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1. Introduction A tsunami is a long ocean surface wave caused most often by an undersea or coastal earthquake. As a tsunami travels across the ocean, its movement generates gravity waves in the atmosphere. Numerical simulations indicate that these tsunami-generated atmospheric gravity waves can propagate rapidly upward and within a few hours reach peak amplitudes at altitudes of 250 km or higher (e.g., Hickey et al. 2009 ; Occhipinti et al. 2011 ). An improved understanding of tsunami
1. Introduction A tsunami is a long ocean surface wave caused most often by an undersea or coastal earthquake. As a tsunami travels across the ocean, its movement generates gravity waves in the atmosphere. Numerical simulations indicate that these tsunami-generated atmospheric gravity waves can propagate rapidly upward and within a few hours reach peak amplitudes at altitudes of 250 km or higher (e.g., Hickey et al. 2009 ; Occhipinti et al. 2011 ). An improved understanding of tsunami
1. Introduction Terrain-induced or mountain gravity waves are capable of vertically transporting horizontal momentum ( Bretherton 1966 ). Once becoming unstable, these waves break up and deposit the momentum carried by them onto the ambient flow. Wave–mean flow interaction is enacted in association with the vertical divergence of wave momentum flux (WMF) ( Fritts and Dunkerton 1984 ; Scinocca and Sutherland 2010 ). It has been recognized that gravity wave breaking plays an important role in
1. Introduction Terrain-induced or mountain gravity waves are capable of vertically transporting horizontal momentum ( Bretherton 1966 ). Once becoming unstable, these waves break up and deposit the momentum carried by them onto the ambient flow. Wave–mean flow interaction is enacted in association with the vertical divergence of wave momentum flux (WMF) ( Fritts and Dunkerton 1984 ; Scinocca and Sutherland 2010 ). It has been recognized that gravity wave breaking plays an important role in
1. Introduction Internal gravity waves are vertically propagating, small-scale waves for which buoyancy is the main restoring force. Gravity waves are known to have a variety of sources (topography, convection, fronts, jet stream, etc.) and are thought to be one of the most essential elements driving the atmospheric circulation in Earth’s stratosphere and mesosphere (e.g., Fritts and Alexander 2003 ). Among various dissipation processes of gravity waves, saturation is considered to be of
1. Introduction Internal gravity waves are vertically propagating, small-scale waves for which buoyancy is the main restoring force. Gravity waves are known to have a variety of sources (topography, convection, fronts, jet stream, etc.) and are thought to be one of the most essential elements driving the atmospheric circulation in Earth’s stratosphere and mesosphere (e.g., Fritts and Alexander 2003 ). Among various dissipation processes of gravity waves, saturation is considered to be of
1. Introduction Inertia–gravity waves (IGWs) become dominant modes of motion at mesoscales of the atmosphere, i.e., at horizontal scales smaller than about 500 km ( Callies et al. 2014 ; Žagar et al. 2017 ), thereby contributing to the loss of predictability in weather prediction ( Judt 2018 ) and model uncertainty in climate prediction ( Liu 2019 ). For current general circulation models (GCMs), the resolvable scales of atmospheric phenomena are on the order of 100 km. Resolving smaller
1. Introduction Inertia–gravity waves (IGWs) become dominant modes of motion at mesoscales of the atmosphere, i.e., at horizontal scales smaller than about 500 km ( Callies et al. 2014 ; Žagar et al. 2017 ), thereby contributing to the loss of predictability in weather prediction ( Judt 2018 ) and model uncertainty in climate prediction ( Liu 2019 ). For current general circulation models (GCMs), the resolvable scales of atmospheric phenomena are on the order of 100 km. Resolving smaller
1. Introduction Inertia–gravity waves (IGWs) are ageostrophic oscillations that are forced by rotation and buoyancy ( Holton 1992 ). They may modify the weather at the surface and contribute to extreme weather events ( Bosart and Cussen 1973 ; Bosart et al. 1998 ; Koch and Dorian 1988 ). In the middle atmosphere, such waves may trigger polar stratospheric clouds ( Dörnbrack et al. 1999 ; Buss et al. 2004 ; Hitchman et al. 2003 ), local ozone reduction ( Kühl et al. 2004 ) and noctilucent
1. Introduction Inertia–gravity waves (IGWs) are ageostrophic oscillations that are forced by rotation and buoyancy ( Holton 1992 ). They may modify the weather at the surface and contribute to extreme weather events ( Bosart and Cussen 1973 ; Bosart et al. 1998 ; Koch and Dorian 1988 ). In the middle atmosphere, such waves may trigger polar stratospheric clouds ( Dörnbrack et al. 1999 ; Buss et al. 2004 ; Hitchman et al. 2003 ), local ozone reduction ( Kühl et al. 2004 ) and noctilucent
1. Introduction Equatorially trapped inertia–gravity waves were first identified in the ocean by Wunsch and Gill (1976) through analysis of Pacific Ocean island tide gauge records. Peaks in the frequency spectra at periods of about 3, 4, and 5.5 days were found to be common to islands over a large range of latitudes and longitudes. The oscillations at these periods were coherent with large-scale equatorial winds, but the available frequency spectra of winds showed either no peaks at these
1. Introduction Equatorially trapped inertia–gravity waves were first identified in the ocean by Wunsch and Gill (1976) through analysis of Pacific Ocean island tide gauge records. Peaks in the frequency spectra at periods of about 3, 4, and 5.5 days were found to be common to islands over a large range of latitudes and longitudes. The oscillations at these periods were coherent with large-scale equatorial winds, but the available frequency spectra of winds showed either no peaks at these
1. Introduction Gravity wave parameterizations are needed in atmospheric climate models in order to simulate the influence of subgrid-scale atmospheric gravity waves, which are necessary to produce realistic winds and temperatures. Gravity wave drag forces are important at levels throughout the atmosphere, including the troposphere, stratosphere, and mesosphere and above in the thermosphere and ionosphere (e.g., Fritts and Alexander 2003 ). There are a variety of different methods of gravity
1. Introduction Gravity wave parameterizations are needed in atmospheric climate models in order to simulate the influence of subgrid-scale atmospheric gravity waves, which are necessary to produce realistic winds and temperatures. Gravity wave drag forces are important at levels throughout the atmosphere, including the troposphere, stratosphere, and mesosphere and above in the thermosphere and ionosphere (e.g., Fritts and Alexander 2003 ). There are a variety of different methods of gravity
1. Introduction Gravity waves generated in Earth’s lower atmosphere grow in amplitude with height, become convectively and/or dynamically unstable, and break in the stratosphere and mesosphere. Under such conditions the amplitude growth stops and the waves are considered “saturated” ( Lindzen 1981 ; Fritts and Alexander 2003 ). Theory predicts that the superposition of saturated gravity waves over a broad spectrum results in the vertical wavenumber spectrum of gravity wave energy following a
1. Introduction Gravity waves generated in Earth’s lower atmosphere grow in amplitude with height, become convectively and/or dynamically unstable, and break in the stratosphere and mesosphere. Under such conditions the amplitude growth stops and the waves are considered “saturated” ( Lindzen 1981 ; Fritts and Alexander 2003 ). Theory predicts that the superposition of saturated gravity waves over a broad spectrum results in the vertical wavenumber spectrum of gravity wave energy following a
1. Introduction The French Atomic Energy Commission (CEA) has performed various measurement campaigns of atmospheric pressure fluctuations using very sensitive (10 −3 Pa) ground-based microbarograph networks. Among recorded pressure fluctuations, gravity wave events have been identified. Previous gravity wave measurement campaigns (e.g., Hauf et al. 1996 ; Rees et al. 2000 ) have shown that it is not easy to determine gravity wave packet characteristics from ground pressure signals and even
1. Introduction The French Atomic Energy Commission (CEA) has performed various measurement campaigns of atmospheric pressure fluctuations using very sensitive (10 −3 Pa) ground-based microbarograph networks. Among recorded pressure fluctuations, gravity wave events have been identified. Previous gravity wave measurement campaigns (e.g., Hauf et al. 1996 ; Rees et al. 2000 ) have shown that it is not easy to determine gravity wave packet characteristics from ground pressure signals and even
1. Introduction Gravity wave generation from a balanced flow by internal mechanisms and the importance of spontaneous loss of balance in the atmospheric and oceanic flows still poses open questions. Gravity wave emission seen in observations (e.g., Plougonven and Zhang 2014 ), laboratory experiments (e.g., Williams et al. 2008 ), and numerical simulations (e.g., Plougonven and Snyder 2007 ) is often attributed to spontaneous loss of balance of the balanced flow. However, to correctly
1. Introduction Gravity wave generation from a balanced flow by internal mechanisms and the importance of spontaneous loss of balance in the atmospheric and oceanic flows still poses open questions. Gravity wave emission seen in observations (e.g., Plougonven and Zhang 2014 ), laboratory experiments (e.g., Williams et al. 2008 ), and numerical simulations (e.g., Plougonven and Snyder 2007 ) is often attributed to spontaneous loss of balance of the balanced flow. However, to correctly
