Gulf Stream and Ring Feature Analyses for Forecast Model Validation*

Abstract

A series of Gulf Stream forecast model test cases were developed for the Data Assimilation and Model Evaluation Experiment (DAMEE). The model initialization and verification procedure relies heavily on a series of accurate synoptic snapshots of the Gulf Stream north wall and ring locations. Satellite infrared imagery, Geosat altimetry, and numerous in situ temperature profiles were combined using a geographic information system to construct Gulf Stream and ring location analyses at approximately weekly intervals during a 6-week, data-rich time period. To improve the accuracy of the feature analyses, a new image compositing technique called patching was developed to decrease the spatial smearing experienced with standard warmest pixel composites. During the 6-week test period, three ring formations, two ring absorptions, and one ring merger event were observed. The average difference between the weekly north wall positions ranged from 20 to 34 km (average 27 km). When the DAMEE GSR north wall positions were compared to two independent analyses for the same time period, the average offsets were found to vary from 14 to 53 km (average 29 km) for the first comparison set and 14 to 30 km (average 22 km) for the second. These differences, which are similar in magnitude to the observed weekly evolution, are attributed to differences in the data treatment for cloudy regions and the subjectivity of the image analysts when dealing with incomplete data.