Jules Aarons

Chapter 13 - Band Emissions at Gyro Frequencies of Ionospheric Ions and Hiss Frequencies

The background noise level in the frequency range 10–10,000 c/s has been monitored at Kiruna and Sagamore Hill. Three emission bands have been found centred at 33, 750, and 2500 c/s, respectively. The 33 c/s and 750 c/s bands have been found to be dependent on the latitude but not the 2500 c/s band. Different properties of the 750 c/s emission and especially a case with good correlation with micropulsations have been discussed. An analysis of the diurnal variation of the background noise level has been made for several frequency bands.

Radio measurements of two total eclipses

Abstract Multifrequency records of two total eclipses of the Sun—October 2, 1959, and February 15, 1961—have been analyzed. The position of the Moons limb during increases and decreases of the slopes of the eclipse curve has been compared with optical maps and radio heliograms in an attempt to study the bright radio regions on the Sun. Angular diameters of a few enhanced regions were found to vary between 0.75 and 1.25 minutes of arc. The brightness temperature of one region was 1.5 × 10 5 °K at 9700 mc and 9 × 10 5 °K at 1270 mc. The heights of emitting regions at various freqeuncies were calculated in two cases. No conclusions as to limb brightening could be reached because of the presence of the enhanced radio regions near both limbs during both eclipses. The residual energy at totality on October 2 was approximately 20% at both 1300 and 3000 mc; on February 15, it was 8.6% at 9700 mc and 25.3% at 1270 mc.

The Great Burst of May 23, 1967

One of the largest radio bursts on record took place on May 23, 1967. Peak flux densities ranged between 23000 flux units (10−22 wm−2 Hz−1) at 8800 MHz to about 370000 units at 606 MHz. In addition to the high-accuracy measurements of the peak flux densities at 606, 1415, 2695, 4995, and 8800 MHz, sweep frequency observations from 19–39 MHz show Type-IV emission with Type-II bursts occurring during the Type-IV continuum. The associated flare was clearly visible in white light. In reviewing and compiling microwave-radio data recorded during earlier white-light flares, it was found that all but one of eight events listed by Svestka (1966) had high microwave flux densities associated with them. In comparing radio-burst intensity with optical flare importance for the series of three flares between 1809 and 2150 UT on May 23, there is only moderate agreement. The first radio burst was small; the third was by far the largest, while the second flare had the highest optical classification. The flux densities of the third burst may have been the highest ever recorded in the decimeter portion of the radio spectrum and amongst the largest four in the 8800 MHz region. It is suggested that the details of the development of the flare might be followed on radio flux-density plots to determine detailed correlation with particle events in space and with terrestrial effects.