Abstract for 2003 EPIC workshop, Boulder, CO.

Title: Mixed-layer microstructure observations within the ITCZ

Author: John Mickett and Mike Gregg, University of Washington

From 12--30 September 2001, profiles of finescale velocity and microscale temperature, salinity, pressure, dissolved oxygen, and dissipation rate of turbulent kinetic energy e were collected aboard the R/V R. H. Brown while within the ITCZ and 5 nm from 9° 56¢ N, 95° W. ADCP velocities showed that most of the variance of the horizontal currents in the mixed layer was due to near-inertial motions with relatively strong semi-diurnal tidal currents (amplitudes of ~0.1 m s^-1). Eight-meter shear-squared, e and K_r at the base of the mixed-layer and in the thermocline were strongly modulated at near-inertial frequencies. Observations suggest that a near-inertial wave persisting throughout most of the time series was the cause of these fluctuations. A diurnal cycle of turbulence intensity in the mixed layer with strong turbulence at night and low levels during the day suggests night-time convection due to surface cooling and day-time near-surface restratification due to solar heating. This diurnal cycle was most evident during periods of strong solar heating and low wind stress. There is some evidence suggesting the near-inertial wave shear may be interacting with the nightly convection to deepen convective cycles and increase turbulent mixing at the base of the surface layer.