Many climate models predict that anthropogenic greenhouse gas emissions may cause a threshold response of the North Atlantic meridional overturning circulation (MOC). These model predictions are, however, uncertain. Reducing this uncertainty can have an economic value, because it would allow for the design of more efficient risk management strategies. Early information about the MOC sensitivity...

Wavelet Analysis provides a new orthogonal basis set which is localized in both physical space and Fourier transform space. Empirical Orthogonal Functions (EOFs), on the other hand, provide a global representation of data sets. Here we investigate the various ways in which one can combine these basis sets for optimal representation of data. EOFs represent the global large scale information and ...

The coupling on decadal time scales of the midlatitude and tropical Pacific via an oceanic 'bridge' in the thermocline is investigated using ocean general circulation model hindcasts and a coupled ocean atmosphere model. Results indicate that in the tropics decadal anomalies of isopycnal depth are forced by Ekman pumping and are largely independent of the arrival of subducted anomalies in the t...

Short-range ocean forecast and reanalysis systems routinely combine observations from satellite altimetry, satellite sea surface temperature (SST), and in situ temperature and salinity, to initialise global and regional ocean models. The most critical observation type for eddy-resolving applications is arguably satellite altimetry. To quantify the impact of satellite altimetry observations on a...

The Agulhas Current system has been analyzed in a nested high-resolution ocean model and compared to observations. The model shows good performance in the western boundary current structure and the transports off the South African coast. This includes the simulation of the northward-flowing Agulhas Undercurrent. It is demonstrated that fluctuations of the Agulhas Current and Undercurrent around...

Propagation of subsurface North Pacific interdecadal variations is investigated with an ocean general circulation model forced by observed sea surface temperature anomalies. Subsurface temperature anomalies subducted in the central subtropical North Pacific take a more westward pathway than a passive “temperature” tracer and reach the western boundary to the north of the bifurcation latitude. T...

[1] The ability to reconstruct the three-dimensional (3D) dynamics of the ocean by an effective version of Surface Quasi-Geostrophy (eSQG) is examined. Using the fact that surface density plays an analogous role as interior potential vorticity (PV), the eSQG method consists in inverting the QG PV generated by sea-surface density only. We also make the extra assumption that sea-surface temperatu...

We develop a simple model of the lower limb of the meridional overturning circulation in the Southern Ocean based on residual mean theory. We hypothesize that the strength of the lower limb (Ψ) is strongly controlled by the magnitude of abyssal diapycnal mixing (κ), and that of mesoscale eddy transfer (K). In particular, we argue that Ψ ∝ √ κK. The scaling and associated theory find support in ...

[1] The annual cycle is one of the most important components of the global climate system Yet little attention has been paid to the response of the equatorial annual cycle to anthropogenic climate change. Here we present results from a global climate model with high tropical resolution that simulates a strong intensification of the annual cycle in the tropical Pacific in response to increased g...

Cloud microphysics and aerosol indirect effects in the global climate model ECHAM5-HAM U. Lohmann, P. Stier, C. Hoose, S. Ferrachat, E. Roeckner, and J. Zhang Institute of Atmospheric and Climate Science, ETH Zurich, Switzerland Department of Environmental Science and Engineering, California Institute of Technology, Pasadena, USA Max Planck Institute for Meteorology, Hamburg, Germany Meteorolog...