Coronal holes, 146 MHz emissions and geomagnetic storms

Our analysis of the relationship between coronal holes and geomagnetic storms lends support to the idea that the so-called M-regions are coronal holes with large areas. For two typical coronal holes examined, their equatorial extensions are found to be 25–50°. The time lag between the onset of the geomagnetic storm and the central meridian passage of the coronal hole is inversely correlated with the area of the latter.

Records of the 164 MHz fan beam interferometer of our Miyun Station at the times of coronal holes are examined. in general, these records show a regular variation, implying a diminished emission from the coronal holes and that the holes follow the solar rotation. Results from a “superposed diagram analysis” of the “central strip flux” demonstrate these effects even more clearly.

The possibility of using radio and sunspot data to determine the CMP of coronal holes is investigated and an attempt is made to evaluate the speed of the high-velocity solar stream and the size of the coronal hole from data on recurrent geomagnetic storms.