted from a latitude-dependent climatology. The obtained momentum flux distributions agree well, both in global distribution and in absolute values, with simulations using the Warner and McIntyre parameterization (WM) scheme. However, discrepancies are found in the annual cycle. Online simulations, implementing the WM scheme in the mechanistic COMMA-LIM (Cologne Model of the Middle Atmosphere—Leipzig Institute for Meteorology) general circulation model (GCM), do not converge, demonstrating that a good representation of GWs in a GCM requires both a realistic launch distribution and an adequate representation of GW breaking and momentum transfer.  相似文献   

8.
A three-dimensional model is used to investigate the relations between parameters of atmospheric gravity waves (GW) and the spatial structure of O2 atmospheric (0,0) nightglow wave perturbations observed from space. It is shown that observed perturbations may be divided into the linear and nonlinear parts. The linear perturbations appear as wavelet signatures observed at certain viewing directions. The nonlinear part of the perturbations causes an increase in all sky brightness of the O2 atmospheric (0,0) nightglow. The model shows that at certain viewing directions the cancellation effect for waves passing through the emission layer disappears. The latter gives the opportunity to create the complete set of functions that may be used for the spectral decomposition of observed brightness field. The obtained spectrum may be interpreted in terms of the Fourier coefficients of 3D-decomposition of the temperature fluctuations induced by gravity waves just near the emission layer.  相似文献   

9.
The coupling of the neutral atmosphere and the ionosphere through planetary waves (PW) (zonal wavenumber 0–5) is investigated by spherical harmonic analyses of the ionospheric total electron content (TEC). These analyses detect mean variations, standing and travelling waves which are assumed to be signatures of PW. Database used for TEC analyses are 3 years of hourly TEC maps covering the higher middle and polar latitudes. They are regularly produced by DLR Neustrelitz. The obtained results are compared with PW analyses using NCEP/NCAR and Met Office stratospheric reanalyses. Case studies show that signatures of PW occur simultaneously in the middle atmosphere and ionosphere.  相似文献   

10.
We present the first observational proof that polar mesospheric cloud (PMC) brightness responds to stratospheric gravity waves (GWs) differently at different latitudes by analyzing the Fe Boltzmann lidar data collected from the South Pole and Rothera (67.5°S, 68.0°W), Antarctica. Stratospheric GW strength is characterized by the root-mean-square (RMS) relative density perturbation in the 30–45 km region and PMC brightness is represented by the total backscatter coefficient (TBC) in austral summer from November to February. The linear correlation coefficient (LCC) between GW strength and PMC brightness is found to be +0.09 with a 42% confidence level at the South Pole and ?0.49 with a 98% confidence level at Rothera. If a PMC case potentially affected by a space shuttle exhaust plume is removed from the Rothera dataset, the negative correlation coefficient and confidence level increase to ?0.61 and 99%, respectively. The Rothera negative correlation increases when shorter-period waves are included while no change is observed in the South Pole correlation. Therefore, observations show statistically that Rothera PMC brightness is negatively correlated with the stratospheric GW strength but no significant correlation exists at the South Pole. A positive correlation of +0.74 with a confidence level of 99.98% is found within a distinct subset of the South Pole data but the rest of the dataset exhibits a random distribution, possibly indicating different populations of ice particles at the South Pole. Our data show that these two locations have similar GW strength and spectrum in the 30–45 km region during summer. The different responses of PMC brightness to GW perturbations are likely caused by the latitudinal differences in background temperatures in the ice crystal growth region between the PMC altitude and the mesopause. At Rothera, where temperatures in this region are relatively warm and supersaturations are not as large, GW-induced temperature perturbations can drive subsaturation in the warm phase. Thus, GWs can destroy growing ice crystals or limit their growth, leading to negative correlation at Rothera. Because the South Pole temperatures in the mesopause region are much colder, GW-perturbed temperature may never be above the frost point and have less of an impact on crystal growth and PMC brightness. The observed phenomena and proposed mechanisms above need to be understood and verified through future modeling of GW effects on PMC microphysics and ray modeling of GW propagation over the South Pole and Rothera.  相似文献   

11.
By the end of 1981 the International Center of Earth Tides (ICET) had collected and evaluated a considerable amount of data from 180 stations, including those of the Trans-World Profile which ensure for the first time a world-wide distribution including the tropical areas and the southern hemisphere. In 1979–80, new oceanic cotidal maps of high quality, established by Schwiderski, became available. These maps fit “on-land” tidal-gravity measurements quite successfully. A new theoretical approach developed by Wahr in 1981 has resulted in a set of theoretical formulae establishing the latitude-dependence of the classical elastic amplitude factors for tidal deformations.We calculate here, for six tidal waves, the correlations between the observed gravity variations and those resulting from a calculation based upon the Schwiderski maps. These correlations are highly significant. After subtraction of these oceanic effects we calculate the latitude-dependences of the experimentally determined amplitude factors, which are found to fit Wahr's theoretical formulae. There remains, however, a serious discrepancy in the constant terms of the various formulae. The effects of heterogeneities in the lithosphere on tidal deformations are also clearly identified.  相似文献   

12.
Planetary waves in coupling the lower and upper atmosphere   总被引：1，自引：1，他引：1  
The purpose of the paper is to answer the question if planetary waves (PW) are capable of propagating into the thermosphere. First the simplest vertical structure equation of the classic tidal theory accounting for a realistic vertical temperature profile is considered. Analysis and simulation show that the well-known normal atmospheric modes (NM), which are trapped in the lower and middle atmosphere, exhibit a wave-like vertical structure with a large vertical wavelength in the thermosphere. Moreover, the reflection of these modes from the vertical temperature gradient in the lower thermosphere causes appearance of the wave-energy upward flux in the middle atmosphere, and in a linearized formulation this flux is constant above the source region. To investigate a possibility of the NM forcing by stratospheric vacillations and to consider the propagation of different PW up to the heights of the upper thermosphere, a set of runs with a mechanistic Middle and Upper Atmosphere Model has been performed. The results of the simulation show that quasi-stationary and longer-period PW are not able to penetrate into the thermosphere. The shorter-period NM and ultra-fast Kelvin wave propagate up to the heights of the lower thermosphere. However, above about 150 km they are strongly suppressed by dissipative processes. The role of the secondary waves (nonmigrating tides) arising from nonlinear interaction between the primary migrating tides and quasi-stationary PW is discussed. We conclude that PW are not capable of propagating directly up to the heights of the ionospheric F2 region. It is suggested that other physical processes (for instance, the electrostatic field perturbations) have to be taken into account to explain the observed PW-like structures in ionospheric parameters.  相似文献   

13.
使用中尺度数值模式WRF-ARW,针对2010年6月发生在中国东北地区一例伴随对流层高空西风急流（位于~9 km高度）演变过程出现的平流层重力波活动特征开展了数值模拟. 事件发生期间,对流层区域环流处在一个东北冷涡系统的控制之下. 模拟结果再现了该东北冷涡的发展和维持过程,以及与之相伴的高空急流的特征. 模拟结果揭示出在急流区域上空的平流层中存在显著重力波活动现象. 分析结果显示,重力波活动与急流存在紧密联系,在水平方向上,重力波呈显著的二维结构,出现在急流出口区上部并逆背景流向西传播. 功率谱分析结果表明盛行波动具有~700 km水平尺度、9~12 h时间尺度以及4~5 km垂直波长. 由于急流的存在,造成其与平流层中下部之间存在显著的水平风速垂直切变,与切变相伴的耗散使得上传的重力波动量通量数值随着高度升高而递减. 同时,在18~20 km高度间出现的西风-东风转换带极大地抑制了波动在垂直方向的传播,形成显著动量通量沉积效应. 估算结果表明,在11~20 km高度之间,这种效应的整体作用相当于对该层背景流施加强度为0.86 m·s-1·day-1的动力阻曳.  相似文献   

14.
Models of spreading ocean ridges are derived by Bayesian gravity inversion with geophysical and geodynamic a priori information. The aim is to investigate the influence of spreading rate, plate dynamics and tectonic framework on crust and upper mantle structure by comparing the Mid Atlantic Ridge (MAR), the Indian Ocean Ridge (IND) and the East Pacific Rise (PAC). They differ in mean spreading rate, dynamic settings, as attached slabs, and plume interaction. Topography or bathymetry, gravity, isostasy, seismology and geology, etc. are averaged along the ridges and guide the construction of initial 2D models, including features as mean plumes, i.e. averaged along the ridge. This is a gross simplification, and the results are considered preliminary.Three model types are tested: (a) the temperature anomaly; (b) asthenospheric rise into thickening lithosphere; (c) a crustal root as had been anticipated before seafloor spreading was discovered. Additional model components are a mean plume, a non-compensated ridge uplift, an under-compensated asthenospheric rise, e.g. of partially molten material, and seismic velocity models for P and S waves. Model type (c), tends to permute to model type (b) from thick crust to thin axial lithosphere. Model type (a) renders ‘realistic’ values of the thermal expansivity, but is insufficient to fit the gravity data; partial melt may disturb the simple temperature effect. A combination of (a) and (b) is most adequate. Exclusive seismic velocity models of S or P waves do not lead to acceptable densities nor to adequate gravity fitting. The different ridges exhibit significant differences in the best models: ATL and IND show an axial mass excess fostering enhanced ridge push, and ATL, in addition, suggests a mean plume input, while PAC shows an axial mass deficit reducing ridge push, most probably due to dominance of slab pull in the force balance.Goodness of the gravity fit alone is no justifiable criterion for goodness of model, indeed minor modifications to each model within the uncertainties of the assumptions can make the fit arbitrarily good. Goodness of model is quantified exclusively by a priori information.  相似文献   

15.
Based on the data from the GPS receiving networks in Japan and America which have a high time resolution (2 min), two-dimensional (2D) distributions of the variations in the ionospheric total electron content (TEC) are constructed both close to and far from of the epicenter of the submarine earthquake of March 11, 2011 in Japan. Above the epicenter, a diverging multi-period disturbance appears after the main shock due to the acoustic gravity waves. Far from the epicenter, the wave trains associated with the tsunamigenic atmospheric internal gravity waves are revealed. These atmospheric waves significantly advance the arrival of the tsunami signal initially on the Hawaiian islands and then on the western coast of North America. The presence of the tsunami precursor in the form of atmospheric gravity waves is supported by the numerical calculations and by the analysis of the dispersion relation for the waves in the atmosphere. The detected ionospheric responses close and far from the epicenter can be used in the early tsunami warning systems.  相似文献   

16.
On variable configuration in the horizontal direction, Winninghoff[1] had some discussions in the 1960s. Subsequently, according to the thoughts of Winning- hoff, Liu Yudi[2―9] has widely and deeply studied al- most all the existing horizontal grids from the fre- quency and group velocity of inertia gravity and Rossby waves. Results show that although Arakawa C grid is the best one among all existing horizontal grids, it also has some shortcomings. For example, there is still an “average…  相似文献   

17.
We study the modification of the frequency of small amplitude acoustic gravity waves which propagate in an isothermal turbulent atmosphere that is stratified by a homogeneous gravitational field. Using a Green's function method, the dispersion relation for the frequency of the waves is formulated as an integral eigenvalue equation and it is solved by perturbation techniques. We draw the following main conclusions: (a) for an arbitrary turbulent correlation spectrum the dispersion relation has a root with a negative imaginary part in the unphysical Riemann sheet of the dispersion function, leading to wave attenuation, much in the same way as it happens for Landau damping; (b) the real part of this root differs from the frequency of an acoustic gravity wave propagating in a nonturbulent medium and, for all forms of the turbulent correlation spectrum, the absolute value of this difference increases if gravity increases; (c) for a Gaussian turbulent correlation spectrum, this difference is always positive; (d) conversely if this frequency difference is known from observations, the auto-correlation function of the temperature fluctuations can be calculated through a simple inversion formula.  相似文献   

18.
It has become increasingly clear that Gravity Waves (GW) have an essential and often dominant role in the dynamics of the Middle Atmosphere. This leads to them having strong impacts upon the thermal structure and the distribution of atmospheric constituents. However, the radar observations of GW have been limited in their latitudinal extent during the past decade, and although satellite observations are now significantly contributing, global-seasonal climatologies of important characteristics are still inadequate. With regard to models, the inclusion of GW-drag effects has been problematic. Usually no seasonal or latitudinal variation in the subgrid-scale GW-drag parameterization scheme is included, and varieties of parameterization schemes have been used. Although these often make conflicting assumptions, they generally produce similarly acceptable end-products, e.g. zonal-mean zonal wind fields. In this paper, we report upon the beginnings of a substantial program, using observations from a network of MF radars (North America, Pacific and Europe), and data from the Canadian Middle Atmosphere Model (CMAM). This model allows the tidal and planetary wave fields to be assessed, characteristics and climatologies of which are well known from the MF Radars. Here we focus upon the tides. There are useful similarities in the observed and modeled background wind and wave fields, and strong indications that the two non-orographic GW-drag parameterization schemes (Hines; Medvedev–Klaassen) have significant and differing effects upon the dynamics of the modeled atmosphere. It is shown that this comparison process is valuable in the evaluation, and potentially the optimization, of parameterization schemes.  相似文献   

19.
Recent investigations of atmospheric gravity waves (AGW) and travelling ionospheric disturbances (TID) in the Earth’s thermosphere and ionosphere are reviewed. In the past decade, the generation of gravity waves at high latitudes and their subsequent propagation to low latitudes have been studied by several global model simulations and coordinated observation campaigns such as the Worldwide Atmospheric Gravity-wave Study (WAGS), the results are presented in the first part of the review. The second part describes the progress towards understanding the AGW/TID characteristics. It points to the AGW/TID relationship which has been recently revealed with the aid of model-data comparisons and by the application of new inversion techniques. We describe the morphology and climatology of gravity waves and their ionospheric manifestations, TIDs, from numerous new observations.  相似文献   

20.
利用日本GPS网探测2011年Tohoku海啸引发的电离层扰动   总被引：2，自引：1，他引：1       下载免费PDF全文
海平面的海啸波会产生大气重力波进而引发电离层扰动.本文利用日本GPS总电子含量数据来探测2011年3月11日Tohoku海啸引发的电离层扰动.观测结果表明,在日本上空的电离层中存在两种重力波信号,分别由海平面的海啸波以及地震破裂过程产生.地震产生的电离层重力波分布在震中周围（包括海洋上空以及远离海洋的区域）,而海啸引发的电离层重力波主要分布在海洋上空.地震产生的电离层重力波具有不同的水平速度,包括约210 m·s-1以及170 m·s-1,其频率为1.5 mHz;而海啸引发的电离层重力波水平速度快于前者,约为280 m·s-1,其频率为1.0 mHz.此外,海啸引发电离层重力波与海平面上的海啸波有相似的水平速度、方向、运行时间、波形以及频率等传播特征.本文的研究将电离层中的海啸信号与地震信号区分开来,进一步确认电离层对海啸波的敏感性.  相似文献   

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