GEOSTROPHIC, EKMAN & ADCP VOLUME TRANSPORT Objective: Compute geostrophic, Ekman and ADCP volume transport Verify whether Ekman covergence transport is balanced by geostrophic convergence Estimate the net velocity profile (sfc to –20 m) CalCOFI Line 67 Line 70 CalCOFI Line 77

REFERENCES The Sea, Volume 11 – edited by Allan R. Robinson and Kenneth H. Brink Regional Oceanography: an Introduction - Matthias Tomczak & J. Stuart Godfrey at Pergamon, New York, 1994 Introductory dynamical oceanography - Butterworth, Oxford, 1983. “Pond, S. and Pickard, G. L., 1983. Mean structure of the inshore countercurrent and California undercurrent off Point Sur, CA. – C.A. Collins, N Garfield, T.A. Rago, F.W. Rischmiller, E. Carter The nature of the cold filaments in the California current system – P. Ted Strub, P. Michael Kosro and Adriana Huyer

SCOPE Data processing & Analysis Methods & Results: Upwelling Geostrophic Transport Ekman Transport Comparison with ADCP transport Estimated net velocity (surface to –20 m) Conclusion Upwelling

DATA PROCESSING & ANALYSIS Raw data analysis - wind speed & direction position & time relative humidity sea surface & air temp CTD and ADCP data Time-series plotted Windward side of the anemometer readings used Another approach was to use starboard anemometer readings CalCOFI Line 67 Line 70 CalCOFI Line 77

WIND IS RELATIVELY CONSISTENT     WIND IS RELATIVELY CONSISTENT   Line 67 Line 70 Line 77 Max starboard wind and corresponding direction (knot / ) 26.4 / 333.8 22.7 / 319.3 27.7 / 339.4 Max port wind and corresponding direction (knot / ) 27.5 / 333.7 22.9 / 319.2 26.9/ 318.0 Min starboard wind and corresponding direction (knot / ) 3.4 / 223.7 2.0 / 66.7 0.6 / 173.0 Min Port wind and corresponding direction (knot / ) 3.6 / 51.0 2.2 / 45.7 0.6/ 140.6 Percentage of samples with wind speed (%wd spd) < 10 kts 8% 0.6% 11% 14 <= %wd spd <= 20 kts 51% 71% 53% %wd spd > 20 kts 15% 2% 28%  

Time series of port wind speed Time series of starboard wind speed TIME SERIES OF DATA   Time series of port wind speed Time series of starboard wind speed kts kts Vessel sheltered by mountains from station 34 to 35 along line 77

AUTOCORRELATION FUNCTION OF DATA Length scale ~ 5 hrs (Zero-crossing method) 2-hourly averaged was chosen More than 10 data points for each line – No Aliasing

GEOSTROPHIC VOLUME TPT COMPUTATION Geostrophic velocities computed from D = Reference level for D Line 67 - computed down to 1000m depth except 1st & 2nd stations Along line 70 - computed down to 1000m Along line 77 - numerous variations in cast depth from station 26 to station 35 CalCOFI Line 67 Line 70 CalCOFI Line 77

GEOSTROPHIC VOLUME TPT THROUGH COASTAL BOX -0.16427 Sv -0.01889 Sv +0.16388 Sv Vol Transport into the box (+) Vol Transport out of the box (-) Net Geostrophic Volume transport: -0.01928675 Sv

GESTROPHIC VOL TRANSPORT PROFILE BETW STATION 2 & 10 Local max value at a depth of about 200 m Flows Northward along upper continental slope with its core at a depth of about 200 m (Hickey, 1979) This feature can be seen in other plots of volume transport profile Core of the California undercurrent

EKMAN VOLUME TRANSPORT COMPUTATION Difficult to measure the perturbed motion (u’ and v’) Solve for surface friction velocity based on drag coefficient and 2 Derived Wind Stress was resolved along 150 & 060

EKMAN VOLUME TRANSPORT +0.02171 Sv -0.19090 Sv -0.00548 Sv :Taux along CalCOFI line 67 & 77 :Tauy along CalCOFI line 70 (+): Vol Transport into the box (-) : Vol Transport out of the box CalCOFI Line 67 2-hourly average was taken & multiplied to the distance traveled in each two-hourly segment Line 70 CalCOFI Line 77 Net Ekman Vol transport : -0.17467 Sv

Sum of Geostrophic & Ekman volume transport CalCOFI Line Net volume into the box (Sv) Net volume out of the box (Sv) Net total (Sv) 67 +0.0217098(E) -0.16427373 (G) -0.14256393 70   -0.01888842 (G) -0.1909018(E) -0.20979022 77 +0.1638754 (G) -0.0054774(E) +0.1583980 Total +0.1855852 -0.37954135 -0.19395615 Net ADCP Vol Transport = -0.14671494 Sv Difference could be due to inertial & tidal currents

CONCLUSION FOR EKMAN AND GEOSTROPHIC TRANSPORT Ekman divergence transport does not seems to balanced by geostrophic convergence - Net Geostrophic Vol transport: -0.01928675 Sv - Net Ekman Vol transport: -0.17467 Sv Plausible explanation: Geostrophic volume transport does not calculate to the full water depth Time-lagged in the data collection Inertial and tidal current

ESTIMATED NET VELOCITY (SURFACE TO –20 M DEPTH) De = 4.3*W/(sin||)½ (W:m/s) (1) Vo = **1.8*10-3*W2/(De*1025*|f|) (2) ue = Vo*COS(/4 + *z/De)*exp(*z/De) ve = Vo*SIN(/4 + *z/De)*exp(*z/De)   Vel Normal to line 67

ESTIMATE NET VELOCITY (SURFACE TO –20 M DEPTH) Along line 70 – Ekman Velocity dominate Vel Normal to line 70

Ekman velocity is weak through line 67 and 77 CONCLUSION Ekman velocity is weak through line 67 and 77 - Wind is predominantly from NW - Steepest isopycnal lines is cross-shore Sfc velocity profile normal to 67 & 77 similar to geo velocity Vel Normal to line 67 Vel Normal to line 70