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

Overview Introduction Method Sources of Error Assumptions Results 1 Overview Introduction Method Sources of Error Assumptions Results Conclusions Questions

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

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

Sources of Error Misalignment angle Schuler Oscillation 4 Sources of Error Misalignment angle Known for R/V Point Sur and accounted for Schuler Oscillation Known and accounted for

Sources of Error Ageostrophic velocities Drift currents Tides 5 Sources of Error Ageostrophic velocities Drift currents Tides Internal waves Inertial oscillations

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

7 Results

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

Raw ADCP Level 31 Velocities 9 Raw ADCP Level 31 Velocities

Interpolated Level 31 Velocities 10 Interpolated Level 31 Velocities u’ v’

CTD-Derived Velocities 11 CTD-Derived Velocities Level 31

12 CTD & ADCP At Level 31 u’ cm/s

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’ = -1.0433 cm/s By ADCP: u’ = -0.0616 cm/s Correction to Geo. Vel. = +0.9817 cm/s

ADCP-Corrected Transport 14 ADCP-Corrected Transport

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 3500+ m

Please address your questions to me!