Image measurements of short‐period gravity waves at equatorial latitudes

A high-performance, all-sky imaging system has been used to obtain novel data on the morphology and dynamics of short-period (<1 hour) gravity waves at equatorial latitudes. Gravity waves imaged in the upper mesosphere and lower thermosphere were recorded in three nightglow emissions, the near-infrared OH emission, and the visible wavelength OI (557.7 nm) and Na (589.2 nm) emissions spanning the altitude range ∼80–100 km. The measurements were made from Alcantara, Brazil (2.3°S, 44.5°W), during the period August-October 1994 as part of the NASA/Instituto Nacional de Pesquisas Espaciais “Guara campaign”. Over 50 wave events were imaged from which a statistical study of the characteristics of equatorial gravity waves has been performed. The data were found to divide naturally into two groups. The first group corresponded to extensive, freely propagating (or ducted) gravity waves with observed periods ranging from 3.7 to 36.6 min, while the second group consisted of waves of a much smaller scale and transient nature. The later group exhibited a bimodal distribution for the observed periods at 5.18±0.26 min and 4.32±0.15 min, close to the local Brunt-Vaisala period and the acoustic cutoff period, respectively. In comparison, the larger-scale waves exhibited a clear tendency for their horizontal wavelengths to increase almost linearly with observed period. This trend was particularly well defined around the equinox and can be represented by a power-law relationship of the form λh=(3.1±0.5)τob1.06±0.10, where λh is measured in kilometers and τob in minutes. This result is in very good agreement with previous radar and passive optical measurements but differs significantly from the relationship λh ∝ τ1.5ob inferred from recent lidar studies. The larger-scale waves were also found to exhibit strong anisotropy in their propagation headings with the dominant direction of motion toward the-NE-ENE suggesting a preponderance for wave generation over the South American continent.

[1]  M. Yamamoto,et al.  Characteristics of gravity waves in the mesosphere observed with the middle and upper atmosphere radar: 1. Momentum flux , 1993 .

[2]  Guy Moreels,et al.  Bi-dimensional observation of waves near the mesopause at auroral latitudes , 1985 .

[3]  Gerard Thuillier,et al.  Ground based instrument for observing near IR nightglow inhomogeneities at zenith and throughout the sky. , 1989, Applied optics.

[4]  Chester S. Gardner,et al.  Lidar observations of gravity waves and their spectra near the mesopause and stratopause at Arecibo , 1992 .

[5]  M. Taylor,et al.  Analysis of Airglow Image Data , 1982 .

[6]  H. Takahashi,et al.  Airglow O2(1Σ) atmospheric band at 8645 Å and the rotational temperature observed at 23°S , 1986 .

[7]  A. W. Peterson,et al.  Airglow events visible to the naked eye. , 1979, Applied optics.

[8]  D. Fritts,et al.  Wave breaking signatures in sodium densities and OH nightglow: 2. Simulation of wave and instability structures , 1997 .

[9]  E. B. Armstrong.  The association of visible airglow features with a gravity wave , 1982 .

[10]  Toshitaka Tsuda,et al.  Simultaneous observations of mesospheric gravity waves with the MU radar and a sodium lidar , 1996 .

[11]  C. Hines.  INTERNAL ATMOSPHERIC GRAVITY WAVES AT IONOSPHERIC HEIGHTS , 1960 .

[12]  M. Hill,et al.  Near infrared imaging of hydroxyl wave structure over an ocean site at low latitudes , 1991 .

[13]  G. Thomas,et al.  Wave breaking signatures in noctilucent clouds , 1993 .

[14]  M. Herse,et al.  Photographic evidence of waves around the 85 km level , 1977 .

[15]  G. Schubert,et al.  Gravity Wave-Driven Fluctuations in OH Nightglow from an Extended, Dissipative Emission Region , 1991 .

[16]  A. Manson,et al.  Gravity Wave Propagation Characteristics (60–120 km) as Determined by the Saskatoon MF Radar (Gravnet) System: 1983–85 at 52°N, 107°W , 1988 .

[17]  C. Hines.  On the Nature of Traveling Ionospheric Disturbances Launched by Low‐Altitude Nuclear Explosions , 1967 .

[18]  Chester S. Gardner,et al.  ALOHA‐93 measurements of intrinsic AGW characteristics using airborne airglow imager and groundbased Na wind/temperature lidar , 1995 .

[19]  M. Yamamoto,et al.  Characteristics of gravity waves in the mesosphere observed with the middle and upper atmosphere radar: 2. Propagation direction , 1993 .

[20]  Michael J. Taylor,et al.  A two‐dimensional spectral analysis of short period gravity waves imaged in the OI(557.7 nm) and near infra red OH nightglow emissions over Arecibo, Puerto Rico , 1995 .

[21]  C. Gardner.  Diffusive filtering theory of gravity wave spectra in the atmosphere , 1994 .

[22]  Michael J. Taylor,et al.  Evidence of preferential directions for gravity wave propagation due to wind filtering in the middle atmosphere , 1993 .

[23]  R. Vincent,et al.  Measurements of the horizontal scales and phase velocities of short period mesospheric gravity waves at Adelaide, Australia , 1987 .

[24]  Mike Hapgood,et al.  Observations of gravity wave propagation in the OI (557.7 nm), Na (589.2 nm) and the near infrared OH nightglow emissions , 1987 .

[25]  M. Taylor,et al.  An Investigation of Thunderstorms as a Source of Short Period Mesospheric Gravity Waves , 1995 .

[26]  David C. Fritts,et al.  Mesospheric Momentum Flux Studies at Adelaide, Australia: Observations and a Gravity Wave–Tidal Interaction Model , 1987 .

[27]  M. Taylor,et al.  OBSERVATIONS OF SHORT PERIOD MESOSPHERIC WAVE PATTERNS: IN SITU OR TROPOSPHERIC WAVE GENERATION? , 1991 .

[28]  S. Silverman,et al.  On gravity wave induced Brunt-Vaisala oscillations , 1979 .

[29]  E. B. Armstrong.  Irregularities in the 80–100 km region: A photographic approach , 1986 .

[30]  A. Manson,et al.  Observations of mesospheric wind velocities: 1. Gravity wave horizontal scales and phase velocities determined from spaced wind observations , 1985 .

[31]  Mike Hapgood,et al.  On the Origin of Ripple-type Wave Structure in the OH Nightglow Emission , 1990 .

[32]  Chester S. Gardner,et al.  Lidar studies of the nighttime sodium layer over Urbana, Illinois: 2. Gravity waves , 1987 .

[33]  C. Gardner,et al.  Gravity wave activity in the upper mesosphere over Urbana, Illinois: lidar observations and analysis of gravity wave propagation models , 1996 .

[34]  B. Haurwitz,et al.  Wave forms in noctilucent clouds , 1969 .

[35]  H. Takahashi,et al.  Observations of gravity waves from multispectral mesospheric nightglow emissions observed at 23°S , 1995 .

[36]  A. T. Stair,et al.  Rocket measurements of the altitude distributions of the hydroxyl airglow. , 1988 .

[37]  Susan K. Avery,et al.  Empirical wind model for the middle and lower atmosphere. Part 1: Local time average , 1993 .

[38]  I. Reid.  Gravity wave motions in the upper middle atmosphere (60―110 km) , 1986 .

[39]  A. Ebel,et al.  Short period fluctuations of the horizontal wind measured in the upper middle atmosphere and possible relationships to internal gravity waves , 1987 .

[40]  Gary R. Swenson,et al.  OH emission and gravity waves (including a breaking wave) in all-sky imagery from Bear Lake, UT , 1994 .

[41]  A. Manson.  Gravity Wave Horizontal and Vertical Wavelengths: An Update of Measurements in the Mesopause Region (∼80–100 km) , 1990 .

[42]  Michael J. Taylor,et al.  All‐sky measurements of short period waves imaged in the OI(557.7 nm), Na(589.2 nm) and near infrared OH and O2(0,1) nightglow emissions during the ALOHA‐93 Campaign , 1995 .

[43]  Thomas H. Wonnacott,et al.  Regression: A Second Course in Statistics. , 1981 .

[44]  Chester S. Gardner,et al.  An investigation of intrinsic gravity wave signatures using coordinated lidar and nightglow image measurements , 1995 .

[45]  M. Taylor,et al.  Identification of a Thunderstorm as a Source of Short Period Gravity Waves in the Upper Atmospheric Nightglow Emissions , 1988 .

[46]  T. Tsuda,et al.  Empirical wind model for the middle and lower atmosphere. Part 2: Local time variations , 1993 .

[47]  G. Witt.  Height, structure and displacements of noctilucent clouds , 1962 .