Low-frequency climate variability of an aquaplanet

Abstract

The long-term variability of an aquaplanet climate is analyzed with a coupled atmosphere–ocean–sea ice general circulation model. The main result of the 20,000 years simulation is a very dominant low-frequency oscillation with a period of approximately 700 years. All compartments of the aquaplanet (atmosphere, ocean, and sea ice) are involved as the climate alternates between warmer and colder states. Comprehensive time series analyses, as well as a comparison between mean states of cold and warm phases, give a detailed picture of the life cycle of the low-frequency oscillation. The warm phases are characterized by ice-free polar waters and a weaker meridional overturning circulation. During cold phases, the poles are completely covered by sea ice (down to 65∘ N/S) and the overturning cells in the ocean are stronger. The climate state changes throughout atmosphere and ocean; however, surface areas in high latitudes are especially affected due to the changing sea ice cover. The meridional energy transport in atmosphere and ocean alternates with the climate regime, since the ocean is more efficient in transporting heat poleward when the poles are ice-free

The role of atmospheric greenhouse gases, orbital parameters, and southern ocean gateways: an idealized model study

“…An aquaplanet, which includes a circular continent at the south pole and a meridional barrier in the ocean, is applied for the sensitivity experiments. While idealized set-ups like aquaplanets are not a tool for producing realistic climate simulations in a quantitative sense, they can significantly contribute to our understanding of the climate system in its most elemental form (see for example Smith et al, 2006;Marshall et al, 2007;Enderton and Marshall, 2009;Ferreira et al, 2010Ferreira et al, , 2011Dahms et al, 2011;Hertwig et al, 2015).…”

“…The meridional overturning circulation in the ocean (MOC), which is displayed in figure 4d, is very much affected by the opening of the Drake Passage. In a pure aquaplanet (no orographic barriers at all), a tropical and an extra-tropical circulation cell develops on each side of the equator (for a discussion of pure aquaplanets see Smith et al, 2006;Marshall et al, 2007;Hertwig et al, 2015). In this case with a meridional barrier in the ocean, a large cross-equatorial (positive) cell develops in the northern hemisphere (in each simulation), which reaches into the subtropics of the southern hemisphere.…”

Stable Equatorial Ice Belts at High Obliquity in a Coupled Atmosphere–Ocean Model

“…The model has 22 vertical levels of 50 to 1000 m spacing and a flat bottom at a depth of 5500 m. The model is formulated on a semi-staggered E-grid with 72 × 76 grid cells and is in the aquaplanet configuration, i.e. there are no continents (Hertwig et al 2015). The atmospheric component of PlaSim in version OD has a spectral resolution of T21 (approximately 5.6°) and 10 vertical levels.…”

Evaluation and climate sensitivity of the PlaSim v.17 Earth System Model coupled with ocean model components of different complexity

“…The Planet Simulator (PlaSim) is an EMIC developed at the University of Hamburg (Fraedrich et al, 2005a, b;Fraedrich, 2012) which has been used, among other applications, to explore past conditions of the Earth such as the snowball Earth (Micheels & Montenari, 2008) or the Permian climate (Roscher et al, 2011), to perform specific experiments to test processes like tropical convection or mid-latitude storm tracks using an Aquaplanet configuration (Dahms et al, 2011(Dahms et al, , 2012Hertwig et al, 2014), to investigate the global entropy budget (Fraedrich & Lunkeit, 2008), and for exoplanetary studies (Kilic et al, 2017). The source code of the model is freely available (https://www.mi.uni-hamburg.de/en/arbeitsgruppen/theoretischemeteorologie/modelle/plasim.html).…”

“…The oceanic component of the model can be either represented by a simple mixed-layer model (ML) (Lunkeit et al, 2011) or by a more complex, though simplified, fully 3D dynamical ocean model, the Large Scale Geostrophic (LSG) model, based on primitive equations (Maier-Reimer et al, 1993). While the LSG ocean module allows to use Plasim as a fully coupled Atmosphere-Ocean GCM, it has found only limited application so far, mainly in aquaplanet and paleoclimatic studies (Dahms et al, 2012;Hertwig et al, 2014;Andres & Tarasov, 2019). Other configurations have also been developed, such as an integration of Plasim with the oceanic component of GENIE (Holden et al, 2016).…”