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.

The Southern Argentina Agile MEteor Radar (SAAMER), located at Tierra del Fuego (53.7°S, 67.7°W), has been providing near‐continuous high‐resolution measurements of winds and high‐frequency gravity wave (GW) momentum fluxes of the mesopause region since May 2008. As SAAMER is located in the lee of the largest seasonal GW hot spot on Earth, this is a key location to study GWs and their interaction with large‐scale motions. GW momentum flux climatologies are shown for the first time for this location and discussed in light of these unique dynamics. Particularly, the large eastward GW momentum fluxes during local winter are surprising, as these observations cannot be explained by the direct upward propagation of expected large‐amplitude mountain waves (MWs) through the eastward stratospheric jet. Instead, these results are interpreted as secondary GWs propagating away from stratospheric sources over the Andes accompanying MW breaking over the Southern Andes.

On 4 July 2014, during the Deep Propagating Gravity Wave Experiment (DEEPWAVE), strong low‐level horizontal winds of up to 35 m s⁻¹ over 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.

An anelastic numerical model is used to explore the dynamics accompanying the attainment of large amplitudes by gravity waves (GWs) that are localized in altitude and time. GW momentum transport induces mean flow variations accompanying a GW packet that grows exponentially with altitude, is localized in altitude, and induces significant GW phase speed, and phase, variations across the GW packet. These variations arise because the GW occupies the region undergoing accelerations, with the induced phase speed variations referred to as “self-acceleration.” Results presented here reveal that self-acceleration of a GW packet localized in time and altitude ultimately leads to stalling of the vertical propagation of the GW packet and accompanying two- and three-dimensional (2-D and 3-D) instabilities of the superposed GW and mean motion field. The altitudes at which these effects occur depend on the initial GW amplitude, intrinsic frequency, and degree of localization in time and altitude. Larger amplitudes and higher intrinsic frequencies yield strong self-acceleration effects at lower altitudes, while smaller amplitudes yield similar effects at higher altitudes, provided the Reynolds number, Re, is sufficiently large. Three-dimensional instabilities follow 2-D “self-acceleration instability” for sufficiently high Re. GW packets can also exhibit self-acceleration dynamics at more than one altitude because of continued growth of the GW packet leading edge above the previous self-acceleration event.

A high–Reynolds number direct numerical simulation (DNS) is employed to explore the instability and turbulence dynamics accompanying an idealized multiscale flow that approximates such environments observed throughout the atmosphere. The DNS describes the superposition of a stable gravity wave (GW) and a stable, oscillatory, finescale shear flow that together yield significant wave–wave interactions, GW breaking, Kelvin–Helmholtz instabilities (KHI), fluid intrusions, and turbulence. Larger-scale GW breaking and KHI events account for the strongest turbulence intensities, with intrusions competing with KHI and GW breaking at smaller spatial scales and later times. These dynamics drive a series of sheet-and-layer structures in the velocity, stability, and dissipation fields that persist for many buoyancy periods. Measures of local turbulence intensities include energy dissipation rates, Ozmidov and Thorpe scales ( L _O and L _T , respectively), and a buoyancy Reynolds number sufficient to ensure sustained, strong turbulence events. These exhibit significant variability between and within instability events of different types. The Ozmidov and Thorpe scales for individual events are employed to assess variations of their ratio, C = L _O / L _T , with time. The value of C is highly variable with event type and time but typically increases with time because significant fluid overturning most often precedes turbulence. The value of C determined for the entire domain varies from 0 prior to instability to approximately 2 or larger at late times, with minima (maxima) prior to (following) significant instability and turbulence events. This appears to preclude an assumption that C is constant in stratified flows, except perhaps as an event average that may depend on event type.