Mass convergence from geostrophy and ADCP measurements

1
Mass convergence from geostrophy and ADCP
measurements

• Winter cruise.
• LCDR Patrice Pauly

2
Cast locations
Location CalCOFI CenCal Box (California
Cooperative Oceanic Fisheries Investigation) Date
s 27 29 jan. 04
3
Mind refresher
is the geopotential anomaly and
the specific volume anomaly.

• The geostrophic velocity at one level V1 relative
  to a lower level V2 between two stations denoted
  by A and B is estimated by

4
Conclusion

• We need a reference level
• Level of known value,
• Level of no motion.

5
Tools

• conductivity, depth, pressure

• CTD

• Acoustic Doppler Current Profiler

• ADCP

• MATLAB

6
(No Transcript)
7
relative geostrophic velocity across the box
31 stations
Level of no motion 1000 meters
8
ADCP measurements across the box
51 stations
9
Data comparison
10
Big problem

• CTD stations reported in ( , G)
• ADCP stations reported either in either in G
  depending the leg we were cruising on.

• As a result, length between first (1) and last
  (31 or 51) stations was
• 550 km for CTD,
• 505 km for ADCP.

11
Nice solution

• Apply a fitted coefficient in order to make the
  two lengths match.

• Distances between all ADCP stations were
  multiplied by 0.9

12

• If we consider the ADCP gave the real current
  value, beneath the thermocline,
• CTD ADCP

13
CTD - ADCP comparison
Reference level level of no motion (1000m)
14
CTD-ADCP difference
Thermocline influenced by - wind motion, -
tidal motion.
Reference level 250m ADCP value
15
TOPEX-POSEIDON altimetry28 jan -2004
16
Mass transport

• 3.06
• - 1.78
• - 0.18
• 1.10 Sv

Reference level 250m ADCP value
17
Different justifications

• The neglected CTD ADCP,

18
The neglected CTD ADCP

• Same computation based upon values obtained
  through the comparison between CTD and ADCP.

Neglected mass transport 0.15 Sv
Total mass transport 1.24 Sv
19
Different justifications

• The neglected CTD ADCP,

• The Ekman transport,

20
Ekman transport
Globally directed 90º to the right of wind
direction. Winds were blowing northeast until
the 27th, southeast later on.

21
Ekman transport
Globally directed 90º to the right of wind
direction. Winds were blowing northeast until
the 27th, southeast later on.

• Ends up at Ekman layer depth (50m)

22
Ekman transport
Globally directed 90º to the right of wind
direction. Winds were blowing northeast until
the 27th, southeast later on.

• Ends up at Ekman layer depth (50m)

Computed value during the cruise 0.4 Sv
23
Different justifications

• The neglected CTD ADCP,

• The Ekman transport,

• Finally, currents beneath 1000m.

24
Currents beneath 1000m 1/4
Leg 1 extra transport 2.5 10-3 Sv/m
25
Currents beneath 1000m 2/4
Leg 2 extra transport -6 10-3 Sv/m
26
Currents beneath 1000m 3/4
Leg 3 extra transport 2 10-3 Sv/m
27
Currents beneath 1000m 4/4
2.5 10-3 mSv/m - 6.0 10-3 mSv/m 2.0
10-3 mSv/m - 1.5 Sv
x 1000m
28
Conclusion

• Is the residual 1.10 Sv a big value?

Total amount of water across the box is 34 Sv.
29
Conclusion

• Is the 1000m level of no motion valid in Monterey
  area?

• Is a remaining 1.24 Sv a big value?

No, because of
- strong undercurrents,
- up/downwellings.
30
Conclusion

• Finally, was the geostrophic method accurate?

• Is a remaining 1.24 Sv a big value?

• Is the 1000m level of no motion valid in Monterey
  area?

31
Study comparison 1/3
January 2004
June 2003
32
Study comparison 2/3
January 2004
June 2003
33
Study comparison 3/3
January 2004
June 2003
34
Happy Easter
35
T-S diagram