R. Redler

Tropical Pacific Climate and Its Response to Global Warming in the Kiel Climate Model

Abstract A new, non-flux-corrected, global climate model is introduced, the Kiel Climate Model (KCM), which will be used to study internal climate variability from interannual to millennial time scales and climate predictability of the first and second kind. The version described here is a coarse-resolution version that will be employed in extended-range integrations of several millennia. KCM’s performance in the tropical Pacific with respect to mean state, annual cycle, and El Nino–Southern Oscillation (ENSO) is described. Additionally, the tropical Pacific response to global warming is studied. Overall, climate drift in a multicentury control integration is small. However, KCM exhibits an equatorial cold bias at the surface of the order 1°C, while strong warm biases of several degrees are simulated in the eastern tropical Pacific on both sides off the equator, with maxima near the coasts. The annual and semiannual cycles are realistically simulated in the eastern and western equatorial Pacific, respecti...

The Relative Importance of Northern Overflow and Subpolar Deep Convection for the North Atlantic Thermohaline Circulation

The relative importance of the formation of different North Atlantic Deep Water masses on the meridional overturning is examined with a non-eddy-resolving version of the CME model. In contrast to a frequently held belief, convective deep-water formation south of the North Atlantic sill does not significantly force the large-scale overturning if an adequate overflow across the sill can be represented by the model. The sensitivity of the meridional transport to the surface thermohaline forcing is increased under alternate climatic conditions such as increased surface cooling or reduced overflow compared to the present-day situation. The results indicate that climate models may be too sensitive to decadal timescale variability of the surface forcing in subpolar regions.

Effect of the overflows on the circulation in the subpolar North Atlantic: A regional model study

An ocean circulation model for process studies of the Subpolar North Atlantic is developed based on the Geophysical Fluid Dynamics Laboratory (GFDL) Modular Ocean Model (MOM) code. The basic model configuration is identical with that of the high-resolution model (with a grid size of 1/3° × 2/5°) of the World Ocean Circulation Experiment (WOCE) Community Modeling Effort (CME), except that the domain of integration is confined to the area from 43° to 65°N. Open boundary conditions are used for the inflows and outflows across the northern and southern boundaries. A comparison with the CME model covering the whole North Atlantic (from 15°S to 65°N) shows that the regional model, with inflow conditions at 43°N from a CME solution, is able to reproduce the CME results for the subpolar area. Thus the potential of a regional model lies in its use as an efficient tool for numerical experiments aiming at an identification of the key physical processes that determine the circulation and water mass transformations in the subpolar gyre. This study deals primarily with the representation and role of the overflow waters that enter the domain at the northern boundary. Sensitivity experiments show the effect of closed versus open boundaries, of different hydrographic conditions at inflow points, and of the representation of the narrow Faeroe Bank Channel. The representation of overflow processes in the Denmark Strait is the main controlling mechanism for the net transport of the deep boundary current along the Greenland continental slope and further downstream. Changes in the Faeroe Bank Channel throughflow conditions have a comparatively smaller effect on the deep transport in the western basin but strongly affect the water mass characteristics in the eastern North Atlantic. The deep water transport at Cape Farewell and further downstream is enhanced compared to the combined Denmark Strait and Iceland-Scotland overflows. This enhancement can be attributed to a barotropic recirculation in the Irminger Basin which is very sensitive to the outflow conditions in the Denmark Strait. The representation of both overflow regions determine the upper layer circulation in the Irminger and Iceland Basins, in particular the path of the North Atlantic Current.

A European Network for Earth System Modeling

The increasing complexity of Earth system models and the computing facilities needed to run those models put a heavy technical burden on research teams active in climate modeling. To ease this burden, a European collaborative venture called PRISM was initiated in December 2001 to organize a network of experts in order to share the development, maintenance, and support of Earth system modeling software tools and community standards. PRISM was recently reorganized, and a new Web portal (http://prism.enes.org) was unveiled in July 2006. The PRISM network was developed with the hope that advancing specific common standards and tools will reduce the technical development efforts of individual research teams, facilitate the assembling, running, and postprocessing of Earth system models based on state-of-the-art component models, and hence facilitate scientific collaboration between the different research groups in Europe and elsewhere.

Estimating a Mean Ocean State from Hydrography and Sea-Surface Height Data with a Nonlinear Inverse Section Model: Twin Experiments with a Synthetic Dataset

The recovery of the oceanic flow field from in situ data is one of the oldest problems of modern oceanography. In this study, a stationary, nonlinear inverse model is used to estimate a mean geostrophic flow field from hydrographic data along a hydrographic section. The model is augmented to improve these estimates with measurements of the absolute sea-surface height by satellite altimetry. Measurements of the absolute sea-surface height include estimates of an equipotential surface, the geoid. Compared to oceanographic measurements, the geoid is known only to low accuracy and spatial resolution, which restricts the use of sea-surface height data to applications of large-scale phenomena of the circulation. Dedicated satellite missions that are designed for high precision, high-resolution geoid models are planned and/or in preparation. This study, which relies on twin experiments, assesses the important contribution of improved geoid models to estimating the mean flow field along a hydrographic section. When the sea-surface height data are weighted according to the error estimates of the future highly accurate geoid models GRACE (Gravity Recovery And Climate Experiment) and GOCE (Gravity Field and Steady-State Ocean Circulation Explorer), integrated fluxes of mass and temperature can be determined with an accuracy that is improved over the case with no sea-surface height data by up to 55%. With the error estimates of the currently best geoid model EGM96, the reduction of the estimated flux errors does not exceed 18%.

Earth system modelling 3: Coupling software and strategies

Collected articles in this series are dedicated to the development and use of software for earth system modelling and aims at bridging the gap between IT solutions and climate science. The particular topic covered in this volume addresses the major coupling software developed and used in the climate modelling community.

Parallel coupling of regional atmosphere and ocean models

In coupled models the performance of massively parallelmodel components strongly suffers from sequential coupling overhead.A coupling interface for parallel interpolation and parallelcommunication is urgently required to work out this performancedilemma. Performance measurements for a parallel coupling ofparallel regional atmosphere and ocean models are presented for theCRAY-T3E-1200 using the coupling library MpCCI. The differentrotated grids of the models MOM2 (ocean-seaice) and PARHAM(atmosphere) are configured for the arctic region. In particular, asunderlying MPI-implementations CRAY-MPI and MetaMPI are compared intheir performance for some relevant massive parallel configurations.It is demonstrated that an overhead of 10\% for coupling, includinginterpolation and communication, can be achieved. Perspectives for acommon coupling specification are given enabling the modelingcommunity to easily exchange model components as well as couplingsoftware, making model components reusable in other couplingprojects and on next generation computing architectures. Futureapplications of parallel coupling software in parallel nesting anddata assimilation are discussed.

Earth system modelling 4 : IO and postprocessing

Collected articles in this series are dedicated to the development and use of software for earth system modelling and aims at bridging the gap between IT solutions and climate science. The particular topic covered in this volume addresses the issue of data input/output and post-processing in the context of Earth system modeling, with an emphasis on parallel I/O, storage management and analysis subsystems for very large scale data requirements.

Earth System Modelling - Volume 6: ESM Data Archives in the Times of the Grid

Collected articles in this series are dedicated to the development and use of software for earth system modelling and aims at bridging the gap between IT solutions and climate science. The particular topic covered in this volume addresses the Grid software which has become an important enabling technology for several national climate community Grids that led to a new dimension of distributed data access and pre- and post-processing capabilities worldwide.

The OASIS Coupler

In 1991, CERFACS was commissioned by the French climate modelling community to perform the technical assembling of an ocean General Circulation Model (GCM), Ocean Parallelise (OPA) developed by the Laboratoire d’Oceanographie Dynamique et de Climatologie (LODYC), and two different atmospheric GCMs, Action de Recherche Petite Echelle Grande Echelle (ARPEGE) and the Laboratoire de Meteorologie Dynamique zoom (LMDz) model developed respectively by Meteo-France and the Laboratoire de Meteorologie Dynamique (LMD).