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1.
Masahisa Kubota 《Journal of Oceanography》1994,50(1):31-41
A new cloud detection algorithm for nighttime Advanced Very High Resolution Radiometer (AVHRR) data has been developed and applied to a large number of images from various locations around Japan. The algorithm is characterized by a recovery function and the use of a two-dimensional histogram. Results obtained after applying the algorithm are presented and compared with those of previous algorithms. The comparison reveals that the new algorithm appears to be more successful than the previous algorithms. 相似文献
2.
Masahisa Kubota 《Journal of Oceanography》1982,38(5):323-330
Past observations and theories have indicated the importance of the constitution of the lowest-mode of shelf waves to the velocity field. However, significant contributions of the higher mode waves to current velocity fluctuations in the vicinity of the coast are suggested in observational results obtained along the Fukushima coast in Pt. I of this study (Kubota et al., 1981). To understand the importance of the higher modes, the generation of shelf waves is investigated theoretically by two methods. First, the generation of long shelf waves by monochromatic forcing is examined, and it is concluded that near the coast the second mode's contribution to the longshore velocity is the largest for the Fukushima coast. Second, the response of shelf waves to broad-band forcing is investigated by taking the dispersive characteristics of shelf waves into consideration. It is concluded that shelf waves with zero group velocity are selectively excited if the forcing has a broad-band spectrum. According to observational results obtained along the Fukushima coast, the wind spectrum has a broad peak at about 100 hours (Kubota et al., 1981). Since the third mode of shelf waves has zero group velocity around the period of 100 hours, the third mode can be selectively generated off the Fukushima coast. From this it is suggested that the Fukushima coast is in the forced region and that observed current fluctuations are motions associated with the second- and third-mode shelf waves. 相似文献
3.
Masahisa YanagisawaNarumi Kisaichi 《Icarus》2002,159(1):31-38
Optical flashes observed on the night side of the Moon during the 1999 Leonid meteor shower have attracted the interest of astronomers. These flashes are attributed to high-velocity impacts of Leonid meteoroids on the lunar surface. Here, we report five lunar flashes detected over a 5.8-h observation period centered at 11:25 UT on Nov. 18, 1999, in Japan. The flashes are characterized by an abrupt brightening. Three flashes exhibited afterglows that remained visible for at least 50 ms, which is longer than the duration predicted for radiation from an impact-generated plasma cloud. We show that thermal radiation from hot droplets ejected from the lunar surface during high-velocity impacts could be the cause of the afterglows. 相似文献
4.
Seasonal variation in the tropical Pacific is studied by use of climatological monthly mean data of upper layer thickness of a linear reduced-gravity model with realistic basin geometry. Complex empirical orthogonal function (CEOF) analysis is applied to the data on a closed circuit which consists of the equator, eastern boundary, 7° latitude, and western boundary. The first and second CEOF represent the annual and semiannual variations, respectively. At the equator, absolute maximum anomalies associated with the first CEOF can be found near 160°W in spring and fall. Westward propagation of the annual variation is remarkable west of 130°W. However, similar westward propagation cannot be detected in either the eastern or western part of the equator. Maximum anomalies at 7° and the equator can be found in similar longitude and time. These maxima at both latitudes originate from the annual variation of Ekman pumping associated with the meridional movement of wind fields. We also decomposed the model results into Kelvin and Rossby modes. The Kelvin mode is characterized by seminnual variation, while first and third-mode Rossby waves have annual variations. In the present results, first and third-mode Rossby waves do not appear to be a trigger for Kelvin waves. 相似文献
5.
Akio Ishida Kisaburo Nakata Shigeaki Aoki Hiroshi Kutsukake Michio J. Kishi Masahisa Kubota 《Journal of Oceanography》2001,57(4):433-450
Distributions and characteristics of water mass and chlorofluorocarbons (CFCs) in the North Pacific are investigated by using
a General Circulation Model (GCM). The anthropogenic CO2 uptake by the ocean is estimated with velocity fields derived from the GCM experiments. The sensitivity of the uptake to
different diffusion parameterizations and different surface forcing used in the GCM is investigated by conducting the three
GCM experiments; the diffusive processes are parameterized by horizontal and vertical eddy diffusion which is used in many
previous models (RUN1), parameterized by isopycnal diffusion (RUN2), and isopycnal diffusion and perpetual winter forcing
for surface temperature and salinity (RUN3). Realistic features for water masses and CFCs can be simulated by the isopycnal
diffusion models. The horizontal and vertical diffusion model fails to simulate the salinity minimum and realistic penetration
of CFCs into the ocean. The depth of the salinity minimum layer is better simulated under the winter forcing. The results
suggest that both isopycnal parameterization and winter forcing are crucial for the model water masses and CFCs simulations.
The oceanic uptake of anthropogenic CO2 in RUN3 is about 19.8 GtC in 1990, which is larger by about 10% than that in RUN1 with horizontal and vertical diffusive
parameterization. RUN3 well simulates the realistic water mass structure of the intermediate layer considered as a candidate
of oceanic sink for anthropogenic CO2. The results suggest that the previous models with horizontal and vertical diffusive parameterization may give the oceanic
uptake of anthropogenic CO2 underestimated.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
6.
Masahisa Yanagisawa 《Icarus》2002,159(2):300-305
We investigate the spin up of nonspherical asteroids by successive random collisions with other smaller asteroids. The spin-up rates are calculated for ellipsoidal and spherical bodies of the same mass. Then, we derive the relative spin-up efficiency, that is, the ratio of the spin-up rate of the ellipsoidal body to that of the spherical body. We suppose a collisional process in our model different from that adopted in the previous works. The results show that ellipsoidal bodies can spin up more rapidly than spherical bodies. 相似文献
7.
Masahisa Yanagisawa 《Earth, Moon, and Planets》1994,66(1):129-136
Europa was eclipsed but not occulted when the K-nucleus of comet Shoemaker-Levy 9 collided with Jupiter. We tried to detect brightening of the satellite due to the reflection of impact flash, from 10:05 to 10:40 on July 19, 1994 (UT). We monitored Jupiter and its surrounding area by a CCD video movie camera attached to a telescope of 28 cm in aperture and 280 cm in focal length. We could not find any brightening even though we could detect a 10.0 V-magnitude star of F8 type near Jupiter. 相似文献
8.
9.
Masahisa Kubota Naoto Iwasaka Shoichi Kizu Masanori Konda Kunio Kutsuwada 《Journal of Oceanography》2002,58(1):213-225
We have constructed ocean surface data sets using mainly satellite data and called them Japanese Ocean Flux data sets with
Use of Remote sensing Observations (J-OFURO). The data sets include shortwave radiation, longwave radiation, latent heat flux,
sensible heat flux, and momentum flux etc. This article introduces J-OFURO and compares it with other global flux data sets
such as European Centre for Medium Range Weather Forecasting (ECMWF) and National Center for Environmental Prediction (NCEP)
reanalysis data and da Silva et al. (1994). The usual ECMWF data are used for comparison of zonal wind. The comparison is carried out for a meridional profile
along the dateline for January and July 1993. Although the overall spatial variation is common for all the products, there
is a large difference between them in places. J-OFURO shortwave radiation in July shows larger meridional contrast than other
data sets. On the other hand, J-OFURO underestimates longwave radiation flux at low- and mid-latitudes in the Southern Hemisphere.
J-OFURO latent heat flux in January overestimates at 10°N–20°N and underestimates at 25°N–40°N. Finally, J-OFURO shows a larger
oceanic net heat loss at 10°N–20°N and a smaller loss north of 20°N in January. The data of da Silva et al. in July show small net heat loss around 20°S and large gain around 20°N, while the NCEP reanalysis (NRA) data show the opposite.
The da Silva et al. zonal wind speed overestimates at low-latitudes in January, while ECMWF wind data seem to underestimate the easterlies.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
10.
Masahisa Kubota 《Journal of Oceanography》1978,34(6):307-309
The stability of ocean currents is considered using a two-layer model including the vertical shear in the geostrophic balance and bottom topography. Applying the results, the Kuroshio current along the bottom contour seems to be more stable than any other combination of the current direction and the bottom contour. 相似文献