A low resolution spectral general circulation model has been developed for two aims. The first is to use the model as a tool to study the mechanisms of the atmospheric variations of longer terms than 10 days. The second is to perform preliminary studies on the dynamical long-range forecast. The model adopts primitive equations in which the dependent variables, except the mixing ratio of water vapor, are expressed by spherical harmonic functions with rhomboidal truncation of wavenumber 10. It has 10 layers including the lower stratosphere. To drive and maintain the general circulation of the model atmosphere, radiation, convection, turbulent vertical mixing in the planetary boundary layer, ground thermodynamics and hydrology are all incorporated by their widely used parameterization schemes. This paper describes the model performance by showing calculated monthly fields for January and July. These are obtained from the last 5 years results of simulated 6.5-year seasonal changes. We show that the major large-scale phenomena of the real atmosphere have been successfully simulated by the model. For example the stratospheric polar night jet and tropospheric subtropical jet are clearly separated in the winter hemisphere. Zonal mean and geographical distribution of monthly mean fields of wind, temperature and other parameters are realistic, although the model includes some defects such as the broader ITCZ and weakened Hadley circulation. In the stratosphere of the winter Northern Hemisphere, geopotential height and temperature structures well resemble the observed ones in both amplitude and phase. Stationary wave structures of geopotential height throughout the troposphere and stratosphere are also similar to the observed ones in the winter Northern Hemisphere, but not in the winter Southern Hemisphere.
Computational accuracy of the flux, radiance and polarization degrees of upwelling radiation from the inhomogeneous atmosphere-ocean system is examined at wavelengths 0.40, 0.50 and 0.60 μm by increasing the number of homogeneous sub-layers. The LOWTRAN atmospheric model is adopted in mid-latitudes in summer. It was found from the computations that five homogeneous sub-layers simulate the inhomogeneous atmosphere fairly well in the visible region.
Since 1983, the Meteorological Research Institute has been conducting a research project on the prediction of intraplate earthquakes occurring in the Japanese islands. In connection with the project, a statistical study on the seismicity patterns has been carried out and is reported here. In the study are used 288 earthquake sequences whose main shock magnitude is 5 or larger. The identification of various seismic precursors in these events is executed as objectively as possible. The regional variations and the occurrence rates of various seismic precursors are studied by use of the identified precursors. Moreover, the selection of seismic precursors having stronger dependence on larger earthquakes and the relationship between the occurrence of the precursors and the main shock magnitude are statistically investigated. Based on the results obtained from the investigations, procedures of identifying significant precursors for long-term or medium-term earthquake prediction are proposed.
Space-time distribution in recent seismic activities around Shizuoka City are investigated using data of hypocenters recalculated by the new method which has been adopted by the JMA since 1983. A difference in hypocentral distribution is found between the north-eastern side and the southwestern side of a tectonic line connecting the southern tip of the Izu Peninsula and Shizuoka City. In the northeastern side shocks deeper than 30 km are seldom, as well as shocks whose depth of hypocenter is shallower than 10 km. The difference of hypocentral distribution is clearly recognized in the cross section taken in the direction perpendicular to the tectonic line. It is also noted that very shallow earthquakes are seen to be distributed around the tectonic line. Concerning the temporal change, seismic activities in the northeastern side of the tectonic line resumed after the 1974 Izu-hanto-oki earthquake, while occurrence of shocks had been relatively concentrated near the line before the event. In relation to this fact it should be noted that the seismicity in the Izu Peninsula became active after the 1974 Izu-hanto-oki earthquake. It is very probable that concurrent activation of seismicity in the Izu Peninsula and in the northeastern side of Suruga Bay is not a mere coincidence. It may indicate that in accordance with the activation of crustal movement in the Izu Peninsula the stress in the coupling region between the Eurasian plate and the Philippine sea plate also increased. Further, it is found that the seismicity in the western side of Suruga Bay was more active before the earthquake with a magnitude of 6.1 in 1965 than after the event. This is confirmed by the change of the number of felt earthquakes within 30 km of epicentral distance from the Shizuoka Local Meteorological Observatory. A tendency of concentration and diffusion of seismic activity is observed before and after the 1965 event along the tectonic line, though it is not highly distinct. In the regions around Shizuoka City it is certain that many shocks occurred immediately after the 1944 Tonankai earthquake, the correlation between earthquake occurrence in this region and that in the southern Izu Peninsula is recognized as well. All these characteristics indicate that the area around Shizuoka City is remarkable in being sensitive to the change of stress in the surrounding regions.