RegCM3: Changes in Model Configuration to better

Represent Lakes

Mark A. Snyder, Lisa C. Sloan, Travis O’Brien, and Kathleen Uzilov

Climate Change and Impacts Laboratory

Dept. of Earth and Planetary Sciences

University of California, Santa Cruz

NARCCAP User’s Meeting | April 10, 2012

RegCM3-GFDL and CGCM3 Great Lakes treatment

• Lakes in the RegCM3-NCEP runs were set to SST values and don’t have the seasonality problem

• Why were the RegCM3-GFDL and CGCM3 runs done differently?– SST data was not available over land areas in the driving

data

RegCM3-GFDL and CGCM3 Great Lakes treatment

• Without SSTs over land, RegCM3 reverts to a simplified treatment of lakes.

• Initial lake SSTs were assigned using downward-extrapolated air temperature.

• After the initial time step, the BATS land surface model calculates the temperatures at lake grid points. Grid points designated as lakes use the BATS parameterization for inland water (land use category 14).

RegCM3-GFDL and CGCM3 Great Lakes treatment

• The problem with the simplified lake treatment is that the lake SSTs are tied to surface air temperature and are too cool in winter and too warm in summer

• Original GFDL historical run on left, DJF average temperature

RegCM3-GFDL and CGCM3 Great Lakes treatment

• The problem with the simplified lake treatment is that the lake SSTs are tied to surface air temperature and are too cool in winter and too warm in summer

• Original GFDL historical run on left, JJA average temperature

RegCM3-GFDL and CGCM3 Great Lakes treatment

• Re-run of RegCM3-GFDL and CGCM3 cases– Take original SST datasets from GFDL and

CGCM3, with no values over land, and create new interpolated across land datasets.

– Use the NCL poisson_grid_fill function to do this (http://www.ncl.ucar.edu/Document/Functions/Built-in/poisson_grid_fill.shtml)

– Use new SST datasets to create boundary conditions for RegCM3

RegCM3-GFDL and CGCM3 Great Lakes treatment

Original GFDL SSTs, at one time slice

RegCM3-GFDL and CGCM3 Great Lakes treatment

SSTs after interpolation, note the function does not effect values over the ocean, it only generates values over land

RegCM3-GFDL and CGCM3 Great Lakes treatment

• Re-run of RegCM3-GFDL and CGCM3 cases– Values of SSTs for the Great Lakes are now

assigned using the new interpolated SST datasets– Re-runs of RegCM3-GFDL and CGCM3 historical

and future cases are now complete (Historical v2 and Future v2)

– Seasonal SSTs for the Great Lakes are now more realistic

• GFDL DJF surface air temperature from the original (left) and v2 (right) historical runs

• Note the warmer temps over Great Lakes in the v2 runs on the right

• GFDL DJF surface air temperature from the original and v2 future runs

• Note the warmer temps over Great Lakes in the v2 runs on the right

• GFDL JJA surface air temperature from the original and v2 historical runs

• Note the cooler temps over Great Lakes in the v2 runs on the right

• GFDL JJA surface air temperature from the original and v2 future runs

• Note the cooler temps over Great Lakes in the v2 runs on the right

Conclusions

• Great Lakes SSTs in original RegCM3-GFDL and CGCM3 runs were getting the seasonal cycle wrong

• Re-run of RegCM3-GFDL and CGCM3 with new SST treatment has improved the seasonal cycle

End