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.

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 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 Characteristics of gravity waves generated in a convective and a non-convective environment revealed from hourly radiosonde observation under CPEA-II campaign

2011 ◽  
Vol 29 (12) ◽  
pp. 2259-2276 ◽  
Author(s):  
S. K. Dhaka ◽  
R. Bhatnagar ◽  
Y. Shibagaki ◽  
H. Hashiguchi ◽  
S. Fukao ◽  
...  
Keyword(s):  
Gravity Waves ◽  
Zonal Wind ◽  
Wind Shear ◽  
Radiosonde Data ◽  
Strong Wind ◽  
Mean Flow ◽  
Vertical Wavelength ◽  
Short Period ◽  
Radiosonde Observation ◽  
Wind Shears

Abstract. Analyses of hourly radiosonde data of temperature, wind, and relative humidity during four days (two with convection and two with no convection) as a part of an intensive observation period in CPEA-2 campaign over Koto Tabang (100.32° E, 0.20° S), Indonesia, are presented. Characteristics of gravity waves in terms of dominant wave frequencies at different heights and their vertical wavelengths are shown in the lower stratosphere during a convective and non-convective period. Gravity waves with periods ~10 h and ~4–5 h were found dominant near tropopause (a region of high stability) on all days of observation. Vertical propagation of gravity waves were seen modified near heights of the three identified strong wind shears (at ~16, 20, and 25 km heights) due to wave-mean flow interaction. Between 17 and 21 km heights, meridional wind fluctuations dominated over zonal wind, whereas from 22 to 30 km heights, wave fluctuations with periods ~3–5 h and ~8–10 h in zonal wind and temperature were highly associated, suggesting zonal orientation of wave propagation. Gravity waves from tropopause region to 30 km heights were analyzed. In general, vertical wavelength of 2–5 km dominated in all the mean-removed (~ weekly mean) wind and temperature hourly profiles. Computed vertical wavelength spectra are similar, in most of the cases, to the source spectra (1–16 km height) except that of zonal wind spectra, which is broad during active convection. Interestingly, during and after convection, gravity waves with short vertical wavelength (~2 km) and short period (~2–3 h) emerged, which were confined in the close vicinity of tropopause, and were not identified on non-convective days, suggesting convection to be the source for them. Some wave features near strong wind shear (at 25 km height) were also observed with short vertical wavelengths in both convective and non-convective days, suggesting wind shear to be the sole cause of generation and seemingly not associated with deep convection below. A drop in the temperature up to ~4–5 K (after removal of diurnal component) was observed at ~16 km height near a strong wind shear (~45–55 m s−1 km−1) during active period of convection.

Improved Middle Atmosphere Climate and Forecasts in the ECMWF Model through a Nonorographic Gravity Wave Drag Parameterization

2010 ◽  
Vol 23 (22) ◽  
pp. 5905-5926 ◽  
Author(s):  
Andrew Orr ◽  
Peter Bechtold ◽  
John Scinocca ◽  
Manfred Ern ◽  
Marta Janiskova
Keyword(s):  
Gravity Wave ◽  
Gravity Waves ◽  
Middle Atmosphere ◽  
Forecast Error ◽  
Wave Structure ◽  
Stationary Wave ◽  
Wave Drag ◽  
Horizontal Distribution ◽  
Small Scale ◽  
Temperature Structure

Abstract In model cycle 35r3 (Cy35r3) of the ECMWF Integrated Forecast System (IFS), the momentum deposition from small-scale nonorographic gravity waves is parameterized by the Scinocca scheme, which uses hydrostatic nonrotational wave dynamics to describe the vertical evolution of a broad, constant, and isotropic spectrum of gravity waves emanating from the troposphere. The Cy35r3 middle atmosphere climate shows the following: (i) an improved representation of the zonal-mean circulation and temperature structure; (ii) a realistic parameterized gravity wave drag; (iii) a reasonable stationary planetary wave structure and stationary wave driving in July and an underestimate of the generation of stationary wave activity in the troposphere and stationary wave driving in January; (iv) an improved representation of the tropical variability of the stratospheric circulation, although the westerly phase of the semiannual oscillation is missing; and (v) a realistic horizontal distribution of momentum flux in the stratosphere. By contrast, the middle atmosphere climate is much too close to radiative equilibrium when the Scinocca scheme is replaced by Rayleigh friction, which was the standard method of parameterizing the effects of nonorographic gravity waves in the IFS prior to Cy35r3. Finally, there is a reduction in Cy35r3 short-range high-resolution forecast error in the upper stratosphere.

scholarly journals Numerical Simulation of a Lee Wave Case over Three-Dimensional Mountainous Terrain under Strong Wind Condition

2013 ◽  
Vol 2013 ◽  
pp. 1-13 ◽  
Author(s):  
Lei Li ◽  
P. W. Chan ◽  
Lijie Zhang ◽  
Fei Hu
Keyword(s):  
Mesoscale Model ◽  
Three Dimensional ◽  
Wave Structure ◽  
Energy Utilization ◽  
Small Scale ◽  
Mountainous Terrain ◽  
Water Tank ◽  
Wind Condition ◽  
Strong Wind ◽  
Lee Wave

This study of a lee wave event over three-dimensional (3D) mountainous terrain in Lantau Island, Hong Kong, using a simulation combining mesoscale model and computational fluid dynamics (CFD) model has shown that (1) 3D steep mountainous terrain can trigger small scale lee waves under strong wind condition, and the horizontal extent of the wave structure is in a dimension of few kilometers and corresponds to the dimension of the horizontal cross-section of the mountain; (2) the life cycle of the lee wave is short, and the wave structures will continuously form roughly in the same location, then gradually move downstream, and dissipate over time; (3) the lee wave triggered by the mountainous terrain in this case can be categorized into “nonsymmetric vortex shedding” or “turbulent wake,” as defined before based on water tank experiments; (4) the magnitude of the wave is related to strength of wind shear. This study also shows that a simulation combining mesoscale model and CFD can capture complex wave structure in the boundary layer over realistic 3D steep terrain, and have a potential value for operational jobs on air traffic warning, wind energy utilization, and atmospheric environmental assessment.

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.

scholarly journals Characteristics of equatorial gravity waves derived from mesospheric airglow imaging observations

2009 ◽  
Vol 27 (4) ◽  
pp. 1625-1629 ◽  
Author(s):  
S. Suzuki ◽  
K. Shiokawa ◽  
A. Z. Liu ◽  
Y. Otsuka ◽  
T. Ogawa ◽  
...  
Keyword(s):  
Gravity Waves ◽  
Power Spectra ◽  
Small Scale ◽  
Two Dimensional ◽  
Quasi Biennial Oscillation ◽  
Mesopause Region ◽  
The Waves ◽  
Biennial Oscillation

Abstract. We present the characteristics of small-scale (<100 km) gravity waves in the equatorial mesopause region derived from OH airglow imaging observations at Kototabang (100.3° E, 0.2° S), Indonesia, from 2002 to 2005. We adopted a method that could automatically detect gravity waves in the airglow images using two-dimensional cross power spectra of gravity waves. The propagation directions of the waves were likely controlled by zonal filtering due to stratospheric mean winds that show a quasi-biennial oscillation (QBO) and the presence of many wave sources in the troposphere.

scholarly journals A remarkable correlation between short period gravity waves and semiannual oscillation of the zonal wind in the equatorial mesopause region

2012 ◽  
Vol 30 (4) ◽  
pp. 703-710 ◽  
Author(s):  
N. Venkateswara Rao ◽  
T. Tsuda ◽  
Y. Kawatani
Keyword(s):  
Gravity Waves ◽  
Horizontal Wind ◽  
Mesopause Region ◽  
Zonal Winds ◽  
Short Period ◽  
Velocity Variance ◽  
The Times ◽  
Semiannual Oscillation ◽  
Observation Period ◽  
Mf Radar

Abstract. The variability of zonal winds and the horizontal wind velocity variance of short period (20–120 min) gravity waves (GWs) in the equatorial mesopause region are studied using medium frequency (MF) radar observations from Pameungpeuk (7.4° S, 107.4° E) during 2004–2010. The zonal winds display a distinct semiannual oscillation (called mesospheric semiannual oscillation, MSAO), with westward winds during equinoxes and eastward winds during solstices. Furthermore, the westward winds during March equinox are larger during 2008 and 2009. The short period GW variance also shows a semiannual oscillation with enhanced activity during equinoxes. A good correlation is observed between the zonal winds and the short period GW variance from 2008–2010, with the winds being westward during the times of enhanced GW activity. Such a correlation, however, is less obvious during 2004–2006. The long period (10–20 h) GW variance, on the other hand, does not show such a correlation throughout the observation period.

Waves at the edge of space revealed by noctilucent cloud observations using camera and lidar

2021 ◽  
Author(s):  
Gerd Baumgarten ◽  
J. Federico Conte ◽  
Jens Fiedler ◽  
Michael Gerding ◽  
Franz-Josef Lübken
Keyword(s):  
Gravity Waves ◽  
Radiative Forcing ◽  
Transition To Turbulence ◽  
Small Scale ◽  
High Time Resolution ◽  
Noctilucent Cloud ◽  
Mesopause Region ◽  
Acoustic Gravity Waves ◽  
Global Circulation ◽  
Small Scale Structures

&lt;p&gt;Noctilucent clouds (NLC) exist at an altitude of about 83 km during the summer season at middle and polar latitudes. They consist of icy particles that exist in the polar summer mesopause region where the atmosphere is about 100 K colder than expected from pure radiative forcing. Dynamical effects, for example the dissipation of gravity waves, play an important role in the global circulation finally leading to the cold summer mesopause region. Ever since the first reports on the occurrence of NLC in 1885 the observers noticed distinct structures in the clouds that are most often wave-like. However at times the wave field becomes seemingly chaotic. &lt;br&gt;&lt;br&gt;State of the art lidar and camera observations of NLC allow studying small-scale structures of tens of meters in the vertical and horizontal direction. Given a high time resolution (about one second), the development of these structures is measured on temporal scales spanning the range from inertia gravity waves to acoustic gravity waves. We will show observations with the RMR-lidars at ALOMAR (Northern Norway at 69&amp;#176;N) and K&amp;#252;hlungsborn (54&amp;#176;N) as well as cameras located nearby these stations. Using these combined observations we study waves and their transition to turbulence.&lt;/p&gt;

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