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 m 2 s À2.

Abstract. This paper assesses the ability of a recently installed 55 MHz multistatic meteor radar to measure gravity-wave-driven momentum fluxes around the mesopause and applies it in a case study of measuring gravity wave forcing on the diurnal tide during a period following the autumnal equinox of 2018. The radar considered is in the vicinity of Adelaide, South Australia (34.9∘ S, 138.6∘ E), and consists of a monostatic radar and bistatic receiver separated by approximately 55 km. The assessment shows that the inclusion of the bistatic receiver reduces the relative uncertainty of the momentum flux estimate from about 75 % to 65 % (for a flux magnitude of ∼20 m2 s−2, 1 d's worth of integration, and for a gravity wave field synthesized from a realistic spectral model). This increase in precision appears to be entirely attributable to the increased number of meteor detections associated with the combined monostatic and bistatic receivers rather than changes in the meteors' spatial distribution. The case study reveals large modulations in the diurnal tidal amplitudes, with a maximum tidal amplitude of ∼50 m s−1 and an associated maximum zonal wind velocity of around 140 m s−1. While the observed gravity wave forcing exhibits a complex relationship with the tidal winds during this period, the components of the forcing are seen to be approximately out of phase with the tidal winds above 88 km. No clear phase relationship has been observed below 88 km.

We present a first analysis of 9 and 6.75 day periodic oscillations observed in the neutral mesospheric density in 2005 and 2006. Mesospheric densities near 90 km are derived using data from the Davis meteor radar (68.5°S, 77.9°E; magnetic latitude, 74.6°S), Antarctica. Spectral analysis indicates that the pronounced periodicities of 9 and 6.75 days observed in the mesosphere densities are associated with variations in solar wind high‐speed streams and recurrent geomagnetic activity. Neutral mesospheric winds and temperatures, simultaneously measured by the Davis meteor radar, also exhibit 9 and 6.75 day periodicities. A Morlet wavelet analysis shows that the time evolution of the 9 and 6.75 day oscillations in the neutral mesosphere densities and winds are similar to those in the solar wind and in planetary magnetic activity index, Kp in 2005 and 2006. These results demonstrate a direct coupling between Sun's corona (upper atmosphere) and the Earth's mesosphere.

We analyze 15 years of atomic oxygen (OI) 558 nm and hydroxyl (OH) (8-3) 730 nm nightglow emission intensities from heights near 96 and 87 km, respectively, measured using filter photometers at the Buckland Park Field Station (34.6°S, 138.6°E) near Adelaide, Australia. The intensity of both emissions exhibits clear seasonal and interannual periodicities, with annual, semiannual, and quasi-biennial oscillations, as well as a solar cycle influence. In addition, there is a terannual and 4.1 year component in the OI airglow intensity and both a quasi-biennial and quasi-triennial oscillation in the OH intensity. The results are in very good agreement with simultaneous collocated measurements made with an imager, and with global satellite climatologies of OI and OH intensities reported for the Wind Imaging Interferometer instrument. The mean value of the OI annual oscillation intensity is the same as that of the semiannual oscillation at this location to within the experimental uncertainty. The OI annual oscillation maximizes in summer, and the semiannual oscillation maximizes in autumn and spring, with the largest maximum in autumn. The terannual component in the OI nightglow maximizes in early summer, autumn, and spring. The quasi-biennial oscillation in the OI nightglow takes its first maximum value in autumn 1996, and the 4.1 year period in this emission first maximizes in summer 1998. The OH annual and semiannual oscillation intensities also agree to within the experimental uncertainties and are observed to peak in early winter. The quasi-biennial and quasi-triennial oscillations in this emission take their first maximum value in summer 1996.

There is increasing interest in space situational awareness worldwide, motivating investigation of the use of nontraditional sensors for space surveillance. This paper presents preliminary results investigating the use of a VHF wind profiling radar for observing objects in low Earth orbit. This radar class is low cost relative to other radars typically applied to this task. The results reveal that 2,410 objects were detected over 15 days, with 1,392 unique objects detected. The daily detection count rates ranged from 150 to 200, and the maximum detection height observed was 2,491 km. The radar's utility for object catalog maintenance is demonstrated by its ability to determine propagation state vector errors, and through observations of the Chinese space station Tiangong‐1 in the last months of its return to Earth. The results suggest the measurements may be able to provide useful ionospheric parameters such as total electron content (TEC) measurements, provided high precision ephemeris data are available for the detected objects.