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Stratospheric gravity waves observed during the DEEPWAVE research flight RF25 over the Southern Ocean are analyzed and compared with numerical weather prediction (NWP) model results. The quantitative agreement of the NWP model output and the tropospheric and lower-stratospheric observations is remarkable. The high-resolution NWP models are even able to reproduce qualitatively the observed upper-stratospheric gravity waves detected by an airborne Rayleigh lidar. The usage of high-resolution ERA5 data—partially capturing the long internal gravity waves—enabled a thorough interpretation of the particular event. Here, the observed and modeled gravity waves are excited by the stratospheric flow past a deep tropopause depression belonging to an eastward-propagating Rossby wave train. In the reference frame of the propagating Rossby wave, vertically propagating hydrostatic gravity waves appear stationary; in reality, of course, they are transient and propagate horizontally at the phase speed of the Rossby wave. The subsequent refraction of these transient gravity waves into the polar night jet explains their observed and modeled patchy stratospheric occurrence near 60°S. The combination of both unique airborne observations and high-resolution NWP output provides evidence for the one case investigated in this paper. As the excitation of such gravity waves persists during the quasi-linear propagation phase of the Rossby wave’s life cycle, a hypothesis is formulated that parts of the stratospheric gravity wave belt over the Southern Ocean might be generated by such Rossby wave trains propagating along the midlatitude waveguide.

Noctilucent clouds are optically thin layers of ice particles occuring around 83 km altitude during polar summer. Their intriguing fine-scale structure provides a means to study atmospheric waves and instabilities in the sensitive mesopause region of our atmosphere. For the first time, noctilucent clouds were observed using a backscatter lidar and multiple cameras from a balloon platform. The NASA long-duration balloon PMC-Turbo was launched in July 2018 from Kiruna, Sweden, and floated at 40 km altitude during six days to northern Canada. During the mission, a large dataset with unprecedented high-resolution soundings of noctilucent clouds down to scales of few meters were obtained. The combination of near-vertical lidar soundings with horizontal structures visible in narrow- and wide-field of view cameras allows to fully characterize the morphological structures of noctilucent clouds that are modulated by gravity waves, and reveal dynamic processes such as the breaking of these waves, the generation of various types of instabilities and transitions to turbulence.

In this paper we present an overview of measurements conducted during the WADIS-2 rocket campaign. We investigate the effect of small-scale processes like gravity waves and turbulence on the distribution of atomic oxygen and other species in the mesosphere–lower thermosphere (MLT) region. Our analysis suggests that density fluctuations of atomic oxygen are coupled to fluctuations of other constituents, i.e., plasma and neutrals. Our measurements Show that all measured quantities, including winds, densities, and temperatures, reveal signatures of both waves and turbulence.

PMC-Turbo is a balloon-borne experiment that will fly at an altitude between 35 and 40 km. It is designed to record gravity wave events in polar mesospheric clouds with high spatial and temporal resolution as they unfold across a large field of the sky. The project is motivated by the serendipitous observation of PMCs during the balloon flight of EBEX, an observational cosmology experiment which flew in 2013 at an altitude of about 35 km. EBEX included two star cameras, each of which had a field of view of 4 by 3 degrees, a resolution of 2.5 m at 80 km altitude, and an image cadence of 30 seconds. Even though EBEX was not designed to observe PMCs, instability and turbulent structures were visible with features at scales down to 20 m in the star camera images. However, it is difficult to put the images in context due to the inconsistent pointing, slow image cadence, and the narrow field of view. PMC-Turbo was designed leverage the strengths of the EBEX star cameras to observe gravity wave events at various length scales. This requires capturing a wide view while remaining sensitive to small features, as well as recording images at a high cadence. It carries seven cameras, four of which are wide field cameras that together cover a field of view of about 150 by 40 degrees with an 8 m per pixel resolution. Cameras with narrow field lenses provide smaller fields of view of 10 by 15 degrees with about 3 m per pixel resolution and are situated within in the larger field of view. The cameras can sustain 3.5 frames per second and can capture bursts of images up to 8 frames per second. The payload also carries BOLIDE, a Rayleigh lidar from the DLR Institute of Atmospheric Physics and an airglow camera from Utah State University. These instruments will provide additional context to observed events in the form of thermal profiles and infrared mapping. The Balloon Lidar Experiment BOLIDE is a miniaturized Rayleigh backscatter lidar developed for PMC-Turbo that will provide observations of PMC with unprecedented resolution and signal to noise ratio. PMC-Turbo is scheduled to fly next year from either Sweden or Antarctica. We anticipate a fourteen day flight over Antarctica, and we expect to capture about 14 million images. An arctic flight would last around 5 days, but we anticipate several gravity wave events during this time. In addition to lab testing of our equipment, we have had opportunities to collect data with the PMC-Turbo instruments in the field. This December we will fly one camera as a piggyback on the Super Tiger payload from Antarctica. In July, we used several cameras on the ground to capture PMC images in High Level, Alberta. We hope to resolve tomography from the images captured during that campaign. If we fly from Sweden, we plan to coordinate ground-based tomographic imaging with the balloon flight.

On 14 July 2014 during the Deep Propagating Gravity Wave Experiment (DEEPWAVE), aircraft remote sensing instruments detected large-amplitude gravity wave oscillations within mesospheric airglow and sodium layers at altitudes z ~ 78–83 km downstream of the Auckland Islands, located ~1000 km south of Christchurch, New Zealand. A high-altitude reanalysis and a three-dimensional Fourier gravity wave model are used to investigate the dynamics of this event. At 0700 UTC when the first observations were made, surface flow across the islands’ terrain generated linear three-dimensional wave fields that propagated rapidly to z ~ 78 km, where intense breaking occurred in a narrow layer beneath a zero-wind region at z ~ 83 km. In the following hours, the altitude of weak winds descended under the influence of a large-amplitude migrating semidiurnal tide, leading to intense breaking of these wave fields in subsequent observations starting at 1000 UTC. The linear Fourier model constrained by upstream reanalysis reproduces the salient aspects of observed wave fields, including horizontal wavelengths, phase orientations, temperature and vertical displacement amplitudes, heights and locations of incipient wave breaking, and momentum fluxes. Wave breaking has huge effects on local circulations, with inferred layer-averaged westward flow accelerations of ~350 m s−1 h−1 and dynamical heating rates of ~8 K h−1, supporting recent speculation of important impacts of orographic gravity waves from subantarctic islands on the mean circulation and climate of the middle atmosphere during austral winter.

New measurements at the ALOMAR observatory in northern Norway (69°N, 16°E) using the Weber sodium lidar and the Advanced Mesospheric Temperature Mapper (AMTM) allow for a comprehensive investigation of a gravity wave (GW) event on 22 and 23 January 2012 and the complex and varying propagation environment in which the GW was observed. These observational techniques provide insight into the altitude ranges over which a GW may be evanescent or propagating and enable a clear distinction in specific cases. Weber sodium lidar measurements provide estimates of background temperature, wind, and stability profiles at altitudes from ~78 to 105 km. Detailed AMTM temperature maps of GWs in the OH emission layer together with lidar measurements quantify estimates of the observed and intrinsic GW parameters centered near 87 km. Lidar measurements of sodium densities also allow more precise identification of GW phase structures extending over a broad altitude range. We find for this particular event that the extent of evanescent regions versus regions allowing GW propagation can vary largely over a period of hours and significantly change the range of altitudes over which a GW can propagate.