Sudden Increase in Long-wave Field Intensity (SIL) and Its Association with Solar Flares and Other Geophysical Events

ABSTRACT

The paper deals with a radio method developed recently at the Research Department of All India Radio for detecting the occurrence of solar flares. Continuous recording at Delhi of the received field strength of sky-wave from Radio Tashkent (164 kc/s., distance: 1630 km. from Delhi) has indicated that a sudden increase in the amplitude of the received signal (abbreviated SIL) is almost always associated with the occurrence of a solar flare. SIL data presented in this paper cover the period August 1958 to July 1960 during which 567 SIL's have been observed. The observed SIL's have been compared with flare data collected from observatories and nearly 85 per cent of the total number of SIL's are found to agree with optical flares. The timings of SIL have been compared with corresponding flare and very good agreement found to exist between the times of beginning, maximum and total duration of the two events. A quantitative classification of flare has also been attempted from the relative increase in signal during an SIL.

The other radio methods of detecting solar flare, namely SWF, SCNA, SEA, SNB and magnetic crotchets have also been considered in order to assess the relative advantage of the SIL method over others. It is observed that as a single method known at present, the SIL gives the highest number of flares from a single reporting station. The timings of a flare can also be given much more precisely and accurately from the recording of an SIL than from the observation of an ‘optical’ flare.

The SIL method of detecting solar flare thus appears to be a very promising one. A system of reliable short term forecast of ionospheric and magnetic storms from the observed SIL can be envisaged in the near future.