The Vertical Structure of Linear Coastal-Trapped Disturbances

R. M. Samelson Woods Hole Oceanographic Institution, Woods Hole, Massachusetts

Search for other papers by R. M. Samelson in
Current site
Google Scholar
PubMed
Close
Restricted access

We are aware of a technical issue preventing figures and tables from showing in some newly published articles in the full-text HTML view.
While we are resolving the problem, please use the online PDF version of these articles to view figures and tables.

Abstract

The vertical structure of coastal-trapped disturbances in several idealized models of a stably stratified lower atmosphere is examined. The vertical structure and phase speeds of the trapped modes depend on the resting stratification and the height of the orographic step. The presence of a stable layer above the boundary layer inversion increases the gravest-mode phase speed and supports the existence of higher vertical modes. Trapped wave solutions for the step orography are obtained for a lower atmosphere with constant buoyancy frequency. The modes are primarily concentrated below the step but penetrate weakly into the stratified region above the step. The phase speed of the gravest trapped mode is greater than the gravest-mode Kelvin wave speed based on the height of the step. Results from a linear two-layer model suggest that the observed vertical structure of isotherms at the leading edge of a 10–11 June 1994 event may arise during a transition from a directly forced, barotropic, alongshore velocity response to a regime influenced by wave propagation, as the coastal-trapped vertical modes excited by the mesoscale pressure gradients begin to disperse at their respective phase speeds. The results suggest also that the observed vertical structure of alongshore velocity, with largest velocities in the stable layer above the boundary layer, may arise from drag at the sea surface.

Current affiliation: College of Oceanic and Atmospheric Sciences, Oregon State University, Corvallis, Oregon.

Corresponding author address: Dr. R. M. Samelson, College of Oceanic and Atmospheric Sciences, Oregon State University, 104 Ocean. Admin. Bldg., Corvallis, OR 97331-5503.

Abstract

The vertical structure of coastal-trapped disturbances in several idealized models of a stably stratified lower atmosphere is examined. The vertical structure and phase speeds of the trapped modes depend on the resting stratification and the height of the orographic step. The presence of a stable layer above the boundary layer inversion increases the gravest-mode phase speed and supports the existence of higher vertical modes. Trapped wave solutions for the step orography are obtained for a lower atmosphere with constant buoyancy frequency. The modes are primarily concentrated below the step but penetrate weakly into the stratified region above the step. The phase speed of the gravest trapped mode is greater than the gravest-mode Kelvin wave speed based on the height of the step. Results from a linear two-layer model suggest that the observed vertical structure of isotherms at the leading edge of a 10–11 June 1994 event may arise during a transition from a directly forced, barotropic, alongshore velocity response to a regime influenced by wave propagation, as the coastal-trapped vertical modes excited by the mesoscale pressure gradients begin to disperse at their respective phase speeds. The results suggest also that the observed vertical structure of alongshore velocity, with largest velocities in the stable layer above the boundary layer, may arise from drag at the sea surface.

Current affiliation: College of Oceanic and Atmospheric Sciences, Oregon State University, Corvallis, Oregon.

Corresponding author address: Dr. R. M. Samelson, College of Oceanic and Atmospheric Sciences, Oregon State University, 104 Ocean. Admin. Bldg., Corvallis, OR 97331-5503.

Save
  • Bannon, P. R., 1981: Synoptic-scale forcing of coastal lows: Forced double Kelvin waves in the atmosphere. Quart. J. Roy. Meteor. Soc.;107, 313–327.

  • Bond, N., C. Mass, and J. Overland, 1996: Coastally trapped wind reversals along the U.S. west coast during the warm season. Part I: Climatology and temporal evolution. Mon. Wea. Rev.,124, 430–445.

  • Chapman, D. C., 1982: On the failure of Laplace’s tidal equations to model subinertial motions at a discontinuity in depth. Dyn. Atmos. Oceans,7, 1–16.

  • Dorman, C. E., 1985: Evidence of Kelvin waves in California’s marine layer and related eddy generation. Mon. Wea. Rev.,113, 827–839.

  • ——, 1987: Possible role of gravity currents in northern California’s coastal summer wind reversals. J. Geophys. Res.,92, 1497–1506.

  • Gill, A. E., 1977: Coastally trapped waves in the atmosphere. Quart. J. Roy. Meteor. Soc.,103, 431–440.

  • ——, 1982: Atmosphere–Ocean Dynamics. Academic Press, 662 pp.

  • Hermann, A. J., B. M. Hickey, C. F. Mass, and M. D. Albright, 1990:Orographically trapped coastal wind events in the Pacific Northwest and their oceanic response. J. Geophys. Res.,95, 13 169–13 193.

  • Holland, G., and L. Leslie, 1986: Ducted coastal ridging over S.E. Australia. Quart. J. Roy. Meteor. Soc.,112, 731–748.

  • Jury, M., C. MacArthur, and C. Reason, 1990: Observations of trapped waves in the atmosphere and ocean along the coast of southern Africa. South Afr. Geogr. J.,72, 33–46.

  • Mass, C. F., and M. D. Albright, 1987: Coastal southerlies and alongshore surges of the west coast of North America: Evidence of mesoscale topographically trapped response to synoptic forcing. Mon. Wea. Rev.,115, 1707–1738.

  • ——, and N. Bond, 1996: Coastally trapped wind reversals along the United States west coast during the warm season. Part II: Synoptic evolution. Mon. Wea. Rev.,124, 446–461.

  • Nguyen, N. A., and A. E. Gill, 1981: Generation of coastal lows by synoptic-scale waves. Quart. J. Roy. Meteor. Soc.,107, 521–530.

  • Ralph, F. M., L. Armi, J. Bane, C. Dorman, W. Neff, P. J. Neiman, W. Nuss, and P. O. Persson, 1998: Observations and analysis of the 10–11 June 1994 coastally trapped disturbance. Mon. Wea. Rev.,126, 2435–2465.

  • Reason, C., and M. Jury, 1990: On the generation and propagation of the southern Africa coastal low. Quart. J. Roy. Meteor. Soc.,116, 1133–1151.

  • ——, and D. Steyn, 1990: Coastally trapped disturbances in the lower atmosphere: Dynamic commonalities and geographic diversity. Prog. Phys. Geogr.,14, 178–198.

  • ——, and ——, 1992: The dynamics of coastally trapped mesoscale ridges in the lower atmosphere. J. Atmos. Sci.,49, 1677–1692.

  • Rogerson, A. M., and R. M. Samelson, 1995: Synoptic forcing of coastal-trapped disturbances in the marine atmospheric boundary layer. J. Atmos. Sci.,52, 2025–2040.

  • Samelson, R. M., and A. M. Rogerson, 1996: Life-cycle of a linear coastal-trapped disturbance. Mon. Wea. Rev.,124, 1853–1863.

  • Thompson, W., T. Haack, J. Doyle, and S. Burk, 1997: A nonhydrostatic mesoscale simulation of the 10–11 June 1994 coastally trapped wind reversal. Mon. Wea. Rev.,125, 3211–3230.

All Time Past Year Past 30 Days
Abstract Views 0 0 0
Full Text Views 251 180 55
PDF Downloads 57 24 3