VHF radar measurements of small-scale and meso-scale dynamical processes in the middle atmosphere

1987 ◽  
Vol 323 (1575) ◽  
pp. 611-628 ◽  
Keyword(s):  
Gravity Waves ◽  
Middle Atmosphere ◽  
Electron Density Profile ◽  
Small Scale ◽  
Vhf Radar ◽  
Radar Echoes ◽  
Passive Tracers ◽  
Generation Mechanisms ◽  
Energy And Momentum ◽  
Meso Scale

The principle of VHF radar observations of the atmosphere is briefly summarized. Gravity-wave and turbulence sources, as seen by VHF radar, are described, followed by an outline of observations of upward-propagating gravity waves and the corresponding transport of energy and momentum. Frequency and wavenumber spectra are discussed in terms of a universal spectrum of waves and quasi-two-dimensional turbulence. The divergence of vertical flux of horizontal momentum, which indicates the interaction of waves with the mean wind, is considered. Saturation of gravity waves often occurs in the middle atmosphere where it can cause turbulence. This controls the vertical transport of passive tracers by means of turbulent diffusion. These phenomena are investigated by VHF radars, particularly in the mesosphere. The phenomenology of ‘turbulence echoes' from the mesosphere, influenced considerably by the electron density profile, is examined. The generation mechanisms of turbulence and its coexistence with stable stratifications are explored. The presented model offers an explanation of the different features of the observed radar echoes and provides a better understanding of the interaction of meso-scale and small-scale phenomena of waves and turbulence in the middle atmosphere. Finally, a summary of some remaining questions that could be solved by further collaborative efforts, including the application of radars, is given.

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 thermal and dynamical state of the atmosphere during polar mesosphere winter echoes

2005 ◽  
Vol 5 (4) ◽  
pp. 7613-7645
Author(s):  
F.-J. Lübken ◽  
B. Strelnikov ◽  
M. Rapp ◽  
W. Singer ◽  
R. Latteck ◽  
...  
Keyword(s):  
Absolute Magnitude ◽  
Quantitative Agreement ◽  
Solar Proton ◽  
Density Fluctuations ◽  
Small Scale ◽  
Vhf Radar ◽  
Model Calculations ◽  
Dynamical State ◽  
Air Turbulence ◽  
Radar Echoes

Abstract. In January 2005, a total of 18 rockets were launched from the Andøya Rocket Range in Northern Norway (69° N) into strong VHF radar echoes called 'Polar Mesosphere Winter Echoes' (PMWE). The echoes were observed in the lower and middle mesosphere during large solar proton fluxes. In general, PMWE are much more seldom compared to their summer counterparts PMSE (typical occurrence rates at 69° N are 1–3% vs. 80%, respectively). Our in-situ measurements by falling sphere, chaff, and instrumented payloads provide detailed information about the thermal and dynamical state of the atmosphere and therefore allow an unprecedented study of the background atmosphere during PMWE. There are a number of independent observations indicating that neutral air turbulence has caused PMWE. Ion density fluctuations show a turbulence spectrum within PMWE and no fluctuations outside. Temperature lapse rates close to the adiabatic gradient are observed in the vicinity of PMWE indicating persistent turbulent mixing. The spectral broadening of radar echoes is consistent with turbulent velocity fluctuations. Turbulence also explains the mean occurrence height of PMWE (~68–75 km): Viscosity increases rapidly with altitude and destroys any small scale fluctuations in the upper mesosphere, whereas electron densities are usually too low in the lower mesosphere to cause significant backscatter. The seasonal variation of echoes in the lower mesosphere is in agreement with a turbulence climatology derived from earlier sounding rocket flights. We have performed model calculations to study the absolute magnitude of backscatter from plasma fluctuations caused by neutral air turbulence. We find that volume reflectivities observed during PMWE are in quantitative agreement with theory. Apart from turbulence the most crucial requirement for PMWE is a sufficiently large number of electrons, for example produced by solar protons. We have studied the sensitivity of the radar echo strength on various parameters, most important electron number density and turbulence intensity. Our observational and theoretical considerations do not provide any evidence that charged aerosol particles are needed to explain PMWE, in contrast to the summer echoes which owe their existence to charged ice particles.

scholarly journals Transition from geostrophic flows to inertia-gravity waves in the spectrum of a differentially heated rotating annulus experiment.

2020 ◽  
Author(s):  
Costanza Rodda ◽  
Uwe Harlander
Keyword(s):  
Gravity Waves ◽  
Large Scale ◽  
Small Scale ◽  
Turbulent Regime ◽  
Weakly Nonlinear ◽  
Geostrophic Flows ◽  
Balanced Flow ◽  
Energy And Momentum ◽  
Open Question ◽  
Inertia Gravity Waves

<p>Inertia-gravity waves (IGWs) are known to play an essential role in the terrestrial atmospheric dynamics as they can lead to energy and momentum flux when they propagate upwards. An open question is to which extent nearly linear IGWs contribute to the total energy and to flattening of the energy spectrum observed at the mesoscale.<br>In this work, we present an experimental investigation of the energy distribution between the large-scale balanced flow and the small-scale imbalanced flow. Weakly nonlinear IGWs emitted from baroclinic jets are observed in the differentially heated rotating annulus experiment. Similar to the atmospheric spectra, the experimental kinetic energy spectra reveal the typical subdivision into two distinct regimes with slopes <em>k</em><sup>-3</sup> for the large scales and <em>k<sup>-</sup></em><sup>5/3</sup> for smaller scales. By separating the spectra into a vortex and wave part, it emerges that at the largest scales in the mesoscale range the gravity waves observed in the experiment cause a flattening of the spectra and provide most of the energy. At smaller scales, our data analysis suggests a transition towards a turbulent regime with a forward energy cascade up to where dissipation by diffusive processes occurs.</p>

scholarly journals Influence of tides and gravity waves on layering processes in the polar summer mesopause region

2008 ◽  
Vol 26 (12) ◽  
pp. 4013-4022 ◽  
Author(s):  
P. Hoffmann ◽  
M. Rapp ◽  
J. Fiedler ◽  
R. Latteck
Keyword(s):  
Gravity Waves ◽  
Lower Layer ◽  
Vhf Radar ◽  
Remarkable Feature ◽  
Ice Cloud ◽  
Radar Echoes ◽  
Layer Structures ◽  
Short Period ◽  
Summer Echoes ◽  
Polar Mesosphere Summer Echoes

Abstract. Polar Mesosphere Summer Echoes (PMSE) have been studied at Andenes (69° N, 16° E), Norway, using VHF radar observations since 1994. One remarkable feature of these observations is the fact that {during 50% of the time,} the radar echoes occur in the form of two or more distinct layers. In the case of multiple PMSE layers, statistical analysis shows that the lower layer occurs at a mean height of ~83.4 km, which is almost identical to the mean height of noctilucent clouds (NLC) derived from observation with the ALOMAR Rayleigh/Mie/Raman lidar at the same site. To investigate the layering processes microphysical model simulations under the influence of tidal and gravity waves were performed. In the presence of long period gravity waves, these model investigations predict an enhanced formation of multiple PMSE layer structures, where the lower layer is a consequence of the occurrence of the largest particles at the bottom of the ice cloud. This explains the coincidence of the lowermost PMSE layers and NLC. During periods with enhanced amplitudes of the semidiurnal tide, the observed NLC and PMSE show pronounced tidal structures comparable to the results of corresponding microphysical simulations. At periods with short period gravity waves there is a tendency for a decreasing occurrence of NLC and for variable weak PMSE structures.

scholarly journals Transition from Geostrophic Flows to Inertia–Gravity Waves in the Spectrum of a Differentially Heated Rotating Annulus Experiment

2020 ◽  
Vol 77 (8) ◽  
pp. 2793-2806
Author(s):  
Costanza Rodda ◽  
Uwe Harlander
Keyword(s):  
Gravity Waves ◽  
Large Scale ◽  
Small Scale ◽  
Turbulent Regime ◽  
Weakly Nonlinear ◽  
Geostrophic Flows ◽  
Balanced Flow ◽  
Energy And Momentum ◽  
Open Question ◽  
Inertia Gravity Waves

Abstract Inertia–gravity waves (IGWs) play an essential role in the terrestrial atmospheric dynamics as they can lead to energy and momentum flux when propagating upward. An open question is to what extent IGWs contribute to the total energy and to the flattening of the energy spectrum observed at the mesoscale. In this work, we present an experimental investigation of the energy distribution between the large-scale balanced flow and the small-scale imbalanced flow. Weakly nonlinear IGWs emitted from baroclinic jets are observed in the differentially heated rotating annulus experiment. Similar to the atmospheric spectra, the experimental kinetic energy spectra reveal the typical subdivision into two distinct regimes with slopes k−3 for the large scales and k−5/3 for the small scales. By separating the spectra into the vortex and wave components, it emerges that at the large-scale end of the mesoscale the gravity waves observed in the experiment cause a flattening of the spectra and provide most of the energy. At smaller scales, our data analysis suggests a transition toward a turbulent regime with a forward energy cascade up to where dissipation by diffusive processes occurs.

A study of the occurrence of dynamically unstable conditions in the middle atmosphere

1984 ◽  
Vol 62 (10) ◽  
pp. 963-967 ◽  
Author(s):  
Kevin Hamilton
Keyword(s):  
Gravity Waves ◽  
Wave Breaking ◽  
Middle Atmosphere ◽  
Internal Gravity Waves ◽  
Small Scale ◽  
Simple Analysis ◽  
Quantitative Estimates ◽  
Shear Instabilities ◽  
Vertically Propagating ◽  
The Tropics

There has recently been a great deal of interest in the possibility that vertically propagating internal gravity waves may be dissipated by small-scale convective or shear instabilities in the upper stratosphere and mesosphere. In the present study, a very simple analysis of about 3000 rocket soundings of temperature and wind at several stations between 8°N and 59°N was conducted in order to obtain quantitative estimates of the frequency of occurrence of dynamically unstable conditions as a function of height, latitude, and season. It was found that in about one-third of the profiles, the local Richardson number dropped below 0.25 at some level near the stratopause. From the results, it appears that gravity wave "breaking" generally occurs at considerably higher altitudes in the tropics than in midlatitudes. There is also a fairly clear indication of higher wave breaking levels in summer than in winter, at least at high latitudes.

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.

Equatorial oscillations in the middle atmosphere generated by small scale gravity waves

1995 ◽  
Vol 22 (22) ◽  
pp. 3027-3030 ◽  
Author(s):  
J. G. Mengel ◽  
H. G. Mayr ◽  
K. L. Chan ◽  
C. O. Hines ◽  
C. A. Reddy ◽  
...  
Keyword(s):  
Gravity Waves ◽  
Middle Atmosphere ◽  
Small Scale

scholarly journals Temperature sheets and aspect sensitive radar echoes

2001 ◽  
Vol 19 (8) ◽  
pp. 899-920 ◽  
Author(s):  
H. Luce ◽  
M. Crochet ◽  
F. Dalaudier
Keyword(s):  
High Resolution ◽  
Sheet Thickness ◽  
Internal Gravity Waves ◽  
Small Scale ◽  
Free Atmosphere ◽  
Vhf Radar ◽  
High Resolution Data ◽  
Anisotropic Turbulence ◽  
Radar Echoes ◽  
Very High

Abstract. here have been years of discussion and controversy about the existence of very thin and stable temperature sheets and their relationship to the VHF radar aspect sensitivity. It is only recently that very high-resolution in situ temperature observations have brought credence to the reality and ubiquity of these structures in the free atmosphere and to their contribution to radar echo enhancements along the vertical. Indeed, measurements with very high-resolution sensors are still extremely rare and rather difficult to obtain outside of the planetary boundary layer. They have only been carried out up to the lower stratosphere by Service d’A´ eronomie (CNRS, France) for about 10 years. The controversy also persisted due to the volume resolution of the (Mesosphere)-Stratosphere-Troposphere VHF radars which is coarse with respect to sheet thickness, although widely sufficient for meteorological or mesoscale investigations. The contribution within the range gate of many of these structures, which are advected by the wind, and decay and grow at different instants and could be distorted either by internal gravity waves or turbulence fields, could lead to radar echoes with statistical properties similar to those produced by anisotropic turbulence. Some questions thus remain regarding the manner in which temperature sheets contribute to VHF radar echoes. In particular, the zenithal and azimuthal angular dependence of the echo power may not only be produced by diffuse reflection on stable distorted or corrugated sheets, but also by extra contributions from anisotropic turbulence occurring in the stratified atmosphere. Thus, for several years, efforts have been put forth to improve the radar height resolution in order to better describe thin structures. Frequency interferometric techniques are widely used and have been recently further developed with the implementation of high-resolution data processings. We begin by reviewing briefly some characteristics of the ST radar echoes with a particular emphasis on recent works. Their possible coupling with stable sheets is then presented and their known characteristics are described with some hypotheses concerning their generation mechanisms. Finally, measurement campaigns that took recently place or will be carried out in the near future for improving our knowledge of these small-scale structures are presented briefly.Key words. Meteorology and atmospheric dynamics (turbulence; instruments and techniques) – Radio Science (remote sensing)

scholarly journals Diurnal Characteristics of Gravity Waves over the Tibetan Plateau in 2015 Summer Using 10-km Downscaled Simulations from WRF-EnKF Regional Reanalysis

Atmosphere ◽  
2020 ◽  
Vol 11 (6) ◽  
pp. 631
Author(s):  
Tingting Qian ◽  
Fuqing Zhang ◽  
Junhong Wei ◽  
Jie He ◽  
Yinghui Lu
Keyword(s):  
Tibetan Plateau ◽  
Gravity Waves ◽  
Power Spectra ◽  
Reanalysis Data ◽  
Small Scale ◽  
The Tibetan Plateau ◽  
Wave Source ◽  
Momentum Fluxes ◽  
Regional Reanalysis ◽  
Meso Scale

Diurnal variations of gravity waves over the Tibetan Plateau (TP) in summer 2015 were investigated based on high-resolution downscaled simulations from WRF-EnKF (Weather Research and Forecasting model and an ensemble Kalman filter) regional reanalysis data with particular emphasis on wave source, wave momentum fluxes and wave energies. Strong diurnal precipitations, which mainly happen along the south slope of the TP, tend to excite upward-propagating gravity waves. The spatial and temporal distributions of the momentum fluxes of small-scale (10–200 km) and meso-scale (200–500 km) gravity waves agree well with the diurnal precipitation distributions. The power spectra of momentum fluxes also show that the small- and meso-scale atmospheric processes become important during the period of the strongest rainfall. Eastward momentum fluxes and northward momentum fluxes are dominant. Wave energies are described in terms of kinetic energy (KE), potential energy (PE) and vertical fluctuation energy (VE). The diurnal variation and spatial distribution of VE in the lower stratosphere correspond to the diurnal rainfall in the troposphere.

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