NOAA's Ocean Climate Change Web Portal

Regional Ocean Model:

We used the Regional Ocean Modeling System (ROMS, Shchepetkin and McWilliams 2003, 2005) to investigate the effects of climate change on the northwest Atlantic. ROMS is a terrain-following primitive equation model with a free surface using incompressible and hydrostatic approximations. The version used here was configured by Kang and Curchitser (2003) has a horizontal grid spacing of 7 km and 40 vertical levels with higher resolution near the surface. The domain extends along the east coast of North America from approximately 10N to 52N, covering the western Caribbean, Gulf of Mexico, and the western North Atlantic from Florida to Newfoundland and includes the Loop Current, Florida Current, Gulf Stream and the southern portion of the Labrador current. The initial and oceanic boundary forcing for the control simulation over the period 1976 to 2005 is obtained from the Simple Ocean Data Assimilation (SODA v2.1.6; Carton and Giese 2008) and the surface forcing from the Co-ordinated Ocean-Ice Reference Experiments (CORE v2; Large and Yeager 2009). Kang and Curchitser (2013) found that the mean path of the Gulf Stream and the distribution of eddy kinetic energy simulated by ROMS was in good agreement with satellite observations.

Climate change simulations "Delta Method":

The large-scale climate change forcing is implemented using the "delta method" where the difference between mean conditions from a future and recent period are added to the observed recent period. Since the recent periods mean climate and high-frequency variability is retained from observations, this method removes the mean bias and retains realistic unforced climate variability; however, the imposed climate change signal at the boundaries is still at a coarse resolution, it does not allow for a change in variability in the future, and assumes that the mean climate state and the projected change are not highly correlated (e.g., Hare et al. 2012). The delta values were obtained from the difference in the mean values between 2070-2099 and 1976-2005, where the future period is simulated based on the Representative Concentration Pathway 8.5 (RCP8.5 scenario,, which represents a "business-as-usual" scenario assuming little to no stabilization of greenhouse gas emissions by 2100. The deltas were computed for each calendar month and then interpolated to daily values, which are then added to the observed forcing and initial ocean conditions in the control simulation. Both the control (CTRL) and RCP8.5 (CTRL+delta forcing) ROMS simulations are 30 years long and the results are based on the difference between them. The delta initial conditions and boundary forcing were obtained from three Earth System Models (ESMs, GCMS that also include biogeochemistry) used in the fifth IPCC assessment: the GFDL ESM2M, Institute Pierre Simon Laplace (IPSL) CM5A-MR, and the Hadley Center (HC) HadGem2-CC. These three models, were chosen in part due to their differences in the climatological and response to greenhouse gas forcing of AMOC. The surface fields need to drive ROMS include sea level pressure, zonal and meridional winds, air temperature and humidity, downwelling shortwave and long wave radiation, and precipitation. The delta values for these fields from the three GCMS on a monthly based and then interpolated to daily values.

References

Alexander, M. A., S. Shin, J. D. Scott, E. Curchitser, C. Stock, 2019: The Response of the Northwest Atlantic Ocean to Climate Change J. Climate, Submitted.

Carton, J. A., and B. S. Giese, 2008: A reanalysis of ocean climate using Simple Ocean Data Assimilation (SODA). Mon. Wea. Rev., 136, 2999-3017, doi:https://doi.org/10.1175/2007MWR1978.1.

Hare, J. A., J. Manderson, J. Nye, M. Alexander, P. J. Auster, D. Borggaard, A. Capotondi, K. Damon-Randall, E. Heupel, I. Mateo, L. O'Brien, D. Richardson, C. Stock, and S. T. Biegel, 2012: Cusk (Brosme brosme) and climate change: assessing the threat to a candidate marine fish species under the U.S. Endangered Species Act ICES Journal of Marine Science, 69, 1753-1768.

Kang, D., and E. N. Curchitser, 2013: Gulf Stream eddy characteristics in a high-resolution ocean model. J. Geophys. Res. Oceans, 118, 4474-4487, doi:https://doi.org/10.1002/jgrc.20318.

Large, W. G., and S. G. Yeager, 2009: The global climatology of an interannually varying air-sea flux data set. Climate Dyn., 33, 341-364, doi:https://doi.org/10.1007/s00382-008-0441-3.

Shchepetkin, A. F., and J. C. McWilliams, 2003: A method for computing horizontal pressure-gradient force in an oceanic model with a nonaligned vertical coordinate, J. Geophys. Res., 108(C3), 3090, doi:10.1029/2001JC001047.

Shchepetkin, A. F., and J. C. McWilliams, 2005: The Regional Oceanic Modeling System (ROMS): A split-explicit, free-surface, topography-following-coordinate oceanic model, Ocean Modell., 9, 347-404.

This page is maintained by Jamie Scott