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Volume 20 (1969)
- Issue 4 Pages 289-
- Issue 3 Pages 207-
- Issue 2 Pages 91-
- Issue 1 Pages 1-
Volume 20, Issue 2
Displaying 1-4 of 4 articles from this issue
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Mitsuo Magata1969 Volume 20 Issue 2 Pages 91-110
Published: October 25, 1969
Released on J-STAGE: December 11, 2012
JOURNAL FREE ACCESSDisturbances of the airflow originating from small-scale mountains where the hydrostatic relation does not hold good, are here discussed. Numerical experiments are carried out on the airflow over mountains with a two-layer model corresponding to the observed clouds over Mt. Fuji. The lee-wave cloud, hydraulic jump cloud and banner cloud over Mt. Fuji are dynamically studied, taking the effects of heating and cooling from the surface ground into account.View full abstractDownload PDF (2917K) -
Seiji Soma1969 Volume 20 Issue 2 Pages 111-174
Published: October 25, 1969
Released on J-STAGE: December 11, 2012
JOURNAL FREE ACCESSThere are two types of separation in the boundary layer of an airflow. One of them is laminar separation and the other is turbulent. The problem of laminar separation has long been studied, and the condition of the separation or the mechanism of the transition from the laminar separation to the turbulent boundary layer have been made clear. On the other hand, in the study of the turbulent separation, which was started at the same time, the problem of the transition from the turbulent separation to a more turbulent boundary layer has hardly been dealt with. As shown in this report, however, the formation of turbulent separation or its dissolution can be seen frequently in the meteorological phenomena. For instance, there is a local wind called“Oroshi”in Japan. There is an airflow like“Föhn”blowing severely down the slope of a mountain and occasional ly bringing about as great disasters as a typhoon. In this phenomenon, it is found that if the general wind is not so strong, the airflow forms turbulent separation in the leeside, causing a reverse flow near the ground surface. But, when the intensity of the turbulence increase with the growth of the general wind, the reverse flow changes into a strong descending flow. This closely resembles the process of the transition from the laminar separation to the turbulent boundary layer with the increase of the Reynolds number. CAT in the leeside of Mt. Fuji which has recently been much discussed in relation to the great aircraft accident, seems to have something to do with turbulent separation. In basin-type topography or on the leeside of a mountain the air will become stagnant and be polluted. This phenomenon is also closely related to the turbulent separation. It may be said from the above considerations that the phenomenon of turbulent separation can never be disregarded when the effects of topography on airflows are in question.View full abstractDownload PDF (12378K) -
Shigeji Suyehiro1969 Volume 20 Issue 2 Pages 175-187
Published: October 25, 1969
Released on J-STAGE: December 11, 2012
JOURNAL FREE ACCESSAn earthquake of magnitude 5.1 occurred in central Japan in September 1967 in almost the same place where the event of 1964took place with different“b”values for foreshocks and aftershocks. The 1967 sequence was completely recorded by a set of comprehensive magnetic tape seismographs of broad frequency band and large dynamic range;“b”values of 0.59 and 0.89 were found for foreshocks and aftershocks as compared with 0.35 and 0.76 for the 1964 sequence.
The main differences between the events of 1964 and 196 7, which shared the same epicenter region and the same pattern in sequence, are the magnitude of main shocks and the background seismic activity. The magnitude of the main shock was 3.3 in 1964 and 5.1 in 1967. The background activity was very quiet in 1964, while in 1967 the Matsushiro swarm had extended outward to include the present region where the activity was already high. If similarities are assumed in larger and smaller earthquakes, the difference in the combination of“b”values for foreshocks and aftershocks must be attributed to the difference in the background activities rather than to the magnitudes of the main shocks. Accordingly, the larger“b”value of 0.59 for foreshocks in 1967 as compared with the 1964 event was interpreted as resulting from the superposition of high background activity of b=1 upon the pure foreshock activity with the same“b”value of 0.35as in 1964. A slight difference of“b”value in the two aftershock sequences can also be explained in the same way. Without the high background activity in 1967,“b”values of foreshocks and aftershocks in the same region would have been as they were in 1964.View full abstractDownload PDF (1652K) -
Improvement of Signal to Noise RatioTakuzo Hirono, Shigeji Suyehiro, Misao Furuta, Kaoru Sato1969 Volume 20 Issue 2 Pages 189-206
Published: October 25, 1969
Released on J-STAGE: December 11, 2012
JOURNAL FREE ACCESSThe present observations and analyses were made as a continuation of the study on“Noise Attenuation in Shallow Holes (I)”(T. HIRONO, S. SINEHIRO, M. FURUTAa nd K. KOIDE,1968). The test s ite was moved to the Onahama Weather Station on the Pacific Coast of Northeastern Japan, where the seismicity is high. The magnification of seismographs at the station, however, is limited only to 100 around a period of 1 sec owing to high background noise.
The instrumentation and method of analyses were basically the same as in the previous study. In the present study, more efforts were made to study the reduction of amplitudes of earthquakes in depth to discuss the change of the signal to noise ratio (StoNratio)with depth in detail.View full abstractDownload PDF (2704K)
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