3. Evaluation of the new initialization procedure
b. Comparison to AXBT profiles and another ocean data assimilation technique
Assuming the NHC d26 map (Fig. 1d) is reasonably accurate, comparison of the data-assimilated d26 map (Fig. 2a) with the original GDEM climatology (Fig. 2b) reveals the former estimates the actual LC position and ring locations more accurately than the latter does.2 To determine whether or not the data-assimilated vertical temperature profiles are accurate in the upper ocean, however, it is necessary to compare these profiles to the 18 available AXBT profiles. Also, it is instructive to compare these profiles to concurrent profiles obtained using an alternative ocean data assimilation technique.
Here, the daily North & Equatorial Atlantic Ocean Prediction System Best Estimate (hereafter RSMAS HYCOM) is used to represent an alternative data assimilation technique. This product is the output from a publicly available version of the HYbrid Coordinate Ocean Model (HYCOM) (Chassignet et al. 2005, 2006). The RSMAS HYCOM dataset from 15 September 2005 was downloaded from the University of Miami’s HYCOM consortium data server website (RSMAS 2006). RSMAS HYCOM assimilates SST and satellite altimetry from the Modular Ocean Data Assimilation System (MODAS) (Fox et al. 2002), whereby vertical projection is performed using the Cooper and Haines (1996) technique.
All GDEM, data(2)-assimilated, and RSMAS HYCOM temperature profiles are bilinearally interpolated to each AXBT profile’s location. Visual analysis of these temperature profiles allows for comparison of individual aspects of the profile (e.g. mixed layer temperature and depth, upper thermocline temperature and vertical temperature gradient, etc.), but conclusions drawn from such an analysis are necessarily subjective. Calculation of the TCHP provides a quantitative measure of the accuracy of each profile. Recall, however, that TCHP is a measure of the oceanic heat content integrated from the surface to d26; two temperature profiles with the same TCHP may experience differing degrees of SST cooling due to hurricane wind stress if the shapes of the two profiles are different. Therefore, TCHP comparisons can supplement but should not replace analysis of the vertical temperature profile shape. In the first and second subsections below (subsections 3b1 and 3b2), the temperature profiles are compared individually, and only the upper 150 m of the ocean is examined. In the third subsection below (subsection 3b3), the TCHP is compared.