It has been suggested (Lindzen, 1967, 1968a, b; Lindzen and Blake, 1971; Hodges, 1969) that turbulence in the upper mesosphere arises from the unstable breakdown of tides and gravity waves. Crudely speaking, it was expected that sufficient turbulence would be generated to prevent the growth of wave amplitude with height (roughly as (basic pressure)−1/2). This work has been extended to allow for the generation of turbulence by smaller amplitude waves, the effects of mean winds on the waves, and the effects of the waves on the mean momentum budget. The effects of mean winds, while of relatively small importance for tides, are crucial for internal gravity waves originating in the troposphere. Winds in the troposphere and stratosphere sharply limit the phase speeds of waves capable of reaching the upper mesosphere. In addition, the existence of critical levels in the mesosphere significantly limits the ability of gravity waves to generate turbulence, while the breakdown of gravity waves contributes to the development of critical levels. The results of the present study suggest that at middle latitudes in winter, eddy coefficients may peak at relatively low altitudes (50 km) and at higher altitudes in summer and during sudden warmings (70–80 km), and decrease with height rather sharply above these levels. Rocket observations are used to estimate momentum deposition by gravity waves. Accelerations of about 100 m/s/day are suggested. Such accelerations are entirely capable of producing the warm winter and cold summer mesopauses.

http://climateknowledge.org/figures/Rood_Climate_Change_AOSS480_Documents/QC114_Lindzen_Gravity_Wave_Stress_JGR_1981.pdf

Turbulence and stress owing to gravity wave and tidal breakdown

A comprehensive review of zonal flow phenomena in plasmas is presented. While the emphasis is on zonal flows in laboratory plasmas, planetary zonal flows are discussed as well. The review presents the status of theory, numerical simulation and experiments relevant to zonal flows. The emphasis is on developing an integrated understanding of the dynamics of drift wave–zonal flow turbulence by combining detailed studies of the generation of zonal flows by drift waves, the back-interaction of zonal flows on the drift waves, and the various feedback loops by which the system regulates and organizes itself. The implications of zonal flow phenomena for confinement in, and the phenomena of fusion devices are discussed. Special attention is given to the comparison of experiment with theory and to identifying directions for progress in future research.

/pdf/zonal-flows-in-plasma-a-review-3byloag115.pdf

Zonal flows in plasma—a review

Review and intercomparison of operational methods for the determination of the mixing height

This report has been prepared as part of an effort by IUCN to define its position on Nature-based Solutions (NbS) and plan for future work to advance this concept and support effective implementation of NbS to enhance ecosystem services provision and address societal challenges. The report proposes a definitional framework for NbS, including a set of general principles for any NbS intervention. The report also defines the scope of NbS as an umbrella concept embracing a number of different ecosystem-based approaches.

/pdf/nature-based-solutions-to-address-global-societal-challenges-1oepeqve5i.pdf

Nature-based solutions to address global societal challenges

A review of theoretical and observational results describing atmospheric gravity wave (AGW)/traveling ionospheric disturbance (TID) phenomena at high latitudes is presented. Some recent experimental studies of AGW's using the Chatanika incoherent scatter radar and other geophysical sensors are reported. Specifically, the following features are described in detail: (1) cause/effect relations between aurorally generated AGW's and TID's detected at mid-latitudes, including probable ‘source signature’ identification, (2) AGW source phenomenology, particularly a semiquantitative assessment of the relative importance of Joule heating, Lorentz forces, intense particle precipitation, and other mechanisms in generating AGW's, and (3) detection of TID's in the auroral ionosphere. Several instances of F region electron density, temperature, and plasma periodicities accompanied by horizontal plasma velocities which were consistent with theoretical AGW/TID models are documented.

Atmospheric gravity waves generated in the high‐latitude ionosphere: A review

Observations of a single boundary-layer event — the generation of an atmospheric gravity wave by an unstable shear flow at Haswell, Colorado on November 12, 1971 — are briefly described and discussed. The observations were made using: (a) an acoustic echo sounder, (b) anemometers mounted at two fixed levels on a 150-m tower, (c) an anemometer and a thermometer mounted on a movable carriage on the tower, and (d) a microbarograph array, including one microbarograph mounted atop the tower. The wave phase velocity (−3.5–4.0 m s−1) was found to equal the wind velocity in the middle of the shear flow, as assumed by other authors. The wave-associated vertical fluxes of momentum and energy measured just above the wave critical layer were estimated to be −5 dyn cm−2 and −800 erg cm−2 s−1, respectively. These are large values. The annual average vertical flux of momentum at temperate and high latitudes is −0.25 dyn cm−2, while the average kinetic energy dissipation rate in a unit column of atmosphere is −5 × 103 erg cm−2 s−1. If the region of wave generation was itself propagating horizontally, its propagation velocity was large compared with the horizontal phase speed of the small-scale waves generated. Wave generation appeared to occur over an area large compared with the size of the microbarograph array (i.e., ≫ 2 km).

Observed generation of an atmospheric gravity wave by shear instability in the mean flow of the planetary boundary layer

This paper is a brief summary of recent experimental studies conducted by the WPL staff in order to: (a) compare acoustic echo strengths with those predicted from measured turbulence intensities and scatter theory; (b) develop optimum experimental geometries for Doppler work, and (c) use the acoustic echo-sounder as a quantitative tool in studies of gravity wave dynamics in, and immediately above, the stable planetary boundary layer. We find that the observed acoustic echo strengths are roughly an order of magnitude greater than those predicted theoretically. This discrepancy might be in part due to partial reflection although the comparison is somewhat clouded by uncertainties in our knowledge of the equipment characteristics, propagation losses, etc. Comparisons between Doppler and in situ wind measurements give confidence in the Doppler results, but further experimentation and comparisons are needed. Preliminary use of acoustic Doppler data in a case study of gravity-wave dynamics in the planetary boundary layer has yielded boundary-layer wind speed and direction profiles which give insight into the mechanisms responsible for the wave generation. The Doppler data yield estimates of the wave associated momentum fluxes (∼a few dyn cm−2) as well. The results derived from the acoustic techniques are quite encouraging, but thus far remain unsubstantiated by independent wind and flux measurements.

Acoustic echo-sounding techniques and their application to gravity-wave, turbulence, and stability studies

The United Nations' International Decade for Natural Disaster Reduction has now concluded. The time has come to take stock. Decade framers set forth 3 targets for each nation: hazard identification and risk assessment; a mitigation strategy, couched in terms of plans for sustainable development; and improved warning and dissemination. By this measure, the U.S. experience was moderately successful. Public awareness of natural hazards is growing rapidly. Correspondingly, national policies toward natural disasters are shifting dramatically; aligning better with the nature of the problem as experts currently understand it. The 1990s saw natural hazards lose much of the element of surprise; today, natural extremes are forecast and their threats anticipated more successfully than ever before. However, despite this progress, losses in the U.S. due to natural disasters continued to rise sharply during the decade. More ominously, the nature and profile of disasters and their losses appear to be mutating in response to rapid societal change. Advances in our understanding of the geophysical, engineering, and societal causes of citizens are no safer they than were a decade ago. Local and regional economies are proving too vulnerable to disruption; even the national economy may be significantly affected under some scenarios. Major obstacles will continue to challenge U.S. efforts to reduce natural disasters in the decades ahead.

U.s. participation in international decade for natural disaster reduction

The response of the lower F region ionosphere to individual internal gravity waves is calculated as a function of the azimuth of wave propagation. This response is shown to be highly anisotropic, with the anisotropy itself depending on time of day, season, wave parameters, height, and geographic and geomagnetic location. Wave-associated changes in photoionization rate, and their dependence on the degree of alignment between the incoming solar radiation flux and surfaces of constant wave phase, play a dominant role in determining the anisotropy. Wave-associated changes in attachmentlike chemical loss are also important. The response of the lower F region ionosphere to internal gravity waves therefore differs fundamentally from the response at higher levels, where ion lifetimes are long and wave-associated photochemical effects can be ignored, so that geomagnetic constraints on ion motion play the primary role in determining the anisotropy.

Ionospheric response to internal gravity waves: 2. Lower F region response

Traveling ionospheric disturbances at magnetic equator, determining electron concentration profiles by incoherent scatter radar

William H. Hooke

Papers

Observed generation of an atmospheric gravity wave by shear instability in the mean flow of the planetary boundary layer

Acoustic echo-sounding techniques and their application to gravity-wave, turbulence, and stability studies

U.s. participation in international decade for natural disaster reduction

Ionospheric response to internal gravity waves: 2. Lower F region response

Traveling ionospheric disturbances observed at the magnetic equator