1. Characterization of Sound Speed Profiles
Winter Cruise 2006: January
ENS Vanessa Guthrie

2. Sound Speed (Global Plot)
How can we characterize these profiles without losing the sound speed minimums?

3. Data Collection 63 total CTD casts used in analysis
Data collected every 2 dbar
Deep casts only (depth>=1000 dbar), collected every 2 dbar
All data cut off at 1000 dbar

4. Data Processing
Sound speed profiles from all 63 CTD casts were run through a Hanning filter
Number of weights in filter varied from 7 to 101
Since data is plotted every 2 dbar, filter width = 2*number of weights
For each number of weights, the standard deviation and difference in minimum from the filtered and actual profile was calculated

6. ~200 dbar

7. < 0.5 m/s
Differences in pressure tend to be more significant than differences in sound speed

8. Standard Deviation
Plot of std dev vs. filter width for each cast and mean of all casts
No clear breaking point
Not a good indication of optimal filter width

9. Difference in Sound Speed at the Minimum (Δc)
Value of c at the minimum of the actual data subtracted from c at the minimum of the filtered curve
No breaking point
Expect Δp to be more significant than Δc

10. Difference in Pressure at the Minimum (Δp)
Value of p at the minimum of the actual data subtracted from p at the minimum of the filtered curve
Lots of variation between stations

14. Casts over shelf Casts in deep water Casts in deep water
FWOPT ~ 50 dbar
FWOPT ~ 120 dbar
Casts over shelf
Casts in deep water
FWOPT ~ 160 dbar
FWOPT ~ 30 dbar
Casts in deep water
Casts over shelf

15. Mean of All Stations
Deep Water
FWOPT ~ 50 dbar (all casts)

16. Raw Data
Sound Speed (Global Plot)

17. Filtered Data

18. Conclusions
Elimination of small scale variations in the sound speed profile without losing the value of the sound speed minimum
For all casts, filter width of ~50 dbar can be used to smooth the profile without significant loss of sound speed minimum data, averaging within 16 dbar and 0.12 m/s
Profiles from deep water casts (beyond shelf) are more stable and can be smoothed with a filter width of ~120 dbar, averaging within 16 dbar and 0.21 m/s

19. Questions?