Analysis of the frequency-dependent response to wave forcing in the extratropics A. J. Haklander1,2, P. C. Siegmund2, and H. M. Kelder1,2 1Eindhoven University of Technology (TUE), Department of Applied Physics, P.O. Box 513, 5600 MB Eindhoven, The Netherlands 2Royal Netherlands Meteorological Institute (KNMI), Climate Research and Seismology Department, Atmospheric Composition Division, P.O. Box 201, 3730 AE De Bilt, The Netherlands
Abstract. A quasigeostrophic model for the frequency-dependent response of the
zonal-mean flow to planetary-wave forcing at Northern Hemisphere (NH)
midlatitudes is applied to 4-D-Var ECMWF analysis data for six extended
winter seasons. The theoretical response is a non-linear function of the
frequency of the forcing, the thermal damping time α−1, and a
scaling parameter µ which includes the aspect ratio of the meridional
to the vertical length scale of the response. Regression of the
calculated response from the analyses onto the theoretical response yields
height-dependent estimates for both α−1 and µ. The thermal
damping time estimated from this dynamical model is about 2 days in the
troposphere, 7–10 days in the stratosphere, and 2–4 days in the lower
mesosphere. For the stratosphere and lower mesosphere, the estimates lie
within the range of existing radiative damping time estimates, but for the
troposphere they are significantly smaller.
Citation: Haklander, A. J., Siegmund, P. C., and Kelder, H. M.: Analysis of the frequency-dependent response to wave forcing in the extratropics, Atmos. Chem. Phys., 6, 4477-4481, doi:10.5194/acp-6-4477-2006, 2006.