Earth, Planets and Space

, Volume 51, Issue 7–8, pp 543–562 | Cite as

Gravity wave spectra, directions and wave interactions: Global MLT-MFR network

  • Alan H. Manson
  • Chris E. Meek
  • Chris Hall
  • Wayne K. Hocking
  • John MacDougall
  • Steven Franke
  • Kiyoshi Igarashi
  • Dennis Riggin
  • David C. Fritts
  • Robert A. Vincent
Open Access
Article

Abstract

Observations of winds and gravity waves (GW) by MF radars from the Arctic to the Equator are used to provide frequency spectra and spectral variances of horizontal motions, and information on the predominant azimuthal directions of propagation for the waves. The years used are mainly 1993/4; the height layer 76–88 km; and the GW bands 10 100 min. and 1–6 hrs. The high/mid-latitude locations of Tromsø, Saskatoon, London/Urbana, Yamagawa, generally demonstrate similar behaviour: the monthly spectra have slopes near −5/3 in winter months, but smaller (absolute) slopes at higher frequencies (<2 hrs.) in summer. Corresponding to this, the spectral densities (10–100 min.) are larger for conditions of higher mean background windspeed—this is related by means of a new correlation-vector technique to GW propagating anti-parallel to the mean zonal winds, and the closure of the solstitial mesospheric jets. Also consistent with this, the sizes and orientations of perturbation ovals (fitted to the wind variations), demonstrate strong semi-annual-oscillations (SAO), and generally similar monthly and latitudinal directions. This suggests strong control, especially of the high-frequency GW band, by the dominant zonal wind-structures of the mesosphere. In contrast the low-latitude locations of Hawaii and Christmas Island demonstrate uniquely different behaviours, with indications of significant inter-annual variability. The frequency spectra for all months tend to have smaller slopes at higher frequencies. Also the dependence of spectral density in both GW bands, upon background wind speed, is negative rather than positive, and is shown to be generally consistent with GW propagating parallel to the mean-global winds. This is consistent with weaker vertical shears in the zonal winds (76–88 km), and lower GW momentum depositions. The perturbation ovals reveal much weaker SAO, and more variable orientations, consistent with more dependency upon GW sources, and less control by the mean winds of the mesosphere.

Keywords

Gravity Wave Zonal Wind Middle Atmosphere Canadian Prairie Correlation Vector 

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Copyright information

© The Society of Geomagnetism and Earth, Planetary and Space Sciences (SGEPSS); The Seismological Society of Japan; The Volcanological Society of Japan; The Geodetic Society of Japan; The Japanese Society for Planetary Sciences. 1999

Authors and Affiliations

  • Alan H. Manson
    • 1
  • Chris E. Meek
    • 1
  • Chris Hall
    • 2
  • Wayne K. Hocking
    • 3
  • John MacDougall
    • 3
  • Steven Franke
    • 4
  • Kiyoshi Igarashi
    • 5
  • Dennis Riggin
    • 6
  • David C. Fritts
    • 7
  • Robert A. Vincent
    • 8
  1. 1.Institute of Space and Atmospheric StudiesUniversity of SaskatchewanCanada
  2. 2.Auroral ObservatoryUniversity of TromsøNorway
  3. 3.Dept. of Physics and AstronomyUniversity of Western OntarioCanada
  4. 4.Space Science and Remote Sensing LaboratoryUniversity of IllinoisUSA
  5. 5.Upper Atmosphere SectionCommunications Research LaboratoryTokyoJapan
  6. 6.Colorado Research AssociatesBoulderUSA
  7. 7.Dept. of Electrical and Computer EngineeringUniversity of ColoradoUSA
  8. 8.Dept. of Physics and Mathematical PhysicsUniversity of AdelaideAustralia

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