Cosmic-Ray Intensities and Cyclones: Cosmic-Ray Intensities and Anticyclones

Cosmic Rays as a Possible Meteorological Factor, II

Abstract

In the preceding paper, we have pointed out that cosmic-ray data in Japan indicate a noticeable change in intensity under different air-mass conditions. It is shown below in detail that the cosmic-ray intensity measured during the year 1937 with a Steinke cosmic-ray meter inside 10cm of lead is higher on southeast side of a cyclone and lower on west side of it, which results from the instability of mesotrons.
In Fig. 1 the cyclonic structure after the Norwegian school is shown. In this diagram the light solid lines represent isobars. The right-hand discontinuity of the cyclone stands for a warm front, for here the warm tropical air is forced to override a wedge of cold air underlying it. The left-hand portion of the cyclone stands for the cold front of the system-a wedge of cold air which is displacing the warm air. In normal cases the field of flow is such that the cold front travels faster so that it soon begins to overtake the warm front. The system thus composed is called an occluded front. In Japan proper the air behind a cold front is generally colder than that ahead of a warm front, having had a shorter trajectory over relatively warm sea areas.
From cosmic-ray observations the writers considered it worth the trouble to compile a diagram (Fig. 2) which shows cosmic-ray intensity in the cyclonic area. The method used was as follows:
In each case of 11 developed depressions during the year 1937 where a depression existed and its center was determinable within the radius of about 1100km (or 10 degrees of latitude) from Tokyo, all the hourly cosmic-ray intensities (number of observations=359) and barometric readings were plotted on a large composite diagram. For simplification the cosmic-ray intensities were then reduced to the normal standard pressure, using the absorption coefficient (μ=9.52×10^-3/cm Hg). Numbers of the cosmic-ray data were then reduced, by collecting the adjacent ones, to 49 groups and each group was replaced by one value indicating the average intensity. These average values are the ones actually shown on the diagram. A statistic representation of the data for the year 1937 is shown in Fig. 2. Observations reported in the preceding paper (Cosmic-Ray Intensities and AirMasses) tend to confirm the above results, and the view now generally held is that positive changes of cosmic rays are associated with the passage of airmasses of polar origin and negative changes with that of air-masses of tropical origin. Besides the very striking effect in reduced cosmic-ray intensities associated with the passage of typical cyclones (having low values in the warm-front face and high values in the cold rear), we should emphasize the marked effect of the presence and currents of different sorts of air-masses in the high troposphere, the air-masses being named according to their origin.
The following outlines give the general rela-tions of the cosmic-ray intensity with the passage of different fronts. The cold front and the warm front generally give changes of 2 percent. These are, of course, average conditions which are frequently observed over Japan proper. Individual cases may show quite different characteristics.
A similar determination of the influence of migratory antieyclones on cosmic-ray intensities was carried out. In Fig. 3, it is generally seen that the cosmic-ray intensity is highest in the front of anticyclones and lowest in the rear. Positive changes in cosmic-ray intensities are associated with the passage of cold air-masses of polar origin in the front of anticyclones and negative changes with that of warm air-masses of tropical origin in the rear. The actual intensity of cosmic rays in the different quadrants of an anticyclone is given in the following table, based on 643 hourly obser_??_ations of 25 typical anticyclones.