State Estimation of the North Pacific Ocean by a Four-Dimensional Variational Data Assimilation Experiment   总被引：1，自引：0，他引：1  

Toshiyuki Awaji  Shuhei Masuda  Yoichi Ishikawa  Nozomi Sugiura  Takahiro Toyoda  Tomohiro Nakamura 《Journal of Oceanography》2003,59(6):931-943

A four-dimensional variational data assimilation system has been applied to an experiment to describe the dynamic state of the North Pacific Ocean. A synthesis of available observational records and a sophisticated ocean general circulation model produces a dynamically consistent dataset, which, in contrast to the nudging approach, provides realistic features of the seasonally-varying ocean circulation with no artificial sources/sinks for temperature and salinity fields. This new dataset enables us to estimate heat and water mass transports in addition to the qualification of water mass formation and movement processes. A sensitivity experiment on our assimilation system reveals that the origin of the North Pacific Intermediate Water can be traced back to the Sea of Okhotsk and the Bering Sea in the subarctic region and to the subtropical Kuroshio region further south. These results demonstrate that our data assimilation system is a very powerful tool for the identification and characterization of ocean variabilities and for our understanding of the dynamic state of ocean circulation. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

High parallelization efficiency in barotropic-mode computation of ocean models based on multi-grid boundary ghost area   总被引：1，自引：0，他引：1  

Hiroshi Ishizaki  Ichiro Ishikawa 《Ocean Modelling》2006,13(3-4):238-254

In general, barotropic-mode computation requires the largest communication time in ocean models because of its iterative nature, when parallel computation is performed based on regional partitioning. In this study, reduction in the overhead time included in the communication in the parallel computation of the barotropic mode is considered to achieve a high parallelization efficiency of ocean models. We verify that the reduction in the communication frequency based on the multi-grid boundary ghost area reduces the total communication time. We find that this is because the sum of several kinds of overhead time for communication occupies a fairly large part of the total communication time. We discuss the trade-off between the decrease in communication time and the increase in computation time due to increased boundary area in such cases, leading to a determination of a suitable width of the multi-grid boundary that minimizes the total required time. We also discuss the efficiencies of the one- and two-dimensional partitioning of the model domain, when a multi-grid boundary is used. In general, two-dimensional partitioning is more efficient than one-dimensional for large partitioning numbers.  相似文献   

Bachelor-modon type eddies and isolated eddies near the coast on anf-plane     

Akira Masuda  Kenji Marubayashi  Michiyoshi Ishibashi 《Journal of Oceanography》1987,43(6):383-394

The behavior of isolated meso-scale eddies near the coastal boundary is studied by numerical experiments based on the quasi-geostrophic equation in a basin on an f-plane. First, Bachelor-modon type eddies are investigated as an idealized model of isolated eddies close to the wall. The first-mode Bachelor-modon type eddy is found to be robust enough to recover its original form even after it turns a corner of the basin. In contrast, the second mode is unstable; it tends to move away from the wall and finally splits into two eddies proceeding in opposite directions along the wall. An initially Gaussian eddy a little distant from the boundary interacts with a Bachelor-modon type eddy translating along the boundary, sometimes resulting in vortex merging and pairing just as in the head-on collision of two modons on a beta-plane. It is found that an initially Gaussian eddy located moderately close to the coast rapidly settles down to a steadily translating eddy, which can be approximated remarkably well by a first-mode Bachelor-modon type eddy not only in appearance but also in translation velocity within an error of about 20%.  相似文献   

A note on internal wavetrains and the associated undulation of the sea surface observed upstream of seamounts     

Arata Kaneko  Hiroyuki Honji  Kazuo Kawatate  Shinjiro Mizuno  Akira Masuda  Tsunehiro Miita 《Journal of Oceanography》1986,42(1):75-82

An internal wavetrain, generated by a tidal current in superposition with the Tsushima Warm Current, has been observed by use of an acoustic echo-sounder upstream of the Shichiri-Ga-Sone Seamounts in the East Tsushima Strait of the Japan Sea. The sea surface above the internal wavetrain was simultaneously observed and was found to be undulated at the wavelength of the internal wave.  相似文献   

Difference characteristics of sea surface temperature observed by GLI and AMSR aboard ADEOS-II     

Kohtaro Hosoda  Hiroshi Murakami  Akira Shibata  Futoki Sakaida  Hiroshi Kawamura 《Journal of Oceanography》2006,62(3):339-350

This study compares infrared and microwave measurements of sea surface temperature (SST) obtained by a single satellite. The simultaneous observation from the Global Imager (GLI: infrared) and the Advanced Microwave Scanning Radiometer (AMSR: microwave) aboard the Advanced Earth Observing Satellite-II (ADEOS-II) provided an opportunity for the intercomparison. The GLI-and AMSR-derived SSTs from April to October 2003 are analyzed with other ancillary data including surface wind speed and water vapor retrieved by AMSR and SeaWinds on ADEOS-II. We found no measurable bias (defined as GLI minus AMSR), while the standard deviation of difference is less than 1°C. In low water vapor conditions, the GLI SST has a positive bias less than 0.2°C, and in high water vapor conditions, it has a negative (positive) bias during the daytime (nighttime). The low spatial resolution of AMSR is another factor underlying the geographical distribution of the differences. The cloud detection problem in the GLI algorithm also affects the difference. The large differences in high-latitude region during the nighttime might be due to the GLI cloud-detection algorithm. AMSR SST has a negative bias during the daytime with low wind speed (less than 7 ms⁻¹), which might be related to the correction for surface wind effects in the AMSR SST algorithm.  相似文献   

A shipborne wave-recording system with digital data processing     

Keisuke Taira  Atsushi Takeda  Koji Ishikawa 《Journal of Oceanography》1971,27(4):175-186

A shipborne wave-recording system which consists of a sonic wave gauge, accelerometers, gyroscopes and a computer system is described. Signals from the measuring apparatus are fed directly into a shipborne digital computer system at a prescribed sampling rate. The time series of wave heights and the acceleration are transformed into Fourier series using an algorithm of Fast Fourier Transform. Errors contained in the observed wave heights due to ship motion are corrected in the Fourier series by using the Fourier coefficients for the vertical acceleration. Power spectra and waveforms can also be calculated in a short time with this system from Fourier coefficients. Examples of the observational results obtained in the central part of the East China Sea in 1969 are presented.  相似文献   

The sudden disappearance of a dark filament observed on October 26, 1989     

Jun Kubota  Reizaburo Kitai  Ichiro Tohmura  Akira Uesugi 《Solar physics》1992,139(1):65-79

We present H monochromatic and spectroscopic observations of the sudden disappearance of a dark filament located near the center of the solar disk on October 26, 1989. The event was not associated with the flare activity. The dark filament first disintegrated into two loop-like components, and then each component successively showed ascending motion with a velocity greater than 30 km s^–1. Comparison of the H pictures taken before and after the start of this event suggests that the dark filament was originally composed of two magnetic flux loops.  相似文献   

Detection of a new interstellar molecular ion, H2COH+ (protonated formaldehyde)     

Ohishi M  Ishikawa SI  Amano T  Oka H  Irvine WM  Dickens JE  Ziurys LM  Apponi AJ 《The Astrophysical journal》1996,471(1):L61-L64

A new interstellar molecular ion, H2COH+ (protonated formaldehyde), has been detected toward Sgr B2, Orion KL, W51, and possibly in NGC 7538 and DR21(OH). Six transitions were detected in Sgr B2(M). The 1(1,0)-1(0,1) transition was detected in all sources listed above. Searches were also made toward the cold, dark clouds TMC-1 and L134N, Orion (3N, 1E), and a red giant, IRC + 10216, without success. The excitation temperatures of H2COH+ are calculated to be 60-110 K, and the column densities are on the order of 10(12)-10(14) cm-2 in Sgr B2, Orion KL, and W51. The fractional abundance of H2COH+ is on the order of 10(-11) to 10-(9), and the ratio of H2COH+ to H2CO is in the range 0.001-0.5 in these objects. The values in Orion KL seem to be consistent with the "early time" values of recent model calculations by Lee, Bettens, & Herbst, but they appear to be higher than the model values in Sgr B2 and W51 even if we take the large uncertainties of column densities of H2CO into account. We suggest production routes starting from CH3OH may play an important role in the formation of H2COH+.  相似文献   

X-ray observation of the Jovian impacts of comet Shoemaker - Levy 9     

Kentaro Terada  Hitoshi Negoro  Kiyoshi Hayashida  Shunji Kitamoto  Hiroshi Tsunemi  Hiroshi Oya  Takayuki Ono  Akira Morioka  Yuzuru Tawara  Toshifumi Mukai  Masahiro Hoshino  Toshio Terasawa 《Earth, Moon, and Planets》1994,66(1):75-81

An ASCA observation of the Jovian impact of the comet Shoemaker-Levy 9 is reported. Four impacts of H, L, Q1 and R were observed and four impacts of B, C, G, and Q2 were observed within 60 minutes after their impacts. No significant flaring of X-ray emission was observed. Upper limit X-ray fluxes of 90 % confidence level, averaged 5 minutes just after the impacts, were 2.4 × 10^–13 erg sec^–1 cm^–2, 3.5 × 10^–13 erg sec^–1 cm^–2, 1.6 × 10^–13 erg sec^–1 cm^–2 and 2.9 × 10^–13 erg sec^–1 cm^–2 for the impacts of H, L, Q1 and R, respectively, in the 0.5(0.7 for H and Q1)–10 keV energy range. However, a hint of X-ray enhancement around Jupiter from July 17 to July 19 was detected with about 2 6 × 10^–14 erg sec^–1 cm^–2 in the 0.5–10 keV energy range.  相似文献   

Performance of the complete travel-time equation of state at simultaneous high pressure and temperature     

Hartmut A. Spetzler  Akira Yoneda 《Pure and Applied Geophysics》1993,141(2-4):379-392

The complete travel-time equation of state (CT-EOS) is presented by utilizing thermodynamics relations, such as; $$K_T = K_S (1 + \alpha \gamma T)^{ - 1} , \gamma = \frac{{\alpha K_S }}{{\rho C_P }}, \left. {\frac{{\partial C_P }}{{\partial P}}} \right)_T = - \frac{T}{\rho }\left[ {\alpha ^2 + \left. {\frac{{\partial \alpha }}{{\partial T}}} \right)_P } \right], etc.$$ The CT-EOS enables us to analyze ultrasonic experimental data under simultaneous high pressure and high temperature without introducing any assumption, as long as the density, or thermal expansivity, and heat capacity are also available as functions of temperature at zero pressure. The performance of the CT-EOS was examined by using synthesized travel-time data with random noise of 10^?5 and 10^?4 amplitude up to 4 GPa and 1500 K. Those test conditions are to be met with the newly developed GHz interferometry in a gas medium piston cylinder apparatus. The results suggest that the combination of the CT-EOS and accurate experimental data (10^?4 in travel time) can determine thermodynamic and elastic parameters, as well as their derivatives with unprecedented accuracy, yielding second-order pressure derivatives (?² M/?P ²) of the elastic moduli as well as the temperature derivatives of their first-order pressure derivatives ?² M/?P?T). The completeness of the CT-EOS provides an unambiguous criterion to evaluate the compatibility of empirical EOS with experimental data. Furthermore because of this completeness, it offers the possibility of a new and absolute pressure calibration when X-ray (i.e., volume) measurements are made simultaneously with the travel-time measurements.  相似文献