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Ning Wang - One of the best experts on this subject based on the ideXlab platform.
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stokes parameter analysis of a packet of turbulence generating Gravity Waves
Journal of Geophysical Research, 2005Co-Authors: Steven E. Koch, Ning WangAbstract:[1] Stokes parameter analysis for small-scale Gravity Waves was carried out from a set of aircraft observational data. The goal is to understand the polarization properties associated with Gravity Waves when turbulence is generated so that enough physical knowledge can be gained about the interaction between the two. A wavelet cross-spectrum technique is introduced into the traditional Stokes parameter analysis. From this analysis it is shown that small-scale Gravity Waves possess distinctive polarization signatures. Further extension of the Stokes parameter analysis by a wave-averaging method is also proposed. The analysis using this method indicates that the turbulence production is closely related to an enhanced level of polarization and coherency in the two components of the horizontal wind in the Gravity Waves and that the turbulence surge is accompanied by a tendency for an instantaneous reduction of polarization and abrupt shift of horizontal wave vector of the progenitor Gravity Waves. These findings may be useful in the prediction of the occurrence of turbulence in association with Gravity wave activities in the atmosphere.
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Stokes parameter analysis of a packet of turbulence‐generating Gravity Waves
Journal of Geophysical Research, 2005Co-Authors: Steven E. Koch, Ning WangAbstract:[1] Stokes parameter analysis for small-scale Gravity Waves was carried out from a set of aircraft observational data. The goal is to understand the polarization properties associated with Gravity Waves when turbulence is generated so that enough physical knowledge can be gained about the interaction between the two. A wavelet cross-spectrum technique is introduced into the traditional Stokes parameter analysis. From this analysis it is shown that small-scale Gravity Waves possess distinctive polarization signatures. Further extension of the Stokes parameter analysis by a wave-averaging method is also proposed. The analysis using this method indicates that the turbulence production is closely related to an enhanced level of polarization and coherency in the two components of the horizontal wind in the Gravity Waves and that the turbulence surge is accompanied by a tendency for an instantaneous reduction of polarization and abrupt shift of horizontal wave vector of the progenitor Gravity Waves. These findings may be useful in the prediction of the occurrence of turbulence in association with Gravity wave activities in the atmosphere.
Brian F Farrell - One of the best experts on this subject based on the ideXlab platform.
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on the role of potential vorticity perturbations in the spontaneous generation of Gravity Waves
2013Co-Authors: Nikolaos A Bakas, Brian F FarrellAbstract:Mechanisms of internal Gravity wave generation have been intensively studied because of the role of Gravity Waves in the large-scale atmospheric circulation. One source of Gravity Waves that is poorly understood is spontaneous wave generation by the low frequency mesoscale and large scale motions in the atmosphere. In this work, we study the interaction among potential vorticity perturbations and Gravity Waves in a stably stratified, horizontally sheared zonal flow, with the goal of clarifying the role of these interactions in the process of spontaneous wave generation. We find that vorticity perturbations amplify in energy due to downgradient Reynolds stress when their phase lines tilt towards the west with increasing latitude for a northward increasing shear flow. For a Froude number of order one, there is strong coupling between the vorticity perturbations and the Gravity wave manifold. As a result, the large growth attained by vorticity perturbations is transferred to propagating Gravity Waves. When the flow geometry permits wave propagation, significant Gravity wave emission occurs.
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Gravity Waves in a horizontal shear flow part ii interaction between Gravity Waves and potential vorticity perturbations
Journal of Physical Oceanography, 2009Co-Authors: Nikolaos A Bakas, Brian F FarrellAbstract:Interaction among potential vorticity perturbations and propagating internal Gravity Waves in a horizontally sheared zonal flow is investigated. In the strong stratification limit, an initial vorticity perturbation weakly excites two propagating Gravity Waves while the density component of the potential vorticity perturbation is significantly amplified, potentially leading to convective collapse. If stratification is sufficiently weak, a strong coupling between vorticity perturbations and Gravity Waves is found and spontaneous Gravity wave generation occurs. This coupling can be traced to the nonnormal interaction between the potential vorticity and Gravity wave manifolds in the weak stratification limit. Vorticity perturbations amplify in energy due to downgradient Reynolds stress when their phase lines tilt against the shear and the large growth attained is transferred to propagating Gravity Waves. When the flow geometry is such that the excited Gravity Waves are confined in the vicinity of the vorticity perturbation by their trapping levels, an overall convective collapse of this region can be anticipated. On the other hand, when the flow geometry permits wave propagation, significant Gravity wave emission occurs.
Steven E. Koch - One of the best experts on this subject based on the ideXlab platform.
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stokes parameter analysis of a packet of turbulence generating Gravity Waves
Journal of Geophysical Research, 2005Co-Authors: Steven E. Koch, Ning WangAbstract:[1] Stokes parameter analysis for small-scale Gravity Waves was carried out from a set of aircraft observational data. The goal is to understand the polarization properties associated with Gravity Waves when turbulence is generated so that enough physical knowledge can be gained about the interaction between the two. A wavelet cross-spectrum technique is introduced into the traditional Stokes parameter analysis. From this analysis it is shown that small-scale Gravity Waves possess distinctive polarization signatures. Further extension of the Stokes parameter analysis by a wave-averaging method is also proposed. The analysis using this method indicates that the turbulence production is closely related to an enhanced level of polarization and coherency in the two components of the horizontal wind in the Gravity Waves and that the turbulence surge is accompanied by a tendency for an instantaneous reduction of polarization and abrupt shift of horizontal wave vector of the progenitor Gravity Waves. These findings may be useful in the prediction of the occurrence of turbulence in association with Gravity wave activities in the atmosphere.
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Stokes parameter analysis of a packet of turbulence‐generating Gravity Waves
Journal of Geophysical Research, 2005Co-Authors: Steven E. Koch, Ning WangAbstract:[1] Stokes parameter analysis for small-scale Gravity Waves was carried out from a set of aircraft observational data. The goal is to understand the polarization properties associated with Gravity Waves when turbulence is generated so that enough physical knowledge can be gained about the interaction between the two. A wavelet cross-spectrum technique is introduced into the traditional Stokes parameter analysis. From this analysis it is shown that small-scale Gravity Waves possess distinctive polarization signatures. Further extension of the Stokes parameter analysis by a wave-averaging method is also proposed. The analysis using this method indicates that the turbulence production is closely related to an enhanced level of polarization and coherency in the two components of the horizontal wind in the Gravity Waves and that the turbulence surge is accompanied by a tendency for an instantaneous reduction of polarization and abrupt shift of horizontal wave vector of the progenitor Gravity Waves. These findings may be useful in the prediction of the occurrence of turbulence in association with Gravity wave activities in the atmosphere.
Fuqing Zhang - One of the best experts on this subject based on the ideXlab platform.
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tracking Gravity Waves in moist baroclinic jet front systems
Journal of Advances in Modeling Earth Systems, 2015Co-Authors: Fuqing ZhangAbstract:A series of four-dimensional ray-tracing experiments are performed to investigate the propagating wave characteristics, source mechanisms, and wave number vector refraction budget of six groups of lower-stratospheric Gravity Waves in the moist baroclinic jet-front systems with varying degree of convective instability. On one hand, the resemblance of ray trajectories and propagating characteristics between Gravity Waves in the dry experiment versus those in the experiment with weak diabatic heating demonstrates the limited role of moist convection in modifying those wave modes that are dominated by dry dynamics, including both the short-scale northward-propagating mode and the intermediate-scale northward-propagating mode in the jet exit region (likely induced by upper-level jet imbalance and/or tropospheric frontogenesis), the intermediate-scale eastward-propagating mode from the jet exit region in the ridge down to the jet entrance region in the trough (likely induced by upper-level jet imbalance), and the short-scale southward-propagating mode located far to the south of the jet right above the surface cold front (likely induced by tropospheric frontogenesis). On the other hand, comparisons of the Gravity Waves in the two aforementioned experiments through the ray tracing analysis further demonstrate that moist convection may force new wave modes, modify existing dry wave modes through latent heat release, or modify the new/existing Waves through modification of large-scale flow. Convectively generated Gravity Waves could propagate both upstream and downstream of the latent heating. Lastly, it is indicated in the budget analysis of wave number vector refraction equations that the wind effect on changing the characteristics of propagating Gravity Waves generally dominates over the thermodynamics effect, and that the thermodynamics effect may counteract, enhance, or even take over the effect of background wind for those wave packets crossing the tropopause or frontal systems.
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internal Gravity Waves from atmospheric jets and fronts
Reviews of Geophysics, 2014Co-Authors: Riwal Plougonven, Fuqing ZhangAbstract:For several decades, jets and fronts have been known from observations to be significant sources of internal Gravity Waves in the atmosphere. Motivations to investigate these Waves have included their impact on tropospheric convection, their contribution to local mixing and turbulence in the upper troposphere, their vertical propagation into the middle atmosphere, and the forcing of its global circulation. While many different studies have consistently highlighted jet exit regions as a favored locus for intense Gravity Waves, the mechanisms responsible for their emission had long remained elusive: one reason is the complexity of the environment in which the Waves appear; another reason is that the Waves constitute small deviations from the balanced dynamics of the flow generating them; i.e., they arise beyond our fundamental understanding of jets and fronts based on approximations that filter out Gravity Waves. Over the past two decades, the pressing need for improving parameterizations of nonorographic Gravity Waves in climate models that include a stratosphere has stimulated renewed investigations. The purpose of this review is to present current knowledge and understanding on Gravity Waves near jets and fronts from observations, theory, and modeling, and to discuss challenges for progress in coming years.
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mesoscale Gravity Waves in moist baroclinic jet front systems
Journal of the Atmospheric Sciences, 2014Co-Authors: Fuqing ZhangAbstract:AbstractA series of cloud-permitting simulations with the Weather Research and Forecast model (WRF) are performed to study the characteristics and source mechanisms of mesoscale Gravity Waves in moist baroclinic jet–front systems with varying degrees of convective instability. These idealized experiments are initialized with the same baroclinic jet but with different initial moisture content, which produce different life cycles of moist baroclinic Waves, to investigate the relative roles of moist processes and baroclinicity in the generation and propagation of mesoscale Gravity Waves. The dry experiment with no moisture or convection simulates Gravity Waves that are consistent with past modeling studies. An experiment with a small amount of moisture produces similar baroclinic life cycles to the dry experiment but with the introduction of weak convective instability. Subsequent initiation of convection, although weak, may considerably amplify the Gravity Waves that are propagating away from the upper-leve...
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tracking Gravity Waves in baroclinic jet front systems
Journal of the Atmospheric Sciences, 2008Co-Authors: Fuqing ZhangAbstract:Abstract Using a two-dimensional Fourier decomposition and a four-dimensional ray-tracing technique, the propagating characteristics and source mechanisms of mesoscale Gravity Waves simulated in idealized baroclinic jet-front systems are investigated. The Fourier decomposition successfully separates the simulated Gravity Waves from a complex background flow in the troposphere. Four groups of Gravity Waves in the lower stratosphere are identified from the spectral decomposition. One is a northward-propagating short-scale wave packet with horizontal wavelength of ∼150 km, and another is a northeastward-propagating medium-scale wave packet with horizontal wavelength of ∼350 km. Both of these are most pronounced in the exit region of the upper-tropospheric jet. A third group exists in the deep trough region above (and nearly perpendicular to) the jet, and a fourth group far to the south of the jet right above the surface cold front, both of which are short-scale Waves and have a horizontal wavelength of ∼100–...
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generation of mesoscale Gravity Waves in upper tropospheric jet front systems
Journal of the Atmospheric Sciences, 2004Co-Authors: Fuqing ZhangAbstract:Abstract Multiply nested mesoscale numerical simulations with horizontal resolution up to 3.3 km are performed to study the generation of mesoscale Gravity Waves during the life cycle of idealized baroclinic jet–front systems. Long-lived vertically propagating mesoscale Gravity Waves with horizontal wavelengths ∼100–200 km are simulated originating from the exit region of the upper-tropospheric jet streak, in a manner consistent with past observational studies. The residual of the nonlinear balance equation is found to be a useful index in diagnosing flow imbalance and predicting wave generation. The imbalance diagnosis and model simulations suggest that balance adjustment, as a generalization of geostrophic adjustment, is likely responsible for generating these mesoscale Gravity Waves. It is hypothesized that, through balance adjustment, the continuous generation of flow imbalance from the developing baroclinic wave will lead to the continuous radiation of Gravity Waves.
Anne Loevenbruck - One of the best experts on this subject based on the ideXlab platform.
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Ionospheric Gravity Waves detected offshore Hawaii after tsunamis
Geophysical Research Letters, 2010Co-Authors: Lucie Rolland, Giovanni Occhipinti, Philippe Lognonné, Anne LoevenbruckAbstract:On-board satellites techniques provide global coverage and could play an important role in the continuous oceanic survey to prevent the damage produced by powerful tsunamis. We report here new ionospheric observations related to three significant transpacific tsunami events triggered by the 2006 Kuril earthquake, the 2009 Samoa earthquake and the 2010 Chile earthquake. Total Electron Content (TEC) variations extracted from data recorded by a dense Global Positioning System (GPS) network based in Hawaii show ionospheric disturbances within the hours following the tsunami wave passage at sea-level. For each event, we observe ionospheric Gravity Waves propagating with velocity, direction and arrival time coherent with the tsunami. The tsunamigenic signature in the ionosphere is also compared to in-situ sea-level measurements. These observations provide new examples of the sensitivity of the ionosphere to tsunamigenic Gravity Waves and confirm that ionospheric monitoring by GPS can provide complementary information on tsunami propagation. Citation: Rolland, L. M., G. Occhipinti, P. Lognonne, and A. Loevenbruck (2010), Ionospheric Gravity Waves detected offshore Hawaii after tsunamis, Geophys. Res. Lett., 37, L17101, doi: 10.1029/2010GL044479.
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ionospheric Gravity Waves detected offshore hawaii after tsunamis
Geophysical Research Letters, 2010Co-Authors: Lucie Rolland, Giovanni Occhipinti, Philippe Lognonné, Anne LoevenbruckAbstract:[1] On-board satellites techniques provide global coverage and could play an important role in the continuous oceanic survey to prevent the damage produced by powerful tsunamis. We report here new ionospheric observations related to three significant transpacific tsunami events triggered by the 2006 Kuril earthquake, the 2009 Samoa earthquake and the 2010 Chile earthquake. Total Electron Content (TEC) variations extracted from data recorded by a dense Global Positioning System (GPS) network based in Hawaii show ionospheric disturbances within the hours following the tsunami wave passage at sea-level. For each event, we observe ionospheric Gravity Waves propagating with velocity, direction and arrival time coherent with the tsunami. The tsunamigenic signature in the ionosphere is also compared to in-situ sea-level measurements. These observations provide new examples of the sensitivity of the ionosphere to tsunamigenic Gravity Waves and confirm that ionospheric monitoring by GPS can provide complementary information on tsunami propagation.
