SMAST Technical Report 04-11- 02 An Operational Application of the QUODDY Circulation Model for Nowcasting the Response of the Gulf of Maine/Georges Bank Region to Wind Stress and M2 Tidal Forcing : July 2001

This was a test of a near real-time operational application of the Dartmouth 3-dimensional finite-element circulation model QUODDY designed to nowcast the meteorologically-forced response of the Gulf of Maine region in the presence of the strong semidiurnal tide. The model is forced along the open ocean boundaries with a predicted M2 tidal sea level and at the surface with wind stress derived by an optimal interpolation of an array of NOAA National Weather Service/ National Data Buoy Center measure ments that were obtained in near real-time . In this application, the model is run every 1/16 M2 tidal period (i.e., 0.77625 hours) in near real-time. Because each calculation runs faster than real time, subsequent calculations are delayed until real time catches up with model time, when the model sea level results are output. A model/observation comparison of tidal sea level results at 49 observation stations throughout the Gulf indicated that M2 tidal sea level amplitude differences were typically less than ± 10% and phase differences less than 30 degrees, though there was a bias in the latter. The test of the operational model system was run for the month of July 2001 produced results that are sampled here. Instructions for running this operational model system in the SMAST Unix computing environment are included. I. Introduction This paper describes the first real- time test of an application of the Dartmouth 3- dimensional, finite-element circulation model (QUODDY; Lynch et al. 1996, 1997) for nowcasting the sea level and current variability of the Gulf of Maine region in response to tidal and wind stress forcing. The purpose of this test was to identify the issues in running an operational model system that requires a steady and timely input of data for the model forcing fields and produces products that are accessible to others. This system is being constructed for the operational nowcasting and forecasting of the sea level response to storm forcing. This test just happened to occur during July 2001 and thus did not exhibit the robust model responses that winter storms produce (e.g., see Fan et al., 2004). Nevertheless this test generally advanced the construction of the system and taught us a lot about how to do these kinds of calculations - as described in this report. The details of the model system setup and forcing are described in section II. The details of the model system initialization and operations are described in section III. The operational QUODDY results with M2 tidal forcing only are described in section IV. The operational QUODDY results with M2 tidal and wind forcing are described in section V. The details of the protocol for the near real-time forcing of the model open ocean boundary across the Scotian shelf are described in the section VI Appendix A. A manual for operation of