Marine Ecosystems Research Department - jamstec japan agency ...

JAMSTEC 2002 Annual Report
Frontier Research System for Global Change
RMS of SSH anomaly (year 46-50)
70N
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EQ
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60E 120E 180 120W 60W
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Fig. 2 Distribution of the standard deviation of sea-surface height
anomalies simulated in the OFES with 0.1˚ resolution.
Large variability associated with strong eddy activity along
the western boundary currents and the Antarctic
Circumpolar Current is realistic as compared with satellite
altimetry data.
b. Climate Diagnostics Group
b-. Climate Variability in the Extratropical Atmosphere
We have extended our analysis to multidecadal
modulation in the occurrence of an inter-annual seesaw
(AIS) between the intensities of the Aleutian and
Icelandic lows. We found that the occurrence of AIS
was much less frequent in the s and s than
since the s. The following two factors are likely
to cause this bi-decadal modulation: (i) a recent midwinter
tendency toward a stronger meander of the
westerlies over North America that allowed Rossby
wave activity to be transferred effectively into the
North Atlantic from the North Pacific; and (ii) another
midwinter tendency towards more zonally-elongated
and more persistent anomalies developing over the
North Pacific. We also found that model-simulated
AIS exhibits a multidecadal modulation in each of the
AFES (AGCM for the ES) and ECHAM at IRI without
any SST anomalies imposed, suggesting the
importance of internal dynamics of the atmospheric
flow in causing the long-term AIS modulation.
b-. Climate Variability in the Extratropical Coupled
Atmosphere-Ocean System
Linearizing our high-resolution data of turbulent heat
flux anomalies with respect to anomalies in SST, air
temperature and surface wind speed, we found that
warm (cool) SST anomalies along the Pacific subarctic
front associated with the decadal variability inherent to
the North Pacific accompany the enhanced (suppressed)
heat release into the atmosphere (Fig. ). This
is important evidence that, unlike in other locations in
the extratropics, SST anomalies in the subarctic frontal
zone can force the atmosphere. This is likely through
systematic changes in the storm track activity, reinforcing
stationary atmospheric anomalies over the Pacific.
b-. Collaboration with the ESC
As our continuous contribution to super-high resolution
simulations of the global atmosphere with the
AFES, we analyzed its -day integration with T
resolution and vertical levels under the climatological
SST forcing. We have found that AFES can realistically
simulate synoptic weather systems and their
internal structure. The model can realistically simulate
a polar low over the Sea of Japan with mesoscale precipitation
bands. Organization of shallow convective
clouds along cold surface winds and topographic precipitation
behind those cyclones was also simulated in
a realistically-looking manner.
c. Predictability Research Group
To deepen our understanding of the physical nature of
our climate system, basic studies have been performed
on the thermodynamical properties of turbulent fluid systems.
Each of the mean states of the systems is shown to
correspond to a unique state in which the entropy
production rate by thermal and viscous (turbulent)
dissipation is maximized. An application of a new
method of entropy evaluation to large-scale ocean circulation
models has revealed that the oceanic deep-water
circulation, when perturbed, tends to change its state
from the one with a lower rate of entropy production to
the other with a higher rate. These results suggest that
the dissipation rate of available potential energy may be
used as a measure of the entropy production rate for representing
the relative stability of nonlinear fluid systems.
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