134
Walter Munk
The next step will be to use the acoustic travel times as integral constraints on
the model variability. Using modern ocean state estimation methods, the acoustic data
can be compared to, and ultimately combined with, the upper ocean data to detect
changes in abyssal ocean temperature, and to detect whether the various data types
are complementary. A typical Argo volume-mean is subject to a 0.15
◦ C uncertainty.
The corresponding uncertainty in the ATOC-derived mean is typically only 0.02
◦ C, a
direct result of the suppression of mesoscale variability by the acoustic path averaging.
The seven-year time series (Dushaw, personal communication) reveals a surprising degree of inhomogeneity within the northeast Pacific (Figure 8.6c). From
Kauai northeastward toward California (receiver f) there is a modest cooling trend
from 1997 until the present time; the path to the northwest (receiver k) shows modest
warming from 1997 to 2003, followed by an abrupt cooling. The changes are related
to a warming of the central Pacific during this interval. The climate variability on
a 10 Mm-decadal space-time scale overwhelms a global secular trend. Perhaps this
should have been foreseen; the disappointing message is that our records are too local
and far too brief to contribute to the ongoing debate about “global” warming.
THE FUTURE
In retrospect, the program has suffered from permitting problems, a high start-up cost,
and the mismatch in the time scales of climate and funding cycles. There is some hope
for a partial relief.
At the International Conference on the Ocean Observing System for Climate:
OCEANOBS 99 in St. Raphael, France (18–22 October 1999), Dushaw et al.
31 summarized the appropriate role for acoustic tomography in observing ocean climate.
Some preliminary planning had previously been done for thermometry systems in the
Atlantic, Arctic, and Indian oceans. Plans are underway for a global ocean observing
system. As part of such a system, ORION is to provide a coarse network of about two
dozen deep-sea moorings, the successors to the weather ships of the early twentieth
century (Figure 8.7). The moorings would be instrumented with a diverse array of meteorological and geophysical sensors. We have proposed that acoustic transceivers at
the ORION moorings should monitor the oceans between the moorings. This would
lead to the long-term global exposure required for monitoring the response of the
oceans to greenhouse warming and other long-period forcing.
We envision vertical transceiver arrays plugged in at the bottom of the ORION
moorings. The ORION system would provide for electric power, a millisecond time
base, data transmission via satellite link, plus occasional servicing. This would meet
a large fraction of the present high start-up cost of acoustic tomography deployments.
The primary task is to provide data on ocean warming; preliminary estimates
indicate that deep ocean warming by a few millidegrees could be detected. There is
at present no information on possible large-scale long-term trends between 2000 and
5000 m depths.
Walter Munk
The next step will be to use the acoustic travel times as integral constraints on
the model variability. Using modern ocean state estimation methods, the acoustic data
can be compared to, and ultimately combined with, the upper ocean data to detect
changes in abyssal ocean temperature, and to detect whether the various data types
are complementary. A typical Argo volume-mean is subject to a 0.15
◦ C uncertainty.
The corresponding uncertainty in the ATOC-derived mean is typically only 0.02
◦ C, a
direct result of the suppression of mesoscale variability by the acoustic path averaging.
The seven-year time series (Dushaw, personal communication) reveals a surprising degree of inhomogeneity within the northeast Pacific (Figure 8.6c). From
Kauai northeastward toward California (receiver f) there is a modest cooling trend
from 1997 until the present time; the path to the northwest (receiver k) shows modest
warming from 1997 to 2003, followed by an abrupt cooling. The changes are related
to a warming of the central Pacific during this interval. The climate variability on
a 10 Mm-decadal space-time scale overwhelms a global secular trend. Perhaps this
should have been foreseen; the disappointing message is that our records are too local
and far too brief to contribute to the ongoing debate about “global” warming.
THE FUTURE
In retrospect, the program has suffered from permitting problems, a high start-up cost,
and the mismatch in the time scales of climate and funding cycles. There is some hope
for a partial relief.
At the International Conference on the Ocean Observing System for Climate:
OCEANOBS 99 in St. Raphael, France (18–22 October 1999), Dushaw et al.
31 summarized the appropriate role for acoustic tomography in observing ocean climate.
Some preliminary planning had previously been done for thermometry systems in the
Atlantic, Arctic, and Indian oceans. Plans are underway for a global ocean observing
system. As part of such a system, ORION is to provide a coarse network of about two
dozen deep-sea moorings, the successors to the weather ships of the early twentieth
century (Figure 8.7). The moorings would be instrumented with a diverse array of meteorological and geophysical sensors. We have proposed that acoustic transceivers at
the ORION moorings should monitor the oceans between the moorings. This would
lead to the long-term global exposure required for monitoring the response of the
oceans to greenhouse warming and other long-period forcing.
We envision vertical transceiver arrays plugged in at the bottom of the ORION
moorings. The ORION system would provide for electric power, a millisecond time
base, data transmission via satellite link, plus occasional servicing. This would meet
a large fraction of the present high start-up cost of acoustic tomography deployments.
The primary task is to provide data on ocean warming; preliminary estimates
indicate that deep ocean warming by a few millidegrees could be detected. There is
at present no information on possible large-scale long-term trends between 2000 and
5000 m depths.