Ionospheric disturbances associated with the solar flare of September 28, 1961

Abstract

Changes produced in the phase, frequency, and amplitude of stable HF waves during the solar flare of September 28, 1961, and the geomagnetic sudden commencement of September 30, 1961, are analyzed. The HF waves, of approximately 15 and 18 Mc/s, were transmitted over east-west paths 2420 and 5640 km long. Over the longer path, the phases of both signals were advanced by 1400 and 1200 cycles, respectively, whereas their respective frequencies were increased by 8.4 and 7 cps. Absorption commenced after the major portions of the phase and frequency changes had taken place. Over the shorter path, the frequencies of the 15 and 18 Mc/s signals were increased by 2.4 and 1.4 cps, respectively. Absorption data are not available over the short path. During the SC the frequency of the 18-Mc/s signal transmitted over the short path first increased by I cps and then decreased by 2.2 cps. Following the sudden frequency shift, the instantaneous received frequency oscillated with a period of about 30 sec. Since absorption commenced after the main frequency and phase advance, and since it disappeared before the phase recovery, it is suggested that the changes in the electron density were produced by UV radiation energy in the 140-to 200-km region. This hypothesis is strengthened by the circumstance that the maximum phase changes were--approximately--inversely proportional to the operating frequency. The appearance of solar X rays (•20 key) coincided with the onset of/•bsorption of the signals and the onset of a second phase of peak activity in the phase and amplitude scintillation frequency of the signals. The ionization production, as obtained from the rate of change of the phase of the incoming HF signals, does not correspond exactly with the time history of the solar X rays in the •20-kev energy. Softer X rays must be responsible for the electron production that caused the phase changes. released, URSI-IRE Meeting, Austin, Texas, October 1961; TR 45, Radioscience Laboratory, Stanford University, contract Nonr 225(33), December 4, 1961. Kanellakos, D. P., and O. G. Villard, Jr., Some relationships between frequency and azimuth angle of arrival of h-f waves propagated over long distances, USRI-IRE Meeting, Austin, Texas, October 1961; TR 43, Radioscience Laboratory, Stanford University, contract Nonr 225(33) NR 088 003, in press, 1962. Knecht, R. W., and K. Davies, Solar flare effects in the F region of the ionosphere, Nature, 190 (4778), 797-798, 1961. Kundu, M. R., Bursts of centimeter-wave emission and the region of origin of X rays from solar flares, J. Geophys. Research, 66(12), 4308-4312, 1961.

Response of the incompressible ionosphere to the compression of the magnetosphere during the geomagnetic sudden commencements

“…The electric fields of the SC have been observed with the HF Doppler sounders in midlatitudes [Davies et al, 1962;Kanellakos and Villard, 1962;Chan et al, 1962;Huang et al, 1973Huang et al, , 1976Kikuchi, 1986]. The SC-associated HF Doppler frequency deviations (SCF) are mostly in a bipolar structure, SCF (+ À) and SCF (À +), although single impulses, SCF (+) and SCF (À) are also observed [Huang et al, 1973].…”

Sudden frequency deviations due to immediate effect of geomagnetic sudden commencements.

“…The earlier work on the ionospheric response to geomagnetic sudden commencements using Doppler shift technique reported by DAVIES (1962) and KANELLAKOS and VILLARD (1962) showed that for the SC of September 30, 1961, there occurred a sharp increase in frequency preceded by a definite decrease of frequency. A more detailed study using 12 SC's by CHAN et al (1962) showed that the frequency deviation was always correlated in phase with SC (+) and in opposite phase with SC (-), SC (+-) and SC (-+).…”

“…DAVIES (1962), KANELLAKOS and VILLARD (1962), CHAN et al (1962) and AGY et al (1965) have reported their results regarding the effect of storm sudden commencements on the ionosphere using the above technique. However, the effect has not been studied in detail over low latitude radio paths but for the recent effort of HUANG et al (1973) who studied the Doppler data of a short low latitude path for effects of sudden commencements.…”

Penetration of the electric fields of the geomagnetic sudden commencement over the globe as observed with the HF Doppler sounders and magnetometers

“…The SC electric fields have been observed as the Doppler frequency of the HF radio signals reflected from the F-layer of the ionosphere at middle latitudes (Davies et al 1962;Kanellakos and Villard 1962;Chan et al 1962;Huang et al 1973;Kikuchi et al 1985Kikuchi et al , 2016Kikuchi, 1986;Pilipenko et al 2010;Hashimoto et al 2020). The HF Doppler frequency increases at the arrival of the SC followed by a frequency decrease on the dayside [Davies et al 1962;Kanellakos and Villard 1962;Chan et al 1962;Huang et al 1973], and vice versa on the nightside (Chan et al 1962;Kanellakos and Villard 1962;Sastri and Subrahmanyam 1974;Kikuchi et al 1985). The initial frequency increase on the dayside was explained in terms of the westward induction electric field proportional to dB/ dt (Huang 1976) or by the Earthward motion of the ionospheric plasma caused by the compressional MHD waves (Pilipenko et al 2010).…”