Winds in the mesosphere and lower thermosphere

1965 ◽  
Vol 288 (1415) ◽  
pp. 575-589 ◽  
Keyword(s):  
Gravity Waves ◽  
Cross Sections ◽  
General Circulation ◽  
Lower Thermosphere ◽  
Present Knowledge ◽  
Physical Factors ◽  
Height Range ◽  
General Sequence ◽  
Factors Affecting ◽  
Mesosphere And Lower Thermosphere

A review is given of present knowledge of air motions and physical factors affecting the general circulation in the mesosphere and lower thermosphere. Mean latitudinal cross sections of zonal wind at the equinoxes and solstices are given from pole to pole for the height range 30 to 120 km and used to derive corresponding mean temperatures by means of the thermal wind equation. It is now possible, using rocket data, to construct limited synoptic charts up to about 60 km over North America. The general sequence of synoptic changes in the 30 to 60 km layer throughout the year is described. Above about 80 km measured air m ovem ents reveal large tidal motions and gravity waves of greater magnitude than the winds and the manner in which these vary with altitude and the factors controlling them are discussed.

scholarly journals Mean-Flow Effects of Thermal Tides in the Mesosphere and Lower Thermosphere

2017 ◽  
Vol 74 (6) ◽  
pp. 2043-2063 ◽  
Author(s):  
Erich Becker
Keyword(s):  
Gravity Waves ◽  
General Circulation ◽  
Energy Deposition ◽  
Heat Budget ◽  
Frictional Heating ◽  
Lower Thermosphere ◽  
Mean Flow ◽  
Model Response ◽  
Mesosphere And Lower Thermosphere ◽  
Thermal Tides

Abstract This study addresses the heat budget of the mesosphere and lower thermosphere with regard to the energy deposition of upward-propagating waves. To this end, the energetics of gravity waves are recapitulated using an anelastic version of the primitive equations. This leads to an expression for the energy deposition of waves that is usually resolved in general circulation models. The energy deposition is shown to be mainly due to the frictional heating and, additionally, due to the negative buoyancy production of wave kinetic energy. The frictional heating includes contributions from horizontal and vertical momentum diffusion, as well as from ion drag. This formalism is applied to analyze results from a mechanistic middle-atmosphere general circulation model that includes energetically consistent parameterizations of diffusion, gravity waves, and ion drag. This paper estimates 1) the wave driving and energy deposition of thermal tides, 2) the model response to the excitation of thermal tides, and 3) the model response to the combined energy deposition by parameterized gravity waves and resolved waves. It is found that thermal tides give rise to a significant energy deposition in the lower thermosphere. The temperature response to thermal tides is positive. It maximizes at polar latitudes in the lower thermosphere as a result of poleward circulation branches that are driven by the predominantly westward Eliassen–Palm flux divergence of the tides. In addition, thermal tides give rise to a downward shift and reduction of the gravity wave drag in the upper mesosphere. Including the energy deposition in the model causes a substantial warming in the upper mesosphere and lower thermosphere.

The coupling of planetary waves, tides and gravity waves in the mesosphere and lower thermosphere

1999 ◽  
Vol 24 (11) ◽  
pp. 1571-1576 ◽  
Author(s):  
P.J.S. Williams ◽  
N.J. Mitchell ◽  
A.G. Beard ◽  
V.St.C. Howells ◽  
H.G. Muller
Keyword(s):  
Gravity Waves ◽  
Lower Thermosphere ◽  
Planetary Waves ◽  
Mesosphere And Lower Thermosphere

The Momentum Budget in the Stratosphere, Mesosphere, and Lower Thermosphere. Part II: The In Situ Generation of Gravity Waves

2018 ◽  
Vol 75 (10) ◽  
pp. 3635-3651 ◽  
Author(s):  
Ryosuke Yasui ◽  
Kaoru Sato ◽  
Yasunobu Miyoshi
Keyword(s):  
Gravity Wave ◽  
Gravity Waves ◽  
Lower Thermosphere ◽  
Shear Instability ◽  
Wave Forcing ◽  
Momentum Budget ◽  
Mesosphere And Lower Thermosphere ◽  
In Situ Generation ◽  
Mlt Region

The contributions of gravity waves to the momentum budget in the mesosphere and lower thermosphere (MLT) is examined using simulation data from the Ground-to-Topside Model of Atmosphere and Ionosphere for Aeronomy (GAIA) whole-atmosphere model. Regardless of the relatively coarse model resolution, gravity waves appear in the MLT region. The resolved gravity waves largely contribute to the MLT momentum budget. A pair of positive and negative Eliassen–Palm flux divergences of the resolved gravity waves are observed in the summer MLT region, suggesting that the resolved gravity waves are likely in situ generated in the MLT region. In the summer MLT region, the mean zonal winds have a strong vertical shear that is likely formed by parameterized gravity wave forcing. The Richardson number sometimes becomes less than a quarter in the strong-shear region, suggesting that the resolved gravity waves are generated by shear instability. In addition, shear instability occurs in the low (middle) latitudes of the summer (winter) MLT region and is associated with diurnal (semidiurnal) migrating tides. Resolved gravity waves are also radiated from these regions. In Part I of this paper, it was shown that Rossby waves in the MLT region are also radiated by the barotropic and/or baroclinic instability formed by parameterized gravity wave forcing. These results strongly suggest that the forcing by gravity waves originating from the lower atmosphere causes the barotropic/baroclinic and shear instabilities in the mesosphere that, respectively, generate Rossby and gravity waves and suggest that the in situ generation and dissipation of these waves play important roles in the momentum budget of the MLT region.

scholarly journals Climatologies and long-term changes in mesospheric wind and wave measurements based on radar observations at high and mid latitudes

2019 ◽  
Vol 37 (5) ◽  
pp. 851-875 ◽  
Author(s):  
Sven Wilhelm ◽  
Gunter Stober ◽  
Peter Brown
Keyword(s):  
Kinetic Energy ◽  
Gravity Waves ◽  
Lower Thermosphere ◽  
Atmospheric Parameters ◽  
Amplitude Response ◽  
Wave Measurements ◽  
Long Term Changes ◽  
The Mean ◽  
Mesosphere And Lower Thermosphere

Abstract. We report on long-term observations of atmospheric parameters in the mesosphere and lower thermosphere (MLT) made over the last 2 decades. Within this study, we show, based on meteor wind measurement, the long-term variability of winds, tides, and kinetic energy of planetary and gravity waves. These measurements were done between the years 2002 and 2018 for the high-latitude location of Andenes (69.3∘ N, 16∘ E) and the mid-latitude locations of Juliusruh (54.6∘ N, 13.4∘ E) and Tavistock (43.3∘ N, 80.8∘ W). While the climatologies for each location show a similar pattern, the locations differ strongly with respect to the altitude and season of several parameters. Our results show annual wind tendencies for Andenes which are toward the south and to the west, with changes of up to 3 m s−1 per decade, while the mid-latitude locations show smaller opposite tendencies to negligible changes. The diurnal tides show nearly no significant long-term changes, while changes for the semidiurnal tides differ regarding altitude. Andenes shows only during winter a tidal weakening above 90 km, while for the Canadian Meteor Orbit Radar (CMOR) an enhancement of the semidiurnal tides during the winter and a weakening during fall occur. Furthermore, the kinetic energy for planetary waves showed strong peak values during winters which also featured the occurrence of sudden stratospheric warming. The influence of the 11-year solar cycle on the winds and tides is presented. The amplitudes of the mean winds exhibit a significant amplitude response for the zonal component below 82 km during summer and from November to December between 84 and 95 km at Andenes and CMOR. The semidiurnal tides (SDTs) show a clear 11-year response at all locations, from October to November.

scholarly journals Vertical velocities associated with gravity waves measured in the mesosphere and lower thermosphere with the EISCAT VHF radar

1998 ◽  
Vol 16 (10) ◽  
pp. 1367-1379 ◽  
Author(s):  
N. J. Mitchell ◽  
V. St. C. Howells
Keyword(s):  
Gravity Waves ◽  
Vertical Velocity ◽  
Middle Atmosphere ◽  
Lower Thermosphere ◽  
Motion Field ◽  
Vhf Radar ◽  
Height Range ◽  
The Mean ◽  
Vertical Winds ◽  
Mean Variance

Abstract. The EISCAT VHF radar (69.4°N, 19.1°E) has been used to record vertical winds at mesopause heights on a total of 31 days between June 1990 and January 1993. The data reveal a motion field dominated by quasi-monochromatic gravity waves with representative apparent periods of ~30–40 min, amplitudes of up to ~2.5 m s–1 and large vertical wavelength. In some instances waves appear to be ducted. Vertical profiles of the vertical-velocity variance display a variety of forms, with little indication of systematic wave growth with height. Daily mean variance profiles evaluated for consecutive days of recording show that the general shape of the variance profiles persists over several days. The mean variance evaluated over a 10 km height range has values from 1.2 m2s–2 to 6.5 m2s–2 and suggests a semi-annual seasonal cycle with equinoctial minima and solsticial maxima. The mean vertical wavenumber spectrum evaluated at heights up to 86 km has a slope (spectral index) of –1.36 ± 0.2, consistent with observations at lower heights but disagreeing with the predictions of a number of saturation theories advanced to explain gravity-wave spectra. The spectral slopes evaluated for individual days have a range of values, and steeper slopes are observed in summer than in winter. The spectra also appear to be generally steeper on days with lower mean vertical-velocity variance.Key words. Meteorology and atmospheric dynamics (middle atmosphere dynamics; waves and tides)

scholarly journals The 8-h tide in the mesosphere and lower thermosphere over Maui (20.75° N, 156.43° W)

2009 ◽  
Vol 27 (5) ◽  
pp. 1989-1999 ◽  
Author(s):  
G. Jiang ◽  
J. Xu ◽  
S. J. Franke
Keyword(s):  
Lower Thermosphere ◽  
Time Interval ◽  
Data Set ◽  
Height Range ◽  
Meridional Component ◽  
Zonal Component ◽  
Spring Equinox ◽  
Semiannual Variation ◽  
Mesosphere And Lower Thermosphere ◽  
Seasonal Characteristic

Abstract. Wind data collected by the Maui meteor radar (20.75° N, 156.43° W) are used to study the 8-h tide in the mesosphere and lower thermosphere (MLT) region at a low-latitude station. The data set spans the time interval from 19 May 2002 to 24 May 2007. Our results show that the 8-h tide is a regular and distinct feature over Maui. The meridional component of this wave is significantly larger than the zonal component. The meridional component exhibits a semiannual variation in amplitude, with peaks near the equinoxes, whereas the variation of the zonal component does not show this seasonal characteristic. The strongest wave motions mostly occur in the height range of 92–96 km near spring equinox (March) and at higher altitudes near autumn equinox (October). The vertical variations of 8-h tidal phase at Maui indicate an upward wave energy flux. The vertical wavelengths are ≥54 km in equinox months.

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