Correlation Between Solar Radio Bursts And Sudden Frequency Deviation Events

Solar radio bursts observed at 606, 1415, 2695, 4995 and 8800 MHz have been correlated with Sudden Frequency Deviations (SFD) measured at Boulder, Colorado, in the signals of WWI originating in Havana, Ill. The correlation reaches a not very pronounced maximum near 5000 MHz, and it is higher for stronger events (both large bursts and large SFD's). It increases monotonically with the size of the SFD's correlated with radio bursts observed on centimeter wavelengths, but shows a decrease for SFD's of intermediate size correlated with bursts observed in the decimeter region. Of the five frequencies (8.9, 9.9, 11.1, 12.1 and 13.0 MHz) of WWI used to measure SFD's over the above mentioned ray path, the correlation of the events observed at 9.9 MHz was less than half the mean correlation value obtained from the other four frequencies. The correlation was high for radio bursts with a maximum in the range between 1000 and 5000 MHz and low for radio bursts with intensity spectrum decreasing with frequency in the range from 606 to 8800 MHz. The results are also compared with a similar correlation analysis between solar radio bursts and SCNA events. (Author).

An investigation has been made of the interrelationship of solar extreme ultraviolet (EUV) bursts, solar radio bursts, and terrestrial ionospheric sudden frequency deviations (SFD's). No direct general relationships between radio spectra or burst intensities and SFD incidence or magnitude (Delta f) have been found. If the EUV enhancement is greater than 3 percent at Lambda 304 or Lambda 630 A, there is an 85 percent probability of occurrence of an SFD. Time of maxima of EUV and radio bursts are found to coincide extremely well. (Author).

We have conducted a statistical study of the correlation between solar radio bursts and sudden cosmic noise absorption events. Our main purpose was to study the relative effectiveness of the different microwave frequencies in detecting the radio bursts that are associated with X-ray emission from the Sun. In the frequency range covered (606 to 8800 MHz), it was found that the higher the monitoring frequency, the better the correlation with X-ray emission. It was also found that for centimeter wavelengths the correlation improves as the radio bursts become more intense whereas for decimeter wavelengths this was not found to be true. (Author).

Sudden Ionospheric Disturbances resulting from an interaction of the Solar Flare radiation with the constituents of the upper atmosphere constitute one of the three major aspects of ground level monitoring of solar flares -the other two being optical observations of flares, and the observations of solar bursts in radio wavelengths. SIDs, therefore, form a major part of flare monitoring programme in many observatories. Unlike the other two, however, the ionospheric effects of flares provide one major additional source of interest - the reaction of the ionospheric plasma to an impulsive ionization. The high atmosphere provides a low pressure laboratory without walls in which a host of reactions occur between electrons, ions and neutral particles. The resulting products and their distributions may bear no resemblance to those of the primary neutral constituents or their direct ionization products. The variations with the time of the day, with season and with solar activity that form the bulk of the ionospheric measurements are too slow to allow any insight into the nature of these ionospheric reactions whose lifetimes are often very short. The relaxation time of the ionospheric ionization is only a few minutes or fraction of a minute in the lower ionosphere and in the E-region and is about 30 min to an hour at 300 km. The flares provide a sudden short impulse comparable to these time scales.

One of the largest radio bursts on record took place on May 23, 1967. Peak flux densities ranged between 23,000 flux units (10 to the minus 22nd power sq Wm/Hz) at 8800 MHz to about 370,000 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 to 41 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, 1967, there is only moderate agreement. The first radio burst was small; the second flare had the highest optical classification, while the third radio burst was by far the largest. The flux densities of the third radio burst may have been the highest ever recorded in the decimeter portion of the radio spectrum and among the largest four in the 8800 MHz region. It is suggested that the details of the development of the flare be followed on radio flux density plots to determine detailed correlation with particle events in space and with terrestrial effects. (Author).

An investigation has been made of the interrelationship of solar extreme ultraviolet (EUV) bursts, solar radio bursts, and terrestrial ionospheric sudden frequency deviations (SFD's). No direct general relationships between radio spectra or burst intensities and SFD incidence or magnitude (Delta f) have been found. If the EUV enhancement is greater than 3 percent at Lambda 304 or Lambda 630 A, there is an 85 percent probability of occurrence of an SFD. Time of maxima of EUV and radio bursts are found to coincide extremely well. (Author).

An investigation has been made of the interrelationship of solar extreme ultraviolet (EUV) bursts, solar radio bursts, and terrestrial ionospheric sudden frequency deviations (SFD's). No direct general relationships between radio spectra or burst intensities and SFD incidence or magnitude (Delta f) have been found. If the EUV enhancement is greater than 3 percent at Lambda 304 or Lambda 630 A, there is an 85 percent probability of occurrence of an SFD. Time of maxima of EUV and radio bursts are found to coincide extremely well. (Author)