Temperature sheets and aspect sensitive radar echoes

Abstract. here have been years of discussion and controversy about the existence of very thin and stable temperature sheets and their relationship to the VHF radar aspect sensitivity. It is only recently that very high-resolution in situ temperature observations have brought credence to the reality and ubiquity of these structures in the free atmosphere and to their contribution to radar echo enhancements along the vertical. Indeed, measurements with very high-resolution sensors are still extremely rare and rather difficult to obtain outside of the planetary boundary layer. They have only been carried out up to the lower stratosphere by Service d’A´ eronomie (CNRS, France) for about 10 years. The controversy also persisted due to the volume resolution of the (Mesosphere)-Stratosphere-Troposphere VHF radars which is coarse with respect to sheet thickness, although widely sufficient for meteorological or mesoscale investigations. The contribution within the range gate of many of these structures, which are advected by the wind, and decay and grow at different instants and could be distorted either by internal gravity waves or turbulence fields, could lead to radar echoes with statistical properties similar to those produced by anisotropic turbulence. Some questions thus remain regarding the manner in which temperature sheets contribute to VHF radar echoes. In particular, the zenithal and azimuthal angular dependence of the echo power may not only be produced by diffuse reflection on stable distorted or corrugated sheets, but also by extra contributions from anisotropic turbulence occurring in the stratified atmosphere. Thus, for several years, efforts have been put forth to improve the radar height resolution in order to better describe thin structures. Frequency interferometric techniques are widely used and have been recently further developed with the implementation of high-resolution data processings. We begin by reviewing briefly some characteristics of the ST radar echoes with a particular emphasis on recent works. Their possible coupling with stable sheets is then presented and their known characteristics are described with some hypotheses concerning their generation mechanisms. Finally, measurement campaigns that took recently place or will be carried out in the near future for improving our knowledge of these small-scale structures are presented briefly. Key words. Meteorology and atmospheric dynamics (turbulence; instruments and techniques) – Radio Science (remote sensing)

[1]  J. Röttger,et al.  UHF/VHF radar techniques for atmospheric research and wind profiler applications , 1990 .

[2]  G. Schmidt,et al.  High-Resolution VHF Radar Sounding of the Troposphere and Stratosphere , 1979, IEEE Transactions on Geoscience Electronics.

[3]  S. Fukao,et al.  Coherent radar imaging using Capon's method , 1998 .

[4]  T. Vanzandt,et al.  Biases Due to Gravity Waves in Wind Profiler Measurements of Winds , 1996 .

[5]  J. Weinstock,et al.  Vertical Turbulent Diffusion in a Stably Stratified Fluid , 1978 .

[6]  A. Jain,et al.  Aspect sensitivity of the received radar backscatter at VHF: Preliminary observations using the Indian MST radar , 1997 .

[7]  J. Röttger.  Structure and dynamics of the stratosphere and mesosphere revealed by VHF radar investigations , 1980 .

[8]  A. Muschinski.  Possible Effect of Kelvin-Helmholtz Instability on VHF Radar Observations of the Mean Vertical Wind , 1996 .

[9]  G. Loriot,et al.  Fine Doppler resolution observations of thin turbulence structures in the tropostratosphere at Millstone Hill , 1983 .

[10]  T. Tsuda,et al.  Radar interferometry technique and anisotropy of the echo power distribution: First results , 1991 .

[11]  J A Ratcliffe,et al.  Investigation of molecular motions in supercooled liquids by Mossbauer scattering D C Champeney and F W D Woodhams Some Aspects of Diffraction Theory and their Application to the Ionosphere , 1956 .

[12]  Wayne K. Hocking,et al.  Upper and middle tropospheric kinetic energy dissipation rates from measurements of — review of theories, in-situ investigations, and experimental studies using the Buckland Park atmospheric radar in Australia , 1997 .

[13]  J. L. Lumley,et al.  The Spectrum of Nearly Inertial Turbulence in a Stably Stratified Fluid. , 1964 .

[14]  T. Tsuda,et al.  Azimuth angle variations of specular reflection echoes in the lower atmosphere observed with the MU radar , 1997 .

[15]  Wayne K. Hocking,et al.  Measurement of turbulent energy dissipation rates in the middle atmosphere by radar techniques: A review , 1985 .

[16]  G. R. Stitt,et al.  Frequency domain interferometry: A high resolution radar technique for studies of atmospheric turbulence , 1987 .

[17]  C. Coulman,et al.  Optical seeing-mechanism of formation of thin turbulent laminae in the atmosphere. , 1995, Applied optics.

[18]  T. Tsuda,et al.  Simultaneous observations of reflection echoes and refractive index gradient in the troposphere and lower stratosphere , 1988 .

[19]  J. Rottger.  Radar investigations of the mesosphere, stratosphere and the troposphere in Svalbard , 2000 .

[20]  M. Yamamoto,et al.  Rapid variations in echo power maps of VHF radar backscatter from the lower atmosphere , 2000 .

[21]  Mamoru Yamamoto,et al.  Poststatistic steering wind estimation in the troposphere and lower stratosphere , 1993 .

[22]  O. Phillips.  Turbulence in a strongly stratified fluid—is it unstable? , 1972 .

[23]  P. Műller,et al.  Internal Gravity Waves and Small-Scale Turbulence: Proceedings of 'Aha Huliko'a Hawaiian Winter Workshop (2nd) Held at Manoa on January 17-20, 1984. , 1984 .

[24]  Susumu Kato,et al.  The MU radar with an active phased array system: 1. Antenna and power amplifiers , 1985 .

[25]  W. Ecklund,et al.  A modified Fresnel scattering model for the parameterization of Fresnel returns , 1984 .

[26]  G. D. Nastrom,et al.  Persistent layers of enhanced C2N in the lower stratosphere from VHF radar observations , 2001 .

[27]  K. Gage,et al.  On the vertical‐incidence VHF backscattered power profile from the stratosphere , 1981 .

[28]  Ronald F. Woodman,et al.  Radar Observations of Winds and Turbulence in the Stratosphere and Mesosphere. , 1974 .

[29]  T. Tsuda,et al.  Estimation of turbulence energy dissipation rate and vertical eddy diffusivity with the MU radar RASS , 1999 .

[30]  H. Luce,et al.  An improved interpretation of VHF oblique radar echoes by a direct balloon C2n estimation using a horizontal pair of sensors , 1997 .

[31]  P. Czechowsky,et al.  Spatial variability of the aspect sensitivity of VHF radar echoes in the troposphere and lower stratosphere during jet stream passages , 1994 .

[32]  Hubert Luce,et al.  Direct comparison between in situ and VHF oblique radar measurements of refractive index spectra: A new successful attempt , 1996 .

[33]  James N. Moum,et al.  Length scales of turbulence in stably stratified mixing layers , 2000 .

[34]  J. Röttger.  Reflection and scattering of VHF radar signals from atmospheric refractivity structures , 1980 .

[35]  S. Fukao,et al.  Complete maps of the aspect sensitivity of VHF atmospheric radar echoes , 1999 .

[36]  D. Helal,et al.  Radar imaging and high-resolution array processing applied to a classical VHF-ST profiler , 2001 .

[37]  B. Balsley,et al.  Interpretation of angle‐of‐arrival measurements in the lower atmosphere using spaced antenna radar systems , 1998 .

[38]  A. Waterman,et al.  Measurement of anisotropic permittivity structure of upper troposphere with clear‐air radar , 1985 .

[39]  R. Wand,et al.  Observations of clear air turbulence and winds with the Millstone Hill radar , 1981 .

[40]  J. Röttger,et al.  A study of signal statistics of VHF radar echoes from clear air , 1985 .

[41]  S. Kern,et al.  First Frequency-Domain Interferometry Observations of Large-Scale Vertical Motion in the Atmosphere , 1999 .

[42]  I. Reid,et al.  Evidence of tilted layers in angle of arrival and Doppler beam steering power measurements , 2000 .

[43]  J. Chao,et al.  Spatial interferometer measurements with the Chung-Li VHF radar J. R6ttger 1 , 1990 .

[44]  Richard J. Lataitis,et al.  Cross correlations and cross spectra for spaced antenna wind profilers: 1. Theoretical analysis , 1996 .

[45]  A. B. Crawford,et al.  A reflection theory for propagation beyond the horizon , 1957 .

[46]  F. Castel.  Tropospheric radiowave propagation beyond the horizon , 1966 .

[47]  F. Browand,et al.  The behavior of a turbulent front in a stratified fluid: Experiments with an oscillating grid , 1987 .

[48]  Donald H. Lenschow,et al.  First synthesis of wind‐profiler signals on the basis of large‐eddy simulation data , 1999 .

[49]  Stephen A. Cohn,et al.  Radar Measurements of Turbulent Eddy Dissipation Rate in the Troposphere: A Comparison of Techniques , 1995 .

[50]  W. Hocking,et al.  A quantitative measure of the degree of anisotropy of turbulence in terms of atmospheric parameters, with particular relevance to radar studies , 1997 .

[51]  J. Capon.  High-resolution frequency-wavenumber spectrum analysis , 1969 .

[52]  T. Tsuda,et al.  Zenith-angle dependence of VHF specular reflection echoes in the lower atmosphere , 1997 .

[53]  L. Thomas,et al.  Aspect sensitivity of VHF scatterers in the troposphere and stratosphere from comparisons of powers in off-vertical beams , 1995 .

[54]  T. Tsuda,et al.  Three‐antenna poststatistic steering using the MU radar , 1990 .

[55]  G. D. Nastrom,et al.  High-Resolution VHF Radar Measurements in the Troposphere with a Vertically Pointing Beam , 1998 .

[56]  Ronald F. Woodman,et al.  A poststatistics steering technique for MST radar applications , 1990 .

[57]  S. Fukao,et al.  Combined high-time resolution SDI-FDI experiments with VHF Radars , 2000 .

[58]  P. Chilson,et al.  First observations of Kelvin‐Helmholtz billows in an upper level jet stream using VHF frequency domain interferometry , 1997 .

[59]  B. Campistron,et al.  Aspect sensitivity of VHF radar echoes observed in the middle and upper troposphere during the passage of a cut‐off low , 1999 .

[60]  D. Zrnic,et al.  Reflection and scatter formula for anisotropically turbulent air , 1984 .

[61]  Jenn-Shyong Chen,et al.  Examination of the layer model of the frequency-domain interferometry theory applied in mesosphere-stratosphere-troposphere radars , 2001 .

[62]  Jean Barat,et al.  Some Characteristics of Clear-Air Turbulence in the Middle Stratosphere , 1982 .

[63]  T. Tsuda,et al.  MU radar observations of the aspect sensitivity of backscattered VHF echo power in the troposphere and lower stratosphere , 1986 .

[64]  W. Hocking,et al.  Absolute reflectivities and aspect sensitivities of VHF radio wave scatterers measured with the SOUSY radar , 1986 .

[65]  T. Tsuda,et al.  Aspect sensitivity of stratospheric VHF radio wave scatterers, particularly above 15‐km altitude , 1990 .

[66]  T. Tsuda,et al.  A comparison of VHF radar vertical-velocity measurements by a direct vertical-beam method and by a VAD technique , 1991 .

[67]  Extended radar observations with the frequency radar domain interferometric imaging (FII) technique , 2001 .

[68]  G. I. Barenblatt,et al.  A mathematical model of turbulent heat and mass transfer in stably stratified shear flow , 1993, Journal of Fluid Mechanics.

[69]  Peter Czechowsky,et al.  First low power VHF radar observations of tropospheric, stratospheric and mesospheric winds and turbulence at the Arecibo Observatory , 1981 .

[70]  G. D. Nastrom,et al.  Turbulence eddy dissipation rates from radar observations at 5-20 km at White Sands Missile Range, New mexico , 1997 .

[71]  Susumu Kato,et al.  Observational evidence of a saturated gravity wave spectrum in the troposphere and lower stratosphere , 1988 .

[72]  T. Tsuda,et al.  Viscosity waves and thermal‐conduction waves as a cause of “specular” reflectors in radar studies of the atmosphere , 1991 .

[73]  C. Holloway,et al.  Cross correlations and cross spectra for spaced antenna wind profilers: 2. Algorithms to estimate wind and turbulence , 1997 .

[74]  Earl E. Gossard.  Radar Research on the Atmospheric Boundary Layer , 1990 .

[75]  J. Röttger,et al.  Systematic behavior of signal statistics of MST radar echoes from clear air and their interpretation , 1987 .

[76]  Shoichiro Fukao,et al.  On the interpretation of the layered structures detected by mesosphere-stratosphere-troposphere radars in dual frequency domain interferometry mode , 1999 .

[77]  Toru Sato,et al.  Fine Altitude Resolution Observations of Stratospheric Turbulent Layers by the Arecibo 430 MHz Radar , 1982 .

[78]  M. Yamamoto,et al.  VHF radar interferometry measurements of vertical velocity and the effect of tilted refractivity surfaces on standard Doppler measurements , 1991 .

[79]  J. D. Woods,et al.  On Richardson's Number as a Criterion for Laminar-Turbulent-Laminar Transition in the Ocean and Atmosphere , 1969 .

[80]  R. Woodman,et al.  Ultrahigh vertical resolution radar measurements in the lower stratosphere at Arecibo , 1990 .

[81]  D. Fritts,et al.  Direct numerical simulation of VHF radar measurements of turbulence in the mesosphere , 2000 .

[82]  R. W. Meadows,et al.  Layer structure of the troposphere , 1964 .

[83]  W. Hocking.  Observation and measurement of turbulence m the middle atmosphere with a VHF radar , 1986 .

[84]  J. Pelegrí,et al.  A mechanism for layer formation in stratified geophysical flows , 1998 .

[85]  P. Chilson,et al.  SOMARE‐99: Observations of tropospheric scattering layers using multiple‐frequency range imaging , 2001 .

[86]  Scattering layer thickness and position estimated by radar frequency domain interferometry: 1. Effects of the limited horizontal extent and advection of the scattering layers. , 2000 .

[87]  J. Lane.  Small-scale variations of radio refractive index in the troposphere. Part 1: Relationship to meteorological conditions , 1968 .

[88]  A. S. Gurvich,et al.  Aspect Sensitivity of Radar Returns from Anisotropic Turbulent Irregularities , 1993 .

[89]  Andreas Muschinski,et al.  First In Situ Evidence for Coexisting Submeter Temperature and Humidity Sheets in the Lower Free Troposphere , 1998 .

[90]  M. Yamamoto,et al.  Validation of Winds Measured by MU Radar with GPS Radiosondes during the MUTSI Campaign , 2001 .

[91]  Susumu Kato,et al.  A systematic error in MST/ST radar wind measurement induced by a finite range volume effect: 1. Observational results , 1988 .

[92]  S. A. Thorpe,et al.  Transitional phenomena and the development of turbulence in stratified fluids: A review , 1987 .

[93]  J. Caccia,et al.  VHF-ST Radar Observations of an Upper-Level Front Using Vertical and Oblique-Beam C2N Measurements , 1998 .

[94]  Kenneth S. Gage,et al.  Radar Observations of the Free Atmosphere: Structure and Dynamics , 1990 .

[95]  Phillip B. Chilson,et al.  Range imaging using frequency diversity , 1999 .

[96]  M. Yamamoto,et al.  Frequency domain interferometry observations of tropo/stratospheric scattering layers using the MU radar: Description and first results , 1990 .

[97]  A. W. Friend,et al.  Theory and Practice of Tropospheric Sounding by Radar , 1949, Proceedings of the IRE.

[98]  K. S. Gage,et al.  Observations of stable layers in the troposphere and stratosphere using VHF radar , 1980 .

[99]  B. Bénech,et al.  Space-time description of nonstationary trapped lee waves using ST radars, aircraft, and constant volume balloons during the PYREX experiment , 1997 .

[100]  B. Balsley,et al.  Bias in Mean Vertical Wind Measured by VHF Radars: Significance of Radar Location Relative to Mountains , 2000 .

[101]  R. Wiley,et al.  Billow turbulence and ocean microstructure , 1972 .

[102]  L. Thomas,et al.  Long-period unstable gravity-waves and associated VHF radar echoes , 1997 .

[103]  V. I. Tatarskii.  The effects of the turbulent atmosphere on wave propagation , 1971 .

[104]  Jean Vernin,et al.  Direct Evidence of “Sheets” in the Atmospheric Temperature Field , 1994 .

[105]  P. Chilson,et al.  SOMARE‐99: A demonstrational field campaign for ultrahigh‐resolution VHF atmospheric profiling using frequency diversity , 2001 .

[106]  Susumu Kato,et al.  Air and precipitation particle motions within a cold front measured by the MU VHF radar , 1985 .

[107]  B. Campistron,et al.  Cut-off low monitoring by the French VHF-ST-radar network during the ESTIME campaign , 2000 .

[108]  Stephen Austen Thorpe,et al.  Turbulence and mixing in a Scottish Loch , 1977, Philosophical Transactions of the Royal Society of London. Series A, Mathematical and Physical Sciences.

[109]  J. R. ttger.  ST radar observations of atmospheric waves over mountainous areas : a review , 2022 .

[110]  Steven J Franke,et al.  Pulse compression and frequency domain interferometry with a frequency‐hopped MST radar , 1990 .

[111]  Jürgen Röttger,et al.  Partial reflection and scattering of VHF radar signals from the clear atmosphere , 1978 .

[112]  K. S. Gage,et al.  Evidence for specular reflection from monostatic VHF radar observations of the stratosphere , 1978 .

[113]  Frank D. Eaton,et al.  A new frequency‐modulated continuous wave radar for studying planetary boundary layer morphology , 1995 .

[114]  J. Imberger,et al.  On the nature of turbulence in a stratified fluid , 1991 .

[115]  Earl E. Gossard,et al.  Finestructure of Elevated Stable Layers Observed by Sounder and In Situ Tower Sensors , 1985 .

[116]  B. Balsley,et al.  Doppler-Radar Measurements of Clear Air Atmospheric Turbulence at 1290 MHz , 1981 .

[117]  S. Fukao,et al.  Extended period frequency domain interferometry observations at stratospheric and tropospheric heights , 1995 .

[118]  G. Bienvenu,et al.  Optimality of high resolution array processing using the eigensystem approach , 1983 .

[119]  Rabindra Nath Ghose,et al.  Tropospheric Radio Wave Propagation Beyond the Horizon , 1954 .

[120]  H. Luce,et al.  Interpretation of VHF ST radar vertical echoes from in situ temperature sheet observations , 1995 .

[121]  R. M. Worthington.  Calculating the azimuth of mountain waves, using the effect of tilted fine-scale stable layers on VHF radar echoes , 1999 .

[122]  Ronald F. Woodman,et al.  ASPECT SENSITIVITY MEASUREMENTS OF VHF BACKSCATTER MADE WITH THE CHUNG-LI RADAR - PLAUSIBLE MECHANISMS , 1989 .

[123]  Susumu Kato,et al.  High‐resolution MST observations of turbulence by using the MU radar , 1985 .

[124]  A. Gurvich.  A heuristic model of three-dimensional spectra of temperature inhomogeneities in the stably stratified atmosphere , 1997 .

[125]  W. Hocking,et al.  Pulse length dependence of radar signal strengths for Fresnel backscatter , 1983 .

[126]  M. Yamamoto,et al.  Wind and reflectivity fields around fronts observed with a VHF radar , 1991 .

[127]  Aspect sensitivity at tropospheric heights measured with vertically pointed beam of the Chung-Li VHF radar , 1990 .

[128]  Jean Vernin,et al.  SCIDAR/radar simultaneous measurements of atmospheric turbulence , 1990 .

[129]  Chung-Chih Liu,et al.  New observational techniques for studying the dynamics of the middle atmosphere using the Chung Li VHF radar , 1993 .

[130]  H. Óttersten,et al.  Radar Backscattering from the Turbulent Clear Atmosphere , 1969 .

[131]  J. Chau,et al.  Three-dimensional coherent radar imaging at Jicamarca: comparison of different inversion techniques , 2001 .

[132]  W. Hocking.  An assessment of the capabilities and limitations of radars in measurements of upper atmosphere turbulence , 1996 .

[133]  Jürgen Röttger,et al.  Postset beam steering and interferometer applications of VHF radars to study winds, waves, and turbulence in the lower and middle atmosphere , 1985 .

[134]  M. Yamamoto,et al.  On the relationship between aspect sensitivity and spatial interferometric in-beam incidence angles , 1998 .

[135]  K. S. Gage,et al.  Vertical profiles of refractivity turbulence structure constant: Comparison of observations by the Sunset Radar with a new theoretical model , 1978 .

[136]  Susumu Kato,et al.  The MU radar with an active phased array system: 2. In‐house equipment , 1985 .

[137]  W.E. Gordon,et al.  A Theory of Radio Scattering in the Troposphere , 1950, Proceedings of the IRE.

[138]  D. A. Carter,et al.  The effect of gravity waves on specular echoes observed by the Poker Flat MST Radar , 1981 .

[139]  S. Fukao,et al.  An investigation of tilted aspect‐sensitive scatterers in the lower atmosphere using the MU and Aberystwyth VHF radars , 1999 .

[140]  D. Fritts,et al.  A theory of enhanced saturation of the gravity wave spectrum due to increases in atmospheric stability , 1989 .

[141]  W. Hocking.  Strengths and limitations of MST radar measurements of middle-atmosphere winds , 1997 .