1. ADCP-Corrected Absolute Geostrophic Current and Transport
OC 3570
LT Terry McNamara
7 March 2006

2. Overview Introduction Method Sources of Error Assumptions Results1
Overview
Introduction
Method
Sources of Error
Assumptions
Results
Conclusions
Questions

3. Introduction Cruise: 19-26 January Line 70 Moss Landing Port San Luis
Port Hueneme
Line 70
Cruise: January

4. 3
Method
Calculate onshore geostrophic transport from two deep CTD casts at either end of line 70
Assumes level of no motion (z=3532.5m)
ADCP gives true currents down to approx. 650m
Can use ADCP to obtain correct transport

5. Sources of Error Misalignment angle Schuler Oscillation4
Sources of Error
Misalignment angle
Known for R/V Point Sur and accounted for
Schuler Oscillation
Known and accounted for

6. Sources of Error Ageostrophic velocities Drift currents Tides5
Sources of Error
Ageostrophic velocities
Drift currents
Tides
Internal waves
Inertial oscillations

7. 6
Assumptions
Max depth of Ekman layer well above layer used for correction
Tides negligible out at Line 70
Other ageostrophic currents negligible
ADCP & GPS errors small

8. 7
Results

9. 8
Choosing a Level 31 30 29 33 32 28 du dz
= 0

10. Raw ADCP Level 31 Velocities9
Raw ADCP Level 31 Velocities

11. Interpolated Level 31 Velocities10
Interpolated Level 31 Velocities u’ v’

12. CTD-Derived Velocities11
CTD-Derived Velocities
Level 31

13. 12
CTD & ADCP At Level 31 u’
cm/s

14. Correction u’ averaged over Line 70 at Level 31 (z=259 m)13
Correction
u’ averaged over Line 70 at Level 31 (z=259 m)
By CTD: u’ = cm/s
By ADCP: u’ = cm/s
Correction to Geo. Vel. = cm/s

15. ADCP-Corrected Transport14
ADCP-Corrected Transport

16. 15
Conclusions
Geostrophic Transport referenced to 3532m level of no motion:
3.1 Sv offshore
Absolute Geostrophic Transport:
11.1 Sv onshore
Significant current down to m

17. Please address your questions to me!