• Balasubramanian, G., and S. T. Garner, 1997: The role of momentum fluxes in shaping the life cycle of a baroclinic wave. J. Atmos. Sci.,54, 510–533.

  • Bannon, P. R., and T. L. Salem, 1995: Aspects of the baroclinic boundary layer. J. Atmos. Sci.,52, 574–596.

  • Bluestein, H. B., 1993: Synoptic-Dynamic Meteorology in Midlatitudes. Vol. II. Oxford University Press, 594 pp.

  • Blumen, W., 1980: A comparison between the Hoskins–Bretherton model of frontogenesis and the analysis of an intense surface frontal zone. J. Atmos. Sci.,37, 64–77.

  • Carlson, T. N., 1991: Mid-Latitude Weather Systems. Harper Collins Academic, 507 pp.

  • Gill, A. E., 1982: Atmosphere-Ocean Dynamics. Academic Press, 662 pp.

  • Hines, K. M., and C. R. Mechoso, 1993: Influence of surface drag on the evolution of fronts. Mon. Wea. Rev.,121, 1152–1175.

  • Hoskins, B. J., and F. P. Bretherton, 1972: Atmospheric frontogenesis models: Mathematical formulation and solution. J. Atmos. Sci.,29, 11–37.

  • Keyser, D., and R. A. Anthes, 1982: The influence of planetary boundary layer physics on frontal structure in the Hoskins–Bretherton model. J. Atmos. Sci.,39, 1783–1802.

  • Kuo, Y.-H., and S. Low-Nam, 1994: Effects of surface friction on the thermal structure of an extratropical cyclone. Proc. Int. Symp. on the Life Cycles of Extratropical Cyclones, Vol. II, Bergen, Norway, University of Bergen, 129–134.

  • Orlanski, I., B. Ross, L. Polinsky, and R. Shaginaw, 1985: Advances in the theory of atmospheric fronts. Advances in Geophysics, Vol. 28B, Academic Press, 223–252.

  • Pedlosky, J., 1967: The spin up of a stratified fluid. J. Fluid Mech.,28, 463–479.

  • ——, 1987: Geophysical Fluid Dynamics. Springer-Verlag, 624 pp.

  • Polavarapu, S. M., and W. R. Peltier, 1990: The structure and nonlinear evolution of synoptic-scale cyclones: Life cycle simulations with a cloud-scale model. J. Atmos. Sci.,47, 2645–2672.

  • Rotunno, R., and J.-W. Bao, 1996: A case study of cyclogenesis using a model hierarchy. Mon. Wea. Rev.,124, 1051–1066.

  • ——, W. C. Skamarock, and C. Snyder, 1994: An analysis of frontogenesis in numerical simulations of baroclinic waves. J. Atmos. Sci.,51, 3373–3398.

  • Snyder, C., 1998: Approximate dynamical equations for fronts modified by the planetary boundary layer. J. Atmos. Sci.,55, 777–787.

  • ——, and D. Keyser, 1996: The coupling of fronts and the boundary layer. Preprints, Seventh Conf. on Mesoscale Processes, Reading, United Kingdom, Amer. Meteor. Soc., 520–522.

  • ——, W. C. Skamarock, and R. Rotunno, 1991: A comparison of primitive-equation and semigeostrophic simulations of baroclinic waves. J. Atmos. Sci.,48, 2179–2194.

  • ——, ——, and ——, 1993: Frontal dynamics near and following frontal collapse. J. Atmos. Sci.,50, 3194–3212.

  • Thompson, W. T., and R. T. Williams, 1997: Numerical simulations of maritime frontogenesis. J. Atmos. Sci.,54, 314–331.

  • Thorncroft, C. D., B. J. Hoskins, and M. E. McIntyre, 1993: Two paradigms of baroclinic-wave life-cycle behavior. Quart. J. Roy. Meteor. Soc.,119, 17–55.

  • Troen, I., and L. Mahrt, 1986: A simple model of the atmospheric boundary layer; sensitivity to surface evaporation. Bound.-Layer Meteor.,37, 129–148.

  • Williams, G. P., and J. B. Robinson, 1974: Generalized Eady waves with Ekman pumping. J. Atmos. Sci.,31, 1768–1776.

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Effects of Surface Drag on Fronts within Numerically Simulated Baroclinic Waves

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  • 1 National Center for Atmospheric Research,* Boulder, Colorado
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Abstract

A comparative analysis of simulations of baroclinic waves with and without surface drag is presented, with particular reference to surface features. As in recent studies, the present simulations show that, compared to simulations with no drag, those with surface drag are less inclined to develop a secluded warm sector, and that drag weakens the warm front while the cold front remains strong. The authors demonstrate that analogous effects occur when Ekman pumping is used in nonlinear quasigeostrophic numerical simulations of unstable baroclinic waves in a channel. However, since the quasigeostrophic model produces symmetric highs and lows in the unstable baroclinic wave, the cold and warm fronts are therefore also symmetric and hence equally affected by the Ekman pumping. The different effect that friction has on the warm front with respect to the cold front in the primitive-equation simulations is fundamentally related to the tendency for the lows to be strong and narrow and the highs weak and broad, and for the warm front to form just north of, and extend eastward from, the low, while the cold front extends between the high and the low. The authors’ thesis is that the Ekman pumping associated with the low, at the location where the warm front would form in the absence of surface friction, acts to resist the formation of the warm front, while the cold front, positioned between the high and the low where Ekman pumping associated with the baroclinic wave is weak, is therefore relatively unaffected.

Given the weakness of Ekman pumping associated with the baroclinic wave in the vicinity of the incipient cold front, the present simulations indicate that cold frontogenesis occurs in the drag case in much the same way as in the no-drag case. Present analysis shows that the horizontal advection creating the cold front is a combination of geostrophic and ageostrophic effects. A portion of the ageostrophic frontogenesis is a response to geostrophic frontogenesis, as in the case without surface drag; however with surface drag, a significant portion of the cross-front ageostrophic flow is due to the Ekman layer associated with the front itself.

Corresponding author address: Dr. Richard Rotunno, NCAR/MMM Division, P.O. Box 3000, Boulder, CO 80307.

Email: rotunno@ncar.ucar.edu

Abstract

A comparative analysis of simulations of baroclinic waves with and without surface drag is presented, with particular reference to surface features. As in recent studies, the present simulations show that, compared to simulations with no drag, those with surface drag are less inclined to develop a secluded warm sector, and that drag weakens the warm front while the cold front remains strong. The authors demonstrate that analogous effects occur when Ekman pumping is used in nonlinear quasigeostrophic numerical simulations of unstable baroclinic waves in a channel. However, since the quasigeostrophic model produces symmetric highs and lows in the unstable baroclinic wave, the cold and warm fronts are therefore also symmetric and hence equally affected by the Ekman pumping. The different effect that friction has on the warm front with respect to the cold front in the primitive-equation simulations is fundamentally related to the tendency for the lows to be strong and narrow and the highs weak and broad, and for the warm front to form just north of, and extend eastward from, the low, while the cold front extends between the high and the low. The authors’ thesis is that the Ekman pumping associated with the low, at the location where the warm front would form in the absence of surface friction, acts to resist the formation of the warm front, while the cold front, positioned between the high and the low where Ekman pumping associated with the baroclinic wave is weak, is therefore relatively unaffected.

Given the weakness of Ekman pumping associated with the baroclinic wave in the vicinity of the incipient cold front, the present simulations indicate that cold frontogenesis occurs in the drag case in much the same way as in the no-drag case. Present analysis shows that the horizontal advection creating the cold front is a combination of geostrophic and ageostrophic effects. A portion of the ageostrophic frontogenesis is a response to geostrophic frontogenesis, as in the case without surface drag; however with surface drag, a significant portion of the cross-front ageostrophic flow is due to the Ekman layer associated with the front itself.

Corresponding author address: Dr. Richard Rotunno, NCAR/MMM Division, P.O. Box 3000, Boulder, CO 80307.

Email: rotunno@ncar.ucar.edu

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