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71.
Continuous data of aerosol optical thickness monitored using differential optical absorption spectroscopy (DOAS) are correlated with the concentration of ground-measured suspended particulate matter (SPM). A high correlation is found between the DOAS and the ground SPM data, making it possible to calculate the mass extinction efficiency of the aerosols in the atmosphere. It is found that the value of mean mass extinction efficiency (MEE) varies over a range of 2.6–13.7m2 g?1, with smaller and larger values occurring for size distributions dominated by coarse and fine particles, respectively. 相似文献
72.
Earth, Moon, and Planets - 相似文献
73.
Kensuke Takeuchi 《Journal of Oceanography》1984,40(5):371-381
Using a multi-level numerical model, it is shown that the Subtropical Front and the Subtropical Countercurrent can be reproduced realistically in a highly idealized model, as a consequence of the coupling effect of wind driven gyre circulation and differential heating. In the model, the North Pacific Ocean is idealized as a rectangular flat-bottomed model ocean, and is driven by wind stress, which features the Westerlies and the Trades, and by heat flux through the sea surface formulated after Haney (1971).In the model ocean, a shallow front and an eastward current associated with the front are formed around the central latitude of the Subtropical Gyre, which show close similarities to the Subtropical Front and the Subtropical Countercurrent in the real ocean.Although the detailed mechanism of formation of the Subtropical Front and the Subtropical Countercurrent is not clarified in the present study, two factors are found inessential for the formation of the Subtropical Front and the Subtropical Countercurrent. First, the results of the model indicate that a small trough of wind stress curl in the lower latitudes of the Subtropical Gyre, which Yoshida and Kidokoro (1967a, b) attributed to the Subtropical Countercurrent, is not necessary for the formation of the Subtropical Front and the Subtropical Countercurrent, since they are reproduced well in the model without the trough. Second, using a model driven by meridional wind stress, it is shown that the meridional Ekman convergence, which many authors related to the Subtropical Front, is not essential for the formation of the Subtropical Front and the Subtropical Countercurrent. 相似文献
74.
Volume Transport Variability Southeast of Okinawa Island Estimated from Satellite Altimeter Data 总被引:1,自引:1,他引:1
Xiao-Hua?ZhuEmail author Hiroshi?Ichikawa Kaoru?Ichikawa Kensuke?Takeuchi 《Journal of Oceanography》2004,60(6):953-962
A nine-year-long record of the northeastward volume transport (NVT) in the region southeast of Okinawa Island from 1992 to 2001 was estimated by an empirical relation between the volume transport obtained from the ocean mooring data and the sea surface height anomaly difference across the observation line during 270 days from November 2000. The NVT had large variations ranging from −10.5 Sv (1 Sv ≡ 106 m3s−1) to 30.0 Sv around its mean of 4.5 Sv with a standard deviation of 5.5 Sv. This large variation was accompanied by mesoscale eddies from the east, having a pronounced period from 106 to 160 days. After removal of the eddy, NVT was found to fluctuate from 2 Sv to 12 Sv with a quasi-biennial period. 相似文献
75.
Naoto Iwasaka Toshio Suga Kensuke Takeuchi Keisuke Mizuno Yasushi Takatsuki Kentaro Ando Taiyo Kobayashi Eitarou Oka Yasuko Ichikawa Motoki Miyazaki Hiroshi Matsuura Kenji Izawa Chan-Su Yang Nobuyuki Shikama Momoko Aoshima 《Journal of Oceanography》2003,59(1):119-127
We deployed two profiling floats in the region south of the Kuroshio Extension in March 2000. Temperature and salinity profiles
from a depth of 1500 × 104 Pa to the surface are reported every two and four weeks, respectively. The floats performed very well for first four months
after deployment. Later they failed in surfacing for a few months when the sea surface temperature in the region was high.
The salinity sensors seemed to suffer from some damage during their failure-in-surfacing period. Despite this trouble, the
results clearly demonstrate that the profiling float is a very useful and cost-effective tool for physical oceanographic observation
in the open sea.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
76.
Shigeki?HosodaEmail author Shang-Ping?Xie Kensuke?Takeuchi Masami?Nonaka 《Journal of Oceanography》2004,60(5):865-877
The North Pacific Central Mode Water (CMW) is a water mass that forms in the Kuroshio-Oyashio Extension (KOE) region with
characteristic low potential vorticity. Recent studies have suggested that the CMW, as low potential vorticity water, plays
an important role in the adjustment of the subtropical gyre and subsurface variability on decadal to interdecadal timescales.
We have forced a realistic ocean general circulation model (OGCM) with observed wind stress and sea surface temperature (SST)
forcing to investigate the decadal variations of the CMW. Associated with the large atmospheric changes after the mid-1970s
climate regime shift, the upper thermocline experiences a cooling as negative SST anomalies in the central North Pacific are
subducted and advected southward. In addition to this thermodynamic response, the CMW’s path shifts anomalously eastward in
response to anomalous Ekman pumping. This eastward shift of the core of the CMW produces a lowering of the isotherms, and
a consequent warming, on the path of the CMW core. This warming partially counteracts the cooling associated with subducted
surface anomalies, and it may be responsible for the reduced temperature variations at the climatological position of the
CMW when both anomalous wind and heat fluxes are given. Lateral induction across the sloping bottom of the winter mixed layer
in the KOE is critical to the formation of the low potential vorticity CMW. Coarse resolution models, which are widely used
in climate modeling, underestimate the horizontal gradient of the mixed layer depth and form only a weak CMW or none at all.
We have conducted a coarse resolution experiment with the same OGCM, showing that the subsurface response is much reduced.
In particular, there is no dynamic warming in the CMW and the thermodynamic response to the SST cooling dominates. The resultant
total response differs substantially from that in the finer resolution run where a strong CMW forms. This sensitivity to the
model resolution corroborates the important dynamical role that the CMW may play with its distinctive low potential vorticity
character and calls for its improved simulation. 相似文献
77.
Iridium concentration in extra-terrestrial bodies is an important quantity in relation to Ir-rich geological layers. Ir concentration of a Yamato carbonaceous chondrite (Y-793321) has been measured by a neutron activation method. The measurement yields a value (0.57 ± 0.06) g per gramme for the chondrite. 相似文献
78.
Kuniyoshi Takeuchi Prasantha Hapuarachchi Maichun Zhou Hiroshi Ishidaira Jun Magome 《水文研究》2008,22(17):3236-3251
Topography is a dominant factor in hillslope hydrology. TOPMODEL, which uses a topographical index derived from a simplified steady state assumption of mass balance and empirical equations of motion over a hillslope, has many advantages in this respect. Its use has been demonstrated in many small basins (catchment areas of the order of 2–500 km2) but not in large basins (catchment areas of the order of 10 000–100 000 km2). The objective of this paper is to introduce the Block‐wise TOPMODEL (BTOP) as an extension of the TOPMODEL concept in a grid based framework for distributed hydrological simulation of large river basins. This extension was made by redefining the topographical index by using an effective contributing area af(a) (0?f(a)?1) per unit grid cell area instead of the upstream catchment area per unit contour length and introducing a concept of mean groundwater travel distance. Further the transmissivity parameter T0 was replaced by a groundwater dischargeability D which can provide a link between hill slope hydrology and macro hydrology. The BTOP model uses all the original TOPMODEL equations in their basic form. The BTOP model has been used as the core hydrological module of an integrated distributed hydrological model YHyM with advanced modules of precipitation, evapotranspiration, flow routing etc. Although the model has been successfully applied to many catchments around the world since 1999, there has not been a comprehensive theoretical basis presented in such applications. In this paper, an attempt is made to address this issue highlighted with an example application using the Mekong basin. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
79.
Assessment of flood hazard,vulnerability and risk of mid-eastern Dhaka using DEM and 1D hydrodynamic model 总被引:1,自引:0,他引:1
Floods are regular feature in rapidly urbanizing Dhaka, the capital city of Bangladesh. It is observed that about 60% of the
eastern Dhaka regularly goes under water every year in monsoon due to lack of flood protection. Experience gathered from past
devastating floods shows that, besides structural approach, non-structural approach such as flood hazard map and risk map
is effective tools for reducing flood damages. In this paper, assessment of flood hazard by developing a flood hazard map
for mid-eastern Dhaka (37.16 km2) was carried out by 1D hydrodynamic simulation on the basis of digital elevation model (DEM) data from Shuttle Radar Topography
Mission and the hydrologic field-observed data for 32 years (1972–2004). As the topography of the area has been considerably
changed due to rapid land-filling by land developers which was observed in recent satellite image (DigitalGlobe image; Date
of imagery: 7th March 2007), the acquired DEM data were modified to represent the current topography. The inundation simulation
was conducted using hydrodynamic program HEC-RAS for flood of 100-year return period. The simulation has revealed that the
maximum depth is 7.55 m at the southeastern part of that area and affected area is more than 50%. A flood hazard map was prepared
according to the simulation result using the software ArcGIS. Finally, to assess the flood risk of that area, a risk map was
prepared where risk was defined as the product of hazard (i.e., depth of inundation) and vulnerability (i.e., the exposure
of people or assets to flood). These two maps should be helpful in raising awareness of inhabitants and in assigning priority
for land development and for emergency preparedness including aid and relief operations in high-risk areas in the future. 相似文献
80.
Prediction of pore pressure change is an effective tool to properly monitor changes of groundwater flow caused by any construction
work in fractured rock mass. Due to the complexity of hydrogeologic conditions in fractured rock and the scale of interest
of the study domain, prediction of pore pressure changes by numerical models has not been precise enough to meet monitoring
requirements. Considering these problems, a Grey model that combines the finite element method (FEM) and the artificial neural
network (ANN) was developed for more precise prediction of pore pressure changes. In this model, several patterns of pore
pressure changes were calculated by FEM for a simplified hydrogeologic conceptual model at a scale smaller than a representative
elementary volume. The ANN model was then constructed to predict the actual pore pressure change using these FEM results as
inputs. This modeling approach was adopted to predict the pore pressure changes caused by the construction of shafts of Mizunami
Underground Research Laboratory (MIU), Japan. From the results obtained for MIU, it can be concluded that the proposed Grey
model is a powerful tool for monitoring of pore pressure changes. 相似文献