The effect of sea surface height (SSH) variability is one of the primary factors that limit the accuracy and resolution of altimeter-derived gravity values. We propose a method to estimate the influence of variation of the sea surface height on the accuracy of satellite-derived gravity by simulation technique, with a case study around Indonesian waters. Wederived an Indonesian marine gravity map using the Geosat-geodetic mission (GM). Since most of the area studied is located around coastal and shallow areas, the measurement of SSH of this area is less accurate. To obtain a distribution of SSH variability over the study area, Topex/Poseidon (T/P) data were first processed and assessed. Processing 52 cycles of the Topex/Poseidon data, the root mean square (RMS) of SSH variability for each cycle was found to vary from 1 to 179 cm. Further, for the purpose of estimating the accuracy of altimeter-derived gravity, we derived several levels of Gaussian noise, computed simulation data by adding the Gaussian noise to Geosat data, and determined simulated gravity maps. Based on the distribution of RMS values from T/P data and standard deviation (STD) differences between the simulated and the original gravity maps, we estimated the accuracy of the gravity map. Around Indonesian waters, the accuracy of the gravity map influenced by SSH variation was estimated to be within the range 0.8~93 mgal. 相似文献
Recently,effects of Earth's curvature and radial heterogeneity on coseismic deformations are often investigated based on the 2004 Sumatra earthquake.However,such effects are strongly related to earthquake types.As a low dip angle event,the 2004 Sumatra earthquake is not a good seismic case for such a topic since the effects for moderate dip angle events are much bigger.In this study,the half-space and spherical dislocation theories are used,respectively,to calculate coseismic displacements caused by the 2008 Wenchuan earthquake and the 2004 Sumatra earthquake.Effects of Earth's curvature and stratification are investigated through the discrepancies of results calculated using the two dislocation theories.Results show that the effects of Earth's curvature and stratification for the 2008 Wenchuan earthquake are much larger than those for the 2004 Sumatra earthquake.Ignoring the effects will cause errors up to 100%-200% in far field displacements for a moderate dip angle event like the 2008 Wenchuan earthquake.Such great effects are much bigger than those conclusions of previous studies.Besides,comparison with observations verifies that spherical dislocation theories yield better results than half-space ones in far fields. 相似文献
We investigated the effects of river floods on the macrobenthic community of the intertidal flat in the Ohta River Estuary, Japan, from 2005 to 2010. Sediment erosion by flood events ranged from about 2–3 cm to 12 cm, and the salinity dropped to 0‰ even during low-intensity flood events. Cluster analysis of the macrobenthic population showed that the community structure was controlled by the physical disturbance, decreased salinity, or both. The opportunistic polychaete Capitella sp. was the most dominant species in all clusters, and populations of the long-lived polychaete Ceratonereis erythraeensis increased in years with stable flow and almost disappeared in years with intense flooding. The bivalve Musculista senhousia was also an important opportunistic species that formed mats in summer of the stable years and influenced the structure of the macrobenthic community. Our results demonstrate the substantial effects of flood events on the macrobenthic community structure. 相似文献
Functional MRI (fMRI) is recognized as a well-established non-invasive diagnostic method to image activating cortical areas. Currently, the blood oxygenation level dependent (BOLD) contrast method is widely used in fMRI. BOLD-fMRI images activating are as by detecting a reduced concentration of deoxyhemoglobin during neuronal activity, which is caused by a larger increase in O2 delivery compared with O2 consumption in normal adults. In the present study, near infrared spectroscopy, which is an optical method to evaluate cerebral blood oxygenation changes, has demonstrated an increase of deoxyhcmoglobin associated with increases of oxyhemoglobin and total hemoglobin at activation areas of stroke patients, whereas BOLD-fMRI failed to image the activation areas. The present findings have serious implications for the appiication of BOLD-fMRI to the patients with brain disorders because BOLD-fMRI may overlook neuronal activities in these patients unless both increases and decreases of signals are considered. 相似文献
We investigated the influence of dynamical in-consistency of initial conditions on the predictive skill of decadal climate predictions. The investigation builds on the fully coupled global model “Coupled GCM for Earth Simulator” (CFES). In two separate experiments, the ocean component of the coupled model is full-field initialized with two different initial fields from either the same coupled model CFES or the GECCO2 Ocean Synthesis while the atmosphere is initialized from CFES in both cases. Differences between both experiments show that higher SST forecast skill is obtained when initializing with coupled data assimilation initial conditions (CIH) instead of those from GECCO2 (GIH), with the most significant difference in skill obtained over the tropical Pacific at lead year one. High predictive skill of SST over the tropical Pacific seen in CIH reflects the good reproduction of El Niño events at lead year one. In contrast, GIH produces additional erroneous El Niño events. The tropical Pacific skill differences between both runs can be rationalized in terms of the zonal momentum balance between the wind stress and pressure gradient force, which characterizes the upper equatorial Pacific. In GIH, the differences between the oceanic and atmospheric state at initial time leads to imbalance between the zonal wind stress and pressure gradient force over the equatorial Pacific, which leads to the additional pseudo El Niño events and explains reduced predictive skill. The balance can be reestablished if anomaly initialization strategy is applied with GECCO2 initial conditions and improved predictive skill in the tropical Pacific is observed at lead year one. However, initializing the coupled model with self-consistent initial conditions leads to the highest skill of climate prediction in the tropical Pacific by preserving the momentum balance between zonal wind stress and pressure gradient force along the equatorial Pacific.
A numerical study using a 3-D nonhydrostatic model has been applied to baroclinic processes generated by the K1 tidal flow in and around the Kuril Straits. The result shows that large-amplitude unsteady lee waves are generated and cause
intense diapycnal mixing all along the Kuril Island Chain to levels of a maximum diapycnal diffusivity exceeding 103 cm2s−1. Significant water transformation by the vigorous mixing in shallow regions produces the distinct density and potential vorticity
(PV) fronts along the Island Chain. The pinched-off eddies that arise and move away from the fronts have the ability to transport
a large amount of mixed water (∼14 Sv) to the offshore regions, roughly half being directed to the North Pacific. These features
are consistent with recent satellite imagery and in-situ observations, suggesting that diapycnal mixing within the vicinity
of the Kuril Islands has a greater impact than was previously supposed on the Okhotsk Sea and the North Pacific. To examine
this influence of tidal processes at the Kurils on circulations in the neighboring two basins, another numerical experiment
was conducted using an ocean general circulation model with inclusion of tidal mixing along the islands, which gives a better
representation of the Okhotsk Sea Mode Water than in the case without the tidal mixing. This is mainly attributed to the added
effect of a significant upward salt flux into the surface layer due to tidal mixing in the Kuril Straits, which is subsequently
transported to the interior region of the Okhotsk Sea. With a saline flux into the surface layer, cooling in winter in the
northern part of the Okhotsk Sea can produce heavier water and thus enhance subduction, which is capable of reproducing a
realistic Okhotsk Sea Mode Water. The associated low PV flux from the Kuril Straits to the open North Pacific excites the
2nd baroclinic-mode Kelvin and Rossby waves in addition to the 1st mode. Interestingly, the meridional overturning in the
North Pacific is strengthened as a result of the dynamical adjustment caused by these waves, leading to a more realistic reproduction
of the North Pacific Intermediate Water (NPIW) than in the case without tidal mixing. Accordingly, the joint effect of tidally-induced
transport and transformation dominating in the Kuril Straits and subsequent eddy-transport is considered to play an important
role in the ventilation of both the Okhotsk Sea and the North Pacific Ocean.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
A sensitivity experiment has been performed by assimilating altimetric data into a 1.5-layer primitive equation model as a
first attempt to examine the impact of initialization on forecasts of the Kuroshio path variability south of Japan. By exploiting
the advantage of an adjoint model, our approach clearly shows that a small meander off Shikoku Island has a large impact on
the prediction of meander growth in the Kuroshio region. Further, the strengthening of the Kuroshio current and its recirculation
clearly becomes an important factor in the development of the meander. These results demonstrate the effectiveness of our
assimilation approach in identifying efficient initialization schemes on numerical forecasting of the Kuroshio south of Japan
and should help in the construction of an effective observing system for improving the forecasting.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
The present paper examines the vortex breakdown and large-scale stirring during the final warming of the Southern Hemisphere
stratosphere during the spring of 2005. A unique set of in situ observations collected by 27 superpressure balloons (SPBs)
is used. The balloons, which were launched from McMurdo, Antarctica, by the Stratéole/VORCORE project, drifted for several
weeks on two different isopycnic levels in the lower stratosphere. We describe balloon trajectories and compare them with
simulations obtained on the basis of the velocity field from the GEOS-5 and NCEP/NCAR reanalyses performed with and without
VORCORE data. To gain insight on the mechanisms responsible for the horizontal transport of air inside and outside the well-isolated
vortex we examine the balloon trajectories in the framework of the Lagrangian properties of the stratospheric flow. Coherent
structures of the flow are visualized by computing finite-time Lyapunov exponents (FTLE). A combination of isentropic analysis
and FTLE distributions reveals that air is stripped away from the vortex’s interior as stable manifolds eventually cross the
vortex’s edge. It is shown that two SPBs escaped from the vortex within high potential vorticity tongues that developed in
association with wave breaking at locations along the vortex’s edge where forward and backward FTLE maxima approximately intersect.
The trajectories of three SPBs flying as a group at the same isopycnic level are examined and their behavior is interpreted
in reference to the FTLE field. These results support the concept of stable and unstable manifolds governing transport of
air masses across the periphery of the stratospheric polar vortex. 相似文献
Two sediment cores (pilot gravity and piston) were obtained from the bottom of the Izu-Ogasawara Trench at 9750 m and analyzed for various elements and radioisotopes. The results showed a history of complex and frequent turbidite deposition: In the gravity core, eight layers rich in manganese were observed, of which five are enriched in Cu and Co as well. The other three are also enriched in Mo but no other heavy metals, suggesting the presence of at least two mechanisms of formation. Trapping of iron manganese micronodules can account for the enrichment of Mn, Cu and Co. The other three layers rich in Mn and Mo appear to be formed by a post-depositional diagenetic process of Mn mobilization and redeposition in the sediment column. A strong correlation between 226Ra and Cu in the gravity core suggests that the 226Ra was also carried into the bottom of the trench in turbidites in association with Mn micronodules. Little excess of 210Pb over 226Ra was found at the top but the excess was significant at mid-depths from 30 to 70 cm, indicating that those sediments were deposited within the last 200 y.
In the piston core there is a sharp discontinuity of chemical and radiochemical composition around a depth of 250 cm. Below that depth the sediments appear to be dominated by materials derived from terrestrial sources, as compared with those in the upper layer which are of contemporary marine origin. 226Ra is deficient relative to 230Th throughout the sediment column down to 6 m. This finding is consistent with the finding that the average rate of sediment accumulation is 1–2 orders of magnitude faster than that in the western North Pacific abyssal plain, suggesting the convergence of materials into the bottom of the trench. 相似文献