Velocities continued |
Our GEM's are look-up maps relating tau800 values to water
column profiles of T and specific volume anomaly. They cannot be directly used
with the IES data because an IES measures fluctuations in tau
(designated tau') referenced to the bottom, instead of
total tau referenced to 800 dbar.
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We use the hydrographic data for converting both bottom-referenced
tau' to tau'800, and tau'800 to
tau800. High correlation between tau values for various
pressure levels allow calculation, from the hydrographic data, of
coefficients to convert the bottom-referenced tau' to
tau'800
(figure).
At a given IES site, all
local (i.e., within 10 km) hydrocasts taken during the IES operation
time were used to compute values of total tau800
at the times of
these hydrocasts. By offsetting the IES tau800 time
series to minimize the squared difference between these hydrographic
tau800 and the simultaneous IES
tau'800 values, we
obtained the desired IES tau800 time series.
tau800 mean
values for each mooring were calculated from these time series
(figure).
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After these conversions, the IES data can be directly used with the
GEM maps. Time series of specific volume anomaly
sections were found by applying the
specific volume anomaly GEM to the IES tau800
time series. Using the
geostrophic method, a relative-velocity section time series was then
derived from this specific volume anomaly section time series.
A correspondingly
located T section time series was found by averaging IES
tau800 time series between adjacent
IES sites and applying the T GEM to these averages.
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