Editorial Type:
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Article Type:
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Observed Boundary Layer Wind Structure and Balance in the Hurricane Core. Part I: Hurricane Georges

Jeffrey D. Kepert Bureau of Meteorology Research Centre, Melbourne, Australia

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Print Publication:
01 Sep 2006
DOI:
https://doi.org/10.1175/JAS3745.1
Page(s):
2169–2193
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Abstract

The GPS dropsonde allows observations at unprecedentedly high horizontal and vertical resolution, and of very high accuracy, within the tropical cyclone boundary layer. These data are used to document the boundary layer wind field of the core of Hurricane Georges (1998) when it was close to its maximum intensity. The spatial variability of the boundary layer wind structure is found to agree very well with the theoretical predictions in the works of Kepert and Wang. In particular, the ratio of the near-surface wind speed to that above the boundary layer is found to increase inward toward the radius of maximum winds and to be larger to the left of the track than to the right, while the low-level wind maximum is both more marked and at lower altitude on the left of the storm track than on the right. However, the expected supergradient flow in the upper boundary layer is not found, with the winds being diagnosed as close to gradient balance.

The tropical cyclone boundary layer model of Kepert and Wang is used to simulate the boundary layer flow in Hurricane Georges. The simulated wind profiles are in good agreement with the observations, and the asymmetries are well captured. In addition, it is found that the modeled flow in the upper boundary layer at the eyewall is barely supergradient, in contrast to previously studied cases. It is argued that this lack of supergradient flow is a consequence of the particular radial structure in Georges, which had a comparatively slow decrease of wind speed with radius outside the eyewall. This radial profile leads to a relatively weak gradient of inertial stability near the eyewall and a strong gradient at larger radii, and hence the tropical cyclone boundary layer dynamics described by Kepert and Wang can produce only marginally supergradient flow near the radius of maximum winds. The lack of supergradient flow, diagnosed from the observational analysis, is thus attributed to the large-scale structure of this particular storm. A companion paper presents a similar analysis for Hurricane Mitch (1998), with contrasting results.

Corresponding author address: Dr. Jeff Kepert, Bureau of Meteorology Research Centre, GPO Box 1289K Melbourne, 700 Collins Street, Docklands, VIC 3001, Australia. Email: j.kepert@bom.gov.au

Abstract

The GPS dropsonde allows observations at unprecedentedly high horizontal and vertical resolution, and of very high accuracy, within the tropical cyclone boundary layer. These data are used to document the boundary layer wind field of the core of Hurricane Georges (1998) when it was close to its maximum intensity. The spatial variability of the boundary layer wind structure is found to agree very well with the theoretical predictions in the works of Kepert and Wang. In particular, the ratio of the near-surface wind speed to that above the boundary layer is found to increase inward toward the radius of maximum winds and to be larger to the left of the track than to the right, while the low-level wind maximum is both more marked and at lower altitude on the left of the storm track than on the right. However, the expected supergradient flow in the upper boundary layer is not found, with the winds being diagnosed as close to gradient balance.

The tropical cyclone boundary layer model of Kepert and Wang is used to simulate the boundary layer flow in Hurricane Georges. The simulated wind profiles are in good agreement with the observations, and the asymmetries are well captured. In addition, it is found that the modeled flow in the upper boundary layer at the eyewall is barely supergradient, in contrast to previously studied cases. It is argued that this lack of supergradient flow is a consequence of the particular radial structure in Georges, which had a comparatively slow decrease of wind speed with radius outside the eyewall. This radial profile leads to a relatively weak gradient of inertial stability near the eyewall and a strong gradient at larger radii, and hence the tropical cyclone boundary layer dynamics described by Kepert and Wang can produce only marginally supergradient flow near the radius of maximum winds. The lack of supergradient flow, diagnosed from the observational analysis, is thus attributed to the large-scale structure of this particular storm. A companion paper presents a similar analysis for Hurricane Mitch (1998), with contrasting results.

Corresponding author address: Dr. Jeff Kepert, Bureau of Meteorology Research Centre, GPO Box 1289K Melbourne, 700 Collins Street, Docklands, VIC 3001, Australia. Email: j.kepert@bom.gov.au

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  • Aberson, S., cited. 1998: Mission summary Hurricane Georges 980919h. [Available online at http://www.aoml.noaa.gov/hrd/HFP98/980919h_sum.pdf.].

  • Anthes, R. A., 1971: Iterative solutions to the steady-state axisymmetric boundary-layer equations under an intense pressure gradient. Mon. Wea. Rev., 99 , 261–268.

    • Search Google Scholar
    • Export Citation

  • Black, M. L., cited. 1998: Mission summary 981027I1 Hurricane Mitch modified eyewall vertical motion experiment. [Available online at http://www.aoml.noaa.gov/hrd/HFP98/981027i1_sum.pdf.].

  • Bluestein, H. B., and F. D. Marks Jr., 1987: On the structure of the eyewall of Hurricane Diana (1984): Comparison of radar and visual characteristics. Mon. Wea. Rev., 115 , 2542–2552.

    • Search Google Scholar
    • Export Citation

  • Daley, R., 1985: The analysis of synoptic scale divergence by a statistical interpolation procedure. Mon. Wea. Rev., 113 , 1066–1079.

  • Daley, R., 1991: Atmospheric Data Analysis. Cambridge University Press, 457 pp.

  • DeMaria, M., and J. Kaplan, 1999: An updated statistical hurricane intensity prediction scheme (SHIPS) for the Atlantic and eastern North Pacific basins. Wea. Forecasting, 14 , 326–337.

    • Search Google Scholar
    • Export Citation

  • Eliassen, A., and M. Lystad, 1977: The Ekman layer of a circular vortex: A numerical and theoretical study. Geophys. Norv., 31 , 1–16.

  • Emanuel, K. A., 1986: An air–sea interaction theory for tropical cyclones. Part I: Steady-state maintenance. J. Atmos. Sci., 43 , 585–604.

    • Search Google Scholar
    • Export Citation

  • Frank, W. M., and E. A. Ritchie, 2001: Effects of vertical wind shear on the intensity and structure of numerically simulated hurricanes. Mon. Wea. Rev., 129 , 2249–2269.

    • Search Google Scholar
    • Export Citation

  • Franklin, J. L., M. L. Black, and K. Valde, 2003: GPS dropwindsonde wind profiles in hurricanes and their operational implications. Wea. Forecasting, 18 , 32–44.

    • Search Google Scholar
    • Export Citation

  • Gray, W. M., 1967: The mutual variation of wind, shear and baroclinicity in the cumulus convective atmosphere of the hurricane. Mon. Wea. Rev., 95 , 55–73.

    • Search Google Scholar
    • Export Citation

  • Gray, W. M., 1991: Comments on “Gradient balance in tropical cyclones.”. J. Atmos. Sci., 48 , 1201–1208.

  • Gray, W. M., and D. J. Shea, 1973: The hurricanes inner core region. II: Thermal stability and dynamic characteristics. J. Atmos. Sci., 30 , 1565–1576.

    • Search Google Scholar
    • Export Citation

  • Hock, T. F., and J. L. Franklin, 1999: The NCAR GPS dropwindsonde. Bull. Amer. Meteor. Soc., 80 , 407–420.

  • Holland, G. J., 1980: An analytic model of the wind and pressure profiles in hurricanes. Mon. Wea. Rev., 108 , 1212–1218.

  • Jelesnianski, C., 1993: The habitation layer. WMO Global Guide to Tropical Cyclone Forecasting, G. J. Holland, Ed., WMO Tech. Doc. TCP–31, 356 pp.

  • Jorgensen, D. P., 1984: Mesoscale and convective-scale characteristics of mature hurricane. Part I: General observations by research aircraft. J. Atmos. Sci., 41 , 1268–1285.

    • Search Google Scholar
    • Export Citation

  • Kepert, J. D., 2001: The dynamics of boundary layer jets within the tropical cyclone core. Part I: Linear theory. J. Atmos. Sci., 58 , 2469–2484.

    • Search Google Scholar
    • Export Citation

  • Kepert, J. D., 2002: The wind-field structure of the tropical cyclone boundary-layer. Ph.D. thesis, Monash University, 350 pp.

  • Kepert, J. D., 2005: Objective analysis of tropical cyclone location and motion from high density observations. Mon. Wea. Rev., 133 , 2406–2421.

    • Search Google Scholar
    • Export Citation

  • Kepert, J. D., 2006: Observed boundary layer wind structure and balance in the hurricane core. Part II: Hurricane Mitch. J. Atmos. Sci., 63 , 2194–2211.

    • Search Google Scholar
    • Export Citation

  • Kepert, J. D., and Y. Wang, 2001: The dynamics of boundary layer jets within the tropical cyclone core. Part II: Nonlinear enhancement. J. Atmos. Sci., 58 , 2485–2501.

    • Search Google Scholar
    • Export Citation

  • Knaff, J. A., J. P. Kossin, and M. DeMaria, 2003: Annular hurricanes. Wea. Forecasting, 18 , 204–223.

  • Kuo, H. L., 1971: Axisymmetric flow in the boundary layer of a maintained vortex. J. Atmos. Sci., 28 , 20–41.

  • Kuo, H. L., 1982: Vortex boundary layer under quadratic surface stress. Bound.-Layer Meteor., 22 , 151–169.

  • Landsea, C. W., J. L. Franklin, C. J. McAdie, J. L. Benen II, J. M. Gross, B. R. Jarvinen, J. P. Dunion, and P. P. P. Dodge, 2004: A reanalysis of Hurricane Andrew’s (1992) intensity. Bull. Amer. Meteor. Soc., 85 , 1699–1712.

    • Search Google Scholar
    • Export Citation

  • Lorenc, A. C., 1981: A global three-dimensional multivariate statistical interpolation scheme. Mon. Wea. Rev., 109 , 701–721.

  • Lorenc, A. C., 1986: Analysis methods for numerical weather prediction. Quart. J. Roy. Meteor. Soc., 112 , 1177–1194.

  • Marks, F. D., R. A. Houze, and J. F. Gamache, 1992: Dual-aircraft investigation of the inner core of Hurricane Norbert. Part I: Kinematic structure. J. Atmos. Sci., 49 , 919–942.

    • Search Google Scholar
    • Export Citation

  • Mitsuta, Y., T. Suenobu, and T. Fujii, 1988: Supergradient surface wind in the eye of a typhoon. J. Meteor. Soc. Japan, 66 , 505–508.

  • Montgomery, M. T., H. D. Snell, and Z. Yang, 2001: Axisymmetric spindown dynamics of hurricanelike vortices. J. Atmos. Sci., 58 , 421–435.

    • Search Google Scholar
    • Export Citation

  • Pasch, R. J., L. A. Avila, and J. L. Guiney, 2001: Atlantic hurricane season of 1998. Mon. Wea. Rev., 129 , 3085–3123.

  • Powell, M. D., 1980: Evaluations of diagnostic marine boundary layer models applied to hurricanes. Mon. Wea. Rev., 108 , 757–766.

  • Powell, M. D., S. H. Houston, and T. A. Reinhold, 1996: Hurricane Andrew’s landfall in south Florida. Part I: Standardizing measurements for documentation of surface wind fields. Wea. Forecasting, 11 , 304–328.

    • Search Google Scholar
    • Export Citation

  • Powell, M. D., P. J. Vickery, and T. A. Reinhold, 2003: Reduced drag coefficient for high wind speeds in tropical cyclones. Nature, 422 , 279–283.

    • Search Google Scholar
    • Export Citation

  • Press, W. H., S. A. Teukolsky, W. Y. Vetterling, and B. P. Flannery, 1992: Numerical Recipes in C. Cambridge University Press, 994 pp.

  • Reasor, P. D., M. T. Montgomery, and L. D. Grasso, 2004: A new look at the problem of tropical cyclones in vertical shear flow: Vortex resiliency. J. Atmos. Sci., 61 , 3–22.

    • Search Google Scholar
    • Export Citation

  • Rosenthal, S. L., 1962: A Theoretical Analysis of the Field of Motion in the Hurricane Boundary Layer. National Hurricane Research Project Rep. 56, Washington, DC, 12 pp.

    • Search Google Scholar
    • Export Citation

  • Shapiro, L. J., 1983: The asymmetric boundary layer under a translating hurricane. J. Atmos. Sci., 40 , 1984–1998.

  • Simmons, A. J., and J. K. Gibson, 2000: The ERA-40 project plan. ERA-40 Project Rep. Series 1, European Centre for Medium-Range Weather Forecasting, 63 pp.

  • Wang, J., H. L. Cole, D. J. Carlson, E. R. Miller, K. Beierle, A. Paukkunen, and T. K. Laine, 2002: Corrections of humidity measurement errors from the Vaisala RS80 Radiosonde—Application to TOGA COARE data. J. Atmos. Oceanic Technol., 19 , 981–1002.

    • Search Google Scholar
    • Export Citation

  • Willoughby, H. E., 1990: Gradient balance in tropical cyclones. J. Atmos. Sci., 47 , 265–274.

  • Willoughby, H. E., 1991: Reply. J. Atmos. Sci., 48 , 1209–1212.

  • Willoughby, H. E., 1995: Mature structure and evolution. Global Perspectives on Tropical Cyclones, R. L. Elsberry, Ed., WMO Rep. TCP-38, 21–62.

  • Willoughby, H. E., and M. Chelmow, 1982: Objective determination of hurricane tracks from aircraft observations. Mon. Wea. Rev., 110 , 1298–1305.

    • Search Google Scholar
    • Export Citation

  • Willoughby, H. E., R. W. R. Darling, and M. E. Rahn, 2006: Parametric representation of the primary hurricane vortex. Part II: A new family of sectionally continuous profiles. Mon. Wea. Rev., 134 , 1102–1120.

    • Search Google Scholar
    • Export Citation

  • Zhang, D-L., Y. Liu, and M. K. Yau, 2001: A multiscale numerical study of Hurricane Andrew (1992). Part IV: Unbalanced flows. Mon. Wea. Rev., 129 , 92–107.

    • Search Google Scholar
    • Export Citation
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