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%                    C M / E V E N T . T E X 
%                    doc: Fri Mar  3 12:50:20 2000
%                    dlm: Wed Jun  7 22:38:06 2000
%                    (c) 2000 A.M. Thurnherr
%                    uE-Info: 69 48 NIL 0 0 72 3 2 4 ofnI
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\begin{figure}[t]

\placeFig{CM/BF18_temp}

\caption[Current-meter temperatures at \protect\m{1800}]{Daily-averaged
in-situ temperatures at \m{1800} recorded at moorings B and F (the
latter vertically offset by \degC{0.2}); time is given in days since
the beginning of 1997; the vertical lines indicate separation into
three temporal regimes (pre-warming, warming, post-warming); see
\rtabNP{CM-sensors} for instrument-naming convention.}

\labelFig{BF18-temp}

\end{figure}

For a visual assessment of the instrument performance and to
investigate non-periodic low-frequency signals poorly resolved by
spectral methods \rsecs{CM-energy}{CM-tempvar}, daily averages were
calculated from all current meter records. \rFigNP{BF18-temp} shows the
temperatures recorded at \m{1800} on moorings B and F (see
\rfigNP{CM-stations} for mooring positions). The temperature records
from all instruments at \m{1800} show a transient warming of
\degC{0.4}, beginning near day 300. (Current-meter time is referenced
to the beginning of 1997.) With the exception of mooring F the
temperature evolution is similar at all locations, lasting
approximately until day 435. The salinity recorded by instrument B18
(the only working conductivity sensor at \m{1800}, see
\rtabNP{CM-sensors} for instrument-naming convention and installed
sensors) shows no indication for water of different hydrographic
properties (the \degC{0.4} warming is accompanied by a salinity
increase of \psu{0.04}, consistent with the slope of the rift-valley
\ThetaS properties, e.g.\ \rfigNP{tscompare}; salinity scatter is
approximately \psu*{7}{-3} in the daily-averaged records). The
temperature maxima indicate that the warming was recorded at mooring F
\d{15} before arriving at mooring E and \d{18$--$19} before reaching
the remainder of the instruments. The apparent propagation speed
between moorings F and G (\km{30} apart) is
\kmpd{1.6}.\REM{dist(36.4235, -33.6446666666667, 36.2443333333333,
-33.9003333333333)/19} There are no visually detectable velocity
signals at \m{1800} associated with the warming, neither in \PVDs nor
in the weekly-averaged velocities but there is evidence for a relative
increase of the anticlockwise-polarized energy component at \m{1800}
and at \m{2100} during passage of the event \rsec{CM-pies}. The
consistency of the hydrographic properties recorded by instrument B18
during passage of the event with the mean properties observed during
the hydrographic surveys indicates that the temperature increase is
most likely a signature of isopycnal surface depression and that the
hydrographic profiles from the two surveys can be used to estimate the
amount of displacement, yielding a value of \m{150\pm15}. Combined with
the apparent propagation speed and the relative increase of the \ACW
energy component, this suggests a cyclonic eddy moving across the \R
region but other interpretations may be possible.

%----------------------------------------------------------------------

\begin{figure}[t]

\placeFig[1.2]{CM/ovsticks}

\caption[\RS velocity and temperature observations]{Daily-averaged
overflow velocities and temperatures recorded on mooring B (\m{2100}
and \m{2300}); flow speed is measured along the sticks; the horizontal
lines indicate separation into the pre-warming, warming and
post-warming regimes; time is given in days since the beginning of
1997.}

\labelFig{CM-ovsticks}

\end{figure}

The warming was recorded by the instruments below \m{2000} as well.
\rFigNP{CM-ovsticks} shows the corresponding velocities and
temperatures recorded on \RS (mooring B). Warming of order \degC{0.1}
at \m{2300} (consistent with a \m{200} downward displacement of the
isopycnal surfaces) occurred at all moorings. At this depth the
temperatures do not drop back to pre-event levels, i.e.\ the warming is
persistent. At \m{2100} the recorded data exhibit an intermediate
behavior with warming of order \degC{0.2}\REM{again \m{200}} followed
by cooling of oder \degC{0.1}. The average temperatures of the first
and the last weeks of mooring deployment indicate net increases
($\pm1\sigma$\ls{sigma}) of \REM{\degC{0.09(\pm0.05)} at \m{1800},}
\degC{0.14(\pm0.05)} at \m{2100} and \degC{0.04(\pm0.01)} at \m{2300}.
It will be noted that no such warming had been observed when comparing
data from the two hydrographic surveys \rsec{HYD-FF2}. Close inspection
of the temperature ranges shown in \rfigNP{tempcompare} indicate lower
minimum temperatures at \m{2100} and \m{2300} in 1997 compared to 1998
whereas the maximum temperatures remained similar.

\rFigNP{CM-ovsticks} also suggests that the pre-warming NE-ward flow
across \RS was persistent and strong whereas the variability increased
during passage of the event with a few days when the mean flow was
reversed. (The highest pre-warming variability is observed during the
week following day 252 which coincides with the minimum temperature
recorded by instrument B18, see \rfigNP{BF18-temp}.) The post-warming
overflow variability displays an intermediate behavior. At \m{2100} the
overflow was less persistent than at \m{2300} with the longest period
of near-zero mean flow coinciding with the rising temperature flank of
the warming event. The temperatures and flow velocities recorded on the
second overflow mooring (D) are similar to the ones shown.

