Simulated pre-industrial climate in Bergen Climate Model (version 2): model description and large-scale circulation features

[摘要] The Bergen Climate Model (BCM) is a fully-coupled atmosphere-ocean-sea-icemodel that provides state-of-the-art computer simulations of the Earth'spast, present, and future climate. Here, a pre-industrial multi-centurysimulation with an updated version of BCM is described and compared toobservational data. The model is run without any form of flux adjustments andis stable for several centuries. The simulated climate reproduces the generallarge-scale circulation in the atmosphere reasonably well, except for apositive bias in the high latitude sea level pressure distribution. Also, byintroducing an updated turbulence scheme in the atmosphere model a persistentcold bias has been eliminated. For the ocean part, the model drifts in seasurface temperatures and salinities are considerably reduced compared toearlier versions of BCM. Improved conservation properties in the ocean modelhave contributed to this. Furthermore, by choosing a reference pressure at2000 m and including thermobaric effects in the ocean model, a morerealistic meridional overturning circulation is simulated in the AtlanticOcean. The simulated sea-ice extent in the Northern Hemisphere is in generalagreement with observational data except for summer where the extent issomewhat underestimated. In the Southern Hemisphere, large negative biasesare found in the simulated sea-ice extent. This is partly related to problemswith the mixed layer parametrization, causing the mixed layer in the SouthernOcean to be too deep, which in turn makes it hard to maintain a realisticsea-ice cover here. However, despite some problematic issues, thepre-industrial control simulation presented here should still be appropriatefor climate change studies requiring multi-century simulations.

[学科分类] 天文学(综合)