An altimetric based metric for Gulf Stream position in climate models

Andrew Davis (University of Washington, United States)

CoAuthors

Thompson LuAnne (University of Washington, USA)

Event: 2015 Ocean Surface Topography Science Team Meeting

Session: Science III: Large scale and global change ocean processes: the ocean's role in climate

Presentation type: Type Poster

The long spin-up time of the ocean requires multiple centuries, precluding coupled equilibrium simulations at eddy resolving scales. As such, the Coupled Modeling Intercomparison Project (CMIP) guidelines suggest a nominal 1° ocean resolution with higher meridional resolution in the tropics. Additional CMIP6 simulations will be run at 0.25°, however, while baroclinic instability generates eddies in mid-latitudes at this resolution, they are not well resolved. Detailed comparisons of SST biases in ocean-only simulations show that even at 0.25° degree, there is a greater than 5°C warm bias North of Cape Hatteras along the Eastern Seaboard and a greater than 5°C cold bias in the North Atlantic Current at 40°W. At 1/12° these biases are much diminished and of smaller spatial scale owing to the increased strength and higher Reynold’s number of the Gulf Stream and North Atlantic Current.

Here we present model metrics for Gulf Stream position and strength, providing both their climatological mean and variance. For high-resolution models we fit the sea level across the Gulf Stream to an error function. In a comparison between and North Atlantic ocean-only and coupled simulations at high resolution (0.1°) we find qualitative agreement with observations in both mean and variance of position. We also develop a metric for low-resolution models based on the location of maximum zonal velocity and apply it to historical simulations of models in the CMIP5 archive. While the mean position of the Gulf Stream is qualitatively similar among the models, there are large differences in the spatial and temporal variance of its position.

Quantifying biases in Gulf Stream position and strength (both mean and variability) is vital to evaluating and improving the performance of climate models in the North Atlantic as Gulf Stream strength and position are closely related to sea surface temperature in the subpolar North Atlantic. In addition, understanding and predicting decadal-scale changes in the Gulf Stream can provide insight into the decadal variability of the North Atlantic processes to which it is closely linked.

 

Poster show times:

RoomStart DateEnd Date
Grand Ballroom Foyer Thu, Oct 22 2015,11:00 Thu, Oct 22 2015,18:00
Andrew Davis
University of Washington
United States
adavis44@u.washington.edu