Validation Test Report for the First-Generation Dart Gulf Stream Forecasting System
NAVAL OCEANOGRAPHIC AND ATMOSPHERIC RESEARCH LAB STENNIS SPACE CENTER MS
Pagination or Media Count:
Acoustic propagation within the Northwest Atlantic is highly dependent on the meandering Gulf Stream front and its associated drifting rings, the so called mesoscale structure of the ocean. Considerable variability in space and time characterize this structure. This report documents the validation of a system that makes nowcasts and forecasts of the Gulf Stream frontal path. The validation was done as part of the transition of the first-generation Data Assimilation Research and Transition DART model to operational Navy use. Two sets of experiments designed to evaluate the forecast skill of the system in a quasi-operational environment are the crux of the validation. In one set of experiments, operational front and ring maps are used to initialize and verify 1- and 2 week forecast experiments. In the other set of experiments, the value the DART model adds to the present operational capability is estimated. The proposed operational use of the model is simulated by setting up a simple data assimilation system that uses a 1-week forecast to interpolate across long data gaps that arise during the mapping of front and ring positions. The gappy paths are constructed by superimposing observed data gaps on complete frontal paths. This report also provides guidance to an operator on how to use a model forecast to fill in the data gaps. Both sets of experiments show the system to be a statistically significant improvement over an assumption of persistence, i.e., no change over time. The principal technical issues identified in the report are the inference of the Gulf Stream north wall from the forecasted axis path, as well as the need to develop and test a more objective means to assimilate observations and a forecast into a composite frontal path. It is recommended that these issues be pursued.
- Physical and Dynamic Oceanography