scholarly journals Short-period mesospheric gravity waves and their sources at the South Pole

2017 ◽  
Vol 17 (2) ◽  
pp. 911-919 ◽  
Author(s):  
Dhvanit Mehta ◽  
Andrew J. Gerrard ◽  
Yusuke Ebihara ◽  
Allan T. Weatherwax ◽  
Louis J. Lanzerotti
Keyword(s):  
Gravity Waves ◽  
Baroclinic Instability ◽  
Significant Proportion ◽  
Polar Vortex ◽  
Small Scale ◽  
South Pole ◽  
Background Wind ◽  
Wind Fields ◽  
Short Period ◽  
Spatial And Temporal Characteristics

Abstract. The sourcing locations and mechanisms for short-period, upward-propagating gravity waves at high polar latitudes remain largely unknown. Using all-sky imager data from the Amundsen–Scott South Pole Station, we determine the spatial and temporal characteristics of 94 observed small-scale waves in 3 austral winter months in 2003 and 2004. These data, together with background atmospheres from synoptic and/or climatological empirical models, are used to model gravity wave propagation from the polar mesosphere to each wave's source using a ray-tracing model. Our results provide a compelling case that a significant proportion of the observed waves are launched in several discrete layers in the tropopause and/or stratosphere. Analyses of synoptic geopotentials and temperatures indicate that wave formation is a result of baroclinic instability processes in the stratosphere and the interaction of planetary waves with the background wind fields in the tropopause. These results are significant for defining the influences of the polar vortex on the production of these small-scale, upward-propagating gravity waves at the highest polar latitudes.

scholarly journals Mesospheric gravity waves and their sources at the South Pole

2016 ◽  
Author(s):  
Dhvanit Mehta ◽  
Andrew J. Gerrard ◽  
Yusuke Ebihara ◽  
Allan T. Weatherwax ◽  
Louis J. Lanzerotti
Keyword(s):  
Gravity Waves ◽  
Baroclinic Instability ◽  
Significant Proportion ◽  
Polar Vortex ◽  
Small Scale ◽  
South Pole ◽  
Wind Fields ◽  
Vertical Wavelength ◽  
Short Period ◽  
Spatial And Temporal Characteristics

Abstract. The sourcing locations and mechanisms for short period, long vertical wavelength upward-propagating gravity waves at high polar latitudes remain largely unknown. Using all-sky imager data from the Amundsen-Scott South Pole Station we determine the spatial and temporal characteristics of 94 observed small-scale waves in three austral winter months in 2003 and 2004. These data, together with background atmospheres from synoptic and/or climatological empirical models, are used to model gravity wave propagation from the polar mesosphere to each wave's source using a ray-tracing model. Our results provide a compelling case that a significant proportion of the observed waves are launched in several discrete layers in the tropopause and/or stratosphere. Analyses of synoptic geopotentials and temperatures indicate that wave formation is a result of baroclinic instability processes in the stratosphere and the interaction of planetary waves with the background wind fields in the tropopause. These results are significant for defining the influences of the polar vortex on the production of these small-scale, upward propagating gravity waves at the highest polar latitudes.

Atmospheric general circulation and waves simulated by a Venus AORI GCM with topographical and radiative forcings

2021 ◽  
Author(s):  
Masaru Yamamoto ◽  
Takumi Hirose ◽  
Kohei Ikeda ◽  
Masaaki Takahashi
Keyword(s):  
Gravity Waves ◽  
General Circulation ◽  
Circulation Model ◽  
Stationary Wave ◽  
Static Stability ◽  
Small Scale ◽  
Mean Flow ◽  
Short Period ◽  
Low Latitudes ◽  
Thermal Tides

<p>General circulation and waves are investigated using a T63 Venus general circulation model (GCM) with solar and thermal radiative transfer in the presence of high-resolution surface topography. This model has been developed by Ikeda (2011) at the Atmosphere and Ocean Research Institute (AORI), the University of Tokyo, and was used in Yamamoto et al. (2019, 2021). In the wind and static stability structures similar to the observed ones, the waves are investigated. Around the cloud-heating maximum (~65 km), the simulated thermal tides accelerate an equatorial superrotational flow with a speed of ~90 m/s<sup></sup>with rates of 0.2–0.5 m/s/(Earth day) via both horizontal and vertical momentum fluxes at low latitudes. Over the high mountains at low latitudes, the vertical wind variance at the cloud top is produced by topographically-fixed, short-period eddies, indicating penetrative plumes and gravity waves. In the solar-fixed coordinate system, the variances (i.e., the activity of waves other than thermal tides) of flow are relatively higher on the night-side than on the dayside at the cloud top. The local-time variation of the vertical eddy momentum flux is produced by both thermal tides and solar-related, small-scale gravity waves. Around the cloud bottom, the 9-day super-rotation of the zonal mean flow has a weak equatorial maximum and the 7.5-day Kelvin-like wave has an equatorial jet-like wind of 60-70 m/s. Because we discussed the thermal tide and topographically stationary wave in Yamamoto et al. (2021), we focus on the short-period eddies in the presentation.</p>

scholarly journals Synoptic Responses to Mountain Gravity Waves Encountering Directional Critical Levels

2007 ◽  
Vol 64 (3) ◽  
pp. 828-848 ◽  
Author(s):  
Armel Martin ◽  
François Lott
Keyword(s):  
Gravity Waves ◽  
General Circulation ◽  
Large Scale ◽  
Baroclinic Instability ◽  
General Circulation Models ◽  
Small Scale ◽  
Mountain Range ◽  
Critical Levels ◽  
Sensitivity Tests ◽  
Large Scale Flow

Abstract A heuristic model is used to study the synoptic response to mountain gravity waves (GWs) absorbed at directional critical levels. The model is a semigeostrophic version of the Eady model for baroclinic instability adapted by Smith to study lee cyclogenesis. The GWs exert a force on the large-scale flow where they encounter directional critical levels. This force is taken into account in the model herein and produces potential vorticity (PV) anomalies in the midtroposphere. First, the authors consider the case of an idealized mountain range such that the orographic variance is well separated between small- and large-scale contributions. In the absence of tropopause, the PV produced by the GW force has a surface impact that is significant compared to the surface response due to the large scales. For a cold front, the GW force produces a trough over the mountain and a larger-amplitude ridge immediately downstream. It opposes somehow to the response due to the large scales of the mountain range, which is anticyclonic aloft and cyclonic downstream. For a warm front, the GW force produces a ridge over the mountain and a trough downstream; hence it reinforces the response due to the large scales. Second, the robustness of the previous results is verified by a series of sensitivity tests. The authors change the specifications of the mountain range and of the background flow. They also repeat some experiments by including baroclinic instabilities, or by using the quasigeostrophic approximation. Finally, they consider the case of a small-scale orographic spectrum representative of the Alps. The significance of the results is discussed in the context of GW parameterization in the general circulation models. The results may also help to interpret the complex PV structures occurring when mountain gravity waves break in a baroclinic environment.

scholarly journals Studies on atmospheric gravity wave activity in the troposphere and lower stratosphere over a tropical station at Gadanki

2005 ◽  
Vol 23 (10) ◽  
pp. 3237-3260 ◽  
Author(s):  
I. V. Subba Reddy ◽  
D. Narayana Rao ◽  
A. Narendra Babu ◽  
M. Venkat Ratnam ◽  
P. Kishore ◽  
...  
Keyword(s):  
Gravity Wave ◽  
Gravity Waves ◽  
Lower Stratosphere ◽  
Wave Length ◽  
Wave Activity ◽  
Lower Atmosphere ◽  
Wind Fields ◽  
Atmospheric Gravity Wave ◽  
Short Period ◽  
Atmospheric Gravity

Abstract. MST radars are powerful tools to study the mesosphere, stratosphere and troposphere and have made considerable contributions to the studies of the dynamics of the upper, middle and lower atmosphere. Atmospheric gravity waves play a significant role in controlling middle and upper atmospheric dynamics. To date, frontal systems, convection, wind shear and topography have been thought to be the sources of gravity waves in the troposphere. All these studies pointed out that it is very essential to understand the generation, propagation and climatology of gravity waves. In this regard, several campaigns using Indian MST Radar observations have been carried out to explore the gravity wave activity over Gadanki in the troposphere and the lower stratosphere. The signatures of the gravity waves in the wind fields have been studied in four seasons viz., summer, monsoon, post-monsoon and winter. The large wind fluctuations were more prominent above 10 km during the summer and monsoon seasons. The wave periods are ranging from 10 min-175 min. The power spectral densities of gravity waves are found to be maximum in the stratospheric region. The vertical wavelength and the propagation direction of gravity waves were determined using hodograph analysis. The results show both down ward and upward propagating waves with a maximum vertical wave length of 3.3 km. The gravity wave associated momentum fluxes show that long period gravity waves carry more momentum flux than the short period waves and this is presented.

Inertia–gravity waves in a liquid-filled, differentially heated, rotating annulus

2015 ◽  
Vol 782 ◽  
pp. 144-177 ◽  
Author(s):  
Anthony Randriamampianina ◽  
Emilia Crespo del Arco
Keyword(s):  
Prandtl Number ◽  
Gravity Waves ◽  
Large Scale ◽  
Baroclinic Instability ◽  
Zonal Flow ◽  
Small Scale ◽  
Mean Flow ◽  
Baroclinic Waves ◽  
Fluid Properties ◽  
Spatio Temporal

Direct numerical simulations based on high-resolution pseudospectral methods are carried out for detailed investigation into the instabilities arising in a differentially heated, rotating annulus, the baroclinic cavity. Following previous works using air (Randriamampianina et al., J. Fluid Mech., vol. 561, 2006, pp. 359–389), a liquid defined by Prandtl number $Pr=16$ is considered in order to better understand, via the Prandtl number, the effects of fluid properties on the onset of gravity waves. The computations are particularly aimed at identifying and characterizing the spontaneously emitted small-scale fluctuations occurring simultaneously with the baroclinic waves. These features have been observed as soon as the baroclinic instability sets in. A three-term decomposition is introduced to isolate the fluctuation field from the large-scale baroclinic waves and the time-averaged mean flow. Even though these fluctuations are found to propagate as packets, they remain attached to the background baroclinic waves, locally triggering spatio-temporal chaos, a behaviour not observed with the air-filled cavity. The properties of these features are analysed and discussed in the context of linear theory. Based on the Richardson number criterion, the characteristics of the generation mechanism are consistent with a localized instability of the shear zonal flow, invoking resonant over-reflection.

scholarly journals Stratospheric Gravity Waves Generated by Typhoon Saomai (2006): Numerical Modeling in a Moving Frame Following the Typhoon

2010 ◽  
Vol 67 (11) ◽  
pp. 3617-3636 ◽  
Author(s):  
So-Young Kim ◽  
Hye-Yeong Chun
Keyword(s):  
Gravity Waves ◽  
Momentum Flux ◽  
Mesoscale Model ◽  
Horizontal Resolution ◽  
Moving Frame ◽  
Mature Stage ◽  
Small Scale ◽  
Background Wind ◽  
Spiral Bands ◽  
Typhoon Saomai

Abstract Stratospheric gravity waves generated by Typhoon Saomai (2006) were simulated using a mesoscale model in a moving frame of reference following the typhoon. Waves with large amplitudes appear near the domain center because of strong convection in the eyewall of the typhoon. Convection bands propagating outward from the storm center also generate waves propagating to the stratosphere. Convective forcing is significant in various propagation directions, with maximum power in slowly moving eastward components due to convection in the eyewall. The forcing exhibits large amplitude at a speed of 8–16 m s−1 in the eastward direction in which spiral bands are mainly developed. Induced gravity waves in the stratosphere are dominant in the eastward, northeastward, and southeastward propagation directions, since westward waves are mostly filtered by the background wind below z = 25 km. While the typhoon moves northwestward for 78 h, the wave characteristics vary through time depending on the evolution of the eyewall and spiral bands. Horizontal wavelengths of waves are longer in the mature and decaying stages than in the developing stage of the typhoon, likely because of a more dominant concentric eyewall in the mature and decaying stages. The spectral peak of the waves is at ∼20 km (∼50 km) horizontal wavelength in the developing (mature) stage, and the wave amplitudes are larger in the developing stages. The dominant contribution to the momentum flux is from waves with horizontal wavelengths longer than 80 km. Positive momentum flux decreases with overall height and the resultant positive drag can cause deceleration of northeasterly background wind. Sensitivity of the model results to horizontal resolution reveals that small-scale waves resolved in the present simulations with 3-km resolution cannot be fully represented with 9- or 27-km resolutions.

scholarly journals Wind-profiler observations of gravity waves produced by convection at mid-latitudes

2006 ◽  
Vol 6 (10) ◽  
pp. 2825-2836 ◽  
Author(s):  
Y. G. Choi ◽  
S. C. Lee ◽  
A. J. McDonald ◽  
D. A. Hooper
Keyword(s):  
Gravity Waves ◽  
Vertical Velocity ◽  
Small Scale ◽  
Wind Profiler ◽  
Convective Activity ◽  
Velocity Fluctuations ◽  
Short Period ◽  
Horizontal Momentum ◽  
Scale Inhomogeneity

Abstract. This work presents a case study which includes regions of large rapidly varying vertical velocities observed by a VHF wind-profiler at Aberystwyth (52.4° N, 4.1° W). Analysis indicates that this region is associated with gravity waves above the tropopause level and simultaneous regions of convective activity below the tropopause level. This case study also suggests that convective activity can be identified effectively by finding periods of large uncertainties on the derived velocities. These regions are hypothesized to be related to regions of small-scale inhomogeneity in the wind field. Examination suggests that the large vertical velocity fluctuations above these convective regions are short period gravity wave packets as expected from theory. In addition the vertical flux of the horizontal momentum associated with the gravity waves also displays the pattern of reversal observed in previous studies.

scholarly journals Observations of in-situ generated gravity waves during a stratospheric temperature enhancement (STE) event

2011 ◽  
Vol 11 (22) ◽  
pp. 11913-11917 ◽  
Author(s):  
A. J. Gerrard ◽  
Y. Bhattacharya ◽  
J. P. Thayer
Keyword(s):  
Gravity Waves ◽  
Background Wind ◽  
Wind Fields ◽  
Vertical Wavelength ◽  
Stratospheric Temperature ◽  
Wave Parameters ◽  
Phase Progression ◽  
Temperature Enhancement ◽  
Atmospheric Gravity

Abstract. Evidence for in situ generated atmospheric gravity waves associated with a stratospheric temperature enhancement (STE) are presented. The signatures of two sets of gravity waves are observed by molecular-aerosol lidar in conjunction with the early December 2000 STE event above Sondrestrom, Greenland. The first set of gravity waves shows downward phase progression with a vertical wavelength of ~8 km while the second set shows upward phase progression with a vertical wavelength of ~9 km. With estimates of the background wind fields from synoptic analyses, the various intrinsic gravity wave parameters of these two wave structures are found. The observed wave features compare well to previous numerical modeling predictions.

scholarly journals Analysis and modeling of ducted and evanescent gravity waves observed in the Hawaiian airglow

2009 ◽  
Vol 27 (8) ◽  
pp. 3213-3224 ◽  
Author(s):  
D. B. Simkhada ◽  
J. B. Snively ◽  
M. J. Taylor ◽  
S. J. Franke
Keyword(s):  
Gravity Waves ◽  
Wave Structure ◽  
Small Scale ◽  
Wind Flow ◽  
Strong Wind ◽  
Mesopause Region ◽  
Opposite Case ◽  
Local Propagation ◽  
First Case ◽  
Short Period

Abstract. Short-period gravity waves of especially-small horizontal scale have been observed in the Maui, Hawaii airglow. Typical small-scale gravity wave events have been investigated, and intrinsic wave propagation characteristics have been calculated from simultaneous meteor radar wind measurements. Here we report specific cases where wave structure is significantly determined by the local wind structure, and where wave characteristics are consistent with ducted or evanescent waves throughout the mesopause region. Two of the documented events, exhibiting similar airglow signatures but dramatically different propagation conditions, are selected for simple numerical modeling case studies. First, a Doppler-ducted wave trapped within relatively weak wind flow is examined. Model results confirm that the wave is propagating in the 85–95 km region, trapped weakly by evanescence above and below. Second, an evanescent wave in strong wind flow is examined. Model results suggest an opposite case from the first case study, where the wave is instead trapped above or below the mesopause region, with strong evanescence arising in the 85–95 km airglow region. Distinct differences between the characteristics of these visibly-similar wave events demonstrate the need for simultaneous observations of mesopause winds to properly assess local propagation conditions.

scholarly journals Modeling study of mesospheric planetary waves: genesis and characteristics

2004 ◽  
Vol 22 (6) ◽  
pp. 1885-1902 ◽  
Author(s):  
H. G. Mayr ◽  
J. G. Mengel ◽  
E. R. Talaat ◽  
H. S. Porter ◽  
K. L. Chan
Keyword(s):  
Heat Source ◽  
Gravity Waves ◽  
Zonal Flow ◽  
Planetary Waves ◽  
Wave Number ◽  
Horizontal Wind ◽  
Small Scale ◽  
Wind Fields ◽  
Zonal Jets ◽  
Nonmigrating Tides

Abstract. The Numerical Spectral Model (NSM) extends from the ground into the thermosphere and incorporates Hines' Doppler Spread Parameterization for small-scale gravity waves (GWs). In the present version of the model we account for a tropospheric heat source in the zonal mean (m=0), which reproduces qualitatively the observed zonal jets near the tropopause and the accompanying reversal in the latitudinal temperature variations. In the study presented here, we discuss the planetary waves (PWs) that are solely generated internally, i.e. without the explicit excitation sources related to tropospheric convection or topography. Our analysis shows that PWs are not produced when the zonally averaged heat source into the atmosphere is artificially suppressed, and that the PWs are generally weaker when the tropospheric source is not applied. Instabilities associated with the zonal mean temperature, pressure and wind fields, which still need to be explored, are exciting PWs that have amplitudes in the mesosphere comparable to those observed. Three classes of PWs are generated in the NSM. (1) Rossby type PWs, which slowly propagate westward relative to the mean zonal flow, are carried by the winds so that they appear (from the ground) to propagate, respectively, eastward and westward in the winter and summer hemispheres below 80km. Depending on the zonal wave number and magnitudes of the zonal winds, and under the influence of the equatorial oscillations, these PWs typically have periods between 2 and 20 days. Their horizontal wind amplitudes can exceed 40 m/s in the lower mesosphere. (2) Rossby-gravity waves, which propagate westward at low latitudes and have periods around 2 days for zonal wave numbers m=2 to 4. (3) Eastward propagating equatorial Kelvin waves, which are generated in the upper mesosphere with periods between 1 and 3 days depending on m. A survey of the PWs reveals that the largest wind amplitudes tend to occur below 80km in the winter hemisphere; but above that altitude the amplitudes are larger in the summer hemisphere where the winds can approach 50m/s. This pattern in the seasonal variations also appears in the baroclinity of the zonal mean (m=0). The nonmigrating tides in the mesosphere are significantly larger for the model with the tropospheric heat source, in which PWs are apparently generated by the instabilities that arise around the tropopause.

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