P1.12
A dynamical stabilizing mechanism in the climate system: a linear eigenmode analysis
Vladimir A. Alexeev, Univ. of Copenhagen, Copenhagen, Denmark
A dynamical mechanism of sufficient strength to maintain the stability of the observed annual mean climate against the destabilizing influence of the positive lower tropospheric water vapour/infrared radiative (WVIR) feedback on SST perturbations has recently been proposed (Bates, 1999, Tellus, 51A, 349-372.). The mechanism, based on angular momentum (AM) transport and its link to surface winds and evaporation, has been found from an analysis of a simple atmosphere-ocean model. Numerical experiments with an atmospheric GCM with a uniform +2K SST perturbation aimed at testing the conclusions of the simple model have been carried out (Alexeev and Bates, 1999, Tellus, 51A, 630-651.).
Here we employ a similar approach using the GCM to study the response of the atmosphere to SST perturbations. An aquaplanet with prescribed latitudinally varying SSTs is adopted. An equinoctial distribution of solar radiation is assumed. An equilibrium climate, with the surface fluxes integrating globally to zero, is first established. A series of perturbation experiments is then carried out. An orthogonal set of Legendre polynomials with no longitudinal dependence is used for perturbing the SST. Any SST perturbation can be expressed in terms of these basis functions for a given truncation number. The functions are first scaled properly to be small enough and then added to the reference SST. The GCM is run long enough to reach some other quasi-stationary state. The change in the surface budget between the reference experiment and perturbation experiments is then projected onto the set of basis functions which results in a NxN matrix (N being a truncation number). This matrix describes a quasilinear response of the surface budget to SST perturbations in the space of the orthogonal set of our basis functions. These allows the response of the surface budget to any SST perturbations to be determined. The linear operator obtained can be expanded into parts corresponding to the response of the short- and longwave radiation, the latent and sensible heat fluxes. Furthermore, the latent heat flux response operator as the one of interest is subdivided into two - the wind and humidity components. Stabilizing properties of the whole surface budget response operator and of each part of it are studied.
Poster Session 1, Natural Climate Variability Posters
Monday, 15 January 2001, 1:30 PM-3:30 PM
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