It is well known that the occurrence of a solar flare causes many simultaneous and delayed geo-physical effects. Amongst its simultaneous effects on the propagation of radio waves, the following terminology has been accepted internationally:
(1) SWF: Short wave fade-out on medium and high frequency waves.
(2) SCNA: Sudden cosmic noise absorption on high and very high frequency waves.
(3) SEA: Sudden enhancement of atmospherics on 27 kHz.
(4) SPA: Sudden phase anomaly on very low frequency waves.
(5) SFD: Sudden frequency deviation on high frequency waves.
(6) SNB: Solar noise burst on very high and ultrahigh frequencies. ( 7) SES: Sudden enhancement of signal.
It will be noted that while there are discrete effects observed on very low, high and very high frequencies, there is no particular nomenclature to indicate any distinctive effect of a flare on the propagation of long waves (30-300 kHz). The term SES is now generally used to denote such effects and is applicable also to any frequency whose signal strength increases suddenly with the onset of a flare.
We wish to introduce a new terminology for the solar flare effect on the field intensity of longwaves and would recommend its universal acceptance.
The author has been conducting at Delhi since 1958 experiments with the skywave (single hop) propagation of Radio Tashkent radiating on 164 kHz. This experiment has shown promising results as a means of flare patrol, for flares of all types had given rise to sudden changes in the field intensity of the received wave (Mitra, 1959(Mitra, , 1964a, b), b). The catalogues of all these events have been prepared since 1958 and they agree well with corresponding optical flares and the associated geo-physical effects.
During a decade of observation of the effect of a solar flare on the propagation of longwave signal, we have observed the following distinct types of effect:
(1) Sudden increase in the signal followed by gradual recovery.
(2) Sudden initial decrease followed by another sudden increase and then gradual recovery.
(3) Sudden decrease and then gradually recovery to normal. Typical examples of the above three types are given in Figures 1, 2 and 3. There are many instances of each type of the effect now available on our records and all these can be explained from the following theoretical considerations. It may however, be re-