1. Winds vs. Currents An Analysis of Wind Forcing
Presented by
ENS Rebecca Wolf
16 March 2007

2. Project Objective
-Real time analysis of wind forcing on current circulation

3. Presentation Guidelines
Experiment
Background
Analysis
Conclusion

4. Experiment Adaptive Sampling and Prediction System 2 ADCP moorings
Aug 2006
ADCP 1 (56m)
ADCP 2 (92m)
meters

5. Workhorse Sentinel ADCP in mooring
Hardware
MBARI M2
Workhorse Sentinel ADCP in mooring
Underwater ADCP

6. Wind Forcing
Wind forcing in terms of upwelling and relaxation events appears to be responsible for coastal circulation within the Monterey Bay.

7. Upwelling Events 2-D Process The first dimension is the winds.
Equatorward winds blow warm surface water offshore
&
Colder bottom water starts to rise to the surface near the coast  relocates the warmer surface water offshore.
The second dimension is the winds effects on the circulation.
Cross shelf temperature and density gradients at surface/ sloped upwards to the coast

8. Relaxation Events
A relaxation event is defined as a phenomenon when there is no significant wind.
During typical relaxation events described in previous studies warm water remains farther off shore and does not provide significant surface heating.
In the northern California shelf region relaxation events occur most frequently throughout the spring-summer upwelling season.

9. What is causing the action?
…is it the wind?
Poleward flow

10. Visual Analysis How to interpret the following plots Winds:
Relaxation events are positive
Upwelling events are negative
ADCP (current flow)
Poleward current flow is positive
Equatorward current flow is negative
Relaxation events poleward current
Upwelling eventsequatorward current

11. Indications of strong equatorward and poleward flow.

12. R R R
Strong depth

13. Observations 4 day Relaxation period
Poleward flow (north; +) Evident with no wind
Stronger correlations in beginning than end of time series

14. Do the numbers work?
Correlation Values
Autospectra
Coherence & Phase

15. Cross Correlation Values for Winds and ADCP data
Max
Across Shore
Sig
Along Shore
Surface (12.24m)
0.4738/0
0.5233
0.6526/0
Mid Depth (52.24m)
-0.583
0.5944/0
0.3556/0
Near Bottom (72.24m)
0.6346/0
0.3937/1
Short Time Series (1 month)  Small DOF High Significance LevelLess Correlation
-No evident correlation
-As expected evidence of Ekman turning (50m)
Vector Correlations
ADCP 2
compcorr
angcorr
Surface (12.24m)
0.4282
Mid Depth (52.24m)
0.1453
Near Bottom (72.24m)
0.1041
Better analysis look at spectra…

16. Spectra Analysis Autospectra / Coherence & Phase
Detrend method Linear detrend
5 Overlapping pieces 1/3 total points
Hourly Sample Interval
Confidence Interval of 95%

17. ADCP 2

18. Observations
During rotation energy was forced into the along shelf component
Across Shelf is smaller by order of magnitude (10^4 vs 10^3)
Low pass energy points up in Along Shore/down in Across Shoremore low freq energy in along shelf
Dirunal and semi diurnal tidal peaks
Along shelf/Near bottom currentsdistinct inertial peaks
Wind generated peak; primary wind pumps energy into ocean; ~20hrs

19. Wind Spectra Sea breeze
-More energy in along shelf  result of rotation
-Diurnal sea breeze peak present

20. ADCP 2
2 coherent points
consistent phase = coherence

21. Positive phase indicates wind leads current
Across Shelf
No coherence
Period to small; need 5-10 days for sufficient current spin up from wind
Positive phase indicates wind leads current
Along Shelf
Coherence observed at all three depths
5-10 day period with expected lag times
Current follows the wind
Similar phase angles and lag times
ADCP 2
Across Shelf
Period (days)
Period (hrs)
Coherence
Phase
Lag(hrs)
Surface
2.06
0.747
-61.19
-8.41
1.03
0.951
-11.81
0.54
0.769
-6.40
Mid Depth
3.44
0.827
-27.94
2.55
0.778
-95.99
-16.31
Near Bottom
0.874
-19.35
0.79
-83.62
-11.50
Along Shelf
10.31
0.811
44.33
30.47
0.737
48.42
3.33
0.94
22.497
0.735
-7.90
0.841
25.09
17.25
5.16
0.863
28.07
9.65
0.896
27.48
18.89
0.78
35.44
12.18

22. No coherence

23. One more consideration Along Shelf Wind & Across Shelf Current
ADCP1
Along Shelf Wind/Across Shelf Current
Period (days)
Period (hrs)
Coherence
Phase (deg)
Lag (hrs)
Surface
3.44
0.741
106.55
24.41
1.03
0.781
-23.98
-1.65
0.94
22.497
0.775
-17.81
-1.11
Mid Depth
2.58
0.784
143.9
24.73
0.74
17.67
0.773
-20.52
-1.01
Near Bottom
0.86
68.57
4.71
0.69
0.764
-67.23
-3.08
ADCP 2
Phase
Lag(hrs)
10.31
0.911
14.25
9.80
5.16
0.874
11.97
4.11
0.731
-26.27
-1.64
0.00
0.804
-95.81
No coherence in ADCP 1
Along Shelf
Coherence observed surface and near bottom currents
No coherence in mid depth due to Eckman dynamics
Current
45º
Wind

24. Conclusions Correlations do not show concrete local wind forcing
Coherence found in along shelf components not across shelf components
Currents appear to be forced by non local events (eddies, meanders, along shore pressure gradient)

25. Future Research/ Military Applications
Data comparison with model outputs
Regional Ocean Modeling System
Harvard Ocean Prediction System
Navy Coastal Ocean Model
Decipher the differences in model accuracy and prediction.
Accurate current prediction by ocean models will benefit amphibious operations, special warfare operations, and mine warfare in the littoral zone.

26. Resources MATLAB Dr. Steve Ramp Fred Bahr
Korso, P.M., 1987: Structure of the coastal current field off northern California during thr coastal ocean dynamics experiment, Journal of Geophysical Research,92,
Ramp, S.R. , J.D. Paduan, I. Shulman, J. Kindle, F.L. Bahr, and F. Chavez ,2005: Observations of upwelling and relaxation events in the northern Monterey Bay during August 2000, Journal of Geophysical Research, 111, C07013, doi: /2004JC
Send, U., R.C. Beardsley, C.D. Winant, 1987: Relaxation from upwelling in the coastal ocean dynamics experiments, Journal of Geophysical Research, 92,

27. Questions ?