Variabitity on decadal scales in Pacific sea surface temperatures and atmosphere ocean interaction in the coupled general circulation model ECHAM4/OPYC3

• Main Author: Bacher, A.
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: University of Hamburg 1998
• Subjects: Pacific; Sea ice
• Online Access: http://hdl.handle.net/21.11116/0000-0009-E314-0; http://hdl.handle.net/21.11116/0000-0009-E316-E

The work presented in this thesis consists of both practical development and analytical investigation of a run with the coupled climate model ECHAM4/OPYC3. The practical aspect involved the devel- opment of a coupling interface for synchronizing ECHAM and OPYC and performing the regridding of the surface fluxes and SST. The numerical treatment of the regridding problem is innovative in coupled climate modelling. A meshwidth refinement strategy in analogy to interpolatory subdivision, widespread in Computer Aided Geometric Design (CAGD), was developed which preserves positiv- ity for fields such as river discharge. It includes special treatment of the irregular domain given by ocean grid points only and employs open boundaries at the latitudinal extremities. The annual mean flux adjustment used was based on ideas by Oberhuber (pers. comm.), in collaboration with whom a scheme for heat flux adjustment for sea ice covered grid points was implemented. The coupled model simulation for the Pacific reproduces the mean climate simulated by the uncou- pled model as discussed in Roeckner et al. (1996b). Temperature, zonal wind, 500 hPa height and preciptation annual mean and seasonal results deviate little from the uncoupled reference. For sea surface temperature (SST) the seasonal cycle of warm pool and cold tongue extent is similar to observations, apart from cooling in the north-eastern warm pool area about one month prematurely and a premature termination of the cold tongue cold phase. Surface heat fluxes and wind stress agree with the Oberhuber (1988) and ECMWF reanalysis climatologies, respectively, if the uncertainties in the heat flux climatology, e.g. over the warm pool domain, are taken into account. Exceptions are excessive heat flux in areas with stratus over the eastern subtropical oceans and the substantial over- estimation of boreal summer south-eastern trades on the equator. Mixed layers are predicted success- fully. The tropical thermocline and currents due to the use of isopycnic coordinates are located ...