For several decades, jets and fronts have been known from observations to be significant sources of internal gravity waves in the atmosphere. Motivations to investigate these waves have included their impact on tropospheric convection, their contribution to local mixing and turbulence in the upper troposphere, their vertical propagation into the middle atmosphere, and the forcing of its global circulation. While many different studies have consistently highlighted jet exit regions as a favored locus for intense gravity waves, the mechanisms responsible for their emission had long remained elusive: one reason is the complexity of the environment in which the waves appear; another reason is that the waves constitute small deviations from the balanced dynamics of the flow generating them; i.e., they arise beyond our fundamental understanding of jets and fronts based on approximations that filter out gravity waves. Over the past two decades, the pressing need for improving parameterizations of nonorographic gravity waves in climate models that include a stratosphere has stimulated renewed investigations. The purpose of this review is to present current knowledge and understanding on gravity waves near jets and fronts from observations, theory, and modeling, and to discuss challenges for progress in coming years.

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Internal gravity waves from atmospheric jets and fronts

/pdf/energetic-oxygen-in-the-upper-atmosphere-and-the-laboratory-5evi3ku7f6.pdf

Energetic oxygen in the upper atmosphere and the laboratory.

A technique to analyze short-period (<1 hour) gravity wave structure
in all-sky images of the airglow emissions is described. The technique
involves spatial calibration, star removal, geographic projection, regridding,
and flat fielding of the data prior to the determination of the horizontal
wave parameters (wavelength, velocity, and period), by use of standard
two-dimensional Fourier analysis techniques. The method was developed to
exploit the information that is now available with wide-field solid state
imaging systems. This technique permits interactive and quantitative
investigations of large, complex data sets. Such studies are important for
investigating gravity wave characteristics, their interaction with the airglow
emissions, and their geographic and seasonal variability. We study one event
of this type here and present possible evidence of a nonlinear wave–wave
interaction in the upper atmosphere.

/pdf/two-dimensional-spectral-analysis-of-mesospheric-airglow-u4it2zhgtx.pdf

Two-dimensional spectral analysis of mesospheric airglow image data.

The Optical Mesosphere Thermosphere Imagers (OMTI) have been developed to investigate the dynamics of the upper atmosphere through nocturnal airglow emissions. The OMTI consist of an imaging Fabry-Perot interferometer, three all-sky cooled-CCD cameras, three tilting photometers, and a Spectral Airglow Temperature Imager (SATI) with two container houses to install them in. These instruments measure wind, temperature and 2-dimensional airglow patterns in the upper atmosphere at multi-wavelengths of OI (557.7 nm and 630.0 nm), OH (6–2) bands, O2 (0, 1) bands, and Na (589.3 nm), simultaneously. Examples of the data are shown for the cameras, the photometers, and the SATI based on the airglow observation at a mid-latitude station in Japan. Good correlation of the photometer and SATI observations is obtained. A comparison is shown for small- and large-scale wave structures in airglow images at four wavelengths around the mesopause region using four cooled-CCD cameras. We found an event during which large-scale bands, small-scale row-like structures, and large-scale front passage occur simultaneously.

/pdf/development-of-optical-mesosphere-thermosphere-imagers-omti-2i17cccuzn.pdf

Development of Optical Mesosphere Thermosphere Imagers (OMTI)

Analysis and interpretation of airglow and radar observations of quasi-monochromatic gravity waves in the upper mesosphere and lower thermosphere over Adelaide, Australia (35°S, 138°E)

As part of the ALOHA-93 campaign a high performance all-sky CCD imaging system was operated at Haleakala Crater, Maui, to obtain novel information on the properties and sources of short period gravity waves over an extended height range ∼80-100 km. Sequential observations of the near infrared OH and O 2 (0,1) bands and the visible wavelength OI(557.7 nm) and Na(589.2 nm) line emissions have enabled a unique comparison of the morphology and dynamics of the wave motions and their occurrence frequency at each emission altitude to be made. Two major findings are: (a) the detection of significantly higher amounts of wave structure at OI altitudes (∼96 km) compared with that in the OH emission (∼87 km) and (b) the discovery of an unusual morphology, small-scale wave pattern that was most conspicuous in the OI emission and essentially absent at OH heights. These data provide strong evidence for the presence of ducted wave motions in the lower thermosphere.

/pdf/all-sky-measurements-of-short-period-waves-imaged-in-the-oi-1o530preck.pdf

All‐sky measurements of short period waves imaged in the OI(557.7 nm), Na(589.2 nm) and near infrared OH and O2(0,1) nightglow emissions during the ALOHA‐93 Campaign

During the ALOHA-93 campaign simultaneous observations of gravity wave structure in the OI(557.7 nm) nightglow emission were made using two all-sky CCD imagers; one located near the summit of Haleakala Crater, Maui and the other at Mauna Loa Observatory, Hawaii. On 19 October a set of bright, planar, monochromatic waves was imaged by both systems as it progressed rapidly over the Hawaiian Islands. Triangulation on these wave forms indicates a mean altitude of 95±2 km in good agreement with previous rocket soundings at mid-latitudes. Two methods of triangulation were employed, both achieving similar results.

/pdf/height-measurements-of-oi-557-7-nm-gravity-wave-structure-46gjjpz77g.pdf

Height measurements of OI(557.7 nm) gravity wave structure over the Hawaiian Islands during ALOHA‐93

: For three months during the spring and early summer of 1988, low-light TV images showing wave structure in the near infrared hydroxyl (OH) nightglow emission (peak altitude approx. 87 km) were recorded from the Mountain Research Station near Nederland, Colorado (40.0 deg N, 105.6 deg W) as part of the AFOSR MAPSTAR'88 campaign. Well-defined, coherent wave patterns associated with the passage of short period (<1 hour) gravity waves were observed on a total of 22 occasions. One potential source of these waves has been studied using radar summary charts to identify regions of strong convection associated with the existence or development of thunderstorms. Comparison of the 'storm' positions with the location and direction of motion of the OH patterns shows that there was always at least one disturbance suitably located in both space and time to have been the source. The analysis presented here is qualitative, but the large number of wave events associated with favorably located convective activity provides strong evidence for a relationship between the observed waves and storms. This result, although preliminary, suggests that thunderstorms are an important source of mesospheric gravity waves at this site and time of year. (AN)

/pdf/an-investigation-of-thunderstorms-as-a-source-of-short-2ak3uqtywt.pdf

V. Taylor

Papers

All‐sky measurements of short period waves imaged in the OI(557.7 nm), Na(589.2 nm) and near infrared OH and O2(0,1) nightglow emissions during the ALOHA‐93 Campaign

Height measurements of OI(557.7 nm) gravity wave structure over the Hawaiian Islands during ALOHA‐93

An Investigation of Thunderstorms as a Source of Short Period Mesospheric Gravity Waves