Marine Ecosystems Research Department - jamstec japan agency ...

JAMSTEC 2002 Annual Report
Ocean Observation and Research Department
Strong variations of temperature are seen in both
the northern and southern parts of the western tropical
Pacific (northern part: N to N, southern part:
S to S) in the OGCM data (Fig.). These areas
are the boundary between the mid-latitude and tropical
regions. This indicates the existence of the paths from
the mid-latitude Pacific. Also, we deployed sufficient
XCTD in the western tropical Pacific to analyze
hydrographic structures in the ENSO period.
Study for the better estimation of the rainfall
amount over the tropical ocean
The fresh water flux is the one of the most important
factors to understand the behavior of the tropical western
Pacific "warm water pool". We started this study
from this year to investigate the more accurate estimation
of the rainfall amount by combining different raingauges:
buoy-installed raingauges providing directmeasured
continuous data, shipborne radar including
information about the behavior of precipitating systems,
and satellite-borne sensors covering a wide area.
We started this study by obtaining observational data.
We deployed seven optional capacitance raingauges on
the TRITON buoys in addition to the operational optical
raingauges to ensure the data were measured on the
buoys. Observation of these two sensors was also carried
out on land for intercomparison. From the satellite sensor,
the TRMM/PR dataset was collected and processed
for further analyses. Using these data with the shipborne
radar data, intercomparison is done for the case of the
convectively active period of Mirai MR-K cruise.
3. Cooperative Research
Study on sensitive and precise analysis of radionuclides
in oceanic samples
The purpose of this study is to develop preparation
methods for sensitive and precise analysis of radionuclides
in organic matter of sea floor sediments by
accelerator mass spectrometry. We have developed the
preparation system, and with the system, radiocarbon
in organic matter in a small volume of sediment sample
was measured. This result gave new information
about sedimentation in the coastal sea.
Study of intermediate and deep ocean circulation
structure and its variability in the tropical Pacific
Ocean
Ocean circulation in the intermediate water layer
and deep layer driven by the subduction in the higher
latitude plays an important role in long term climate
variations through the global transport of heat and
material. The aims of this cooperative study with the
Ocean Research Institute (ORI), University of Tokyo,
are () to reveal deep water circulation passes north of
Samoan Passage, and () to reveal behavior of the
Antarctic Intermediate Water (AAIW) off the northern
coast of New Guinea.
The deep water circulation passes north of Samoan
Passage were studied with subsurface current meter
mooring array from February -February
maintained by ORI in the Melanesian Basin and the
Wake Island Passage, and the results have already been
published. Behavior of the Antarctic Intermediate
Water (AAIW) off the northern coast of New Guinea
was investigated mainly by JAMSTEC as below.
We found seasonal water variation in the AAIW
core of m- m depth layer in that the water indicated
lower temperature and lower salinity in boreal
summer season compared to the winter season.
Westward current velocities (equator-ward) at m
and m depths are also large during boreal summer.
Thus the water originated in the AAIW is more advected
during the summer season than the winter season by
the enhanced New Guinea Coastal Undercurrent
(NGCUC). We also revealed variations of volume
transport of the NGCUC and the results are consistent
with seasonal water variation, i.e. the time series of
volume transport estimated by combining the data
from moored ADCP data (covering time) and shipboard
ADCP (covering space) indicates the seasonal
variation of Sv, although it has larger intraseasonal
variation (in - day band) of Sv (Fig.).
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