Editorial Type:
Article
Article Type:
Research Article

The Role of Transient Disturbances in the Dynamics of thePacific–North American Pattern

Jian Sheng Canadian Centre for Climate Modelling and Analysis, Victoria, British Columbia, Canada

Search for other papers by Jian Sheng in
Current site
Google Scholar
PubMed Close
,
Jacques Derome Department of Atmospheric and Oceanic Sciences and Centre for Climate and Global Change Research, McGill University, Montreal, Quebec, Canada

Search for other papers by Jacques Derome in
Current site
Google Scholar
PubMed Close
, and
Marc Klasa Department of Atmospheric and Oceanic Sciences and Centre for Climate and Global Change Research, McGill University, Montreal, Quebec, Canada

Search for other papers by Marc Klasa in
Current site
Google Scholar
PubMed Close
Print Publication:
01 Apr 1998
DOI:
https://doi.org/10.1175/1520-0442(1998)011<0523:TROTDI>2.0.CO;2
Page(s):
523–536
Restricted access

Abstract

A 25-yr dataset is used to investigate the role of transient eddies in the dynamics of the Pacific–North American (PNA) pattern. Monthly mean vorticity and sensible heat flux divergences associated with submonthly transients are computed over the Northern Hemisphere for each winter month. These fields are composited over months with strong PNA patterns, and the average over all winter months is subtracted to obtain anomaly fields. The vorticity flux divergence anomaly is found to be well correlated with the PNA height field, particularly in the upper troposphere, where an eddy vorticity flux convergence (divergence) is found in the low (high) height regions of the PNA anomaly. The sensible heat flux divergence, on the other hand, is negatively correlated with the PNA temperature anomaly, so that the transient eddies produce a sensible heat flux out of the warm regions of the PNA and into the cold regions, thus tending to destroy the temperature anomaly.

A linear quasi-nondivergent global steady-state model is constructed using the observed climatology. The eddy vorticity and sensible heat flux divergence anomalies are treated as empirical forcing functions to simulate the response of the atmosphere. The model response to the transient-eddy forcing is found to be qualitatively similar to the PNA pattern. The amplitude of the response is weaker than observed over the North Pacific but nearly as observed over North America. The wave-activity flux computed from the model response is in reasonable agreement with that obtained from the observed PNA, except that the model shows a weaker wave activity and a spurious flux southward from the main cell of the PNA in the North Pacific. A possible explanation for this deficiency, as for the underestimation of the response in the North Pacific, is the absence of tropical forcing in the model. The results clearly show the crucial role of the transient eddies in the dynamics of the PNA, particularly over North America.

Corresponding author address: Prof. Jacques Derome, Dept. of Atmospheric and Oceanic Sciences, McGill University, 805 Sherbrooke Street West, Montreal, PQ H3A 2K6, Canada.

Abstract

A 25-yr dataset is used to investigate the role of transient eddies in the dynamics of the Pacific–North American (PNA) pattern. Monthly mean vorticity and sensible heat flux divergences associated with submonthly transients are computed over the Northern Hemisphere for each winter month. These fields are composited over months with strong PNA patterns, and the average over all winter months is subtracted to obtain anomaly fields. The vorticity flux divergence anomaly is found to be well correlated with the PNA height field, particularly in the upper troposphere, where an eddy vorticity flux convergence (divergence) is found in the low (high) height regions of the PNA anomaly. The sensible heat flux divergence, on the other hand, is negatively correlated with the PNA temperature anomaly, so that the transient eddies produce a sensible heat flux out of the warm regions of the PNA and into the cold regions, thus tending to destroy the temperature anomaly.

A linear quasi-nondivergent global steady-state model is constructed using the observed climatology. The eddy vorticity and sensible heat flux divergence anomalies are treated as empirical forcing functions to simulate the response of the atmosphere. The model response to the transient-eddy forcing is found to be qualitatively similar to the PNA pattern. The amplitude of the response is weaker than observed over the North Pacific but nearly as observed over North America. The wave-activity flux computed from the model response is in reasonable agreement with that obtained from the observed PNA, except that the model shows a weaker wave activity and a spurious flux southward from the main cell of the PNA in the North Pacific. A possible explanation for this deficiency, as for the underestimation of the response in the North Pacific, is the absence of tropical forcing in the model. The results clearly show the crucial role of the transient eddies in the dynamics of the PNA, particularly over North America.

Corresponding author address: Prof. Jacques Derome, Dept. of Atmospheric and Oceanic Sciences, McGill University, 805 Sherbrooke Street West, Montreal, PQ H3A 2K6, Canada.

Save
Cover Journal of Climate
Journal of Climate

  • Barnett, T. P., and Coauthors, 1994: Forecasting global-ENSO-related climate anomalies. Tellus,46A, 381–397.

  • Barnston, A. G., 1994: Linear statistical short-term climate predictive skill in the Northern Hemisphere. J. Climate,7, 1513–1564.

  • Black, R. X., and R. M. Dole, 1993: The dynamics of large-scale cyclogenesis over the northern Pacific Ocean. J. Atmos. Sci.,50,421–442.

  • Blackmon, M. L., 1976: A climatological spectral study of the 500 mb geopotential height of the Northern Hemisphere. J. Atmos. Sci.,33, 1607–1623.

  • Boer, G. J., 1985: Modelling the atmospheric response to the 1982/83 El Niño. Coupled Ocean–Atmosphere Models, J. C. J. Nihoul, Ed., Elsevier Science, 7–17.

  • Branstator, G., 1983: Horizontal energy propagation in a barotropic atmosphere with meridional and zonal structure. J. Atmos. Sci.,40, 1689–1708.

  • ——, 1990: Low-frequency patterns induced by stationary waves. J. Atmos. Sci.,47, 629–648.

  • ——, 1992: The maintenance of low-frequency atmospheric anomalies. J. Atmos. Sci.,49, 1924–1945.

  • Eliassen, A., and E. Palm, 1960: On the transfer of energy in stationary mountain waves. Geofys. Publ.,22, 1–23.

  • Frederiksen, J. S., 1983: Disturbances and eddy fluxes in the Northern Hemisphere flows: Instability of three-dimensional January and July flows. J. Atmos. Sci.,40, 836–855.

  • ——, 1989: The role of instability during the onset of blocking and cyclogenesis in Northern Hemisphere synoptic flow. J. Atmos. Sci.,46, 1076–1092.

  • Graham, N. E., and T. P. Barnett, 1995: ENSO and ENSO-related predictability. Part II: Northern Hemisphere 700-mb predictions based on a hybrid coupled ENSO model. J. Climate,8, 544–549.

  • Held, I. M., S. W. Lyons, and S. Nigam, 1989: Transients and the extratropical response to El Niño. J. Atmos. Sci.,46, 163–174.

  • Hoerling, M. P., and M. Ting, 1994: On the organization of extratropical transients during El Niño. J. Climate,7, 745–766.

  • Holopainen, E. O., 1994: Cyclone climatology and its relationship to planetary waves physiography. The Life Cycles of Extratropical Cyclones, Vol. I, University of Bergen, 72–79.

  • Horel, J. D., and J. M. Wallace, 1981: Planetary-scale atmospheric phenomena associated with the Southern Oscillation. Mon. Wea. Rev.,109, 813–829.

  • Hoskins, B. J., and D. Karoly, 1981: The steady linear response of a spherical atmosphere to thermal and orographic forcing. J. Atmos. Sci.,38, 1179–1196.

  • Karoly, D. J., R. A. Plumb, and M. Ting, 1989: Examples of the horizontal propagation of quasi-stationary waves. J. Atmos. Sci.,46, 2802–2811.

  • Klasa, M., J. Derome, and J. Sheng, 1992: On the interaction between the synoptic-scale eddies and the PNA teleconnection pattern. Beitr. Phys. Atmos.,65, 211–222.

  • Kumar, A., M. Hoerling, M. Ji, A. Leetma, and P. Sardeshmukh, 1996: Assessing a GCM’s suitability for making seasonal predictions. J. Climate,9, 115–129.

  • Lau, N.-C., 1988: Variability of the observed midlatitude storm tracks in relation to low-frequency changes in the circulation pattern. J. Atmos. Sci.,45, 2718–2743.

  • ——, and E. O. Holopainen, 1984: Transient eddy forcing of the time-mean flow as identified by geopotential tendencies. J. Atmos. Sci.,41, 313–328.

  • ——, and M. J. Nath, 1991: Variability of the baroclinic and barotropic transient eddy forcing associated with monthly changes in the midlatitude storm tracks. J. Atmos. Sci.,48, 2589–2613.

  • ——, and ——, 1994: A modeling study of the relative roles of tropical and extratropical SST anomalies in the variability of the global atmosphere–ocean system. J. Climate,7, 1184–1207.

  • Lin, H., and J. Derome, 1995: On the thermal interaction between the synoptic-scale eddies and the intraseasonal fluctuations in the atmosphere. Atmos.–Ocean,33, 81–107.

  • Lorenz, E. N., 1960: Energy and numerical weather prediction. Tellus,12, 364–373.

  • Mahlman, G., 1979: Structure and interpretation of blocking anticyclones as simulated in a GFDL general circulation model. Proc. 13th Stanstead Seminar, Montreal, PQ, Canada, McGill University, 70–76.

  • Mo, K. C., J. Pfaendtner, and E. Kalnay, 1987: A GCM study of the maintenance of the June 1982 blocking in the Southern Hemisphere. J. Atmos. Sci.,44, 297–323.

  • Mullen, S. L., 1987: Transient eddy forcing of blocking flows. J. Atmos. Sci.,44, 3–22.

  • Nakamura, H., M. Tanaka, and J. M. Wallace, 1987: Horizontal structure and energetics of Northern Hemisphere wintertime teleconnection patterns. J. Atmos. Sci.,44, 3377–3391.

  • Nigam, S., I. M. Held, and S. W. Lyons, 1986: Linear simulation of the stationary eddies in a general circulation model. Part I: The no-mountain model. J. Atmos. Sci.,43, 2944–2961.

  • Pitcher, E. J., J. E. Geisler, and M. L. Blackmon, 1983: A general circulation model study of January climate anomaly patterns associated with interannual variations of equatorial Pacific sea surface temperatures. J. Atmos. Sci.,40, 1410–1425.

  • Plumb, R. A., 1985: On the three-dimensional propagation of stationary waves. J. Atmos. Sci.,42, 217–229.

  • Robertson, A. W., and W. Metz, 1989: Three-dimensional linear instability of persistent anomalous large-scale flows. J. Atmos. Sci.,46, 2783–2801.

  • Sheng, J., and Y. Hayashi, 1990a: Observed and simulated energy cycles in the frequency domain. J. Atmos. Sci.,47, 1243–1254.

  • ——, and ——, 1990b: Estimation of atmospheric energetics in the frequency domain during the FGGE year. J. Atmos. Sci.,47,1255–1268.

  • ——, and J. Derome, 1991a: An observational study of the energy transfer between the seasonal mean flow and the transient eddies. Tellus,43A, 128–144.

  • ——, and ——, 1991b: On the interactions among flow components in different frequency bands in the Canadian Climate Centre general circulation model. Atmos.–Ocean,29, 62–84.

  • ——, and ——, 1993: The dynamical forcing of the slow transients by the synoptic scale eddies: An observational study. J. Atmos. Sci.,50, 757–771.

  • Shutts, G. J., 1983: The propagation of eddies in diffluent jetstream: Eddy vorticity forcing of ‘blocking’ flow fields. Quart. J. Roy. Meteor. Soc.,109, 737–761.

  • Simmons, A. J., 1982: The forcing of stationary wave motion by tropical diabatic heating. Quart. J. Roy. Meteor. Soc.,108, 503–534.

  • ——, and B. J. Hoskins, 1978: The life cycles of some nonlinear baroclinic waves. J. Atmos. Sci.,35, 414–432.

  • Ting, M., and M. P. Hoerling, 1993: The dynamics of stationary wave anomalies during the 1986/87 El Niño. Climate Dyn.,9, 147–164.

  • ——, and N.-C. Lau, 1993: A diagnostic and modeling study of the monthly mean wintertime anomalies appearing in a 100-year GCM experiment. J. Atmos. Sci.,50, 2845–2867.

  • Valdes, P. J., and B. J. Hoskins, 1989: Linear stationary wave simulations of the time-mean climatological flow. J. Atmos. Sci.,46, 2509–2527.

  • Wallace, J. M., and D. S. Gutzler, 1981: Teleconnection in the geopotential height field during the Northern Hemisphere winter. Mon. Wea. Rev.,109, 784–812.

All Time Past Year Past 30 Days
Abstract Views 0 0 0
Full Text Views 660 409 21
PDF Downloads 129 27 0