Editorial Type:
Article
Article Type:
Research Article

High-Resolution Observations and Numerical Simulations of Easterly Gap Flow through the Strait of Juan de Fuca on 9–10 December 1995

Brian A. Colle Institute for Terrestrial and Planetary Atmospheres, State University of New York at Stony Brook, Stony Brook, New York

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Clifford F. Mass Department of Atmospheric Sciences, University of Washington, Seattle, Washington

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Print Publication:
01 Jul 2000
DOI:
https://doi.org/10.1175/1520-0493(2000)128<2398:HROANS>2.0.CO;2
Page(s):
2398–2422
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Abstract

This paper examines the three-dimensional flow and dynamics of easterly gap flow through the Strait of Juan de Fuca on 9–10 December 1995 using high-resolution observations and model simulations. The observations were obtained during the fourth intensive observing period during the second phase of the Coastal Observation and Simulation with Topography field experiment. One of the most important data sources was the NOAA P-3 aircraft, which provided flight-level data, reflectivity, and Doppler winds as it flew down the Strait of Juan de Fuca. Below 900 m, the flow accelerated from 7 to 14 m s−1 at the entrance to the strait, with a significant cross-gap component and confluence over the eastern sections of the strait below 500 m. The easterly flow approaching the western exit of the strait accelerated from 15 to 20 m s−1. As the 900 m deep easterly flow exited the gap it decreased in depth and accelerated to ∼25 m s−1, creating a shallow swath of diffluent winds below 300 m. Later in the event when the gap flow became more shallow, the strongest low-level winds shifted eastward into the western section of the strait.

This event was simulated down to 1.33-km horizontal resolution using The Pennsylvania State University–NCAR Mesoscale Model version 5. Although many of the observed structures were realistically simulated, the model underestimated the sea level pressure difference down the strait by 30%, resulting in gap exit winds 2–5 m s−1 weaker than observed. The model also maintained the swath of low-level easterlies too far downwind of the gap. Sensitivity runs illustrate how the gap flow changes with different horizontal and vertical resolutions.

Trajectories and momentum diagnostics from the model indicate that this case did not represent the classic conceptual model of gap flow down a long channel. There was confluence within the gap as a result of northeasterly flow descending into the strait from southern Vancouver Island. This subsidence in the lee (south) of Vancouver Island created lee troughing, a significant cross-strait pressure gradient, and flow curvature over the gap at low levels. The gap outflow is shown to have structural similarities to classical expansion fan theory. However, unlike expansion fan theory, much of the low-level acceleration and subsidence at the gap exit was forced by downslope flow off the surrounding terrain, and the parcels associated with the gap outflow fan originated from many different locations.

Corresponding author address: Dr. B. A. Colle, Marine Science Research Center, State University of New York at Stony Brook, Stony Brook, NY 11794-5000.

Abstract

This paper examines the three-dimensional flow and dynamics of easterly gap flow through the Strait of Juan de Fuca on 9–10 December 1995 using high-resolution observations and model simulations. The observations were obtained during the fourth intensive observing period during the second phase of the Coastal Observation and Simulation with Topography field experiment. One of the most important data sources was the NOAA P-3 aircraft, which provided flight-level data, reflectivity, and Doppler winds as it flew down the Strait of Juan de Fuca. Below 900 m, the flow accelerated from 7 to 14 m s−1 at the entrance to the strait, with a significant cross-gap component and confluence over the eastern sections of the strait below 500 m. The easterly flow approaching the western exit of the strait accelerated from 15 to 20 m s−1. As the 900 m deep easterly flow exited the gap it decreased in depth and accelerated to ∼25 m s−1, creating a shallow swath of diffluent winds below 300 m. Later in the event when the gap flow became more shallow, the strongest low-level winds shifted eastward into the western section of the strait.

This event was simulated down to 1.33-km horizontal resolution using The Pennsylvania State University–NCAR Mesoscale Model version 5. Although many of the observed structures were realistically simulated, the model underestimated the sea level pressure difference down the strait by 30%, resulting in gap exit winds 2–5 m s−1 weaker than observed. The model also maintained the swath of low-level easterlies too far downwind of the gap. Sensitivity runs illustrate how the gap flow changes with different horizontal and vertical resolutions.

Trajectories and momentum diagnostics from the model indicate that this case did not represent the classic conceptual model of gap flow down a long channel. There was confluence within the gap as a result of northeasterly flow descending into the strait from southern Vancouver Island. This subsidence in the lee (south) of Vancouver Island created lee troughing, a significant cross-strait pressure gradient, and flow curvature over the gap at low levels. The gap outflow is shown to have structural similarities to classical expansion fan theory. However, unlike expansion fan theory, much of the low-level acceleration and subsidence at the gap exit was forced by downslope flow off the surrounding terrain, and the parcels associated with the gap outflow fan originated from many different locations.

Corresponding author address: Dr. B. A. Colle, Marine Science Research Center, State University of New York at Stony Brook, Stony Brook, NY 11794-5000.

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  • Benjamin, S. G., and N. L. Seaman, 1985: A simple scheme for objective analysis in curved flow. Mon. Wea. Rev.,113, 1184–1198.

  • Biggerstaff, M. I., and R. A. Houze Jr., 1991: Kinematic and precipitation structure of the 10–11 June 1985 squall line. Mon. Wea. Rev.,119, 3035–3065.

  • Bond, N. A., and S. A. Macklin, 1993: Aircraft observations of offshore directed flow near Wide Bay, Alaska. Mon. Wea. Rev.,121, 150–161.

  • ——, and J. D. Doyle, 1998: A landfalling warm front on Vancouver Island during the COAST experiment: NOAA P-3 aircraft observations. Preprints, Second Conf. on Coastal Prediction, Phoenix, AZ, Amer. Meteor. Soc., 210–212.

  • ——, and P. J. Stabeno, 1998: Analysis of surface winds in Shelikof Strait, Alaska, using moored buoy observations. Wea. Forecasting,13, 547–559.

  • ——, and Coauthors, 1997: The Coastal Observation and Simulation with Topography (COAST) experiment. Bull. Amer. Meteor. Soc.,78, 1941–1955.

  • Burk, S. D., and W. T. Thompson, 1989: A vertically nested regional numerical weather prediction model with second-order closure physics. Mon. Wea. Rev.,117, 2305–2324.

  • ——, T. Haack, and R. M. Samelson, 1999: Mesoscale simulation of supercritical, subcritical, and transcritical flow along coastal topography. J. Atmos. Sci.,56, 2780–2795.

  • Cameron, D. C., 1931: Easterly gales in the Columbia River Gorge during the winter of 1930–1931—Some of their causes and effects. Mon. Wea. Rev.,59, 411–413.

  • ——, and A. B. Carpenter, 1936: Destructive easterly gales in the Columbia River Gorge, December 1935. Mon. Wea. Rev.,65, 264–267.

  • Colle, B. A., and C. F. Mass, 1996: An observational and modeling study of the interaction of low-level southwesterly flow with the Olympic Mountains during COAST IOP 4. Mon. Wea. Rev.,124, 2152–2175.

  • ——, and ——, 1998a: Windstorms along the western side of the Washington Cascade Mountains. Part I: A high resolution observational and modeling study of the 12 February 1995 event. Mon. Wea. Rev.,126, 28–52.

  • ——, and ——, 1998b: Windstorms along the western side of the Washington Cascade Mountains. Part II: Characteristics of past events and three-dimensional idealized simulations. Mon. Wea. Rev.,126, 53–71.

  • Dorman, C. E., R. C. Beardsley, and R. Limeburner, 1995: Winds in the Strait of Gibraltar. Quart. J. Roy. Meteor. Soc.,121, 1903–1921.

  • Doyle, J. D., and N. A. Bond, 1998: A landfalling warm front on Vancouver Island during the COAST experiment: Numerical simulations. Preprints, Second Conf. on Coastal Prediction, Phoenix, AZ, Amer. Meteor. Soc., 212–214.

  • Dudhia, J., 1989: Numerical study of convection observed during the Winter Monsoon Experiment using a mesoscale two-dimensional model. J. Atmos. Sci.,46, 3077–3107.

  • Durran, D. R., 1986: Another look at downslope windstorms. Part I:On the development of supercritical flow in an infinitely deep, continuously stratified fluid. J. Atmos. Sci.,43, 2527–2543.

  • Grell, G. A., J. Dudhia, and D. R. Stauffer, 1994: A description of the fifth-generation Penn State/NCAR Mesoscale Model (MM5). NCAR Tech. Note NCAR/TN-398+STR, 138 pp. [Available from National Center for Atmospheric Research, P.O. Box 3000, Boulder, CO 80307.].

  • Hsie, E.-Y., R. A. Anthes, and D. Keyser, 1984: Numerical simulation of frontogenesis in a moist atmosphere. J. Atmos. Sci.,41, 2581–2594.

  • Jackson, P. L., and D. G. Steyn, 1994a: Gap winds in a fiord. Part I:Observations and numerical simulation. Mon. Wea. Rev.,122, 2654–2665.

  • ——, and ——, 1994b: Gap winds in a fiord. Part II: Hydraulic analog. Mon. Wea. Rev.,122, 2666–2676.

  • Kain, J. S., and J. M. Fritsch, 1990: A one-dimensional entraining/detraining plume model and its application in convective parameterization. J. Atmos. Sci.,47, 2784–2802.

  • Klemp, J. B., and D. R. Durran, 1983: An upper boundary condition permitting internal gravity wave radiation in numerical mesoscale models. Mon. Wea. Rev.,111, 430–444.

  • Lackmann, G. M., and J. E. Overland, 1989: Atmospheric structure and momentum balance during a gap-wind event in the Shelikof Strait, Alaska. Mon. Wea. Rev.,117, 1817–1833.

  • Leise, J. A., 1982: A multidimensional scale-telescoped filter and data extension package. NOAA Tech. Memo. WPL-82, 20 pp. [Available from NOAA ERL, 325 Broadway, Boulder, CO 80303.].

  • Marks, F. D., Jr., and R. A. Houze Jr., 1987: Inner core structure of Hurricane Alicia from airborne Doppler radar observations. J. Atmos. Sci.,44, 1296–1317.

  • Mass, C. F., and M. D. Albright, 1985: A severe windstorm in the lee of the Cascade Mountains of Washington State. Mon. Wea. Rev.,113, 1261–1281.

  • ——, S. Businger, M. D. Albright, and Z. D. Tucker, 1995: A windstorm in the lee of a gap in a coastal mountain barrier. Mon. Wea. Rev.,123, 315–331.

  • Mellor, G. L., and T. Yamada, 1974: A hierarchy of turbulence closure models for planetary boundary layers. J. Atmos. Sci.,31, 1791–1806.

  • Mohr, C. G., and L. J. Miller, 1983: CEDRIC—A software package for Cartesian space editing, synthesis, and display of radar fields under interactive control. Preprints, 21st Conf. on Radar Meteorology, Edmonton, AB, Canada, Amer. Meteor. Soc., 559–574.

  • Overland, J. E., 1984: Scale analysis of marine winds in straits and along mountainous coasts. Mon. Wea. Rev.,112, 2532–2536.

  • ——, and B. A. Walter, 1981: Gap winds in the Strait of Juan de Fuca. Mon. Wea. Rev.,109, 2221–2233.

  • Pan, F., and R. B. Smith, 1999: Gap winds and wakes: SAR observations and numerical simulations. J. Atmos. Sci.,56, 905–923.

  • Reed, T. R., 1931: Gap winds of the Strait of Juan de Fuca. Mon. Wea. Rev.,59, 373–376.

  • Reid, S., 1996: Pressure gradients and winds in Cook Strait. Wea. Forecasting,11, 476–488.

  • Schoenberger, L. M., 1984: Doppler radar observations of a land-breeze cold front. Mon. Wea. Rev.,112, 2455–2464.

  • Scorer, R. S., 1952: Mountain-gap winds—A study of the surface wind at Gibraltar. Mon. Wea. Rev.,78, 53–59.

  • Smith, R. B., 1985: On severe downslope winds. J. Atmos. Sci.,42, 2597–2603.

  • Stauffer, D. R., and N. L. Seaman, 1990: Use of four-dimensional data assimilation in a limited-area mesoscale model. Part I: Experiments with synoptic-scale data. Mon. Wea. Rev.118, 1250–1277.

  • Steenburgh, W. J., D. M. Schultz, and B. A. Colle, 1998: The structure and evolution of gap outflow over the Gulf of Tehuantepec, Mexico. Mon. Wea. Rev.,126, 2673–2691.

  • Winant, C. D., C. E. Dorman, C. A. Friehe, and R. C. Beardsley, 1988: The marine layer off northern California: An example of supercritical channel flow. J. Atmos. Sci.,45, 3588–3605.

  • Wolyn, P., 1994: The importance of cold, dry, easterly Columbia Gorge winds for snowstorms in Portland, Oregon. Preprints, Sixth Conf. on Mesoscale Processes, Portland, OR, Amer. Meteor. Soc., 505–507.

  • Zhang, D., and R. A. Anthes, 1982: A high-resolution model of the planetary boundary layer—Sensitivity test and comparisons with SESAME-79 data. J. Appl. Meteor.,21, 1594–1609.

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