Atmospheric temperature and moisture profiles, and their related sea surface temperature distribution in the western Pacific during the Air Mass Transformation Experiment (AMTEX) are derived, using the NOAA Vertical Temperature Profile Radiometer (VTPR)data, in comparison with the AMTEX special observations. A method for simultaneously deriving atmo s pheric moisture profiles and their related sea surface temperature distribution for given temperature profile using the VTPR water vapour absorption and atmospheric window channel radiances is proposed, so that the effect of the atmospheric attenuation by water vapour absorption is corrected without using conventional radiosonde observations. The AMTEX '74 period was generally under could-free conditions, over the AMTEX area in the western Pacific. Two case studies for February 14 and 18,1974, indicate that the NOAA 2 VTPR data are useful not only for retrieving atmospheric temperature profiles, but also for detecting large-scale ocean currents in the western Pacific. The VTPR derived atmospheric moisture profiles and a simultaneously corrected sea surface temperature distribution are presented. On the other hand, the AMTEX '75 period was mostly under cloudy conditions in the western Pacific. Regression coefficients determined using coincident radiosonde/VTPR clear radiance data for February 18,21 and 26,1975 are used to retrieve atmospheric temperature profiles. A February 26,1975, case study shows that the NOAA 4 VTPR. brightness temperature patterns constructed for all eight channels are closely related to simultaneously observed Very High Resolution Radiometer (VHRR) imageries. The VTPR derived atmospheric moisture profile and a simultaneously corrected sea surface temperature distribution over the AMTEX area are also presented.
An analytical study was done on two cases, that is, on 15th and 22nd Feb., when a typical convective cloud cell structure appeared over the AMTEX area by cold air outbreaks from the continent. DMSP satellite pictures both visual and infrared and the AMTEX aerological data were mainly used for the analysis. According to the result of analysis of the case on 15th Feb., there was a single mixing layer extending from the northwestern coastal region of the East China Sea to the southeast of the AMTEX area. The height and temperature of the mixing layer was, respectively,900 mb and 0°C at the northwestern region, reaching to 800 mb and 4°C around NAHA and then lowering again but further rising in temperature to the southeast. From the consideration of humidity distribution, the existence of clouds could be recognized at the upper part of the mixing layer. This could be interpreted as a continental cold air mass being warmed from the sea surface below and giving rise to a mixing layer which grew taller and taller until around NAHA, until it merged into the inversion layer directly connected with the polar front. In the case of 22nd Fe b., a similar mixing layer to the case of 15 Feb. was observed in the southern part of the East China Sea including NAHA and the RYOFUMARU but another mixing layer, of a different kind, could be observed in the northern part including CHEJU ISLAND and KAGOSHIMA. This second one is taller and colder than the first, that is, with a height and temperature of 700 mb and 20°C respectively. This latter layer corresponded to the cloud region of open cell structure that was discussed by Agee. In this latter case, the air mass transformation was active and the mixing layer reached higher levels on 22nd than on 15th. The difference of the mixing layer thickness seems to be the cause of the appearance of closed and open cell type convective cloud. Following the Agee's discussion of this phenomenon on extensive statistics, our case of the AMTEX satellite pictures seems to have shown the convective cell developing from the less flat radar cell through the flat closed cell until to that of the more flat open cell.
The concentration of thorium isoto p es and the activity ratios of 230Th/232Th and 228Th/232Th in 500 / sea water samples collected in the Pacific Ocean were determined. Thorium isotopes were analyzed by alpha-ray spectrometry after separating them from other elements with an anion exchange resin. The average content of thorium (232Th)of 0.9 ng l-1 was obtained in the open Pacific water. The average contents of 230Th and 228Th were 2.1 x 10-2 pg l-1 and 1.2 ag l-1 respectively. It was found that the ratios of 230Th/232Th and 228Th/232Th ranged respectively from 1.0 to 29, and from 0.4 to as high as 128.
The observational data (Tables 1 and 2) of earthquakes at Unzendake volcano are processed to make clear the features of the recent seismic activities, with the results by previous investigations. There are several epicentral areas in and around this volcano (Fig.1). The period since 1968 through 1974 is one of prominent seismic activitie s, judging from the frequent occurrence of earthquakes and felt shocks and the remarkable energy-release (Table 3, Figs.2,3 and 4). This active stage is peculiar in the past 53 years, because the high level of activities continued for seven years (Fig.4). During the active period, most of the earthquakes showe d P-S time within 2.0 sec.. The epicentral area of such earthquakes is located around the Bay of Tiziwa on the west side of this volcano. The estimation of the critical frequency of earthquakes to detect unusual seismic activity is also discussed by the method of the test of rejection proposed by Thompson on materials processed by the easy normalization test (Figs.5 and 7). As the result, the frequency of 18-19/day was calculated as the critical frequency of earthquakes during the period from 1967 through 1976 and 7-8/month in the case of felt shocks during the period from 1924 through 1976 (Figs.6 and 8). These unusual values are close to the lowermost frequency in the case of earthquake-swarms during the period from 1967 through 1976. It will be possible to use the above-mentioned frequency as the critical frequency of detection of an earthquake-swarm. Remarkable change in Ishimoto-Iida 's Coefficients m in the amplitude-frequency distribution of earthquakes is not detected in and around the active period from 1968 through 1974 (Table 4 and Fig.9). An increase of earthq u akes of P-S time over 3.1 sec. appears in 1967 and 1968, and the frequency lessened during the active period (Figs.10 and 11).
Though active faults of the NW-SE strike are readily recognized in the southern part of the Izu peninsula, there exist conjugate faults or fault-like structures in the NNE-SSW strike. The branch aftershock, activity of the earthquake off the Izu peninsula, which extended to the Amagi area in the NNE direction, is considered to be closely related to the above mentioned structures in this direction. These two conjugate fault systems can be considered to have been formed before the bending of the Izu peninsula to the west, and at present to be active as weak plane systems. Therefore the stress field released as earthquakes due to activation of these fault systems can not be considered to directly reflect the present stress field in the area concerned. This is the reason why there is a significant difference between the stress field deduced from focal mechanisms of earthquakes and one deduced from the crustal movement. The reason why faults of N-W direction are liable to be active in comparison to the other conjugate fault systems can be reasonably explained on the basis of the generalized Coulomb-Mohr fracture theory.
Every day at nine o'clock, the sea surface temperature is observed at the head of the breakwater of the Port of Ito by the Fisheries Experimental Station of Shizuoka Prefecture. Besides, the water temperature at and below the surface are recorded continuously at the Ito Marine Observation Tower, which was erected by the Meteorological Research Institute 400 m off the shore and 20 m under water. The former observation station is situated in the same environments are other coastal stations in general, but the latter station is located in more oceanic enviromental conditions. Accordingly, it is reasonable to suppose that the two stations respond to variations of sea conditions differently from each other. We attempted, therefore, a comparison of variations of sea surface temperature as between the two stations, and found that, though the temperature of the Tower frequently lags by one or two days behind that of the port station, there is a good correlation between them as far as we are dealing with variations of sea conditions whose time scale is longer than several days. Furthermore, from the water t e mperature data of the Tower, it was found that the sea surface temperature which is obtained at nine or ten o'clock is nearly equal to the diurnal mean temperature of the same day, and besides, that a marked water temperature difference occurs between the sea surface and 2 m depth on account of difference in the factors generating the water temperature variation of the respective layer.