1 University of Massachusetts Dartmouth 2 Bigelow Laboratory for Ocean Sciences

1. Towards simulating high and low NAO forced North Atlantic scenarios for flow and nutrient dynamics Avijit Gangopadhyay1, H.S. Kim1, C. Shaji1, J. Bisagni1, J. Goes2 and C. Mouw1 1University of Massachusetts Dartmouth 2Bigelow Laboratory for Ocean Sciences School for Marine Science & Technology West Boothbay Harbor North Dartmouth, MA 02747, USA Maine 04575-0475 Domain Set up Abstract Given the large impact of the western North Atlantic Ocean on the global carbon cycle, it is reasonable to examine the effects of the North Atlantic Oscillation (NAO), the single largest factor affecting atmospheric circulation variability over the North Atlantic. Our project is a three-year, physical and biological data analysis and modeling effort that is aimed at understanding the influence of NAO-related interannual and interdecadal shifts in the path of the Gulf Stream and their effect on availability of macro-nutrients (NO3 and (Si(OH)4) and biological production in the western North Atlantic Ocean. Thus, our proposed data analysis and regional modeling effort is directed towards understanding how ocean circulation, macro-nutrient availability, and biological processes are related to coupled ocean-atmosphere climate variability within continental shelf and slope waters located off the east coast of North America. Most importantly, through our combined data analysis and modeling approach, we intend to examine interannual and interdecadal variability of new primary production (NPP) using potential new production (PNP) as a proxy for NPP within western North Atlantic slope and shelf waters, including the Gulf of Maine (GOM), located off the coast of New England. To address such issues, we are implementing a basin-scale North Atlantic modeling system using the Regional Ocean Modeling System (ROMS) in a parallel computing environment. High-resolution selected coastal regional domains are embedded within the larger basin-scale domain. We are carrying out two 10-year long simulation for a basin-scale eddy-resolving high-resolution domain. These simulations are representative of the two phases of the NAO. Preliminary results and future plans for this long-term project are presented here. Simulations and Applications We have started the first of the two proposed simulations: (i) a basin-scale North Atlantic 10-year long simulation for the High-NAO period. The initial temperature-salinity fields are from Levitus. The forcing fields are based on the annual climatology obtained from the Southampton Oceanographic Center (SOC). The model is currently (April 2005) on its fifth year of simulation and the results and forcing fields are shown for different flow fields in the surrounding figures. (ii)  a basin-scale North Atlantic 10-year long simulation for the Low-NAO period. The initial temperature and salinity fields are again from Levitus. However the wind fields are derived from the ICOADS data set during the sixties. Fields of zonal and meridional wind-stresses are shown in comparison to SOC winds. We will use the above diagnostic fields and objectively-analyzed NO3 and Si(OH)4 fields computed using the new BIOCHEM database to estimate NO3 and Si(OH)4 fluxes across the Gulf Stream and into the slope water region and GOM. We will then compare simulation results with available in-situ and satellite-derived data (including both historical SeaWiFS and newly-collected MODIS data (Bisagni et al., and Goes et al.); Finally, we will synthesize and develop our understanding of climatic impact to the underlying dynamic interdisciplinary processes based on the above model results and data analysis. Future Plans (Near-term) We will carry-out targeted multi-year simulations at high-resolution in the western north Atlantic starting from the results of the 10-year long simulations. For further progress on this research please look at our website: http://www.smast.umassd.edu/modeling/, or send an email to Avijit@umassd.edu. Some relevant references: Petrie, B. and K. Drinkwater, 1993. Temperature and salinity variability on the Scotian Shelf and in the Gulf of Maine 1945-1990. Journal of Geophysical Research, 98, 20,079—20,089. Rossby, T. and R. Benway, 2000. Slow variations in mean path of the Gulf Stream east of Cape Hatteras. Geophysical Research Letters, 27, 117-120. Smith, P.C., R. W. Houghton, R. G. Fairbanks, and D. G. Mountain, 2001. Interannual variability of boundary fluxes ans water mass properties in the Gulf of Maine and on Georges Bank: 1993-97. Deep-Sea Res. II, 48, 37-70. Taylor, A.H. and J.A. Stephens, 1998. The North Atlantic oscillation and the latitude of the Gulf Stream. Tellus, 50:134-142. Taylor, A.H., and A. Gangopadhyay, 2001. A Simple Model of Interannual Shifts of the Gulf Stream, Jour. of Geophys. Res., 106 (C7), 13,849-13,860. SSF GSNW How do we study such climatic impact on our local environment? Low NAO High NAO • North Atlantic domain • (20S-75N, -105W-10E) • Resolution of the simulation:1/6 deg • Grid size: 512 X 512 X 50 • ROMS on an 8-processor Altix. More WSW-- GS moves North LSW Intrusion -- GS moves South High-NAO simulation: day 1500 (5th year) snapshot The Gulf Stream at 32N Northward velocity of the Stream (left) and a cyclonic eddy (right) is shown in the upper panel Acknowledgements: This project is currently funded by a NASA IDS 3-year program. The first author is indebted to his collaborators in an earlier proposal for the development of these ideas. Special thanks to Yi Chao, Charles Hannah, Erica Head, Ross Hendry, Bob Houghton, Andrew Pershing, Chuck Greene and Peter Smith. Additionally, discussions with Hal Batchelder, Dian Gifford, Fei Chai and Dr. Keith Brander are highly appreciated. Previous partial supports from ONR, NASA and UMD Foundation’s Physical Oceanography and Engineering Modeling (POEM) program are greatly appreciated. Northward velocity Section through North East Channel (-65.5 W) Left corner is at 41N, right corner is at 44N Temperature at 75m Zoomed to western north Atlantic Northward velocity across 47 N. Temperature at 5m