Japanese El Niño Experiment 1987 (JENEX-87) was conducted in the central equatorial Pacific in February 1987 with the participation of the ship Natsushima, on which the author made meteorological observations. In this paper, the outline of them is reported, and two remarkable synoptic disturbances observed are discussed. One of the two was a near equatorial (∼10°S) tropical depression with a lower-level strong westerly in the nearer equatorial (0°-5°S) region. The other was an upper-level cyclonic vortex-like disturbance observed around 5°S 180°E. Its southwest-northeast vertical section suggests that this disturbance was associated with upper cold air in a three-dimensional view.
With the development of research on the machine learning technique, several methods of inductive inference have been proposed. Among them are methods that use a decision tree which is inductively constructed for classifying given examples efficiently. In this paper this method is applied to inferring the magnitude class of intraplate earthquakes in Japan by using the seismicity patterns cataloged by Ichikawa (1986). Three methods are introduced here for making a decision tree. The first method, which was originally proposed by Quinlan (1983), uses the entropy as the index to select the node parameters of a decision tree. The second is a new method based on the AIC (Akaike Information Criterion) instead of the entropy. The third one, called here the NAIC method, uses only the node parameters whose AIC value is negative. To compare these three methods the alarm rate and truth rate of inference are calculated for two kinds of data, one containing noise and the other containing no noise. The NAIC method was found to give the highest value for both the alarm rate and truth rate whether the data contain noise or not. These methods do not work well for earthquakes of magnitude 7 class. This is because the frequency of earthquake occurrence of magnitude 7 class is very low, and information on it is not sufficient to get a reliable decision tree.
Data of geophysical observation during the period from July 1984 to December 1986 are analyzed. The data include measurement results of groundwater temperature, ground strain and water level in wells in the Tokai district, the central part of Japan. The main purpose of our observation is to catch a precursory phenomenon which is expected to appear before the occurrence of the ‘predicted’ Tokai earthquake. Ordinary behaviors of the variation of the monitoring data are investigated in special connection with the effects of some environmental elements such as atmospheric temperature, atmospheric pressure and rainfall. No definite relation has yet been found between earthquakes and the observed quantities. However, a large spike-shaped change, observed in the water temperature at the Oshima site prior to the eruption of Mt. Mihara in November 1986, suggests a possibility that other spike-shaped changes, hitherto regarded as noise, may be significant.
An automatic CCN (Cloud Condensation Nucleus) counter has been developed by utilizing a thermal gradient diffusion chamber (Naruse, 1978). The main features of the system are automatic sampling, measurement and recording of CCN concentration with the capability of direct calibration by the photographic method. The concentration of droplets in an illuminated volume was determined by the measurement of the peak intensity scattered at an angle of 45°. The system verified the linear dependence of scattered light on droplet number concentration. The lower limit of supersaturation used in the CCN counter was assessed experimentally, together with the maximum concentration of CCN measured accurately with the counter. Measurements of CCN as a function of supersaturation were carried out with the CCN counter at Tsukuba, which is located in a rural area 50 km apart from Tokyo. Results based on hourly measurements of the CCN spectra were used for the investigation of their seasonal variation, the relation between CCN concentration and aerosol particle concentrations in the Aitken and the large size ranges, and influence of wind and relative humidity on CCN concentration. Difference in the CCN spectra between summer and winter was discussed in relation to the solubility of CCN.