J.-S. von Storch

Wind-Generated Power Input to the Deep Ocean: An Estimate Using a 1/10° General Circulation Model

Abstract Recent studies on the wind-generated power input to the geostrophic and nongeostrophic ocean circulation components have used expressions derived from Ekman dynamics. The present work extends and unifies previous studies by deriving an expression from the kinetic energy budget of the upper layer based on the primitive equations. Using this expression, the wind-generated power available to the deep ocean is estimated from an integration with the 1/10° ocean general circulation model of the Earth Simulator Center. The result shows that the total power generated by the wind at the sea surface is about 3.8 TW. About 30% of this power (1.1 TW) is passed through a surface layer of about 110-m thickness to the ocean beneath. Approximating the wind-generated power to the deep ocean using Ekman dynamics produces two large errors of opposite signs, which cancel each other to a large extent.

Energetics Responses to Increases in Greenhouse Gas Concentration

Abstract Increasing greenhouse gas concentrations warm the troposphere. However, it is not clear whether this implies changes in the energetics. To study the energetics responses to CO2 increases, changes in the Lorenz energy cycle (LEC) are evaluated using output from the atmosphere–ocean ECHAM5/Max Planck Institute Ocean Model (MPI-OM). Equilibrium 2 × CO2 experiments and 10-yr transient experiments with 3% increase per year are analyzed. Globally, doubling of CO2 results in a decrease in the LEC strength—defined as the total conversion of available potential energy P into kinetic energy K—but also in an increase in the zonal-mean K. These global changes are a consequence of the strengthening of the LEC in the upper troposphere and the weakening of the cycle below. The two opposite responses result from the simulated warming pattern that shows the strongest warming in the upper tropical troposphere and in the lower troposphere at high latitudes. This warming structure causes changes in the horizontal te...

Variability of Deep-Ocean Mass Transport: Spectral Shapes and Spatial Scales

Abstract This paper studies the variability of deep-ocean mass transport using four 1000-yr integrations performed with coupled general circulation models. Statistics describing the spectral and spatial features are considered. It is shown that these features depend crucially on the time-mean state. For the transport of tropical and subtropical water masses in three of the integrations, the spectral levels continually increase with decreasing frequency and do not show isolated peaks at low frequencies. The slope of the low-frequency spectrum (in a log–log plot) changes with increasing depth. It has values of about 0 near the surface, about −1 at intermediate depth, and about −2 at or near the bottom. The result indicates that the maximal memory timescale for deep-ocean mass transport is longer than a few centuries. The situation is different in the fourth integration, which has a different mean circulation pattern. In this case, the low-frequency spectrum is more or less flat in the tropical and subtropic...

A Stochastic Analysis of the Impact of Small-Scale Fluctuations on the Tropospheric Temperature Response to CO2 Doubling

Abstract The climate response to increased CO2 concentration is generally studied using climate models that have finite spatial and temporal resolutions. Different parameterizations of the effect of unresolved processes can result in different representations of small-scale fluctuations in the climate model. The representation of small-scale fluctuations can, on the other hand, affect the modeled climate response. In this study the mechanisms by which enhanced small-scale fluctuations alter the climate response to CO2 doubling are investigated. Climate experiments with preindustrial and doubled CO2 concentrations obtained from a comprehensive climate model [ECHAM5/Max Planck Institute Ocean Model (MPI-OM)] are analyzed both with and without enhanced small-scale fluctuations. By applying a stochastic model to the experimental results, two different mechanisms are found. First, the small-scale fluctuations can change the statistical behavior of the global mean temperature as measured by its statistical damp...

Impact of the warming pattern on global energetics

AbstractThe warming pattern due to higher greenhouse gas concentrations is expected to affect the global atmospheric energetics mainly via changes in the (i) meridional temperature gradient and (ii) mean static stability. Changes in surface meridional temperature gradients have been previously regarded as the determining feature for the energetics response, but recent studies suggest that changes in mean static stability may be more relevant than previously thought. This study aims to determine the relative importance of these two effects by comparing the energetics responses due to different warming patterns using a fully coupled atmosphere–ocean general circulation model.By means of an additional diabatic forcing, experiments with different warming patterns are obtained: one with a 2xCO2-like pattern that validates the method, one with only the tropical upper-tropospheric warming, and one with only the high-latitude surface warming. The study’s findings suggest that the dominant aspect of the warming pa...

What Balances the Decrease in Net Upward Thermal Radiation at the Surface in Climate Change Experiments

The direct response of surface fluxes to an increase in green house gas concentration is a decrease in net upward long-wave radiation (NLW). This paper examines the responses of the other three surface fluxes, i.e. the latent heat flux (HL), the sensible heat flux (HS) and the net short wave radiation (NSW), using a set of IPCC AR4 climate experiments performed with the coupled ECHAM5/MPI-OM AO-GCM. In particular, the questions of whether and how these fluxes compensate the warming effect due to a decrease in upward NLW are studied. Consistent with the earlier studies, the decrease in upward NLW is strongly compensated by an increase in upward HL. By using the IPCC scenarios and a coupled AO-GCM, two new aspects of this compensation are identified. First, the degree of compensation decreases with the rate of increase in GHG concentration. Secondly, the compensation does not work over the North Atlantic, where the decrease in upward NLW develops parallel to a reduction in upward HL. This leads to large increases in the net downward heat flux over the North Atlantic and a reduction of the MOC. The responses in HS and NSW can further strengthen or suppress the warming effect of NLW, depending on geographical regions considered. There is a general tendency that HS changes in the same direction as NLW over sea, but in the opposite direction over land. For NSW, the response strengthens the NLW changes over land and suppresses the NLW changes over sea.