Simulating Southern Hemisphere extra-tropical climate variability with an idealised coupled atmosphere-ocean model

Abstract

Abstract.A quasi-geostrophic model of Southern Hemisphere's wintertime atmospheric circulation with horizontal resolution T21 has been coupled to a global ocean circulation model with a resolution of 2 • × 2 • and simplified physics. This simplified coupled model reproduces qualitatively some features of the first and the second EOF of atmospheric 833 hPa geopotential height in accordance with NCEP data. The variability patterns of the simplified coupled model have been compared with variability patterns simulated by four complex state-of-the-art coupled CMIP5 models. The first EOF of the simplified model is too zonal and does not reproduce the right position of the centre of action over the Pacific Ocean and its extension to the tropics. The agreement in the second EOF between the simplified and the CMIP5 models is better. The total variance of the simplified model is weaker than the observational variance and those of the CMIP5 models. The transport properties of the Southern Ocean circulation are in qualitative accord with observations. The simplified model exhibits skill in reproducing essential features of decadal and multi-decadal climate variability in the extratropical Southern Hemisphere. Notably, 800 yr long coupled model simulations reveal sea surface temperature fluctuations on the timescale of several decades in the Antarctic Circumpolar Current region.

Atmospheric Circulation Regimes in a Nonlinear Quasi-Geostrophic Model

“…This paper continues investigations by Sempf et al [12,13], where the atmospheric regime behavior was investigated by means of a quasi-geostrophic (QG) three-level T21 model of the wintertime atmospheric circulation over the Northern Hemisphere (NH), and extends the research with a higher-resolution hemispheric QG three-level T63 model. In Kurzke et al [14] the Southern Hemisphere (SH) version of the three-level quasi-geostrophic T21 model was coupled to a global ocean circulation model with 2 ∘ × 2 ∘ resolution and simplified physics, and the consequent SH wintertime extratropical climate variability has been studied. Here a step toward increasing the horizontal spectral resolution of the atmospheric model has been made by enhancing the resolution to T63.…”