[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

[1] A time-dependent and fully nonlinear numerical model is employed to solve the Navier-Stokes equations in two spatial dimensions and to describe the propagation of a Gaussian gravity wave packet generated in the troposphere. A Fourier spectral analysis is used to analyze the frequency power spectra of the wave packet, which propagates through and dwells within several thermal ducting regions. The frequency power spectra of the wave packet are derived at several discrete altitudes, which allow us to determine the evolution of the packet. This spectral analysis also clearly reveals the existence of a stratospheric duct, a mesospheric and lower thermospheric duct, and a duct lying between the tropopause and the lower thermosphere. In addition, we determine the spatially localized wave kinetic energy density and the horizontally averaged, time-resolved, normalized vertical velocity. Examination of these diagnostic variables allows us to better understand the process of wave ducting and the vertical transport of wave energy among multiple thermal ducts. The spectral analysis allows us to unambiguously identify the ducted wave modes. These results compare favorably with those derived from a full-wave model.

/pdf/numerical-modeling-of-a-gravity-wave-packet-ducted-by-the-2h2wdi7qk7.pdf

Numerical modeling of a gravity wave packet ducted by the thermal structure of the atmosphere

This paper investigates new sources of thermospheric non thermal (hot) oxygen due to exothermic reactions involving numerous minor (ion and neutral) and metastable species. Numerical calculations are performed for low altitude, daytime, winter conditions, with moderately high solar activity and low magnetic activity. Under these conditions we find that the quenching of metastable species are a significant source of hot oxygen, with kinetic energy production rates a factor of ten higher than those due to previously considered O2(+) and NO(+) dissociative recombination reactions. Some of the most significant new sources of hot oxygen are reactions involving quenching of O(+)((sup 2)D), O((sup 1)D), N((sup 2)D), O(+)((sup 2)P) and vibrationally excited N2 by atomic oxygen.

/pdf/new-sources-for-the-hot-oxygen-geocorona-s3yiilhfen.pdf

New sources for the hot oxygen geocorona

[1] The response to wave forcing of finite duration comprises a transient forerunner and the steady state signal (or simply the signal). It is the latter that carries information on the spectral content of the forcing, and the signal velocity is the velocity at which wave energy flows. To the extent that group velocity is a good measure of the energy flow velocity, the ray-tracing formalism is a valid description of signal propagation. We have examined vertical group velocities as a measure of vertical energy flow velocity for gravity and acoustic waves propagating into the dissipative lower thermosphere. We find that the effects of dissipation on gravity waves can cause group velocity to become a meaningless measure of the energy flow velocity. When certain terms originating in the diffusion of heat and momentum are neglected, the validity of group velocity can be extended to F region altitudes. For acoustic waves, group velocity can be a good measure of energy flow velocity throughout the lower thermosphere because acoustic waves are far less subject to dissipation.

/pdf/group-velocity-and-energy-flux-in-the-thermosphere-limits-on-numb45ib1k.pdf

Group velocity and energy flux in the thermosphere: Limits on the validity of group velocity in a viscous atmosphere

This paper demonstrates the variability of thermospheric sources of hot oxygen atoms. Numerical calculations were performed for day and night, high and low solar activity, summer and winter, and low- and middle-latitude conditions. Under most conditions, reactions involving metastable species are more important hot O sources than previously considered dissociative recombination of O 2 + and NO + . All the hot O sources are an order of magnitude lower at midnight than at noon. At night, dissociative recombination of O 2 + and NO + are the most important sources. Quenching of vibrationally excited N 2 (N 2 * ) by O is the most important metastable source at night. Above 300 km, hot O sources increase by an order of magnitude between solar minimum and solar maximum. For a given level of solar activity, the high-altitude total production rate of hot O kinetic energy is greater during winter than during summer, indicating a dominance of cooler hot O sources during summer. The N 2 * source dominates at low altitudes. At high altitudes it is almost negligible at solar minimum, but increases to become the dominant source at solar maximum. Atomic oxygen quenching of N( 2 D) is a large source at solar minimum and is still important at solar maximum. Overall, seasonal variations are small compared to solar cycle, diurnal and latitudinal variations. While quenching of metastable species is more important at midlatitudes than at low latitudes, there is little latitudinal variation in hot O production due to dissociative recombination of NO + and O 2 + .

/pdf/new-sources-for-the-hot-oxygen-geocorona-solar-cycle-547ma6lwaj.pdf

New Sources for the Hot Oxygen Geocorona: Solar Cycle, Seasonal, Latitudinal, and Diurnal Variations

[1] A new 2-D time-dependent model is used to simulate the propagation of an acoustic-gravity wave packet in the atmosphere. A Gaussian tropospheric heat source is assumed with a forcing period of 6.276 minutes. The atmospheric thermal structure creates three discrete wave ducts in the stratosphere, mesosphere, and lower thermosphere, respectively. The horizontally averaged vertical energy flux is derived over altitude and time in order to examine the time-resolved ducting. This ducting is characterized by alternating upward and downward energy fluxes within a particular duct, which clearly show the reflections occurring from the duct boundaries. These ducting simulations are the first that resolve the time-dependent vertical energy flux. They suggest that when ducted gravity waves are observed in the mesosphere they may also be observable at greater distances in the stratosphere.

https://commons.erau.edu/cgi/viewcontent.cgi?article=1025&context=publication

Michael P. Hickey

Papers

Numerical modeling of a gravity wave packet ducted by the thermal structure of the atmosphere

New sources for the hot oxygen geocorona

Group velocity and energy flux in the thermosphere: Limits on the validity of group velocity in a viscous atmosphere

New Sources for the Hot Oxygen Geocorona: Solar Cycle, Seasonal, Latitudinal, and Diurnal Variations

Time-resolved Ducting of Atmospheric Acoustic-gravity Waves by Analysis of the Vertical Energy Flux