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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 λHof ~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 λHMW and 4–8 K for the smaller λHMWs. 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/s2across 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. 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

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. 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. 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 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 hemisphere MSTAD variability in the thermosphere over Alaska during winter months demonstrates a correlation with dynamics in the stratosphere Increased MSTAD activity in the thermosphere correlates with increasing meridional planetary wave amplitudes in the stratosphere

Multiple events during the Deep Propagating Gravity Wave Experiment measurement program revealed mountain wave (MW) breaking at multiple altitudes over the Southern Island of New Zealand. These events were measured during several research flights from the National Science Foundation/National Center for Atmospheric Research Gulfstream V aircraft, utilizing a Rayleigh lidar, an Na lidar, and an Advanced Mesospheric Temperature Mapper simultaneously. A flight on 29 June 2014 observed MWs with horizontal wavelengths of ~80–120 km breaking in the stratosphere from ~10 to 50 km altitude. A flight on 13 July 2014 observed a horizontal wavelength of ~200–240 km MW extending from 20 to 90 km in altitude before breaking. Data from these flights show evidence for secondary gravity wave (SGW) generation near the breaking regions. The horizontal wavelengths of these SGWs are smaller than those of the breaking MWs, indicating a nonlinear generation mechanism. These observations reveal some of the complexities associated with MW breaking and the implications this can have on momentum fluxes accompanying SGWs over MW breaking regions. DEEPWAVE measurements revealed multiple mountain wave breaking eventsSecondary gravity waves were observed at altitudes above breaking regionsSecondary gravity waves demonstrate the complexity of breaking events and variable momentum fluxes

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. 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. 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 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 vortex The primary GWs are created from imbalance of the polar vortex and are amplified below the wind maximum where the vertical wind shear is large The primary and secondary GWs from the polar vortex simulated by the nudged HIAMCM agree well with lidar and Atmospheric InfraRed Sounder observations

Observations performed with a Rayleigh lidar and an Advanced Mesosphere Temperature Mapper aboard the National Science Foundation/National Center for Atmospheric Research Gulfstream V research aircraft on 13 July 2014 during the Deep Propagating Gravity Wave Experiment (DEEPWAVE) measurement program revealed a large‐amplitude, multiscale gravity wave (GW) environment extending from ~20 to 90 km on flight tracks over Mount Cook, New Zealand. Data from four successive flight tracks are employed here to assess the characteristics and variability of the larger‐ and smaller‐scale GWs, including their spatial scales, amplitudes, phase speeds, and momentum fluxes. On each flight, a large‐scale mountain wave (MW) having a horizontal wavelength ~200–300 km was observed. Smaller‐scale GWs over the island appeared to correlate within the warmer phase of this large‐scale MW. This analysis reveals that momentum fluxes accompanying small‐scale MWs and propagating GWs significantly exceed those of the large‐scale MW and the mean values typical for these altitudes, with maxima for the various small‐scale events in the range ~20–105 m2s−2. Mountain waves penetrate the mesosphere under suitable propagation conditionsSmall‐scale gravity waves can attain very large momentum fluxesOccurrence of peak momentum fluxes is often dictated by multiscale environments

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. 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 Mountain wave breaking generates a broad range of secondary waves The secondary wave parameters and morphology are significantly influenced by the tidal winds The secondary waves contribute significant forcing in the tidal shears and over a large area in the thermosphere

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. 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. 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 Nudging in spectral space allows for self‐consistent simulation of gravity waves up to the thermosphere Simulated gravity waves in the winter stratosphere agree well with satellite observations Spontaneous emission of GWs in the winter stratosphere depends critically on vertical wind shear

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. 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

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. 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

On 4 July 2014, during the Deep Propagating Gravity Wave Experiment (DEEPWAVE), strong low‐level horizontal winds of up to 35 m s−1over the Southern Alps, New Zealand, caused the excitation of gravity waves having the largest vertical energy fluxes of the whole campaign (38 W m−2). At the same time, large‐amplitude mesospheric gravity waves were detected by the Temperature Lidar for Middle Atmospheric Research (TELMA) located at Lauder (45.0°S, 169.7°E), New Zealand. The coincidence of these two events leads to the question of whether the mesospheric gravity waves were generated by the strong tropospheric forcing. To answer this, an extensive data set is analyzed, comprising TELMA, in situ aircraft measurements, radiosondes, wind lidar measurements aboard the DLR Falcon as well as Rayleigh lidar and advanced mesospheric temperature mapper measurements aboard the National Science Foundation/National Center for Atmospheric Research Gulfstream V. These measurements are further complemented by limited area simulations using a numerical weather prediction model. This unique data set confirms that strong tropospheric forcing can cause large‐amplitude gravity waves in the mesosphere, and that three essential ingredients are required to achieve this: first, nearly linear propagation across the tropopause; second, leakage through the stratospheric wind minimum; and third, amplification in the polar night jet. Stationary gravity waves were detected in all atmospheric layers up to the mesosphere with horizontal wavelengths between 20 and 100 km. The complete coverage of our data set from troposphere to mesosphere proved to be valuable to identify the processes involved in deep gravity wave propagation. Mountain waves can propagate upward to the mesosphere also under strong low‐level tropospheric forcing conditionsRequired elements for propagation under strong forcing: linear propagation across tropopause, valve layer, and amplification in polar night jetObservations covering the atmosphere from troposphere to mesosphere were valuable to study deep propagation under strong forcing conditions