Consistent Predictability of the Ocean State Ocean

18 The Ocean State Ocean Model OSOM is an application of the Regional Ocean Mod19 eling System spanning the Rhode Island waterways, including Narragansett Bay, Mt. 20 Hope Bay, larger rivers, and the Block Island Shelf circulation from Long Island to 21 Nantucket. This paper discusses the physical aspects of the estuary (Narragansett 22 and Mount Hope Bays and larger rivers) to evaluate physical circulation predictabil23 ity. This estimate is intended to help decide if a forecast and prediction system is 24 warranted, to prepare for coupling with biogeochemistry and fisheries models with 25 widely disparate timescales, and to find the spin-up time needed to establish the cli26 matological circulation of the region. Perturbed initial condition ensemble simulations 27 are combined with metrics from information theory to quantify the predictability of the 28 OSOM forecast system–i.e., how long anomalies from different initial conditions per29 sist. The predictability timescale in this model agrees with readily estimable timescales 30 such as the freshwater flushing timescale evaluated using the total exchange flow (TEF) 31 framework, indicating that the estuarine dynamics rather than chaotic transport is the 32 dominant model behavior limiting predictions. The predictability of the OSOM is ∼7 33 to 40 days, varying with parameters, region, and season. 34 Plain Language Summary 35 A new model of waterways near Rhode Island is introduced and examined. The 36 model is intended for studying the physical circulation of this region and its ecosystem 37 changes. This study uses a variety of metrics to assess for how long a forecast with this 38 model might be useful (i.e., how long the model’s initial state determines its behavior) 39 and relatedly how long to run (or spin up) the model to have poorly known initial 40 conditions not affect the result systematically. 41

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