On decadal-scale ocean-atmosphere interactions in the extended ECHAM1/LSG climate simulation |
| |
Authors: | C Frankignoul E Kestenare N Sennéchael G de Coëtlogon F D'Andrea |
| |
Institution: | (1) Laboratoire d'Océanographie Dynamique et de Climatologie, Unité mixte de recherche CNRS-ORSTOM-UPMC, Université Pierre et Marie Curie, Case 100, 4 place Jussieu, 75252 Paris Cedex 05, France E-mail: cf@lodyc.jussieu.fr, FR;(2) Laboratoire de Météorologie Dynamique, Ecole Normale Supérieure, 24, rue Lhomond, 75231 Paris Cedex 05, France, FR |
| |
Abstract: | The last 810 years of a control integration with the ECHAM1/LSG coupled model are used to clarify the nature of the ocean-atmosphere
interactions at low frequencies in the North Atlantic and the North Pacific. To a first approximation, the atmosphere acts
as a white noise forcing and the ocean responds as a passive integrator. The sea surface temperature (SST) variability primarily
results from short time scale fluctuations in surface heat exchanges and Ekman currents, and the former also damp the SST
anomalies after they are generated. The thermocline variability is primarily driven by Ekman pumping. Because the heat, momentum,
and vorticity fluxes at the sea surface are correlated in space and time, the SST variability is directly linked to that in
the ocean interior. The SST is also modulated by the wind-driven geostrophic fluctuations, resulting in persistent correlation
with the thermocline changes and a slight low-frequency redness of the SST spectra. The main dynamics are similar in the two
oceans, although in the North Pacific the SST variability is more strongly influenced by advection changes and the oceanic
time scales are larger. A maximum covariance analysis based on singular value decomposition in lead and lag conditions indicates
that some of the main modes of atmospheric variability in the two oceans are sustained by a very weak positive feedback between
the atmosphere, SST, and the strength of the subtropical and subpolar gyres. In addition, in the North Atlantic the main surface
pressure mode has a small quasi-oscillatory component at 6-year period, and advective resonance occurs for SST around 10-year
period, both periods being also singled out by multichannel singular spectrum analysis. The ocean-atmosphere coupling is however
much too weak to redden the tropospheric spectra or create anything more than tiny spectral peaks, so that the atmospheric
and oceanic variability is dominated in both ocean sectors by the one-way interactions.
Received: 2 April 1999 / Accepted: 14 October 1999 |
| |
Keywords: | |
本文献已被 SpringerLink 等数据库收录! |
|