Editorial Type:
Article
Article Type:
Research Article

VHF-ST Radar Observations of an Upper-Level Front Using Vertical and Oblique-Beam C2N Measurements

J-L. Caccia Laboratoire de Sondages Electromagnétiques de l’Environnement Terrestre, Université de Toulon et du Var, La Garde, France

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J-P. Cammas Laboratoire d’Aérologie, Université Paul Sabatier, Toulouse, France

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Print Publication:
01 Feb 1998
DOI:
https://doi.org/10.1175/1520-0493(1998)126<0483:VSROOA>2.0.CO;2
Page(s):
483–501
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Abstract

Mesoscale aspects of an upper-level front that moved over Brittany (France) during the Mesoscale Frontal Dynamical Project 1987 experiment are investigated using very high frequency stratospheric–tropospheric (VHF-ST) radar data and European Centre for Medium-Range Weather Forecasts (ECMWF) analyses. The synoptic study shows that the upper-level front moved without significant change over the radar during the observation period, from 0000 UTC 14 November 1987 to 0000 UTC 15 November 1987. This allows radar data height–time cross sections to be interpreted as representing the corresponding spatial data distributions. A radar technique of stable airmass detection using the measurement of the aspect ratio, that is, the vertical to oblique power ratio, and the turbulence, that is, the structure constant of the refractive index fluctuations C2N, is developed. This method is applied to the case study of the upper-level frontal passage, which allows the associated stable air masses above the radar site to be monitored when going from 9 km down to the lower troposphere in the 2–4-km altitude range. Mesoscale dynamical aspects of the upper-level frontal zone are described using time series of radar-derived vertical wind shear. The 0.3° slope of the upper-level front, evaluated from the radar data and a 20 m s−1 eastward propagation velocity of the large-scale baroclinic system, agrees well with the one derived from radiosounding data of the nearest synoptic stations. Along this slope, an enhancement of the turbulence and a maximum vertical wind shear of 20 m s−1 km−1 were found. At a larger scale (timescale of 6 h), the reliability of the VHF-ST radar measurements of the air vertical velocity in the vicinity of the frontal zone is supported by both a favorable cross comparison with the vertical velocity calculated from the ECMWF analyses and downward motions roughly deduced from the winds on the isentropic surfaces.

Corresponding author address: Dr. J.-L. Caccia, Laboratoire de Sondages Electromagnetiques de l’Environment Terrestre, Universite de Toulon et du Var, BP 132, 83957 La Garde Cedex, France.

Abstract

Mesoscale aspects of an upper-level front that moved over Brittany (France) during the Mesoscale Frontal Dynamical Project 1987 experiment are investigated using very high frequency stratospheric–tropospheric (VHF-ST) radar data and European Centre for Medium-Range Weather Forecasts (ECMWF) analyses. The synoptic study shows that the upper-level front moved without significant change over the radar during the observation period, from 0000 UTC 14 November 1987 to 0000 UTC 15 November 1987. This allows radar data height–time cross sections to be interpreted as representing the corresponding spatial data distributions. A radar technique of stable airmass detection using the measurement of the aspect ratio, that is, the vertical to oblique power ratio, and the turbulence, that is, the structure constant of the refractive index fluctuations C2N, is developed. This method is applied to the case study of the upper-level frontal passage, which allows the associated stable air masses above the radar site to be monitored when going from 9 km down to the lower troposphere in the 2–4-km altitude range. Mesoscale dynamical aspects of the upper-level frontal zone are described using time series of radar-derived vertical wind shear. The 0.3° slope of the upper-level front, evaluated from the radar data and a 20 m s−1 eastward propagation velocity of the large-scale baroclinic system, agrees well with the one derived from radiosounding data of the nearest synoptic stations. Along this slope, an enhancement of the turbulence and a maximum vertical wind shear of 20 m s−1 km−1 were found. At a larger scale (timescale of 6 h), the reliability of the VHF-ST radar measurements of the air vertical velocity in the vicinity of the frontal zone is supported by both a favorable cross comparison with the vertical velocity calculated from the ECMWF analyses and downward motions roughly deduced from the winds on the isentropic surfaces.

Corresponding author address: Dr. J.-L. Caccia, Laboratoire de Sondages Electromagnetiques de l’Environment Terrestre, Universite de Toulon et du Var, BP 132, 83957 La Garde Cedex, France.

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  • Browning, K. A., B. J. Hoskins, P. R. Jonas, and A. J. Thorpe, 1986:European collaboration on atmospheric fronts. Nature,322, 114–115.

  • Clough, S. A., 1987: The mesoscale frontal dynamic project. Meteor. Mag.,116, 32–42.

  • Crochet, M., 1990: Atmospheric profiler radar. Developments and outstanding questions. Meteor. Rundsch.,42, 123–136.

  • ——, E. Bazile, and G. Rougier, 1990a: Comparison of thermal advection measurements by clear-air radar and radiosonde techniques. Radio Sci.,25, 907–915.

  • ——, F. Cuq, F. M. Ralph, and S. V. Venkateswaran, 1990b: Clear air radar observations of the great October storm of 1987. Dyn. Atmos. Oceans,14, 443–461.

  • Dalaudier, F., C. Sidi, M. Crochet, and J. Vernin, 1994: Direct evidence of “sheets” in the atmospheric temperature field. J. Atmos. Sci.,51, 237–248.

  • Ecklund, W. L., D. A. Carter, and B. B. Balsley, 1979: Continuous measurement of upper atmospheric winds and turbulence using a VHF Doppler radar: Preliminary results. J. Atmos. Terr. Phys.,41, 983–994.

  • Fisher, C., and F. Lalaurette, 1995a: Meso-beta-scale circulations in realistic fronts. I: Steady basic state. Quart. J. Roy. Meteor. Soc.,121, 1255–1283.

  • ——, and ——, 1995b: Meso-beta-scale circulations in realistic fronts. II: Frontogenetically forced basic states. Quart. J. Roy. Meteor. Soc.,121, 1285–1321.

  • Fukao, S., T. Sato, N. Yamasaki, R. Harper, and S. Kato, 1982: Winds measured by a UHF Doppler radar and rawinsondes: Comparisons made on twenty-six days (August–September 1977) at Arecibo, Puerto Rico. J. Appl. Meteor.,21, 1357–1363.

  • Gage, K. S., and B. B. Balsley, 1978: Doppler radar probing of the clear atmosphere. Bull. Amer. Meteor. Soc.,59, 1074–1093.

  • ——, and J. L. Green, 1978: Evidence for specular reflection from monostatic VHF radar observations of the stratosphere. Radio Sci.,13, 991–1001.

  • ——, and B. B. Balsley, 1980: On the scattering and reflection mechanisms contributing to clear air radar echoes from the troposphere, stratosphere, and mesosphere, Radio Sci.,15, 243–257.

  • Gidel, L. T., and M. A. Shapiro, 1979: The role of clear air turbulence in the production of potential vorticity in the vicinity of jet-stream–frontal systems. J. Atmos. Sci.,36, 2125–2138.

  • Green, J. L., and K. S. Gage, 1980: Observations of stable layers in the troposphere and stratosphere using VHF radar. Radio Sci.,15, 395–405.

  • ——, T. E. VanZandt, W. L. Clark, J. M. Warnock, and G. D. Nastrom, 1988: Observations of vertical velocity over Illinois by the Flatland radar. Geophys. Res. Lett.,15, 269–272.

  • Hocking, W. K., S. Fukao, T. Tsuda, M. Yamamoto, T. Sato, and S. Kato, 1990: Aspect sensitivity of stratospheric VHF radio wave scatterers, particularly above 15-km altitude. Radio Sci.,25, 613–627.

  • Hoskins, B. J., M. E. McIntyre, and A. W. Robertson, 1985: On the use and significance of isentropic potential vorticity maps. Quart. J. Roy. Meteor. Soc.,111, 877–946.

  • Keyser, D., and M. A. Shapiro, 1986: A review of the structure and dynamics of the upper-level frontal zones. Mon. Wea. Rev.,114, 452–499.

  • Larsen, M. F., and J. Röttger, 1982: VHF and UHF Doppler radars as tools for synoptic research. Bull. Amer. Meteor. Soc.,63, 996–1008.

  • ——, and ——, 1985: Observations of frontal zone and tropopause structures with a VHF Doppler radar and radiosondes. Radio Sci.,20, 1223–1232.

  • ——, and ——, 1991: VHF radar measurements of in-beam incidence angles and associated vertical-beam radial velocity corrections. J. Atmos. Oceanic Technol.,8, 477–490.

  • ——, ——, and T. S. Dennis, 1988: A comparison of operational analyses and VHF wind profiler vertical velocities. Mon. Wea. Rev.,116, 48–59.

  • ——, S. Fukao, O. Aruga, M. D. Yamanaka, T. Tsuda, and S. Kato, 1991: A comparison of VHF radial vertical-velocity measurements by a direct vertical-beam method and by a VAD technique. J. Atmos. Oceanic Technol.,8, 766–776.

  • Lott, F., 1995: Comparison between the orographic response of the ECMWF model and the PYREX 1990 data. Quart. J. Roy. Meteor. Soc.,121, 1323–1348.

  • Luce, H., M. Crochet, F. Dalaudier, and C. Sidi, 1995: Interpretation of VHF ST radar vertical echoes from in situ temperature sheet observations. Radio Sci.,30, 1003–1025.

  • ——, F. Dalaudier, M. Crochet, and C. Sidi, 1996: Direct comparison between in situ and VHF oblique radar measurements of refractive index spectra: a new successful attempt. Radio Sci.,31, 1487–1500.

  • May, P. T., M. Yamamoto, S. Fukao, T. Sato, S. Kato, and T. Tsuda, 1991: Wind and reflectivity fields around fronts observed with a VHF radar. Radio Sci.,26, 1245–1249.

  • Nastrom, G. D., W. L. Ecklund, and K. S. Gage, 1985: On the direct measurement of large-scale vertical velocities using clear-air Doppler radars. Mon. Wea. Rev.,113, 708–718.

  • ——, W. L. Clark, K. S. Gage, T. E. VanZandt, J. M. Warnock, R. Creasey, and P. M. Pauley, 1994: Case studies of the vertical velocity seen by the Flatland radar compared with indirectly computed values. J. Atmos. Oceanic Technol.,11, 14–21.

  • Neiman, P. J., and M. A. Shapiro, 1989: Retrieving horizontal temperature gradients and advections from single-station wind profiler observations. Wea. Forecasting,4, 222–233.

  • ——, P. T. May, and M. A. Shapiro, 1992: Radio acoustic sounding system (RASS) and wind profiler observations of lower- and midtropospheric weather system. Mon. Wea. Rev.,120, 2298–2313.

  • O’Brien, J. J., 1970: Alternative solutions to the classical vertical velocity problem. J. Appl. Meteor.,9, 197–203.

  • Redelsperger, J.-L., and J.-P. Lafore, 1994: Non-hydrostatic simulations of a cold front observed during the FRONTS 87 experiment. Quart. J. Roy. Meteor. Soc.,120, 519–555.

  • Röttger, J., 1979: VHF radar observations of a frontal passage. J. Appl. Meteor.,18, 85–91.

  • ——, 1980: Reflection and scattering of VHF radar signals from atmospheric refractivity structures. Radio Sci.,15, 259–276.

  • ——, and C. H. Liu, 1978: Partial reflection and scattering of VHF radar signals from the clear air atmosphere. Geophys. Res. Lett.,5, 357–360.

  • Sortais, J.-L., J.-P. Cammas, X. D. Yu, E. Richard, and R. Rosset, 1993: A case study of coupling between low- and upper-level jet-front systems: Investigation of dynamical and diabatical processes. Mon. Wea. Rev.,121, 2239–2253.

  • Strauch, R. G., B. L. Weber, A. S. Frisch, C. G. Little, D. A. Merritt, K. P. Moran, and D. C. Welsh, 1987: The precision and relative accuracy of profiler wind measurements. J. Atmos. Oceanic Technol.,4, 563–571.

  • Tennekes, H., and J. L. Lumley, 1972: A First Course in Turbulence. MIT Press, 300 pp.

  • Thorpe, A. J., and S. A. Clough, 1991: Mesoscale dynamics of cold fronts: Structures described by dropsoundings in FRONTS 87. Quart. J. Roy. Meteor. Soc.,117, 903–941.

  • ——, S. T. Garner, and J. Testud, 1987: Theoretical aspects of the project “Mesoscale Frontal Dynamical Project.” Rep. 33, 24 pp. [Available from A. J. Thorpe, JCMM Pitt Building, University of Reading, White Kings Road, P.O. Box 240, Reading RG62FN, United Kingdom.].

  • Tsuda, T., T. Sato, K. Hirose, S. Fukao, and S. Kato, 1986: MU radar observations of the aspect sensitivity of backscattered VHF echo power in the troposphere and lower stratosphere. Radio Sci.,21, 971–980.

  • van Baelen, J. S., A. D. Richmond, T. Tsuda, S. K. Avery, S. Kato, S. Fukao, and M. Yamamoto, 1991: Radar interferometry technique and anisotropy of the echo power distribution: First results. Radio Sci.,26, 1315–1326.

  • Yoe, J. G., and R. Rüster, 1992: VHF Doppler radar observations of vertical velocities in the vicinity of the jet stream. Mon. Wea. Rev.,120, 2378–2382.

  • ——, P. Czechowsky, R. Rüster, and G. Schmidt, 1994: Spatial variability of the aspect sensitivity of VHF radar echoes in the troposphere and lower stratosphere during jet stream passages. Ann. Geophys.,12, 733–745.

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