Colin O. Hines

Nonlinearity of gravity wave saturated spectra in the middle atmosphere

An argument based on general principles and minimal development is presented to establish the role of nonlinearity in producing the observed saturation of gravity-wave spectra in the middle atmosphere. The complementary role of instability of the nonlinear spectrum is discussed. Earlier models of nonlinear saturation are reviewed in the context thus provided.

Initial Doppler Rayleigh lidar results from Arecibo

The first results of the operation of a Rayleigh lidar from the Arecibo Observatory are presented. The device consists of an injection seeded, frequency doubled, Nd:YAG laser coupled with a single etalon, Fabry-Perot interferometer in the receiver, the combination of which permits Doppler observations of the backscattered spectral emission from the mesosphere. The measured winds from the initial experiments show a great deal of variability on time scales that appear to be less than the hour that it takes to measure a wind profile with the present system

Pseudosaturation of gravity waves in the middle atmosphere: an interpretation of certain lidar observations

Abstract Irregular winds of the middle atmosphere, commonly attributed to gravity waves, often exhibit a vertical-wavenumber ( m ) spectral form approximating to Km −3 at sufficiently large m , with K a constant found to be relatively unvarying with time, location and even height. This behavior is widely believed to result from some saturation process, but the physical mechanism remains a matter for debate. There now exist three theories: 1. (a) linear instability, 2. (b) nonlinear wave-induced diffusion, and 3. (c) nonlinear waveinduced Doppler spreading. Each has produced the Km −3 form (but only as an approximation in the case of Doppler spreading) and values of K within a factor of three of one another and of observed values. New data have revealed circumstances in which an approximation to the form Km −3 is again found, suggestive of saturation, but with values of K that increase by a factor of 5 or 10 on moving from the stratopause to the mesopause region. This height variation is incompatible with theories (a) and (b) if the m −3 form is taken to be induced by the corresponding saturation process (rather than by source spectra), but is shown here to be compatible with the Doppler-spread theory. Because of the continued growth of K with height, which must ultimately cease, the observations and corresponding theory are taken to represent pseudosaturation rather than fully developed saturation per se .

Layer truncation and the Eulerian/Lagrangian duality in the theory of airglow fluctuations induced by gravity waves

Abstract The theory of airglow fluctuations observed from the ground is often advanced by numerical integration of certain parameter combinations through the depth of a model emitting layer. Practical requirements oblige the layer to be truncated above, if not also below, the heights of greatest emission intensity. If the analysis is of an Eulerian type, this truncation requires that edge effects be taken into account if the results are to represent the true situation properly, but no such correction is normally required if the analysis is of a Lagrangian type. The nature of the correction is discussed both for thin layers and for thick layers, and the distinction between the Eulerian and Lagrangian approaches is clarified. The theory for limb-viewing measurements made from spacecraft is somewhat different and is touched upon briefly.

A fundamental theorem of airglow fluctuations induced by gravity waves

Abstract Airglow fluctuations induced by gravity waves and observed from the ground are free from any direct dependence on the scale heights (as distinct from the height profiles) of all minor species involved in the photochemistry of the emission process, under a wide range of circumstances that have been assumed in all theoretical developments to date. The truth of this fundamental theorem is established here, and the limits on it are set out. Contrary conclusions that have been reached by others in earlier publications are shown to be consequences of fallacious mathematical procedures. The theorem is of value not only to an understanding of the fundamentals of the subject, but also as a check on numerical models.

Mesospheric VHF echoing layers: an interpretation of certain observations in terms of wave scavenging

Abstract Excellent observations, obtained with the MU radar in Japan, have exhibited the existence on one occasion of three layers of enhanced VHF echoing from the mesosphere in association with a nearly monochromatic gravity-wave wind profile there. The heights of the layers did not correlate with levels of minimum Richardson number induced by the wave, however, and so an interpretation in terms of wave instability was initially rejected. Here it is shown that smaller-scale waves, unresolved by the radar, would be expected to have been approaching critical layers, and so to have been rendered unstable, at just those heights from which the strongest echoes were obtained. The same mechanism—the scavenging of wave energy for the production of turbulence—is likely to be operative on other occasions and at other heights.

Latitudinal variation of tidal dissipation and upward propagation

Abstract In classical, non-dissipative atmospheric tidal theory, vertical and latitudinal variations of dependent variables are separable. This is no longer the case when dissipation is introduced, and various authors have responded with various methods of dealing with the problem. A new method is developed here, in which an individual tidal mode is followed upward into the dissipating regions by way of a latitudinally variable vertical wavenumber. This method appears to have conceptual and operational advantages, both analytical and numerical, though it, too, has its limitations. In an appendix, the method is sketched also in application to the effects of background zonal winds on tidal propagation.

Earlier Days of Gravity Waves Revisited

The means whereby the author came to be involved in the study of atmospheric gravity waves, and then came to involve others in that study, are outlined. In particular, events leading up to, during and following the International Symposium on Fluid Mechanics in the Ionosphere, of July 1959, are described.