Diapycnal Mixing In A Coastal Regime - AESOP
Grant # N00014-15-1-0362 LONG-TERM GOALS To identify the major processes producing mixing in the upper ocean and to understand their dynamics sufficiently well to permit accurate parameterization of mixing for use in numerical models. OBJECTIVES These measurements during August 2006 were the first attempt we know of to survey a coastal domain with sufficient coverage to assess how mixing levels vary across the domain. Previous measurements have been concentrated in sub-regions, often revealing
... s, often revealing particular mixing processes, but insufficient to represent mixing throughout a regional model. APPROACH We ran lines of microstructure profiles 5-10 km long, balancing needs for rapid temporal sampling against spatial windows containing at least some structure. Staying with each line for 12.5 hours resolved changes produced by the M2 twice-daily tide, and some lines were rerun at different phases of the monthly tide. As we began to understand patterns of tidal currents and mixing, the original set of lines was modified to reveal pulsing of water in and out of the large canyon splitting the bay down its middle. Powerful Doppler sonars installed on R/V Revelle by Rob Pinkel at Scripps, provided excellent velocity records, supplemented by a 300 kHz ADCP we installed on the bottom the bay's southern half. WORK COMPLETED One paper, dealing with the most unexpected aspect of the measurements, is being reviewed for publication in the Journal of Physical Oceanography. Its contents are summarized below. RESULTS The first track run in the bay revealed remarkable vertical bands of intense turbulence, not observed previously by us except when probes were fouled or broken by organisms, such as jelly fish (Fig. 1) . In these cases, however, the probes were not fouled, and there were matching signatures in the ship's ADCP and our acoustic backscatter system.