Short Period Gravity Waves in the Arctic Atmosphere Over Alaska

The propagation nature and sources of short-period gravity waves have been studied extensively at low and mid-latitudes, while their extent and nature at the polar regions are less known. During the last decade, observations from select sites on the Antarctic continent have revealed a significant presence of these waves over the southern Polar Region as well as shown unexpected dynamical behavior. In contrast, observations over the Arctic region are few and the dynamical behavior is unknown. A recent project was initiated in January 2011 to investigate the presence and dynamics of these waves over interior Alaska. This site provides an exceptional opportunity to establish a long-term climatology of short-period gravity waves in the Arctic, including their dominant source regions, influences of large-scale tidal and planetary wave motion, as well as impact of dominant weather systems such as the polar vortex and Aleutian low. Here we present initial measurements of short-period gravity waves in the Arctic atmosphere over Alaska

High Frequency Gravity Waves Observed in OH airglow at Starfire Optical Range, NM: Seasonal Variations in Momentum Flux

Airglow imager and Na wind/temperature lidar measurements at Starfire Optical Range, New Mexico (35ºN, 107ºW) are used to estimate the seasonal variation of the vertical fluxes of horizontal momentum carried by high frequency Atmospheric Gravity Waves (AGWs). The cross-correlation coefficients between the vertical and horizontal wind perturbations were calculated from the OH airglow imager data collected during 32 nights in 1998, 1999 and 2000. The RMS wind velocities were deduced from the lidar measurements. The combined information was used to estimate the upper limit of the momentum flux. The meridional component of the vertical flux of horizontal momentum was observed to be towards the summer pole. The zonal component had westward preference in winter and weak preference in summer. The unanticipated large meridional component may act to regulate the summer to winter circulation in the mesosphere

Observational Limits for Lidar, Radar and Airglow Imager Measurements of Gravity Wave Parameters

By examining the observational limits and biases for lidar, radar, and airglow imager measurements of middle atmosphere gravity waves, we provide plausible explanations for the characteristics of the monochromatic wave parameters that have been reported during the past decade. The systematic dependencies of vertical and horizontal wavelength on wave period, reported in many lidar and some radar studies, are associated with diffusive damping. The prominent waves with the largest amplitudes, most often observed by lidars and radars, are those with vertical phase speeds near the diffusive damping limit. The narrow range of horizontal phase velocities of the waves seen by OH imagers is a consequence of the combined effects of the gravity wave spectrum and the OH layer response to wave perturbations. The strongest airglow fluctuations are associated with waves having vertical wavelengths comparable to the width of the OH layer. These waves have fast horizontal phase speeds near 70 m/s. Simple formulas which describe the regions of the wave spectrum observed by each instrument are derived and compared with published data. Lidars, radars, and imagers are often most sensitive to waves in largely different regions of the spectrum so that their measurements are truly complementary. However, these ground-based techniques are often incapable of observing the large-scale waves with periods longer than about 5 hours and both long vertical (\u3e15 km) and horizontal (\u3e1000 km) wavelengths. Spaceborne instruments, such as the high-resolution Doppler imager (HRDI) and wind imaging interferometer (WINDII) on UARS, are the techniques most likely to provide the key observations of the low wavenumber, low-frequency region of the gravity wave spectrum

Winter Climatology of Short-Period Polar Mesospheric Gravity Waves Observed Over Poker Flat Research Range, Alaska (65 o N, 147 o W)

Short-period gravity wave observations over the Arctic region are few and their impact on the Arctic mesosphere lower thermosphere region via momentum deposition is of high interest. The Mesospheric Airglow Imaging and Dynamics project was initiated in January 2011 to investigate the presence and dynamics of these waves over the interior of Alaska. Observations were made from Poker Flat Research Range (PFRR) using an all-sky imager. This site provides an exceptional opportunity to establish a long-term climatology of short-period gravity waves in the Arctic Region. We present summary measurements of prominent gravity waves over two consecutive winters and compare their characteristics with recent observations at Resolute Bay, Canada (75o N), ALOMAR Station, Norway (69o N), Svalbard (78o N), and Rothera Station (76o S). The wave parameters measured at PFRR were found to be similar to the other high-latitude sites, except for the wave headings. The waves at PFRR exhibited dominant eastward motion, while the other observations reported westward motion. To investigate this wave directionality, we look at the effects of critical level filtering

Gravity Waves Over Antarctica

As part of the international Antarctic Gravity Wave Instrument Network (ANGWIN) program, the Utah State University all sky IR imager has been operated at the British Antarctic Survey (BAS) Halley Station (75°36′ S, 26°12′ W) since 2012, obtaining valuable gravity wave information in the upper mesosphere and lower thermosphere region (~80 to 100 km). In this study, we have utilized a new 3D spectral analysis technique (Matsuda, et al., 2014) to quantify the horizontal phase velocity distributions of gravity waves over Antarctica. This new tool enables us to analyze extensive amounts of airglow imaging data in a relatively short time frame. Additionally, it eliminates the bias present in analyses performed by individuals with varying wave event identification experience. Using this new method, forty nights (total ~500 hours) throughout the 2012 winter season have been analyzed. This study will provide insight into variabilities of the gravity wave energy and propagation characteristics during the 2012 winter season

Propagation of short-period gravity waves at high-latitudes during the MaCWAVE winter campaign

As part of the MaCWAVE (Mountain and Convective Waves Ascending Vertically) winter campaign an all-sky monochromatic CCD imager has been used to investigate the properties of short-period mesospheric gravity waves at high northern latitudes. Sequential measurements of several nightglow emissions were made from Esrange, Sweden, during a limited period from 27–31 January 2003. Coincident wind measurements over the altitude range (~80–100 km) using two meteor radar systems located at Esrange and Andenes have been used to perform a novel investigation of the intrinsic properties of five distinct wave events observed during this period. Additional lidar and MSIS model temperature data have been used to investigate their nature (i.e. freely propagating or ducted). Four of these extensive wave events were found to be freely propagating with potential source regions to the north of Scandinavia. No evidence was found for strong orographic forcing by short-period waves in the airglow emission layers. The fifth event was most unusual exhibiting an extensive, but much smaller and variable wavelength pattern that appeared to be embedded in the background wind field. Coincident wind measurements indicated the presence of a strong shear suggesting this event was probably due to a large-scale Kelvin-Helmholtz instability

Gravity wave characteristics in the mesopause region revealed from OH airglow imager observations over Northern Colorado

Author Posting. © American Geophysical Union, 2014. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Space Physics 119 (2014): 630-645, doi:10.1002/2013JA018955.Using 5 years of all-sky OH airglow imager data over Yucca Ridge Field Station, CO (40.7°N, 104.9°W), from September 2003 to September 2008, we extract and deduce quasi-monochromatic gravity wave (GW) characteristics in the mesopause region. The intrinsic periods are clustered between approximately 4 and 10 min, and many of them are unstable and evanescent. GW occurrence frequency exhibits a clear semiannual variation with equinoctial minima, which is likely related to the seasonal variation of background wind. The anomalous propagation direction in January 2006, with strong southward before major warming starting in 21 January and weak southward propagation afterward, was most likely affected by stratospheric sudden warming. The momentum fluxes show strongly anticorrelated with the tides, with ~180° out of phase in the zonal component. While in the meridional component, the easterly maximum occurred approximately 2–6 h after maximum easterly tidal wind. However, the anticorrelations are both weakest during the summer. The dissipating and breaking of small-scale and high-frequency GW's components could have a potential impact on the general circulation in the mesopause region.This work was carried out at the University of Science and Technology of China, with support from the National Natural Science Foundation of China grants (41025016, 41127901, 41225017, 41074108, and 41121003), the National Basic Research Program of China grant 2012CB825605, the Chinese Academy of Sciences Key Research Program KZZD-EW-01, and the Fundamental Research Funds for the Central Universities.2014-07-3

Propagation of short-period gravity waves at high-latitudes during the MaCWAVE winter campaign

As part of the MaCWAVE (Mountain and Convective Waves Ascending Vertically) winter campaign an all-sky monochromatic CCD imager has been used to investigate the properties of short-period mesospheric gravity waves at high northern latitudes. Sequential measurements of several nightglow emissions were made from Esrange, Sweden, during a limited period from 27–31 January 2003. Coincident wind measurements over the altitude range (~80–100 km) using two meteor radar systems located at Esrange and Andenes have been used to perform a novel investigation of the intrinsic properties of five distinct wave events observed during this period. Additional lidar and MSIS model temperature data have been used to investigate their nature (i.e. freely propagating or ducted). Four of these extensive wave events were found to be freely propagating with potential source regions to the north of Scandinavia. No evidence was found for strong orographic forcing by short-period waves in the airglow emission layers. The fifth event was most unusual exhibiting an extensive, but much smaller and variable wavelength pattern that appeared to be embedded in the background wind field. Coincident wind measurements indicated the presence of a strong shear suggesting this event was probably due to a large-scale Kelvin-Helmholtz instability

Seasonal and intra-diurnal variability of small-scale gravity waves in OH airglow at two Alpine stations

Between December 2013 and August 2017 the instrument FAIM (Fast Airglow IMager) observed the OH airglow emission at two Alpine stations. A year of measurements was performed at Oberpfaffenhofen, Germany (48.09∘&thinsp;N, 11.28∘&thinsp;E) and 2 years at Sonnblick, Austria (47.05∘&thinsp;N, 12.96∘&thinsp;E). Both stations are part of the network for the detection of mesospheric change (NDMC). The temporal resolution is two frames per second and the field-of-view is 55&thinsp;km&thinsp;×&thinsp;60&thinsp;km and 75&thinsp;km&thinsp;×&thinsp;90&thinsp;km at the OH layer altitude of 87&thinsp;km with a spatial resolution of 200 and 280&thinsp;m per pixel, respectively. This resulted in two dense data sets allowing precise derivation of horizontal gravity wave parameters. The analysis is based on a two-dimensional fast Fourier transform with fully automatic peak extraction. By combining the information of consecutive images, time-dependent parameters such as the horizontal phase speed are extracted. The instrument is mainly sensitive to high-frequency small- and medium-scale gravity waves. A clear seasonal dependency concerning the meridional propagation direction is found for these waves in summer in the direction to the summer pole. The zonal direction of propagation is eastwards in summer and westwards in winter. Investigations of the data set revealed an intra-diurnal variability, which may be related to tides. The observed horizontal phase speed and the number of wave events per observation hour are higher in summer than in winter.</p