Gravity wave propagation through a vertically and horizontally inhomogeneous background wind

Heale, C. J.; Snively, J. B.

doi:10.1002/2015jd023505

Cited by 42 publications

(56 citation statements)

References 73 publications

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“…The key physical process that shapes GW upward propagation is the mean wind distribution,

ū

(Heale & Snively, ; Yiğit et al, ). In this context, the earlier phases of a major warming mimic those of a minor warming; that is, the stratospheric westerlies are weakened and the temperature at the North Pole is gradually increasing.…”

Section: Discussionmentioning

confidence: 99%

Variation of Small‐Scale Gravity Wave Activity in the Ionosphere During the Major Sudden Stratospheric Warming Event of 2009

Nayak

Yiğit

2019

JGR Space Physics

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The present study investigates the effect of the major sudden stratospheric warming (SSW) event of 2009, on the small‐scale gravity wave (GW) activity in the ionosphere. Small‐scale fluctuations with time periods within the range of 10–90 min observed in Global Positioning System total electron content (TEC) data have been used as a proxy for GW activity in the ionosphere. TEC data from five longitudinally separated Global Positioning System stations located around 60∘N latitude have been utilized for this purpose. In the initial phase of the major warming, when the stratospheric conditions are similar to a minor warming during which the mean zonal flow starts to weaken, the ionopsheric GW activity tends to increase. However, during the peak phase of the SSW, as the zonal mean wind starts to reverse its direction, and after the peak warming, as the winds remain weak, conditions are less favorable for upward propagation of a spectrum of GWs, and thus the ionospheric GW activity is reduced, as seen from the behavior of the small‐scale TEC fluctuations during the latter period of the SSW. Similar reduction in GW activity is also observed in the middle atmosphere (65–100 km) as seen from GWs derived from SABER (Sounding of the Atmosphere using Broadband Emission Radiometry) temperature profiles. The reductions in GW activity is more prominent during local daytime as compared to nighttime period. The reduction in GW activity shows a longitudinal variation with some locations showing relatively more reduction in the GW activity as compared to others.

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“…The key physical process that shapes GW upward propagation is the mean wind distribution,

ū

Section: Discussionmentioning

confidence: 99%

Variation of Small‐Scale Gravity Wave Activity in the Ionosphere During the Major Sudden Stratospheric Warming Event of 2009

Nayak

Yiğit

2019

JGR Space Physics

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“…As shown in Figure b, the poleward wind at middle latitudes during the daytime is much stronger in the winter hemisphere (50–100 m s −1 ) than in the summer hemisphere (≤50 m s −1 ). Due to Doppler shift, the vertical group velocity and vertical wavelength of equatorward moving GWs become large under the poleward background wind (e.g., Fritts & Alexander, ; Heale & Snively, ). This indicates that the equatorward moving GWs under the poleward wind can easily propagate into the thermosphere.…”

Section: Discussionmentioning

confidence: 99%

Numerical Study of Traveling Ionospheric Disturbances Generated by an Upward Propagating Gravity Wave

et al. 2018

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Using a global atmosphere‐ionosphere coupled model, the characteristics and excitation source of traveling ionospheric disturbances (TIDs) during geomagnetically quiet periods are studied. This is the first paper concerning the simulation of TIDs generated by upward propagating gravity waves (GWs) that are spontaneously generated in the model. The dominant horizontal wavelengths of the simulated TIDs range from 700 to 1,500 km. The dominant periods and horizontal phase velocities of TIDs are 45–90 min and 250–300 m s−1, respectively. These features are the same as those of GWs in the 250–300 km height region. The phase of the electron density variations due to TIDs descends with increasing time, which is characteristic of the upward propagation of GWs. These electron density variations that are caused due to TIDs are explained by the transport processes of a neutral wind along a geomagnetic field line. These results indicate that the electron density variations respond locally to the passage of neutral wind fluctuations associated with upward propagating GWs. The GWs that excite TIDs are secondary GWs, which are generated in the mesosphere and lower thermosphere via the dissipation/breaking of tropospheric GWs. The magnitudes of TIDs at middle latitudes are larger in winter than in summer. The mechanisms of seasonal and day‐to‐day variations in TIDs that are caused due to GWs are discussed in this study.

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“…While critical levels are present from the perspective of linear theory, and the amplitude of the MS wave wind exceeds the SS wave phase speed, the model results reveal significant propagation exists at these levels, which are often considered as impenetrable boundaries for waves. This occurs for several reasons, they are as follows: (1) The SS wave is a packet with a nonmonochromatic spectrum, thus some portion of the packet can penetrate the critical levels (as they have larger phase speeds) (Heale & Snively, ). (2) The critical levels are transient and follow the phase progression of the MS wave; thus, the interaction time between the SS wave and the critical level is reduced (Eckermann, ; Sartelet, ; Senf & Achatz, ; Vanderhoff et al, ).…”

Section: Case 2: Linear Ss Propagation Through a Dynamic Ms Wavementioning

confidence: 99%

“…(2) The critical levels are transient and follow the phase progression of the MS wave; thus, the interaction time between the SS wave and the critical level is reduced (Eckermann, ; Sartelet, ; Senf & Achatz, ; Vanderhoff et al, ). (3) The evolution of the MS wind in time causes frequency variations in the SS wave that tend toward avoidance of filtering (Heale & Snively, ; Huang et al, ). Nevertheless, the finite‐amplitude MS wave deposits its momentum into the background flow, creating a Gaussian‐shaped mean flow and a permanent shear.…”

Section: Case 2: Linear Ss Propagation Through a Dynamic Ms Wavementioning

confidence: 99%

“…Numerical simulation and ray tracing have been used to study the interactions between waves of different scales in both the ocean and the atmosphere (e.g., Broutman & Young, ; Eckermann, ; Heale & Snively, ; Huang et al, ; Liu et al, ; Liu, Xu, Yue, et al, ; Sartelet, ; Senf & Achatz, ; Vanderhoff et al, ). These studies generally concluded that critical level filtering of waves propagating through a larger‐scale wave/ambient wind field can be reduced significantly when time dependence of that larger‐scale wave/ambient wind field is taken into account.…”

Section: Introductionmentioning

confidence: 99%

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A Comparison of Small‐ and Medium‐Scale Gravity Wave Interactions in the Linear and Nonlinear Limits

Heale

Snively

2018

JGR Atmospheres

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A 2‐D numerical model is used to compare interactions between small‐scale (SS) (25 km horizontal wavelength, 10 min period) and medium‐scale (MS, 250 km horizontal wavelength, 90 min period) gravity waves (GWs) in the Mesosphere and Lower Thermosphere within three different limits. First, the MS wave is specified as a static, horizontally homogeneous ambient atmospheric feature; second, a linear interaction is investigated between excited, time‐dependent SS and MS waves, and third, a fully nonlinear interaction at finite amplitudes is considered. It is found that the finite‐amplitude wave interactions can cause SS wave breaking aligned with the phase fronts of the MS waves, which induces a permanent mean flow and shear that is periodic in altitude. This impedes SS wave propagation into in the upper thermosphere and dissipation by molecular diffusion, when compared to linear amplitude simulations. Linear cases also omit self‐acceleration‐related instabilities of the SS wave and secondary wave generation, which modulate the MS wavefield. Neither the linear or nonlinear cases resemble the static approximation, which, by reducing a dynamic wave interaction to a static representation that is vertically varying, produces variable momentum flux distributions that depend strongly upon the amplitude and phase of the larger‐scale wave. This is an approximation made by GW parameterization schemes, and results suggest that including time‐dependent effects and feedback mechanisms for interactions between resolved and parameterized waves will be an important area for future investigations especially as general circulation models begin to resolve MS GWs explicitly.

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Gravity wave propagation through a vertically and horizontally inhomogeneous background wind

Cited by 42 publications

References 73 publications

Variation of Small‐Scale Gravity Wave Activity in the Ionosphere During the Major Sudden Stratospheric Warming Event of 2009

Variation of Small‐Scale Gravity Wave Activity in the Ionosphere During the Major Sudden Stratospheric Warming Event of 2009

Numerical Study of Traveling Ionospheric Disturbances Generated by an Upward Propagating Gravity Wave

A Comparison of Small‐ and Medium‐Scale Gravity Wave Interactions in the Linear and Nonlinear Limits

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