Dynamic Heights |
Inverted echo sounders (IES) have been used for over twenty years to
provide measurements of fluctuations of various water column
properties including dynamic height fluctuations. Dynamic height
anomalies D' can be inferred from IES measurements because of the
high correlation that exists between D' and IES measured round-trip
acoustic travel time tau' for many regions of the ocean (Rossby,
1969; Watts and Rossby, 1977). We used this technique for the ASUKA
region by assuming a linear relationship between tau'800
and D'800.
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D'800 = m tau'800
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The coefficient m was found by calculating
D800 and tau800 from the ASUKA
hydrographic data and determining the
least-squares best fit line to the data. The
number 800 in the previous variable names
refers to the pressure level of 800 dbar, the
depth to which many hydrographic casts were
restricted. The dynamic height anomaly and
acoustic travel times were calculated as
integrals from 800 dbar to the surface. Both
D800 and tau800 were also
seasonally corrected prior to the
calculations to remove any possible seasonal
bias produced by the Surface Layer Annual
Cycle in Temperature and Salinity (SLACTS).
The value of m was found to be -51.8 ±
0.9 (dyn. m)/s for the ASUKA region.
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Correlation between tau800 and
D800 for the ASUKA region.
tau800 and D800
(dots) were calculated from ASUKA CTD and XBT casts and
seasonally corrected.
The line shown was least-squares fitted to the data and has slope m.
r is the correlation coefficient.
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