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71.
72.
A spread of warm water from the first crest of the Kuroshio Extension is periodically enhanced by northward warm water intrusions from the main current. The water type in the spread area was previously found to be the same as that in the Kuroshio front at depth. In looking for the possible mechanism responsible for the northward warm water intrusions, a dynamic analysis in the Kuroshio front was carried out by using CTD, ADCP, AVHRR and ARGOS buoy data, obtained in 1996 by the R.V. Hakuho Maru. Downstream, cross-stream and vertical velocities in the Kuroshio Extension were found by using a "stream coordinate system". The velocity field in the Kuroshio front at the first crest showed a double structure with two surface velocity maxima. In the inner part of the front, relatively high cross-stream (northward) and vertical (upward) velocities were found. Thus, this study suggests that while water particles flow downstream along the first stationary meander of the Kuroshio Extension, they also experience lateral and vertical movements which allow the deeper water from an upstream location to rise to the surface layer, and in certain locations to deflect northward. By assuming isopycnal movement and conservation of potential vorticity, it was found that in those locations where anticyclonic curvature of the meander increases, warm water is more likely to deflect northward. High ageostrophic components observed in the first 300 m of the water column are probably related to the relatively high cross-stream and vertical velocities in the inner part of the front. 相似文献
73.
74.
The S/V Shoyo, of the Hydrographic Department, Japan Coast Guard, has conducted high-density expendable bathythermograph (XBT)
measurements along the 32.5°N line in the North Pacific every year from 1990 to 1993 as a part of the Japanese-World Ocean
Circulation Experiment (WOCE). These XBT data are analyzed here, focusing on year-to-year variations of the inventory and
core layer temperature (CLT) of the North Pacific subtropical mode water (NPSTMW). Large year-to-year changes are found in
the NPSTMW CLTs estimated in longitudes between 140°E and 160°E. CLT values were found of 17.4°C in 1990, 17.1°C in 1991,
17.3°C in 1992 and 17.6°C in 1993. Inspection of the wintertime westerlies over the formation area and sea surface temperature
distribution revealed that this change in CLT can be qualitatively attributed to the strength of atmospheric cooling in the
formation area in the previous winter. Although a large year-to-year variation of NPSTMW inventory was also found, it is hard
to state any relationship between CLT and atmospheric forcing. There is a possibility that different observational seasons
may affect the inventory. It has also been found that the thermocline depth in 1991 was shallower in the sea area east of
180° than in 1992 and 1993. Associated with this change, the North Pacific central mode water (NPCMW), characterized by thermostad
with temperatures ranging from 14°C to 11°C, appears in the sea area east of 180° in the 1992 and 1993 cross sections. The
1993 cross section, which ranged from the Japanese coast to the west coast of North America, possessed another thermostad
in the surface layer, with a temperature of about 17°C in the eastern part of the cross section, off California.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
75.
Following our previous study (Sugimoto and Hanawa, 2005b), we further investigate the reason why reemergence of winter sea
surface temperature anomalies does not occur in the North Pacific eastern subtropical mode water (NPESTMW) area, despite its
occurrence in the North Pacific subtropical mode water and North Pacific central mode water areas. We use vertical temperature
and salinity profiles of the World Ocean Circulation Experiment Hydrographic Program and Argo floats with high vertical and
temporal resolution, together with heat flux data through the sea surface. We point out first that one of the causes for non-occurrence
of reemergence is that the thickness of NPESTMW is very thin. In addition to this basic cause, two major reasons are found:
a vigorous mixing in the lower portion of NPESTMW and less heat input from the atmosphere in the warming season. Since, in
the lower portion of NPESTMW and deeper, the stratification is favorable for salt-finger type convection to occur compared
with the other mode water areas, vigorous mixing takes place. This is confirmed by both a large Turner Angle there and the
existence of staircase structures in vertical temperature and salinity profiles. From the viewpoint of heat input, the NPESTMW
area gradually gains heat in the warming season compared with other mode water areas. As a result, NPESTMW cannot be capped
so quickly by the shallow summer mixed layer, and water properties of NPESTMW are to be gradually modified, even in the upper
portion. 相似文献
76.
77.
The effects of scattering and resonance on the energy dissipation of an internal tide were investigated using a two-dimensional
model which is a reassembled version of the theoretical generation model devised by Rattray et al. (1969) for internal tide. The basic character of the scattering process at the step bottom was first investigated with a
wide shelf model. When the internal wave incited from a deep region (Region II) into the shallow shelf region (Region I),
a passing wave into the shallow region, a reflected wave into the deep region, and a beam-like wave, i.e. a scattered wave
(SW), emanated at the step bottom. The SW, which consists of the superposition of numerous internal modes, propagated upward/downward
into both regions. The general properties of the SW were well expressed around the shelf edge, even in the present model with
viscosity effect. The amplitude of the SW decreased dramatically when the depth of the velocity maximum of the incident internal
wave in Region II corresponded with the depth of the shelf edge. In the narrow shelf model, where the decay distance of the
internal wave in Region I is longer than the shelf width, the incident internal wave reflected at the coast to form a standing
wave. When the internal wave in Region I is enhanced by the resonance, the energy of the SW in Region II is also intensified.
Furthermore, the energy of the modes in Region II predominated when the velocity maximum is identical to that of the dominant
mode in Region I. These results suggest that the spatial scale of shelf region is a very important factor governing the energy
dissipation of the internal tide through reflection and scattering in a narrow shelf. 相似文献
78.
基于EMD与神经网络的机械故障诊断技术 总被引:2,自引:0,他引:2
经验模式分解 (EMD)是分析非线性、非平稳信号的有力工具 ,它将信号分解为突出了原信号的不同时间尺度的局部特征信息的内在模函数 (IMF)分量。本文通过将各 IMF分量输入到 BP网络中进行训练学习和故障诊断 ,比直接输入原信号可以提高 BP网络对故障诊断的准确率 ,而且减少了训练时间。 相似文献
79.
TOGA—COARE强化观测期间,对赤道暖池区海流作了多种方法、多层次的观测;根据美国释放的漂流浮标不同时刻位置的资料,分别对赤道及其南、北海域的表层漂流状况作了计算分析,指出:从1°N向北存在单一的北向流;从1°N~1°S这个近赤道区域内为东向流;1°N~2°S区域为过渡区,以东向流为主,个别浮标出现涡旋状运动。2°S以南为一反时针运动的大涡旋。 相似文献
80.
A Reconstruction of Observed Profiles in the Sea East of Japan Using Vertical Coupled Temperature-Salinity EOF Modes 总被引:4,自引:0,他引:4
It is important to estimate hard-to-observe parameters in the ocean interior from easy-to-observe parameters. This study therefore
demostrates a reconstruction of observed temperature and salinity profiles of the sea east of Japan (30°≈40°N, 140°≈150°E).
The reconstruction was done by estimating suboptimal state from several values of the observed profiles and/or sea surface
dynamic height (SDH) calculated from the profiles. The estimation used a variational method with vertical coupled temperature-salinity
empirical orthogonal function (EOF) modes. Profiles of temperature and salinity in the subtropical region are effectively
reconstructed from in situ temperature profile data, or sea surface temperature (SST) and SDH. For example, the analyzed temperature field from SST
and SDH has an accuracy to within 1°C in the subtropical region. Salinity in the sea north of Kuroshio, however, is difficult
to estimate because of its complex variability which is less correlated with temperature than in the subtropical region. Sea
surface salinity is useful to estimate the subsurface structure. We also show the possibility that the estimation is improved
by considering nonlinearity in the equation calculating SDH from temperature and salinity analysis values in order to examine
the misfit between analysis and observation. Analysis using TOPEX/POSEIDON altimetry data instead of SDH was also performed.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献