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Operational Oceanography OC/MR3570 William Swick
Coupled Atmospheric and Oceanic Effects on Mixed Layer Depth Variability Operational Oceanography OC/MR3570 William Swick
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Project Goals To further understanding of the role of air-sea influences on the oceanic mixed layer. Navy Impacts USW Sound Velocity Profile
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Description of Data Conductivity, temperature and depth (CTD) UDAS
Station S2 (PC Tides Model Run and CTD Timeseries Location Rain Gauge Stations Conductivity, temperature and depth (CTD) 29 hr timeseries (02 – 03 Feb) UDAS Wind Speed Air Temp Humidity Solar Radiation Sea Surface Temperature PC Tides 0900L 02 Feb L 03 Feb Rain Gauge Six Stations
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Coupled Atmosphere-Ocean Effects
Surface stress provided by wind forcing Buoyancy forcing related to the thermal exchanges between atmosphere and ocean Salinity Fluxes related to precipitation and evaporation. Vertical motion at the Mixed Layer Depth (-h) Internal Waves
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Ocean Large Contributor to Variability Tidally Forced Internal Wave
Amplitude increases with depth Internal Wave ~20m Amplitude Tidally Forced Internal Wave Phase Lag Internal wave Experiment ITEX1 (Apr 94)
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Phase Lag observed ~6.5hrs
Are the atmospheric effects negligible compared to such a significant internal wave??? Phase Lag observed ~6.5hrs
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Atmospheric Effects Heating Wind Rain Qo (+) = cooling
Qo (-) = heating Wind Rain
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Entrainment Ocean influences on Entrainment in Delta S, Delta T and h wstar^3 analygis to static stablity in the atmosphere we = (+) means mixing of water from below deeping the mixed layer we = (-) is not physical. Water cannot be unmixed
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Tale of two regimes Deepening regime Shallowing Regime
Only positive or zero Krauss and Turner Mixed Layer Depth Equation only holds for deepening regimes. Atm-Ocean coupling Salinity and Temperature Jumps As h decreases. Entrainment increases Shallowing Regime How it works physically
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Salinity dominates Temperature
~.04 ~.07 Negative effect Positive effect Which is dominant? Salinity dominates Temperature
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Mixed Layer is shallowing due to precipitation!!!
Atmospheric conditions predict the mixed layer depth
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Shallowing Regime _ Using ships winds, calculated cooling rate, and observed mixed layer depth we can calculate the estimated rain rate.
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Rain rate comparision Wind = 5 m/s Cooling rate = 25 W/m/m
Observed mixed layer depth = 16m Calculated rain rate per hour = 0.37 cm/hr
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Is that the answer? Dynamic Problem Rain rate variability
Advection/River Input Function of (Wind, Total Surface Heat Flux, Mixed Layer Depth) Rain rate variability Spatial/Temporal What happened after 1900L?
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Precipitation rate has slowed allowing entrainment.
Mixed Layer is in a deepening regime Ocean inputs provide for a rapid Mixed Layer Deepening
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Conclusion Mixed Layer Depth Variability Two Regimes
Shallowing Atmospheric Inputs determine shallowing Underlying Ocean T-S profile is not “felt” Vertical Motion at –h is still important Deepening Atm-Ocean are strongly coupled Highly variable Atm (Wind/Heat/Rain) Ocean (Salinity and Temperature Jumps, Vertical Motion at –h) In a deepening regime, we(+), in an area like Monterey Bay (large internal waves) the vertical motion will tend to dominant. During a shallowing regime the atmospheric inputs determine mixed layer depth along with the internal wave component.
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Questions?
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References Garwood, R.W., Jr. An oceanic mixed layer model capable of simulating cyclic states. J. Phys. Oceanogr., 7, , 1977. Garwood, R.W., Jr. Enhancements to deep turbulent entrainment. In Deep Convection and Deep Water Formation in the Ocean, Ed. by P. C. Chu and J. C. Gascard, Elsevier, , 1991. Kraus, E.B. and J.S. Turner. A dynamic thermodynamic sea ice model. Tellus, 19, , 1967. Rosenfeld, L.K., J.D. Paduan, E.T. Petruncio, and J.E. Goncalves, 1999: Numerical simulations and observations of the internal tide in a submarine canyon. Proceedings, 'Aha Huliko'a Hawaiian Winter Workshop, University of Hawaii at Manoa, January
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