1. Operational Oceanography OC/MR3570 William Swick
Coupled Atmospheric and Oceanic Effects on Mixed Layer Depth Variability
Operational Oceanography
OC/MR3570
William Swick

2. Project Goals
To further understanding of the role of air-sea influences on the oceanic mixed layer.
Navy Impacts
USW
Sound Velocity Profile

3. 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

4. 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

6. 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)

7. Phase Lag observed ~6.5hrs
Are the atmospheric effects negligible compared to such a significant internal wave???
Phase Lag observed ~6.5hrs

8. Atmospheric Effects Heating Wind Rain Qo (+) = cooling
Qo (-) = heating
Wind
Rain

9. 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

10. 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

11. Salinity dominates Temperature
~.04
~.07
Negative effect
Positive effect
Which is dominant?
Salinity dominates Temperature

12. Mixed Layer is shallowing due to precipitation!!!
Atmospheric conditions predict the mixed layer depth

13. Shallowing Regime _
Using ships winds, calculated cooling rate, and observed mixed layer depth we can calculate the estimated rain rate.

14. 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

15. 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?

16. Precipitation rate has slowed allowing entrainment.
Mixed Layer is in a deepening regime
Ocean inputs provide for a rapid Mixed Layer Deepening

17. 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.

18. Questions?

19. 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