1. Lessons from ARCSyM David Bailey 1 and John Cassano 2 Amanda Lynch, William Chapman, John Walsh, Gunter Weller, Wanli Wu, Andrew Slater, Richard Cullather, Todd Arbetter, Aaron Rivers, Eric Girard, Stacey McIlwaine, Elizabeth Cassano, Leanne Lestak 1 National Center for Atmospheric Research 2 University of Colorado Cooperative Institute for Research in Environmental Sciences Department of Atmospheric and Oceanic Sciences

3. LAND BATS, LSM, CLASS ATMOSPHERE (MM4 / RegCM) Hydrostatic Mesoscale Model CCM2/RRTM radiation Holtslag PBL Moisture and Convective parameterizations SEA ICE CF/EVP 2-layer thermo OCEAN Slab Ocean Model 1D Mixed Layer SPEM/POM Arctic Regional Climate System Model

4. Science Questions Nonlocal response to coupled sea-ice and moisture parameterizations (Lynch et al.) Regional ocean impacts (Bailey, Lynch) Small-scale atmosphere-sea ice interactions such as polynyas (Lynch, Bailey) Land-atmosphere interactions: snow, tundra, boreal forest, fires (Wu, Slater, Lynch) Atmospheric forcing / preconditioning (Lynch et al.) Horizontal and vertical boundaries (Cullather, Wu, Rivers, Lynch) ARCMIP (Lynch, Cassano) Impacts Assessments (Lynch, Cassano) Paleoclimate (Rivers, Lynch)

5. Science Highlights: Impact of Ice Dynamics Experiments with and without ice dynamics show significant differences reaching far inland. Lynch et al. 1995

6. Science Highlights: Polynyas Cosmonaut Sea ( Bailey et al. 2004) St. Lawrence Island Examples of polynyas that are triggered by the atmosphere and maintained by the ocean. Lynch et al. 1997

7. Science Highlights: ARCMIP Wyser et al. 2008 Clouds and surface albedo are the most needed improvements. “I’m not dead yet!”

8. Summary Numerous scientific questions: http://arts.monash.edu.au/ges/research/regclim/pubs.php Ideal for small-scale process studies. Importance of dynamic-thermodynamic sea ice and other high-latitude processes. Timescale falls between weather and climate (1-10 years).

9. ARCSyM Postmortem ARCSyM R.I.P. SPEM RegCM Lack of Support/Personnel for: Running experiments / computational expense. Performance enhancements and new computing architectures. Ongoing model development. Boundary conditions (well-posed, model/data). CSM MM4 “ARCSyM is well and truly dead.” - A. Lynch

10. Lessons Learned (1) Development and maintenance of such a model is very time consuming. –More than a single research group can handle A flexible coupling strategy is the way to go. –Makes upgrading model components or adding new coupling fields much easier. –Decreases possibility of introducing new bugs to model Use of easily upgradeable component models can reduce model development time and effort. –Addition of new high-latitude cloud and boundary layer parameterizations in ARCSyM required significant effort

11. Lessons Learned (2) There is a benefit to using community developed component models and coupler. –Benefit from on-going model development –Addition of new model options / physics –Bug fixes with new releases of model –Availability of model pre and post-processing programs –Keeping model components “current” with community release does require regular updates of model code –Need to have two-way communication so high-latitude physics and parameterizations can find their way back into the global models.