Editorial Type:
Article
Article Type:
Research Article

Terrain-Induced Turbulence over Lantau Island: 7 June 1994 Tropical Storm Russ Case Study

Terry L. Clark National Center for Atmospheric Research, Boulder, Colorado

Search for other papers by Terry L. Clark in
Current site
Google Scholar
PubMed Close
,
Teddie Keller National Center for Atmospheric Research, Boulder, Colorado

Search for other papers by Teddie Keller in
Current site
Google Scholar
PubMed Close
,
Janice Coen National Center for Atmospheric Research, Boulder, Colorado

Search for other papers by Janice Coen in
Current site
Google Scholar
PubMed Close
,
Peter Neilley National Center for Atmospheric Research, Boulder, Colorado

Search for other papers by Peter Neilley in
Current site
Google Scholar
PubMed Close
,
Hsiao-ming Hsu National Center for Atmospheric Research, Boulder, Colorado

Search for other papers by Hsiao-ming Hsu in
Current site
Google Scholar
PubMed Close
, and
William D. Hall National Center for Atmospheric Research, Boulder, Colorado

Search for other papers by William D. Hall in
Current site
Google Scholar
PubMed Close
Print Publication:
01 Jul 1997
DOI:
https://doi.org/10.1175/1520-0469(1997)054<1795:TITOLI>2.0.CO;2
Page(s):
1795–1814
Restricted access

Abstract

Numerical simulations of terrain-induced turbulence associated with airflow over Lantau Island of Hong Kong are presented. Lantau is a relatively small island with three narrow peaks rising to between 700 and 950 m above mean sea level. This research was undertaken as part of a project to better understand and predict the nature of turbulence and shear at the new airport site on the island of Chek Lap Kok, which is located to the lee of Lantau. Intensive ground and aerial observations were taken from May through June 1994, during the Lantau Experiment (LANTEX). This paper focuses on flow associated with the passage of Tropical Storm Russ on 7 June 1994, during which severe turbulence was observed.

The nature of the environmental and topographic forcing on 7 June 1994 resulted in the turbulence and shear being dominated by the combination of topographic effects and surface friction. High-resolution numerical simulations, initialized using local sounding data, were performed using the Clark model. The simulation results indicate that gravity-wave dynamics played a very minor role in the flow distortion and generation of turbulence. As a result of this flow regime, relatively high vertical and horizontal resolution was required to simulate the mechanically generated turbulence associated with Tropical Storm Russ.

Results are presented using a vertical resolution of 10 m near the surface and with horizontal resolutions of both 125 and 62.5 m over local, nested domains of about 13–24 km on a side. The 125-m model resolution simulated highly distorted flow in the lee of Lantau, with streaks emanating downstream from regions of sharp orographic gradients. At this resolution the streaks were nearly steady in time. At the higher horizontal resolution of 62.5 m the streaks became unstable, resulting in eddies advecting downstream within a distorted streaky mean flow similar to the 125-m resolution simulation. The temporally averaged fields changed little with the increase in resolution; however, there was a three- to fourfold increase in the temporal variability of the flow, as indicated by the standard deviation of the wind from a 10-min temporal average. Overall, the higher resolution simulations compared quite well with the observations, whereas the lower resolution cases did not. The high-resolution experiments also showed a much broader horizontal and vertical extent for the transient eddies. The depth of orographic influence increased from about 200 m to over 600 m with the increase in resolution. A physical explanation, using simple linear arguments based on the blocking effects of the eddies, is presented. The nature of the flow separation is analyzed using Bernoulli’s energy form to display the geometry of the separation bubbles. The height of the 80 m2 s−2 energy surface shows eddies forming in regions of large orographic gradients and advecting downstream.

Tests using both buoyancy excitation and stochastic backscatter to parameterize the underresolved dynamics at the 125-m resolution are presented, as well as one experiment testing the influence of static stability suppressing turbulence development. All these tests showed no significant effect. Implications of these results to the parameterization of mechanically induced turbulence in complex terrain are discussed.

Corresponding author address: Dr. Terry L. Clark, NCAR/MMM, P.O. Box 3000, Boulder, CO 80307-3000.

Abstract

Numerical simulations of terrain-induced turbulence associated with airflow over Lantau Island of Hong Kong are presented. Lantau is a relatively small island with three narrow peaks rising to between 700 and 950 m above mean sea level. This research was undertaken as part of a project to better understand and predict the nature of turbulence and shear at the new airport site on the island of Chek Lap Kok, which is located to the lee of Lantau. Intensive ground and aerial observations were taken from May through June 1994, during the Lantau Experiment (LANTEX). This paper focuses on flow associated with the passage of Tropical Storm Russ on 7 June 1994, during which severe turbulence was observed.

The nature of the environmental and topographic forcing on 7 June 1994 resulted in the turbulence and shear being dominated by the combination of topographic effects and surface friction. High-resolution numerical simulations, initialized using local sounding data, were performed using the Clark model. The simulation results indicate that gravity-wave dynamics played a very minor role in the flow distortion and generation of turbulence. As a result of this flow regime, relatively high vertical and horizontal resolution was required to simulate the mechanically generated turbulence associated with Tropical Storm Russ.

Results are presented using a vertical resolution of 10 m near the surface and with horizontal resolutions of both 125 and 62.5 m over local, nested domains of about 13–24 km on a side. The 125-m model resolution simulated highly distorted flow in the lee of Lantau, with streaks emanating downstream from regions of sharp orographic gradients. At this resolution the streaks were nearly steady in time. At the higher horizontal resolution of 62.5 m the streaks became unstable, resulting in eddies advecting downstream within a distorted streaky mean flow similar to the 125-m resolution simulation. The temporally averaged fields changed little with the increase in resolution; however, there was a three- to fourfold increase in the temporal variability of the flow, as indicated by the standard deviation of the wind from a 10-min temporal average. Overall, the higher resolution simulations compared quite well with the observations, whereas the lower resolution cases did not. The high-resolution experiments also showed a much broader horizontal and vertical extent for the transient eddies. The depth of orographic influence increased from about 200 m to over 600 m with the increase in resolution. A physical explanation, using simple linear arguments based on the blocking effects of the eddies, is presented. The nature of the flow separation is analyzed using Bernoulli’s energy form to display the geometry of the separation bubbles. The height of the 80 m2 s−2 energy surface shows eddies forming in regions of large orographic gradients and advecting downstream.

Tests using both buoyancy excitation and stochastic backscatter to parameterize the underresolved dynamics at the 125-m resolution are presented, as well as one experiment testing the influence of static stability suppressing turbulence development. All these tests showed no significant effect. Implications of these results to the parameterization of mechanically induced turbulence in complex terrain are discussed.

Corresponding author address: Dr. Terry L. Clark, NCAR/MMM, P.O. Box 3000, Boulder, CO 80307-3000.

Save
Cover Journal of the Atmospheric Sciences
Journal of the Atmospheric Sciences

  • Arakawa, A., 1966: Computational design for long term integration of the equations of fluid motion: Two-dimensional incompressible flow. Part I. J. Comput. Phys.,1, 119–143.

  • Ayotte, K. W., and P. A. Taylor, 1995: A mixed spectral finite-difference 3D model of neutral planetary boundary-layer flow over topography. J. Atmos. Sci.,52, 3523–3537.

  • ——, D. Xu, and P. A. Taylor, 1994: The impact of turbulence closure schemes on predictions of the mixed spectral finite-difference model for flow over topography. Bound.-Layer Meteor.,68, 1–33.

  • Bacmeister, J. T., and R. T. Pierrehumbert, 1988: On high-drag state of nonlinear stratified flow over an obstacle. J. Atmos. Sci.,45, 63–80.

  • Baines, P. G., 1979: Observations of stratified flow past three-dimensional barriers. J. Geophys. Res.,84, 7834–7838.

  • ——, and P. C. Manins, 1989: The principles of laboratory modeling of stratified atmospheric flows over complex terrain. J. Appl. Meteor.,28, 1213–1225.

  • Blackadar, A. K., 1962: The vertical distribution of wind and turbulent exchange in a neutral atmosphere. J. Geophys. Res.,67, 3095–3102.

  • Castro, I. P., W. H. Snyder, and G. L. Marsh, 1983: Stratified flow over three-dimensional ridges. J. Fluid Mech.,135, 261–282.

  • Clark, T. L., 1977: A small scale numerical model using a terrain following coordinate transformation. J. Comput. Phys.,24, 186–215.

  • ——, and R. D. Farley, 1984: Severe downslope windstorm calculations in two and three spatial dimensions using anelastic interactive grid nesting: A possible mechanism for gustiness. J. Atmos. Sci.,41, 329–350.

  • ——, and W. R. Peltier, 1977: On the evolution and stability of finite-amplitude mountain waves. J. Atmos. Sci.,34, 1715–1730.

  • ——, and ——, 1984: Critical level reflection and the resonant growth of nonlinear mountain waves. J. Atmos. Sci.,41, 3122–3134.

  • ——, and W. D. Hall, 1991: Multi-domain simulations of the time dependent Navier–Stokes equation: Benchmark error analysis of some nesting procedures. J. Comput. Phys.,92, 456–481.

  • ——, and ——, 1996: On the design of smooth, conservative vertical grids for interactive grid nesting with vertical stretching. J. Appl. Meteor.,35, 1040–1046.

  • ——, T. Hauf, and J. J. Kuettner, 1986: Convectively forced internal gravity waves: Results from two-dimensional numerical experiments. Quart. J. Roy. Meteor. Soc.,112, 899–925.

  • Durran, D. R., and J. B. Klemp, 1983: A compressible model for the simulation of moist mountain waves. Mon. Wea. Rev.,111, 2341–2361.

  • Finnigan, J. J., 1988: Air flow over complex terrain. Flow and Transport in the Natural Environment: Advances and Applications, W. L. Steffen and O. T. Denmead, Eds., Springer-Verlag, 183–229.

  • Grabowski, W. W., and T. L. Clark, 1991: Cloud-environment interface instability: Rising thermal calculations in two spatial dimensions. J. Atmos. Sci.,48, 527–546.

  • Hunt, J. C. R., and W. H. Snyder, 1980: Experiments on stably and neutrally stratified flow over a model three-dimensional hill. J. Fluid Mech.,96, 671–704.

  • Jackson, P. S., and J. C. R. Hunt, 1975: Turbulent wind flow over a low hill. Quart. J. Roy. Meteor. Soc.,101, 929–955.

  • Jenkins, G. J., P. J. Mason, W. H. Moores, and R. I. Sykes, 1981: Measurements of the flow structure around Alisa Craig, a steep, three-dimensional, isolated hill. Quart. J. Roy. Meteor. Soc.,107, 833–851.

  • Klemp, J. B., and D. K. Lilly, 1978: Numerical simulation of hydrostatic mountain waves. J. Atmos. Sci.,35, 78–107.

  • Laprise, R., and W. R. Peltier, 1989: The linear stability of nonlinear mountain waves: Implications for the understanding of severe downslope windstorms. J. Atmos. Sci.,46, 545–564.

  • Leith, C. E., 1990: Stochastic backscatter in a subgrid-scale model: Plane shear mixing layer. Phys. Fluids A,2, 297–299.

  • Lilly, D. K., 1962: On the numerical simulation of buoyant convection. Tellus,14, 145–172.

  • ——, and E. J. Zipser, 1972: The front range windstorm of 11 January 1972—A meteorological narrative. Weatherwise,25, 56–63.

  • ——, and J. B. Klemp, 1979: The effects of terrain shape on nonlinear hydrostatic mountain waves. J. Fluid Mech.,95, 241–261.

  • Lipps, F. G., and R. S. Hemler, 1982: A scale analysis of deep moist convection and some related numerical calculations. J. Atmos. Sci.,39, 2192–2210.

  • Mason, P. J., 1986: Flow over the summit of an isolated hill. Bound.-Layer Meteor.,37, 385–405.

  • ——, and R. I. Sykes, 1979: Flow over an isolated hill of moderate slope. Quart. J. Roy. Meteor. Soc.,105, 383–395.

  • ——, and J. C. King, 1985: Measurements and predictions of flow and turbulence over an isolated hill of moderate slope. Quart. J. Roy. Meteor. Soc.,111, 617–640.

  • ——, and D. J. Thompson, 1992: Stochastic backscatter in large-eddy simulations of boundary layers. J. Fluid Mech.,242, 51–78.

  • Peltier, W. R., and T. L. Clark, 1979: The evolution and stability of finite-amplitude mountain waves. Part II: Surface wave drag and severe downslope windstorms. J. Atmos. Sci.,36, 1489–1529.

  • ——, and ——, 1983: Non-linear mountain waves in two and three spatial dimensions. Quart. J. Roy. Meteor. Soc.,109, 527–548.

  • Reisner, J. M., and P. K. Smolarkiewicz, 1994: Thermally forced low froude number flow past three-dimensional obstacles. J. Atmos. Sci.,51, 117–133.

  • Romero, R., S. Alonso, E. C. Nickerson, and C. Ramis, 1995: The influence of vegetation on the development and structure of mountain waves. J. Appl. Meteor.,34, 2230–2242.

  • Savill, A. M., 1987: Recent developments in rapid-distortion theory. J. Fluid Mech.,19, 531–575.

  • Schlichting, H., 1960: Boundary-Layer Theory. McGraw-Hill, 647 pp.

  • Scinocca, J. F., and W. R. Peltier, 1991: On the Richardson number dependence of nonlinear critical-layer flow over localized topography. J. Atmos. Sci.,48, 1560–1572.

  • Smagorinsky, J., 1963: General circulation experiments with the primitive equations. Proc. Int. Symp. on Numerical Weather Prediction, Tokyo, Japan, Meteor. Soc. Japan, 85–107.

  • Smith, R. B., A. C. Gleason, P. A. Gluhosky, and V. Grubisic, 1997: The wake of St. Vincent. J. Atmos. Sci.,54, 606–623.

  • Smolarkiewicz, P. K., 1983: A simple positive definite advection scheme with small implicit diffusion. Mon. Wea. Rev.,111, 479–486.

  • ——, 1984: A fully multidimensional positive definite advection transport algorithm with small implicit diffusion. J. Comput. Phys.,54, 325–362.

  • Xu, D., K. W. Ayotte, and P. A. Taylor, 1994: Development of a non-linear mixed spectral finite difference model for turbulent boundary-layer flow over topography. Bound.-Layer Meteor.,70, 341–367.

All Time Past Year Past 30 Days
Abstract Views 0 0 0
Full Text Views 899 513 30
PDF Downloads 152 44 5