Pt Sal DriftersEquipment:27 SIO "CODE" drifters (z=.25-1.25 m) 27 NPS drifters (z=0-.75 m) 8 (2 may be moored though) UW Swift drifters (z=0-1 m)

Data:From GPS (lat,lon)--> velocity, vorticity, divergence, 1 particle and 2 particle diffusivity, etc.

General Approach:SIO, NPS, and UW will release drifters at or before 1st light from small boats in water <30 m. Drifters will be deployed in cross patterns of 9 drifters at similar latitude spanning the cross-shore (see next page). UW drifters at center of cluster. After 6+ hours, drifters will be collected and SIO drifters passed to the Sally Ride, where these drifters will be deployed over night in >25 m water. The specific release locations will depend on conditions...

NPS

SIO

Cross style sample release locations of SIO and NPS drifters. Headland eddy sampling. Spacing between drifters in individual crosses is 150 & 250 m.

Cross style sample release locations of SIO and NPS drifters if strong S current / Oceano module. Spacing between drifters in individual crosses is 150 & 250 m.

-120.75 -120.7 -120.65 -120.6

34.85

34.9

34.95

35

35.05

35.1

5 km

-120.75 -120.7 -120.65

34.85

34.9

34.95

35

35.05

5 km

10/25 11/01

-1

-0.5

0

0.5

1

E

N

W

S

E

simulated trajectories (12 hr long) were obtained for 2 weeks of the 2009 Pt Sal Simulation. Velocities at z=1.5 m were used to advect drifters. 4 "states" were identified: upwelling (v~-.3 m/s), storm (v<-.5 m/s), relaxation (v>0), tidal (v~0).

2009 Simulated Trajectories

Upwelling state

gray box: drifter release times. green: tide [m], black: Pt Sal v [m/s], purple: wind speed/20 [m/s] (colors=direction), blue: Stokes Drift [m/s], red: u [m/s], bathy contours at 10 m intervals.

South currents. possible release locations: N of 34.9 deg, >15 m water.

-120.75 -120.7 -120.65 -120.6

34.75

34.8

34.85

34.9

34.95

35

35.05

35.1

5 km

-120.7 -120.65 -120.6

34.7

34.75

34.8

34.85

34.9

34.95

35

35.05

5 km

10/25 11/01

-1

-0.5

0

0.5

1

E

N

W

S

E

Storm stateVery strong south currents. possible release locations: N of 35 deg, >25 m water. If at all...

-120.75 -120.7 -120.6534.85

34.9

34.95

35

35.05

35.1

5 km

-120.75 -120.7 -120.65 -120.6

34.85

34.9

34.95

35

35.05

35.1

5 km

10/25 11/01

-1

-0.5

0

0.5

1

E

N

W

S

E

Relaxation stateNorth currents. possible release locations: S of 35 deg, and S of Pt Sal>20 m water.

-120.75 -120.7 -120.65

34.85

34.9

34.95

35

35.05

35.1

5 km

-120.75 -120.7 -120.65

34.85

34.9

34.95

35

35.05

35.1

5 km

10/25 11/01

-1

-0.5

0

0.5

1

E

N

W

S

E

Tidal stateweak currents. possible release locations: anywhere, >15 m water.

Conclusions1) Stokes drift concern. Stokes drift varies but beaching is possible,

even in 12 hr for h=20 m. We need to be careful (more analysis to come).

2) 12 hr tracks will be typical both from the Ride and from the small boat ops. However, longer tracks are possible for drifters released in deeper water (and that cannot be retrieved easily).

3) Expect ~5 km displacements over 12 hr. 4) Point Sal area most interesting (largest velocity gradients) for drifter

releases. 5) Cross-shore variation larger, exploit that. Eg. release drifter clusters

every 2.5m of water depth starting in15 m water. 6) Can release drifters in vicinity of UNOLS boats to complement them

for each module (headland eddy, NLIW, etc), otherwise maximize data off Pt Sal ie. Headland eddy (upwelling state) sampling.

7) Sally Ride can release drifters in water > 25 m depth (unless very large waves). They will not release in cross patterns.