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Equatorial Plasma Bubbles (EPBs) are a region of depleted ionospheric densities. EPBs are known to fluctuate both seasonally and day to day, and have been linked to changes in solar activity, geomagnetic activity, and seeding resulting from dynamics occurring at lower altitudes. Here, EPB activity is investigated over a 15-day period with overlapping coincident ground-based 630 nm oxygen airglow measurements, near-infrared hydroxyl mesospheric temperature mapper (MTM) measurements, and Rate Of change of Total Electron Content Index (ROTI) values. The data are compared with the Navy Global Environmental Model (NAVGEM) reanalysis over the same time period. It is found that several days with strong EPB activity coincided with the positive/northward meridional wind phase of the quasi-two-day wave (QTDW) in the mesosphere. These initial observations indicate correlations of the QTDW phase and the occurrence rates of EPBs, and suggest a need for further investigations to assess potential causal relationships that may affect the variability and prevalence of EPBs. [ABSTRACT FROM AUTHOR]

We analyze the gravity waves (GWs) from the ground to the thermosphere during 11–14 January 2016 using the nudged HI Altitude Mechanistic general Circulation Model. We find that the entrance, core and exit regions of the polar vortex jet are important for generating primary GWs and amplifying GWs from below. These primary GWs dissipate in the upper stratosphere/lower mesosphere and deposit momentum there; the atmosphere responds by generating secondary GWs. This process is repeated, resulting in medium to large‐scale higher‐order, thermospheric GWs. We find that the amplitudes of the secondary/higher‐order GWs from sources below the polar vortex jet are exponentially magnified. The higher‐order, thermospheric GWs have concentric ring, arc‐like and planar structures, and spread out latitudinally to 10 − 90°N. Those GWs with the largest amplitudes propagate against the background wind. Some of the higher‐order GWs generated over Europe propagate over the Arctic region then southward over the US to ∼15–20°N daily at ∼14 − 24 UT (∼9 − 16 LT) due to the favorable background wind. These GWs have horizontal wavelengths λH ∼ 200 − 2,200 km, horizontal phase speeds cH ∼ 165 − 260 m/s, and periods τr ∼ 0.3 − 2.4 hr. Such GWs could be misidentified as being generated by auroral activity. The large‐scale, higher‐order GWs are generated in the lower thermosphere and propagate southwestward daily across the northern mid‐thermosphere at ∼8–16 LT with λH ∼ 3,000 km and cH ∼ 650 m/s. We compare the simulated GWs with those observed by AIRS, VIIRS/DNB, lidar and meteor radars and find reasonable to good agreement. Thus the polar vortex jet is important for facilitating the global generation of medium to large‐scale, higher‐order thermospheric GWs via multi‐step vertical coupling. Plain Language Summary: Gravity waves (GWs) are perturbations in the Earth's atmosphere created by various processes. When a GW breaks, it imparts momentum to the atmosphere, which in turn can become unbalanced and generate secondary GWs. The same process happens at higher altitudes where the secondary GWs break, thereby generating higher‐order GWs. We simulate the primary, secondary and higher‐order GWs on 11–14 January 2016 using a GW‐resolving whole atmosphere model. We find that the entrance, core and exit regions of the jet that encircles the polar vortex generate primary GWs. In addition, the polar vortex jet magnifies the amplitudes of higher‐order GWs from sources below the jet, such as mountain waves. The resulting higher‐order GWs have horizontal wavelengths of hundreds to thousands of km with concentric ring, arc‐like and planar structures in the thermosphere. We compare the simulated GWs with AIRS, VIIRS/DNB, lidar, and meteor radar observations and find reasonable to good agreement. Key Points: The vertical shear of the horizontal wind in the entrance, core and exit regions of the polar vortex jet generate GWs in the stratosphereHigher‐order GWs generated over Europe and Asia propagate over the Arctic then southward over the CONUS at ∼9 − 16 LT due to favorable windsLarge‐scale GWs with λH ∼ 3,000 km and cH ∼ 650 m/s propagate southwestward across the northern thermosphere at ∼8–16 LT [ABSTRACT FROM AUTHOR]

This paper investigates the lower‐to‐upper atmosphere coupling at high latitudes (>60°N) during the northern winter months of 2012–2013 years, which includes a period of major Sudden "Stratospheric" Warming (SSW). We perform statistical analysis of thermosphere wind disturbances with periods of 30–70 min, known as the medium scale traveling atmospheric disturbances (MSTADs) in atomic oxygen green line (557.7 nm) near ∼120 km and red line (630.0 nm) emissions near ∼250 km observed from Scanning Doppler Imagers (SDIs) over Alaska. The SDI MSTADs observations (60°–75°N) are interpreted in conjunction with the previous daytime medium‐scale traveling ionospheric disturbance (MSTID) observations by SuperDARN midlatitudes (35°–65°N) radars in the F‐region ionosphere and western hemisphere, which confirm findings from the SDI instruments. Increases in MSTAD activity from SDIs show correlations with the increasing meridional planetary wave (PW) amplitudes in the stratosphere derived from MERRA2 winds. Furthermore, a detailed study of the lower atmospheric conditions from MERRA2 winds indicates that the lower atmospheric sources of MSTADs are likely due to the stratospheric generated Gravity Waves (GWs) and not orographic GWs. Favorable stratospheric propagation conditions and polar vortex disturbances resulting from the increased PW activity in the stratospheric region both appear to contribute to increased MSTAD activity in the thermosphere. Additionally, the results show that the MSTID activity from SuperDARN HF radars at mid latitudes during the January 2013 SSW is lower than the MSTAD activity in SDI winds at high latitudes. Plain Language Summary: The objective of this paper is to investigate how Atmospheric Gravity Waves (GWs) contribute to the vertical coupling of the atmosphere‐ionosphere system. When propagating from below, GWs can create medium‐scale traveling atmospheric disturbances (MSTADs) in the thermosphere, which in turn generate medium‐scale traveling ionospheric disturbances (MSTIDs) in the ionosphere. This study examines the coupling between the lower and upper atmosphere at high latitudes (>60°N) during the winter of 2012–2013, including a period of Sudden "Stratospheric" Warming (SSW) and quiet geomagnetic conditions. The analysis of MSTAD day‐to‐day activity observed using Scanning Doppler Imagers that measure airglow emissions in Alaska confirms similar MSTID activity in observed ion density from SuperDARN mid‐latitudes radars. The study also confirms that the increased MSTAD activity in the lower‐to‐upper thermosphere is due to stratospheric‐generated GWs, rather than orographic GWs, and is linked to increased planetary wave activity in the stratospheric meridional winds and polar vortex disturbances. Therefore, the paper not only highlights the global characteristics of thermosphere GW‐like variations in the western hemisphere but also their connection to lower atmosphere dynamics. Key Points: Variations of medium scale traveling atmospheric disturbances (MSTADs) observed in Scanning Doppler Imager (SDI) winds near ∼250 km agree with SuperDARN HF radars medium‐scale traveling ionospheric disturbances observations over western hemisphereMSTAD variability in the thermosphere over Alaska during winter months demonstrates a correlation with dynamics in the stratosphereIncreased MSTAD activity in the thermosphere correlates with increasing meridional planetary wave amplitudes in the stratosphere [ABSTRACT FROM AUTHOR]

We simulate the gravity waves (GWs) and traveling ionospheric disturbances (TIDs) created by the Hunga Tonga‐Hunga Ha'apai (hereafter "Tonga") volcanic eruption on 15 January 2022 at ∼04:15 UT. We calculate the primary GWs and forces/heatings generated where they dissipate with MESORAC, the secondary GWs with HIAMCM, and the TIDs with SAMI3. We find that medium and large‐scale TIDs (MSTIDs and LSTIDs) are induced by the secondary GWs, with horizontal phase speeds cH ≃ 100–750 m/s, horizontal wavelengths λH ≃ 600–6,000 km, and ground‐based periods τr ≃ 30 min to 3 hr. The LSTID amplitudes over New Zealand are ≃2–3 TECU, but decrease sharply ≃ 5,000 km from Tonga. The LSTID amplitudes are extremely small over Australia and South Africa because body forces create highly asymmetric GW fields and the GWs propagate perpendicular to the magnetic field there. We analyze the TIDs from SAMI3 and find that a 30 min detrend window eliminates the fastest far‐field LSTIDs. We analyze the GPS/TEC via detrending with 2–3 hr windows, and find that the fastest LSTIDs reach the US and South America at ∼8:30–9:00 UT with cH ≃ 680 m/s, λH ≃ 3,400 km, and τr ≃ 83 min, in good agreement with model results. We find good agreement between modeled and observed TIDs over New Zealand, Australia, Hawaii, Japan and Norway. The observed F‐peak height, hmF2, drops by ≃ 110–140 km over the western US with a 2.8 hr periodicity from 8:00 to 13:00 UT. We show that the Lamb waves (LWs) observed by AIRS with λH = 380 km have amplitudes that are ≃ 2.3% that of the primary GWs at z ≃ 110 km. We conclude that the observed TIDs can be fully explained by secondary GWs rather than by "leaked" LWs. Plain Language Summary: Gravity waves (GWs) are created by various processes, such as volcanic eruptions. A breaking GW imparts momentum and energy to the atmosphere, which creates secondary GWs. Traveling ionospheric disturbances (TIDs) are created by GWs through collisions between neutral and ion molecules. We simulate the GWs and TIDs created by the Tonga eruption on 15 January 2022. We find that medium and large‐scale TIDs (MSTIDs and LSTIDs) are induced by the secondary GWs. These TIDs propagate globally, and have speeds of 100–750 m/s and horizontal scales of hundreds to thousands of km. The fastest TIDs reach the United States and South America at ∼8:30–9:00 UT; these TIDs have large scales and large periods, in agreement with observations. These LSTIDs can only be seen if they are not "detrended out" when processing the ionospheric data. Previous studies eliminated these LSTIDs by restricting their detrend windows, and then incorrectly suggested that Lamb waves were responsible for the TIDs they observed. Using longer detrend windows, we find good agreement between the modeled and observed TIDs. We find that the observed TIDs can be fully explained by secondary GWs, rather than by the leakage of Lamb waves into GWs. Key Points: Globally‐propagating concentric TIDs are induced by secondary GWs from the Tonga eruption with cH = 100−750 m/s and τr = 30 min to 3 hrThe fastest LSTIDs from Tonga in the far field are eliminated when detrending SAMI3 and GPS/TEC data with a 30 min windowThe fastest modeled LSTIDs from Tonga reach the US and South America at 8:30‐9:00 UT with cH = 600 m/s, in good agreement with data [ABSTRACT FROM AUTHOR]

We simulate the primary and secondary atmospheric gravity waves (GWs) excited by the upward movement of air generated by the Hunga Tonga‐Hunga Ha'apai (hereafter "Tonga") volcanic eruption on 15 January 2022. The Model for gravity wavE SOurce, Ray trAcing and reConstruction (MESORAC) is used to calculate the primary GWs and the local body forces/heatings generated where they dissipate. We add these forces/heatings to the HIgh Altitude Mechanistic general Circulation Model (HIAMCM) to determine the secondary GWs and large‐scale wind changes that result. We find that a wide range of medium to large‐scale secondary GWs with concentric ring structure are created having horizontal wind amplitudes of u′, v′ ∼ 100–200 m/s, ground‐based periods of τr ∼ 20 min to 7 hr, horizontal phase speeds of cH ∼ 100–600 m/s, and horizontal wavelengths of λH ∼ 400–7,500 km. The fastest secondary GWs with cH ∼ 500–600 m/s are large‐scale GWs with λH ∼ 3,000–7,500 km and τr ∼ 1.5–7 hr. They reach the antipode over Africa ∼9 hr after creation. Large‐scale temporally and spatially varying wind changes of ∼80–120 m/s are created where the secondary GWs dissipate. We analyze the Tonga waves measured by the Michelson Interferometer for Global High‐resolution Thermospheric Imaging (MIGHTI) on the National Aeronautics and Space Administration Ionospheric Connection Explorer (ICON), and find that the observed GWs were medium to large‐scale with cH ∼ 100–600 m/s and λH ∼ 800–7,500 km, in good agreement with the simulated secondary GWs. We also find good agreement between ICON‐MIGHTI and HIAMCM for the timing, amplitudes, locations, and wavelengths of the Tonga waves, provided we increase the GW amplitudes by ∼2 and sample them ∼30 min later than ICON. Plain Language Summary: Atmospheric gravity waves (GWs) are buoyancy driven perturbations in the Earth's atmosphere that can be created by various processes. GW breaking is similar to the breaking of ocean waves when they overturn. A breaking GW imparts momentum to the ambient atmosphere, which can create secondary GWs. We simulated the Tonga eruption on 15 January 2022 using Geostationary Operational Environmental Satellite satellite images, ray tracing, and a GW‐resolving global circulation model. We find that the secondary GWs created by the breaking of the primary GWs from the eruption propagated globally and changed the large‐scale wind patterns in the thermosphere. Furthermore, the phase speeds and wavelengths of these waves simulated by the model agree well with corresponding results from ICON satellite measurements. Thus, this study highlights the importance of a process called "multi‐step vertical coupling", according to which secondary GWs are important drivers in the Earth's thermosphere. Key Points: Modeled secondary gravity waves (GWs) radiate globally from Tonga with cH ∼ 100–600 m/s, λH ∼ 400–7,500 km, and τr ∼ 20 min to 7 hrICON observed northeastward GWs from Tonga with cH ∼ 100–600 m/s and λH ∼ 800–7,500 km, in good agreement with the modelTemporally and spatially variable large‐scale wind changes of ∼80–120 m/s are created by the dissipation of the secondary GWs [ABSTRACT FROM AUTHOR]

We analyze the gravity waves (GWs) observed by a Rayleigh lidar at the Arctic Lidar Observatory for Middle Atmosphere Research (ALOMAR) (16.08°E, 69.38°N) in Norway at z ∼ 20–85 km on 12–14 January 2016. These GWs propagate upward and downward away from zknee = 57 and 64 km at a horizontally‐displaced location with periods τr ∼ 5–10 hr and vertical wavelengths λz ∼ 9–20 km. Because the hodographs are distorted, we introduce an alternative method to determine the GW parameters. We find that these GWs are medium to large‐scale, and propagate north/northwestward with intrinsic horizontal phase speeds of ∼35–65 m/s. Since the GW parameters are similar above and below zknee, these are secondary GWs created by local body forces (LBFs) south/southeast of ALOMAR. We use the nudged HIAMCM (HIgh Altitude Mechanistic general Circulation Model) to model these events. Remarkably, the model reproduces similar GW structures over ALOMAR, with zknee = 58 and 66 km. The event #1 GWs are created by a LBF at ∼35°E, ∼60°N, and z ∼ 58 km. This LBF is created by the breaking and dissipation of primary GWs generated and amplified by the imbalance of the polar night jet below the wind maximum; the primary GWs for this event are created at z ∼ 25–35 km at 49–53°N. We also find that the HIAMCM GWs agree well with those observed by the Atmospheric InfraRed Sounder (AIRS) satellite, and that those AIRS GWs south and north of ∼50°N over Europe are mainly mountain waves and GWs from the polar vortex, respectively. Plain Language Summary: Atmospheric gravity waves (GWs) are perturbations in the Earth's atmosphere which can be created by wind flow over mountains and breaking GWs. Here, a breaking GW is similar to the breaking of an ocean wave when it overturns. A breaking GW imparts momentum to the atmosphere, which creates secondary GWs. We report on the long‐period inertia GWs seen over Arctic Lidar Observatory for Middle Atmosphere Research (ALOMAR) in northern Norway during 12–14 January 2016. We find that the inertia GWs seen over ALOMAR were secondary GWs created by the breaking of primary GWs generated by the imbalance of the polar vortex. We did this via simulating this event with the HIAMCM model and directly comparing these results to lidar and Atmospheric InfraRed Sounder data. After we found that the HIAMCM results agreed very well with these data, we investigated the dynamics which led to the ALOMAR GWs using the HIAMCM model data. This is the first concrete model/data comparison study to show that GWs generated by the polar vortex are important for generating GWs observed in the Earth's mesosphere. This study also highlights the importance of the complicated process dubbed "multi‐step vertical coupling," for which secondary, not primary, GWs can explain the wintertime GWs seen in the mesosphere. Key Points: The upward and downward inertia gravity waves (GWs) over Arctic Lidar Observatory for Middle Atmosphere Research are secondary GWs created by the breaking/dissipation of primary GWs from the polar vortexThe primary GWs are created from imbalance of the polar vortex and are amplified below the wind maximum where the vertical wind shear is largeThe primary and secondary GWs from the polar vortex simulated by the nudged HIAMCM agree well with lidar and Atmospheric InfraRed Sounder observations [ABSTRACT FROM AUTHOR]

This study presents multi‐instrument observations of persistent large‐scale traveling ionosphere/atmospheric disturbances (LSTIDs/LSTADs) observed during moderately increased auroral electrojet activity and a sudden stratospheric warming in the polar winter hemisphere. The Global Ultraviolet Imager (GUVI), Gravity field and steady‐state Ocean Circulation Explorer, Scanning Doppler Imaging Fabry–Perot Interferometers, and the Poker Flat Incoherent Scatter Radar are used to demonstrate the presence of LSTIDs/LSTADs between 19 UT and 5 UT on 18–19 January 2013 over the Alaska region down to lower midlatitudes. This study showcases the first use of GUVI for the study of LSTADs. These novel GUVI observations demonstrate the potential for the GUVI far ultraviolet emissions to be used for global‐scale studies of waves and atmospheric disturbances in the thermosphere, a region lacking in long‐term global measurements. These observations typify changes in the radiance from around 140 to 180 km, opening a new window into the behavior of the thermosphere. Plain Language Summary: The thermosphere is the region of Earth's atmosphere that extends from ∼90 to 500 km. Atmospheric disturbances commonly associated with waves perturb temperatures, densities, and winds in this region. Variability in the thermosphere is important as this altitude range overlaps the low earth orbit region of satellites. Despite its importance, limited global observations of the thermosphere region exist. This study presents a multi‐instrument study of atmospheric disturbances in the thermosphere and demonstrates the first use of the Global Ultraviolet Imager for the study of waves in the thermosphere. Key Points: For the first time, Global Ultraviolet Imager observations of large‐scale traveling ionosphere disturbances (LSTIDs) in far ultraviolet emissions are presented and validatedPersistent LSTID/large‐scale traveling atmospheric disturbances (LSTADs) are observed over several hours coinciding with moderate geomagnetic disturbances and a major sudden stratospheric warming (SSW)Along‐track horizontal wavelengths of the atmospheric disturbances are ∼2,000–2,500 km and periods are ∼2–2.5 hr [ABSTRACT FROM AUTHOR]

In this paper, we simulate an observed mountain wave event over central Europe and investigate the subsequent generation, propagation, phase speeds and spatial scales, and momentum deposition of secondary waves under three different tidal wind conditions. We find the mountain wave breaks just below the lowest critical level in the mesosphere. As the mountain wave breaks, it extends outwards along the phases and fluid associated with the breaking flows downstream of its original location by 500–1,000 km. The breaking generates a broad range of secondary waves with horizontal scales ranging from the mountain wave instability scales (20–300 km), to multiples of the mountain wave packet scale (420 km+) and phase speeds from 40 to 150 m/s in the lower thermosphere. The secondary wave morphology consists of semi‐concentric patterns with wave propagation generally opposing the local tidal winds in the mesosphere. Shears in the tidal winds cause breaking of the secondary waves and local wave forcing which generates even more secondary waves. The tidal winds also influence the dominant wavelengths and phase speeds of secondary waves that reach the thermosphere. The secondary waves that reach the thermosphere deposit their energy and momentum over a broad area of the thermosphere, mostly eastward of the source and concentrated between 110 and 130 km altitude. The secondary wave forcing is significant and will likely be very important for the dynamics of the thermosphere. A large portion of this forcing comes from nonlinearly generated secondary waves at relatively small‐scales which arise from the wave breaking processes. Key Points: Mountain wave breaking generates a broad range of secondary wavesThe secondary wave parameters and morphology are significantly influenced by the tidal windsThe secondary waves contribute significant forcing in the tidal shears and over a large area in the thermosphere [ABSTRACT FROM AUTHOR]

We present a new version of the HIgh Altitude Mechanistic general Circulation Model (HIAMCM) with specified dynamics. We utilize a spectral method that nudges only the large‐scale flow to MERRA‐2 reanalysis. The nudged HIAMCM simulates gravity waves (GWs) down to horizontal wavelengths of about 200 km from the troposphere to the thermosphere like the free‐running model, including the generation of secondary and tertiary GWs. Case studies show that the simulated large‐scale GWs are consistent with those in the reanalysis, while the medium‐scale GWs compare well with observations in the northern winter 2016 stratosphere from the Atmospheric InfraRed Sounder (AIRS). GWs having wavelengths larger than about 1,350 km can be described with the nonlinear balance equation. The GWs relevant in the stratosphere, however, have smaller scales and require a different approach. We propose that the GW amplification due to kinetic energy transfer from the large‐scale flow combined with GW potential energy flux convergence helps to identify the mesoscale GW sources due to spontaneous emission. The GW amplification is strongest in the region of maximum large‐scale vertical wind shear in the mid‐stratosphere. Maps of the time‐averaged stratospheric GW activity simulated by the HIAMCM and computed from AIRS satellite data show a persistent hot spot over Europe during January 2016. At about 40 km, the average GW amplitudes are maximum in the region of fastest large‐scale flow. We argue that refraction of GWs originating in the troposphere, as well as GWs from spontaneous emission in the stratosphere contribute to this effect. Plain Language Summary: We present a new version of the HIgh Altitude Mechanistic general Circulation Model (HIAMCM) with specified dynamics in the troposphere, stratosphere, and lower mesosphere. The HIAMCM is a spectral model with high spatial resolution (the shortest horizontal wavelength is about 156 km) and a model top at about 450 km. The nudging of the model to reanalysis is formulated in spectral space and restricted to the large‐scale flow. This ensures that gravity waves (GWs) are self‐consistently simulated over the whole altitude range like in the free‐running model. The simulated large‐scale GWs are quantitatively consistent with those in the reanalysis, while the medium‐scale GWs compare well with satellite observations in the northern winter 2016 stratosphere. We analyze a case of GW generation in the stratosphere from imbalance of the polar vortex. We propose that this process can be identified by the transfer of kinetic energy transfer from the large‐scale flow to the GWs combined with the GW potential energy flux convergence. The in‐situ generation of GWs in the stratosphere likely contributes to the averaged distribution of GW activity in the upper stratosphere, which is maximum around the edge of the polar vortex. Key Points: Nudging in spectral space allows for self‐consistent simulation of gravity waves up to the thermosphereSimulated gravity waves in the winter stratosphere agree well with satellite observationsSpontaneous emission of GWs in the winter stratosphere depends critically on vertical wind shear [ABSTRACT FROM AUTHOR]

Observations during 12 January 2016 revealed a series of events of significant gravity wave (GW) activity over Europe. Analysis of derived temperatures from the Atmospheric InfraRed Sounder (AIRS) provides insight into the sources of these GWs, and include a new observation of stratosphere polar night jet (PNJ) generated GWs. Mountain waves were present during this time as well over the French Alps and the Carpathian Mountains and had maximum temperature perturbations, T′, as large as 27 K over the French Alps. Further investigation of the mountain waves that demonstrated their presence in the stratosphere was determined not only by stratospheric conditions but also by strong winds in the troposphere and at the surface. GWs generated in the stratosphere by the PNJ had maximum T′ of 7 K. These observations demonstrate multiple sources of GWs during a dynamically active period and implicate the role of the PNJ in both the vertical propagation of GWs generated in the troposphere and the generation of GWs from the PNJ itself. Key Points: AIRS observations demonstrate the presence of gravity waves generated by the polar night jetDownward propagating gravity waves were observed at altitudes below the polar night jetThe polar night jet plays an important role in the growth of mountain waves in the stratosphere [ABSTRACT FROM AUTHOR]

We analyze quiet‐time data from the Gravity Field and Ocean Circulation Explorer satellite as it overpassed the Southern Andes at z≃275 km on 5 July 2010 at 23 UT. We extract the 20 largest traveling atmospheric disturbances from the density perturbations and cross‐track winds using Fourier analysis. Using gravity wave (GW) dissipative theory that includes realistic molecular viscosity, we search parameter space to determine which hot spot traveling atmospheric disturbances are GWs. This results in the identification of 17 GWs having horizontal wavelengths λH = 170–1,850 km, intrinsic periods τIr = 11–54 min, intrinsic horizontal phase speeds cIH = 245–630 m/s, and density perturbations ρ′/ρ¯∼ 0.03–7%. We unambiguously determine the propagation direction for 11 of these GWs and find that most had large meridional components to their propagation directions. Using reverse ray tracing, we find that 10 of these GWs must have been created in the mesosphere or thermosphere. We show that mountain waves (MWs) were observed in the stratosphere earlier that day and that these MWs saturated at z∼ 70–75 km from convective instability. We suggest that these 10 Gravity Field and Ocean Circulation Explorer hot spot GWs are likely tertiary (or higher‐order) GWs created from the dissipation of secondary GWs excited by the local body forces created from MW breaking. We suggest that the other GW is likely a secondary or tertiary (or higher‐order) GW. This study strongly suggests that the hot spot GWs over the Southern Andes in the quiet‐time middle winter thermosphere cannot be successfully modeled by conventional global circulation models where GWs are parameterized and launched in the troposphere or stratosphere. Key Points: The GW dissipative dispersion and polarization relations were used to uniquely characterize the hot spot GWsThe hot spot GWs were medium to large scale, had periods <1 hr, and had horizontal intrinsic phase speeds cIH = 245–630 m/sAll of the hot spot GWs were likely secondary, tertiary, or higher‐order GWs from MW breaking [ABSTRACT FROM AUTHOR]

During the Deep Propagating Gravity Wave Experiment (DEEPWAVE) 13 July 2014 research flight over the South Island of New Zealand, a multiscale spectrum of mountain waves (MWs) was observed. High‐resolution measurements of sodium densities were available from ~70 to 100 km for the duration of this flight. A comprehensive technique is presented for obtaining temperature perturbations, T′, from sodium mixing ratios over a range of altitudes, and these T′ were used to calculate the momentum flux (MF) spectra with respect to horizontal wavelengths, λH, for each flight segment. Spectral analysis revealed MWs with spectral power centered at λH of ~80, 120, and 220 km. The temperature amplitudes of these MWs varied between the four cross‐mountain flight legs occurring between 6:10UT and 9:10UT. The average spectral T′ amplitudes near 80 km in altitude ranged from 7–13 K for the 220 km λH MW and 4–8 K for the smaller λH MWs. These amplitudes decayed significantly up to 90 km, where a critical level for MWs was present. The average MF per unit mass near 80 km in altitude ranged from ~13 to 60 m2/s2 across the varying spectra over the duration of the research flight and decayed to ~0 by 88 km in altitude. These MFs are large compared to zonal means and highlight the importance of MWs in the momentum budget of the mesosphere and lower thermosphere at times when they reach these altitudes. Key Points: A multiscale spectrum of mountain waves was observed during a mesospheric mountain wave event over New ZealandTemperatures of the mountain waves were derived using sodium density mixing ratiosAverage momentum fluxes associated with observed mountain waves were large compared to zonal means [ABSTRACT FROM AUTHOR]

The Deep Propagating Gravity Wave Experiment (DEEPWAVE) was designed to quantify gravity wave (GW) dynamics and effects from orographic and other sources to regions of dissipation at high altitudes. The core DEEPWAVE field phase took place from May through July 2014 using a comprehensive suite of airborne and ground-based instruments providing measurements from Earth's surface to ∼100 km. Austral winter was chosen to observe deep GW propagation to high altitudes. DEEPWAVE was based on South Island, New Zealand, to provide access to the New Zealand and Tasmanian 'hotspots' of GW activity and additional GW sources over the Southern Ocean and Tasman Sea. To observe GWs up to ∼100 km, DEEPWAVE utilized three new instruments built specifically for the National Science Foundation (NSF)/National Center for Atmospheric Research (NCAR) Gulfstream V (GV): a Rayleigh lidar, a sodium resonance lidar, and an advanced mesosphere temperature mapper. These measurements were supplemented by in situ probes, dropsondes, and a microwave temperature profiler on the GV and by in situ probes and a Doppler lidar aboard the German DLR Falcon. Extensive ground-based instrumentation and radiosondes were deployed on South Island, Tasmania, and Southern Ocean islands. Deep orographic GWs were a primary target but multiple flights also observed deep GWs arising from deep convection, jet streams, and frontal systems. Highlights include the following: 1) strong orographic GW forcing accompanying strong cross-mountain flows, 2) strong high-altitude responses even when orographic forcing was weak, 3) large-scale GWs at high altitudes arising from jet stream sources, and 4) significant flight-level energy fluxes and often very large momentum fluxes at high altitudes. [ABSTRACT FROM AUTHOR]

Mountain wave (MW) propagation and dynamics extending into the upper mesosphere accompanying weak forcing are examined using in situ and remote‐sensing measurements aboard the National Science Foundation/National Center for Atmospheric Research Gulfstream V (GV) research aircraft and the German Aerospace Center Falcon. The measurements were obtained during Falcon flights FF9 and FF10 and GV Research Flight RF22 of the Deep Propagating Gravity Wave Experiment (DEEPWAVE) performed over Mount Cook, New Zealand, on 12 and 13 July 2014. In situ measurements revealed both trapped lee waves having zonal wavelengths of λx ~ 12 km and less, and larger‐scale, vertically propagating MWs primarily at λx ~ 20–60 km and ~100–300 km extending from west to ~400 km east of Mount Cook. GV Rayleigh lidar measurements from 25‐ to 60‐km altitudes showed that the weak forcing and zonal winds that increased from ~12 m/s at 12 km to ~40 and 130 m/s at 30 and 55 km, respectively, enabled largely linear MW propagation and strong amplitude growth with altitude into the mesosphere. GV Na lidar and airglow imager measurements revealed an extensive MW response from ~70 to 87 km with large amplitudes and vertical displacements at λx ~ 40–300 km but with both decreasing with altitude approaching a critical level near 90 km. These MWs exhibited large‐scale MW breaking and among the largest sustained momentum fluxes observed in the mesosphere. UK Met Office Unified Model simulations of the RF22 MW event captured many aspects of the observed MW field and revealed that despite the dominant large‐scale MW responses in the stratosphere, the major momentum fluxes accompanied smaller‐scale waves. Key Points: Weak orographic forcing and conducive propagation conditions at lower altitudes can yield large mountain wave amplitudes in the mesosphereMesospheric mountain waves can extend over 1,000 km around the source terrain and persist for many hours after forcing ceasesMesospheric mountain waves having {lambda}h < 100 km can achieve very large momentum fluxes and exhibit strong overturning and instabilities [ABSTRACT FROM AUTHOR]