AIDJEX Bulletin #40 - Polar Science Center - University of Washington

Clock corrections were applied routinely to the data and were effective
in correcting for large nonstandard initial values. An attempt to make the
correction algorithm responsive to diurnal clock variations incorporated
featzres which caused random pressure errors of 0.15 mb and a significant
Loss cf o%hem-Lse good ~ressurs xeasuremmts. The precision of buoy pressures
is significantly better when the buoy clocks are assumed to be
constact with time (Figs. 3 and 4).
A more efficient aljprithm incorporating better resolution and some
averaging could. be used easily, OH simpler checks of clock behavior could
be done periodically by hand. The use of clocks with smaller temperature
coefficients, insulation of the buoy, and relaxation of pressure accuracy
requirements would reduce the need for frequent clock corrections. Selection
of barometers with decreased pressure sensitivity per unit change in
frequency output would increase the need for frequent clock correction.
Wind-Induced Dynamic Pressures
The Parge tails in the pressure difference histograms (Figs. 3 and 4)
and thz ano?iaiy in thc pressure difference time series at day 140 (Fig. 1)
are due to dynamic pressures associated with high winds.
The pressure orifice
of buoy 1663 faced northeast into the strongest prevailing winds occurring in
the first half of the test period, while buoy 1671 faced the opposite direc-
tno~. ligure 8 ~RQWS the distribution of winds for the test period: Figure 9
S~QWS that the pressure errors depend on the component of wind on the pressure
orifice. The effect is most pronounced during the first half of the test,
when the highest on-axis winds occurred.
The suggestion of lower buoy pres-
sures during high on-axis winds for buoy 1671 may be due to sensitivity of
the raWS reference pressures to southwest winds, or to a protective shroud
covering the orifice of that buoy.
The effect of wind gusts on the pressure sample is reduced by the
combination of a teflon filter in the pressure orifice and a one-minute
integration period which produces a two-minute response time to pressure
change,
However, the horizontal orientation of the port makes the pressure
measurement susceptible to the dynamic pressures of the average wind.
occurrence of these errors is frequent enough to affect the sample variances
The
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