Observations of Temperature Microstructure in NATRE

Abstract

A new autonomous instrument collected 76 profiles of temperature microstructure over a ten-day period in the eastern subtropical North Atlantic as part of the North Atlantic Tracer Release Experiment. The data between 200-m and 350-m depth was used to determine the mean rate of temperature variance dissipation ???. The estimated diapycnal diffusivity is Ky = 1.4?10?5 m2 s?1. The distribution of ? is approximately lognormal, suggesting that the 95% confidence limits on ??? are ±4%. This uncertainty is less than that caused by the imperfectly known probe response, possible noise spikes on the probes, and variability in the degree of microstructure anisotropy; the latter two effects were estimated from a pair of closely spaced probes. Each of these uncertainties is about ±15%. Statistically significant low-frequency variability of ? is observed with ??? decreasing by a factor of 2 between the first and second half of the observation. This low-frequency variability is likely the largest cause of error in estimating a seasonally averaged diapycnal diffusivity.