Hindcasting Changes in Thermal Structure and Acoustic Transmission Loss in the Upper Ocean on Short Time Scales with Data from MILE and from Ocean Weather Station Papa.

The skill of mixed-layer hindcasts of short less than 5 d duration was investigated using data from Ocean Weather Station Papa for the years 1960 to 1968, and with data from the Mixed-Layer Experiment MILE, which was conducted about 40 km southwest of Papa in late summer of 1977. The hindcasts were initialized and validated with observed temperature profiles and forced with surface wind stresses and heat fluxes calculated from meteorological observations. Mean and rms hindcast errors for sea-surface temperature SST mixed-layer depth MILD, surface sound-channel depth SCD, and acoustic-detection range ADR were compared with errors for persistence and climatology. Hindcast skill was calculated as the percent improvement of the hindcast rms error over the persistence rms error. The hindcast skill was significantly higher for the MILE data than for the Papa data, and hindcast skill with the Papa data was generally higher in spring and summer than in fall and winter. The range of hindcast skill for hindcasts of 12- and 36-h duration was 39 to 48 for SST, 28 to 37 for MLD, and 38 to 43 for SCD for the MILE data versus 14 to 19 for SST, 22 to 33 for MLI, and 8 to 31 for SCD for the Papa data for the spring and summer. Smoothing the MILE temperature observations with a 2-h running mean resulted in an increase in hindcast skill of about 3 due to the reduction in small-scale noise. AN