• Alexander, C. R., , and J. Wurman, 2005: The 30 May 1998 Spencer, South Dakota, storm. Part I: The structural evolution and environment of the tornadoes. Mon. Wea. Rev., 133 , 7296.

    • Search Google Scholar
    • Export Citation
  • Bluestein, H. B., , and A. L. Pazmany, 2000: Observations of tornadoes and other convective phenomena with a mobile 3-mm wavelength, Doppler radar: The spring 1999 field experiment. Bull. Amer. Meteor. Soc., 81 , 29392951.

    • Search Google Scholar
    • Export Citation
  • Bluestein, H. B., , J. G. LaDue, , H. Stein, , D. Speheger, , and W. P. Unruh, 1993: Doppler radar wind spectra of supercell tornadoes. Mon. Wea. Rev., 121 , 22002221.

    • Search Google Scholar
    • Export Citation
  • Bluestein, H. B., , W-C. Lee, , M. Bell, , C. C. Weiss, , and A. L. Pazmany, 2003: Mobile Doppler radar observations of a tornado in a supercell near Bassett, Nebraska, on 5 June 1999. Part II: Tornado-vortex structure. Mon. Wea. Rev., 131 , 29682984.

    • Search Google Scholar
    • Export Citation
  • Bluestein, H. B., , C. C. Weiss, , and A. L. Pazmany, 2004a: Doppler radar observations of dust devils in Texas. Mon. Wea. Rev., 132 , 209224.

    • Search Google Scholar
    • Export Citation
  • Bluestein, H. B., , C. C. Weiss, , and A. L. Pazmany, 2004b: The vertical structure of a tornado near Happy, Texas, on 5 May 2002: High-resolution, mobile, W-band, Doppler radar observations. Mon. Wea. Rev., 132 , 23252337.

    • Search Google Scholar
    • Export Citation
  • Bohne, A. R., 1982: Radar detection of turbulence in precipitation environments. J. Atmos. Sci., 39 , 18191837.

  • Brown, R. A., , and V. T. Wood, 1991: On the interpretation of single-Doppler velocity patterns within severe thunderstorms. Wea. Forecasting, 6 , 3248.

    • Search Google Scholar
    • Export Citation
  • Burgess, D. B., , M. A. Magsig, , J. Wurman, , D. C. Dowell, , and Y. Richardson, 2002: Radar observations of the 3 May 1999 Oklahoma City tornado. Wea. Forecasting, 17 , 456471.

    • Search Google Scholar
    • Export Citation
  • Davies-Jones, R. P., 1986: Tornado dynamics. Thunderstorm Morphology and Dynamics, E. Kessler, Ed., University of Oklahoma Press, 197–236.

    • Search Google Scholar
    • Export Citation
  • Davies-Jones, R. P., 2000: Can the hook echo instigate tornadogenesis barotropically? Preprints. 20th Conf. on Severe Local Storms, Orlando, FL, Amer. Meteor. Soc., 269–272.

    • Search Google Scholar
    • Export Citation
  • Doviak, R. J., , P. S. Ray, , R. G. Strauch, , and L. J. Miller, 1976: Error estimation in wind fields derived from dual-Doppler radar measurement. J. Appl. Meteor., 15 , 868878.

    • Search Google Scholar
    • Export Citation
  • Dowell, D. C., , and H. B. Bluestein, 2002: The 8 June 1995 McLean, Texas, storm. Part I: Observations of cyclic tornadogenesis. Mon. Wea. Rev., 130 , 26262648.

    • Search Google Scholar
    • Export Citation
  • Eskridge, R. E., , and P. Das, 1976: Effect of a precipitation-driven downdraft on a rotating wind field: A possible trigger mechanism for tornadoes? J. Atmos. Sci., 33 , 7084.

    • Search Google Scholar
    • Export Citation
  • Fiedler, B. H., 1989: Conditions for laminar flow in geophysical vortices. J. Atmos. Sci., 46 , 252259.

  • Fiedler, B. H., 1993: Numerical simulation of axisymmetric tornadogenesis in forced convection. The Tornado: Its Structure, Dynamics, Prediction, and Hazards, Geophys. Monogr., No. 79, Amer. Geophys. Union, 41–48.

  • Fiedler, B. H., , and R. Rotunno, 1986: A theory for the maximum windspeeds in tornado-like vortices. J. Atmos. Sci., 43 , 23282340.

  • Fujita, T. T., 1981: Tornadoes and downbursts in the context of generalized planetary scales. J. Atmos. Sci., 38 , 15111534.

  • Golden, J. H., , and D. Purcell, 1977: Photogrammetric velocities for the Great Bend, Kansas, tornado of 30 August 1974: Accelerations and asymmetries. Mon. Wea. Rev., 105 , 485492.

    • Search Google Scholar
    • Export Citation
  • Gunn, R., , and G. D. Kinzer, 1949: The terminal velocity of fall for water droplets in stagnant air. J. Meteor., 6 , 243248.

  • Hoecker, W. H., 1960: Wind speed and airflow patterns in the Dallas tornado of April 2, 1957. Mon. Wea. Rev., 88 , 167180.

  • Kangieser, P. C., 1954: A physical explanation of the hollow structure of waterspout tubes. Mon. Wea. Rev., 82 , 147152.

  • Lee, W-C., , and J. Wurman, 2005: Diagnosed three-dimensional axisymmetric structure of the Mulhall tornado on 3 May 1999. J. Atmos. Sci., in press.

    • Search Google Scholar
    • Export Citation
  • Lee, W-C., , B. J-D. Jou, , P-L. Chang, , and S-M. Deng, 1999: Tropical cyclone kinematic structure retrieved from single-Doppler radar observations. Part I: Interpretation of Doppler velocity patterns and the GBVTD technique. Mon. Wea. Rev., 127 , 24192439.

    • Search Google Scholar
    • Export Citation
  • Lewellen, W. S., 1993: Tornado vortex theory. The Tornado: Its Structure, Dynamics, Prediction, and Hazards, Geophys. Monogr., No. 79, Amer. Geophys. Union, 19–39.

  • Magsig, M. A., , and J. T. Snow, 1998: Long-distance debris transport by tornadic thunderstorms. Part I: The 7 May 1995 supercell thunderstorm. Mon. Wea. Rev., 126 , 14301449.

    • Search Google Scholar
    • Export Citation
  • Marshall, T. P., 2002: Tornado damage survey at Moore, Oklahoma. Wea. Forecasting, 17 , 582598.

  • Martin, W. J., 1998: Hail trajectories and fall speeds with rotation and wind shear. Preprints, 19th Conf. on Severe Local Storms, Minneapolis, MN, Amer. Meteor. Soc., 64–67.

  • Matson, R. J., , and A. W. Huggins, 1980: The direct measurement of the sizes, shapes and kinematics of falling hailstones. J. Atmos. Sci., 37 , 11071125.

    • Search Google Scholar
    • Export Citation
  • McCaul, E. W., , and M. L. Weisman, 2001: The sensitivity of simulated supercell structure and intensity to variations in the shapes of environmental buoyancy and shear profiles. Mon. Wea. Rev., 129 , 664687.

    • Search Google Scholar
    • Export Citation
  • Minor, J. E., , K. C. Mehta, , and J. R. McDonald, 1977: The tornado: An engineering oriented perspective. NOAA Tech. Memo. ERL, NSSL-82, 196 pp.

  • Pruppacher, H. R., , and K. V. Beard, 1970: A wind tunnel investigation of the internal circulation and shape of water drops falling at terminal velocity in air. Quart. J. Roy. Meteor. Soc., 96 , 247256.

    • Search Google Scholar
    • Export Citation
  • Smith, R. K., , and L. M. Leslie, 1979: A numerical study of tornadogenesis in a rotating thunderstorm. Quart. J. Roy. Meteor. Soc., 105 , 107127.

    • Search Google Scholar
    • Export Citation
  • Snow, J. T., 1984: On the formation of particle sheaths in columnar vortices. J. Atmos. Sci., 41 , 24772491.

  • Stackpole, J. D., 1961: The effectiveness of raindrops as turbulence sensors. Preprints, Ninth Weather Radar Conf., Kansas City, MO, Amer. Meteor. Soc., 212–217.

  • Stout, G. E., , and F. A. Huff, 1953: Radar records Illinois tornadogenesis. Bull. Amer. Meteor. Soc., 34 , 281284.

  • USDOC, 1998: Service assessment: Spencer, South Dakota, tornado May 30, 1998. NOAA/NWS, 11 pp.

  • van Tassell, E. L., 1955: The North Platte Valley tornado outbreak of June 27, 1955. Mon. Wea. Rev., 83 , 255264.

  • Wakimoto, R. M., , and B. E. Martner, 1992: Observations of a Colorado tornado. Part II: Combined photogrammetric and Doppler radar analysis. Mon. Wea. Rev., 120 , 522543.

    • Search Google Scholar
    • Export Citation
  • Wakimoto, R. M., , W-C. Lee, , H. B. Bluestein, , C-H. Liu, , and P. H. Hildebrand, 1996: ELDORA observations during VORTEX 95. Bull. Amer. Meteor. Soc., 77 , 14651481.

    • Search Google Scholar
    • Export Citation
  • Wicker, L. J., , and R. B. Wilhelmson, 1995: Simulation and analysis of tornado development and decay within a three-dimensional supercell thunderstorm. J. Atmos. Sci., 52 , 26752703.

    • Search Google Scholar
    • Export Citation
  • Wicker, L. J., , and W. C. Skamarock, 2002: Time-splitting methods for elastic models using forward time schemes. Mon. Wea. Rev., 130 , 20882097.

    • Search Google Scholar
    • Export Citation
  • Wurman, J., 2001: The DOW mobile multiple-Doppler network. Preprints, 30th Int. Conf. on Radar Meteorology, Munich, Germany, Amer. Meteor. Soc., 95–97.

  • Wurman, J., 2002: The multiple-vortex structure of a tornado. Wea. Forecasting, 17 , 473505.

  • Wurman, J., , and S. Gill, 2000: Finescale radar observations of the Dimmitt, Texas (2 June 1995), tornado. Mon. Wea. Rev., 128 , 21352164.

    • Search Google Scholar
    • Export Citation
  • Wurman, J., , and T. Samaras, 2004: Comparison of in-situ pressure and DOW Doppler winds in a tornado and RHI vertical slices through 4 tornadoes during 1996–2004. Preprints, 22d Conf. on Severe Local Storms, Hyannis, MA, Amer. Meteor. Soc., CD-ROM, 15.4.

  • Wurman, J., , and C. R. Alexander, 2005: The 30 May 1998 Spencer, South Dakota, storm. Part II: Comparison of observed damage and radar-derived winds in the tornadoes. Mon. Wea. Rev., 133 , 97119.

    • Search Google Scholar
    • Export Citation
  • Wurman, J., , J. M. Straka, , and E. N. Rasmussen, 1996: Fine-scale Doppler radar observations of tornadoes. Science, 272 , 17741777.

  • Wurman, J., , M. Randall, , and A. Zahrai, 1997: Design and deployment of a portable, pencil-beam, pulsed, 3-cm Doppler radar. J. Atmos. Oceanic Technol., 14 , 15021512.

    • Search Google Scholar
    • Export Citation
  • Zrnic, D. S., , R. J. Doviak, , and D. W. Burgess, 1977: Probing tornadoes with a pulse-Doppler radar. Quart. J. Roy. Meteor. Soc., 103 , 707720.

    • Search Google Scholar
    • Export Citation
  • Zrnic, D. S., , D. W. Burgess, , and L. Hennington, 1985: Doppler spectra and estimated windspeed of a violent tornado. J. Climate Appl. Meteor., 24 , 10681081.

    • Search Google Scholar
    • Export Citation
All Time Past Year Past 30 Days
Abstract Views 0 0 0
Full Text Views 121 121 28
PDF Downloads 81 81 20

Centrifuging of Hydrometeors and Debris in Tornadoes: Radar-Reflectivity Patterns and Wind-Measurement Errors

View More View Less
  • 1 Advanced Study Program, National Center for Atmospheric Research,* Boulder, Colorado
  • | 2 School of Meteorology, University of Oklahoma, Norman, Oklahoma
  • | 3 Center for Severe Weather Research, Boulder, Colorado
  • | 4 National Severe Storms Laboratory, Norman, Oklahoma
© Get Permissions
Restricted access

Abstract

High-resolution Doppler radar observations of tornadoes reveal a distinctive tornado-scale signature with the following properties: a reflectivity minimum aloft inside the tornado core (described previously as an “eye”), a high-reflectivity tube aloft that is slightly wider than the tornado core, and a tapering of this high-reflectivity tube near the ground. The results of simple one-dimensional and two-dimensional models demonstrate how these characteristics develop. Important processes in the models include centrifugal ejection of hydrometeors and/or debris by the rotating flow and recycling of some objects by the near-surface inflow and updraft.

Doppler radars sample the motion of objects within the tornado rather than the actual airflow. Since objects move at different speeds and along different trajectories than the air, error is introduced into kinematic analyses of tornadoes based on radar observations. In a steady, axisymmetric tornado, objects move outward relative to the air and move more slowly than the air in the tangential direction; in addition, the vertical air-relative speed of an object is less than it is in still air. The differences between air motion and object motion are greater for objects with greater characteristic fall speeds (i.e., larger, denser objects) and can have magnitudes of tens of meters per second. Estimates of these differences for specified object and tornado characteristics can be obtained from an approximation of the one-dimensional model.

Doppler On Wheels observations of the 30 May 1998 Spencer, South Dakota, tornado demonstrate how the apparent tornado structure can change when the radar-scatterer type changes. When the Spencer tornado entered the town and started lofting debris, changes occurred in the Doppler velocity and reflectivity fields that are consistent with an increase in mean scatterer size.

Corresponding author address: David C. Dowell, Cooperative Institute for Mesoscale Meteorological Studies, 1313 Halley Circle, Norman, OK 73069. Email: David.Dowell@noaa.gov

Abstract

High-resolution Doppler radar observations of tornadoes reveal a distinctive tornado-scale signature with the following properties: a reflectivity minimum aloft inside the tornado core (described previously as an “eye”), a high-reflectivity tube aloft that is slightly wider than the tornado core, and a tapering of this high-reflectivity tube near the ground. The results of simple one-dimensional and two-dimensional models demonstrate how these characteristics develop. Important processes in the models include centrifugal ejection of hydrometeors and/or debris by the rotating flow and recycling of some objects by the near-surface inflow and updraft.

Doppler radars sample the motion of objects within the tornado rather than the actual airflow. Since objects move at different speeds and along different trajectories than the air, error is introduced into kinematic analyses of tornadoes based on radar observations. In a steady, axisymmetric tornado, objects move outward relative to the air and move more slowly than the air in the tangential direction; in addition, the vertical air-relative speed of an object is less than it is in still air. The differences between air motion and object motion are greater for objects with greater characteristic fall speeds (i.e., larger, denser objects) and can have magnitudes of tens of meters per second. Estimates of these differences for specified object and tornado characteristics can be obtained from an approximation of the one-dimensional model.

Doppler On Wheels observations of the 30 May 1998 Spencer, South Dakota, tornado demonstrate how the apparent tornado structure can change when the radar-scatterer type changes. When the Spencer tornado entered the town and started lofting debris, changes occurred in the Doppler velocity and reflectivity fields that are consistent with an increase in mean scatterer size.

Corresponding author address: David C. Dowell, Cooperative Institute for Mesoscale Meteorological Studies, 1313 Halley Circle, Norman, OK 73069. Email: David.Dowell@noaa.gov

Save