Sudden Frequency Deviations Solar Extreme Ultraviolets Bursts And Solar Radio Bursts

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)

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).

High time and intensity resolution satellite measurements of X-ray and extreme ultraviolet (EUV) radiation during solar flares are studied to determine the wavelength dependence of the flare radiation responsible for sudden frequency deviations (SFD). SFD's measure the flare-induced effects in the E and F1 regions of the ionosphere and are in effect like a broadband (1-1030 Å) detector for impulsive flare enhancements. He II 303.8 Å, O V 629.7 Å, H Ly [upsilon] 972.5 Å, C III 977.0 Å, and H Ly [alpha] 1215.7 Å were found to have essentially the same time dependence as the total ionizing radiation producing SFD's, except that they decay faster than the net 1-1030 Å radiation. Flare enhancements of Fe XV 284.1 Å, Fe XVI 335.3 Å, Si XII 499.3 Å. Mg X 625.3 Å, and Ne VIII 770.4 Å, which are normally coronal lines, appear to have a much slower time dependence than the radiation responsible for SFD's. X-rays in the 0.5-3 Å range are slightly slower than the radiation responsible for SFD's during the decay stage; 1-8 Å X-ray flares are slower, especially during the decay stages; and 8-20 Å flare radiation enhancements are slower throughout the entire SFD.

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).