[1] Atmospheric gravity waves have been a subject of intense research activity in recent years because of their myriad effects and their major contributions to atmospheric circulation, structure, and variability. Apart from occasionally strong lower-atmospheric effects, the major wave influences occur in the middle atmosphere, between ∼ 10 and 110 km altitudes because of decreasing density and increasing wave amplitudes with altitude. Theoretical, numerical, and observational studies have advanced our understanding of gravity waves on many fronts since the review by Fritts [1984a]; the present review will focus on these more recent contributions. Progress includes a better appreciation of gravity wave sources and characteristics, the evolution of the gravity wave spectrum with altitude and with variations of wind and stability, the character and implications of observed climatologies, and the wave interaction and instability processes that constrain wave amplitudes and spectral shape. Recent studies have also expanded dramatically our understanding of gravity wave influences on the large-scale circulation and the thermal and constituent structures of the middle atmosphere. These advances have led to a number of parameterizations of gravity wave effects which are enabling ever more realistic descriptions of gravity wave forcing in large-scale models. There remain, nevertheless, a number of areas in which further progress is needed in refining our understanding of and our ability to describe and predict gravity wave influences in the middle atmosphere. Our view of these unknowns and needs is also offered.

/pdf/gravity-wave-dynamics-and-effects-in-the-middle-atmosphere-4huexaq7y8.pdf

Gravity wave dynamics and effects in the middle atmosphere

https://www.lpl.arizona.edu/~yelle/eprints/Yelle04b.pdf

Aeronomy of extra-solar giant planets at small orbital distances

Atmosphere: State of the Art and Challenges Barbara Nozier̀e,*,† Markus Kalberer,*,‡ Magda Claeys,* James Allan, Barbara D’Anna,† Stefano Decesari, Emanuela Finessi, Marianne Glasius, Irena Grgic,́ Jacqueline F. Hamilton, Thorsten Hoffmann, Yoshiteru Iinuma, Mohammed Jaoui, Ariane Kahnt, Christopher J. Kampf, Ivan Kourtchev,‡ Willy Maenhaut, Nicholas Marsden, Sanna Saarikoski, Jürgen Schnelle-Kreis, Jason D. Surratt, Sönke Szidat, Rafal Szmigielski, and Armin Wisthaler †Ircelyon/CNRS and Universite ́ Lyon 1, 69626 Villeurbanne Cedex, France ‡University of Cambridge, Cambridge CB2 1EW, United Kingdom University of Antwerp, 2000 Antwerp, Belgium The University of Manchester & National Centre for Atmospheric Science, Manchester M13 9PL, United Kingdom Istituto ISAC C.N.R., I-40129 Bologna, Italy University of York, York YO10 5DD, United Kingdom University of Aarhus, 8000 Aarhus C, Denmark National Institute of Chemistry, 1000 Ljubljana, Slovenia Johannes Gutenberg-Universitaẗ, 55122 Mainz, Germany Leibniz-Institut für Troposphar̈enforschung, 04318 Leipzig, Germany Alion Science & Technology, McLean, Virginia 22102, United States Max Planck Institute for Chemistry, 55128 Mainz, Germany Ghent University, 9000 Gent, Belgium Finnish Meteorological Institute, FI-00101 Helsinki, Finland Helmholtz Zentrum München, D-85764 Neuherberg, Germany University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, United States University of Bern, 3012 Bern, Switzerland Institute of Physical Chemistry PAS, Warsaw 01-224, Poland University of Oslo, 0316 Oslo, Norway

/pdf/the-molecular-identification-of-organic-compounds-in-the-1rs6wk4d8f.pdf

The molecular identification of organic compounds in the atmosphere : state of the art and challenges

Global warming is expected to drive increasing extreme sea levels (ESLs) and flood risk along the world's coastlines. In this work we present probabilistic projections of ESLs for the present century taking into consideration changes in mean sea level, tides, wind-waves, and storm surges. Between the year 2000 and 2100 we project a very likely increase of the global average 100-year ESL of 34-76 cm under a moderate-emission-mitigation-policy scenario and of 58-172 cm under a business as usual scenario. Rising ESLs are mostly driven by thermal expansion, followed by contributions from ice mass-loss from glaciers, and ice-sheets in Greenland and Antarctica. Under these scenarios ESL rise would render a large part of the tropics exposed annually to the present-day 100-year event from 2050. By the end of this century this applies to most coastlines around the world, implying unprecedented flood risk levels unless timely adaptation measures are taken.

/pdf/global-probabilistic-projections-of-extreme-sea-levels-show-1suozfqs6n.pdf

Global probabilistic projections of extreme sea levels show intensification of coastal flood hazard.

Forcing of the ionosphere by waves from below

Observations of fluctuations in the intensity and temperature of the O I (557.7 nm) airglow taken at Arecibo in 1989 are reported and interpreted on the assumption that they are caused by gravity waves propagating through the emission layer. The data give the magnitude of Krassovsky's ratio as 3.5 ± 2.2, at periods between about 5 and 10 hours. Comparison with theory shows that the gravity waves responsible for the measured airglow variations must have long wavelengths of several thousand kilometers. The observed phases of Krassovsky's ratio are in good agreement with theoretically predicted values at the long wavelengths and large periods for about half the cases. In the other cases, observed phases are near - 180°, suggesting that the waves responsible for the airglow fluctuations have experienced strong reflections in the emission layer. The observations emphasize the importance of knowing the full altitude profiles of temperature and winds for extraction of wave information from the airglow fluctuations.

/pdf/observations-and-interpretation-of-gravity-wave-induced-27ih9xo9wp.pdf

Observations and interpretation of gravity wave induced fluctuations in the O I (557.7 nm) airglow

[1] A new nonlinear and time-dependent model is used to derive the total perturbation energy flux of two gravity wave packets propagating from the troposphere to the lower thermosphere. They are excited by a heat source and respectively propagate in an eastward and westward direction in the presence of a zonal wind. Analysis of the refractive index, the power spectra and the total perturbation energy flux allows us to correctly interpret the ducting characteristics of these two wave packets. In our study the wind acts as a directional filter to the wave propagations and causes noticeable spectral variations at higher altitudes. We are the first that time-resolve the total perturbation energy flux influenced by the winds and the simulations have immediate impacts to the airglow observations on certain wave spectra.

/pdf/simulated-ducting-of-high-frequency-atmospheric-gravity-1zddoaio1r.pdf

Simulated ducting of high-frequency atmospheric gravity waves in the presence of background winds

[1] In November 1999 a new near-IR airglow imaging system was deployed at the Starfire Optical Range outside of Albuquerque, New Mexico. This system allowed wide angle images of the airglow to be collected, with high signal to noise, every 3 seconds with a one second integration time. At approximately 1000 UT on November 17, 1999, a fast wavelike disturbance was seen propagating through the OH Meinel airglow layer. This wave had an observed period of ≈215 seconds, an observed phase velocity of ≈160 m/s and a horizontal wavelength of ≈35 km. This phase velocity is among the fastest yet reported using an imager viewing the OH Meinel bands, while the wave period is among the shortest. Simultaneous Na lidar wind and temperature data from 80 to nearly 110 km altitude allow the intrinsic properties of the wave to be calculated. The Einaudi and Hines [1970] WKB approximation for the acoustic-gravity wave dispersion relation was used to calculate the wave's intrinsic properties. Using this approach indicates that the observed disturbance was an external acoustic wave in the 90 to 107 km altitude region and an external gravity wave at other altitudes between 80 and 90 km. Using model atmospheric data for altitudes below and above this altitude regime indicates that the wave is essentially external everywhere except perhaps in narrow regions around 80 and 105–110 km. This is confirmed using a more exact full-wave model analysis. The observations and model results suggest that this wave was not generated in the troposphere and propagated up to the mesosphere, but rather near 100 km altitude where it was possibly generated by a Leonids meteor.

/pdf/an-observation-of-a-fast-external-atmospheric-acoustic-2l4p8bidzf.pdf

An observation of a fast external atmospheric acoustic-gravity wave

[1] We present a full-wave model that simulates acoustic-gravity wave propagation in a binary-gas mixture of atomic oxygen and molecular nitrogen, including molecular viscosity and thermal conductivity appropriately partitioned between the two gases. Compositional effects include the collisional transfer of heat and momentum by mutual diffusion between the two gases. An important result of compositional effects is that the velocity and temperature summed over species can be significantly different from the results of one-gas models with the same height dependent mean molecular weight (M(z)). We compare the results of our binary-gas model to two one-gas full-wave models: one where M is fixed and fluctuations of M (M′) are zero and the other where M is conserved following parcel displacement (whence M′ is nonzero). The former is the usual approach and is equivalent to assuming that mutual diffusion acts instantaneously to restore composition to its ambient value. In all cases we considered, the single gas model results obtained assuming that M is conserved following parcels gave significantly better agreement with the binary-gas model. This implies that compositional effects may be included in one-gas models by simply adding a conservation equation for M and for the specific gas at constant pressure, which depends on M.

/pdf/gravity-wave-propagation-in-a-diffusively-separated-gas-13cmjktbs0.pdf

Gravity wave propagation in a diffusively separated gas: Effects on the total gas

A full-wave dynamical model and chemistry models that simulate ground-based observations of gravity wave-driven O2 atmospheric and O I 5577 airglow fluctuations in the mesopause region are used to demonstrate that for many observable gravity waves modeling is required to infer temperature perturbation amplitudes from airglow observations. We demonstrate that the amplitude of the altitude-integrated volume emission rate weighted temperature perturbation differs by at least about 30% from the amplitude of the temperature perturbation of the major gas in the vicinity of the peak of the airglow volume emission rate for gravity waves with horizontal phase speeds less than about 150 m s−1 and vertical wavelengths less than about 50 km and that the amplitude of the altitude-integrated volume emission rate weighted temperature perturbation differs considerably from the amplitude of the temperature perturbation averaged over the vertical extent of the emission layer for waves with horizontal phase speeds less than about 65 m s−1 and vertical wavelengths less than about 20 km. For waves with phase speeds less than about 100 m s−1 and vertical wavelengths less than about 30 km the amplitude of the altitude-integrated volume emission rate weighted temperature perturbation differs by at least about 30% from the altitude-integrated mean volume emission rate weighted temperature perturbation, demonstrating that the nonthermal fluctuation contribution to the former (involving volume emission rate perturbations) needs to be included in such modeling. We conjecture that the observed brightness perturbation is a simpler and better quantity to simulate using detailed modeling than the observed airglow temperature perturbation for the determination of wave amplitude in cases where nonthermal effects or cancellation effects (for short vertical wavelengths) are strong.

/pdf/a-note-on-gravity-wave-driven-volume-emission-rate-weighted-2kw4pgn737.pdf

Michael P. Hickey

Papers

Observations and interpretation of gravity wave induced fluctuations in the O I (557.7 nm) airglow

Simulated ducting of high-frequency atmospheric gravity waves in the presence of background winds

An observation of a fast external atmospheric acoustic-gravity wave

Gravity wave propagation in a diffusively separated gas: Effects on the total gas

A note on gravity wave‐driven volume emission rate weighted temperature perturbations inferred from O2 atmospheric and O I 5577 airglow observations