Looking for ship-speed dependency of XBT fall rates XBT Fall Rate Workshop NOAA/AOML, Miami, Florida March 10-12, 2008. John Gilson and Dean Roemmich Scripps Institution of Oceanography Greg Johnson Pacific Marine Environmental Laboratory. - PowerPoint PPT Presentation
Looking for ship-speed dependency of XBT fall rates XBT Fall Rate Workshop NOAA/AOML, Miami, Florida March 10-12, 2008 John Gilson and Dean Roemmich Scripps Institution of Oceanography Greg Johnson Pacific Marine Environmental Laboratory As ships attain greater velocities, it is natural to wonder whether XBTs fall rate is affected. Here 2 comparisons are attempted: - P18: ~0 kn vs ~10 kn with near XBTs (Deep Blues) - HRX: 14-25 kn XBT Deep Blues vs Argo
Transcript
Looking for ship-speed dependency of XBT fall ratesXBT Fall Rate Workshop
NOAA/AOML, Miami, FloridaMarch 10-12, 2008John Gilson and
As ships attain greater velocities, it is natural to wonder whether XBTs fall rate is affected.
Here 2 comparisons are attempted:- P18: ~0 kn vs ~10 kn with
near XBTs (Deep Blues)- HRX: 14-25 kn XBT Deep
Blues vs Argo
NOAA/NSF funded 2007/2008 US Repeat HydrographyProgram reoccupation of WOCE Section P18 in support of
CLIVAR and CO2 programs.
Thanks to:
For leg 1 (San Diego - Easter Island) the chiefs and co-chiefs were John Bullister and Dong-Ha Min.
On leg 2 they wereGregory C. Johnson and Alex Orsi.
The graduate student CTD watchstanders helped on both legs, as well as Pedro Pena, Carlos Fonseca, Andrew Stefanick, and Kyle Seaton from AOML.
Sippican Deep Blue XBTs launched at 3 speeds, 'full' speed, 'half' speed, and 'zero'.
Data received on March 5th
R/V Ronald H. BrownDec 2007-Feb 2008
P18
Method:
- use 1/10th second data- difference, slightly filtered XBT profile- shift 'slow' profile +/- 30m to
find offset that minimizes variance.- variance computed over 150m
window- average of 26 pairs of XBTs
Example: Requires deepening of 8.1m at 700m for profile deployed at a 'slow' speed.
XBT Pair at 2 30.00 S: Good example with deep structure
7.3 kn vs 0.5 kn
The effect on fallrate of Fast vs. Slow deployment speed
- Gradient features in the 'Slow' deployment profile are shallow by a few meters, thus the 'fast' profile is warmer on a each recorded depth level
- The sense of the offset implies the XBT takes a bit more time to reach a depth level from an XBT deployment at a 'fast' speed
- At 500m, 6 'slow' deployments are deep vs. 14 that are shallow
- Need more data
Standard error
Average
Scripps High Resolution XBT (HRX)
Might expect fall rate to be affected more strongly by faster ships- HRX ships travel up to 25 knots (P08)
Compare Sippican Deep Blue XBTs, corrected fallrate by Hanawa et al. 1995, against nearby Argo floats (2004-2007)
- Mid Ocean - Argo floats averaged within 1o and 15 days- Excluded XBTs in regions with weak temperature gradients (WOCE Global Hydrographic Climatology, Gouretski and Koltermann, 2004)
3651 comparisons
(XBT – Argo) is shown
XBT is warm/deep : consistent with recent studies (e. g. Goretski and Koltermann, 2007)
Slight change with speed. From the present data does not appear significant
Lack of data at 'slower' speeds
standard error (n/6)
at 700m
at 700m
uses WGHC
“Conclusions” is too strong a word...
This very limited analysis suggests that a ship-speed dependent fallrate error might exist in todays 'Deep Blue'...
...at least it warrants further investigation
The HRX data does not show a significant change in fall rate as ship speed increases from 14 to 25 knots as might be expected.
More nearly concurrent stopped and slow XBT deployments would be helpful
(XBT – Argo) is shown
XBT is warm/deep : consistent with recent studies (e. g. Goretski and Koltermann, 2007)
Slight change with speed. From the present data does not appear significant
