Abstract
Two hundred and eighty-five hours of solar data obtained from the University of Iowa 2 cm radiometer during 1968–1969 were analyzed for evidence of periodic structure related to the 5 min periodic chromospheric oscillations detected in optical line emissions. A power spectral analysis of the data failed to show any statistically significant (> 96 % confidence) periodic activity in the frequency range 1–15 mHz (periods of 1–16 min) for data organized according to solar activity in Hα, soft solar X-rays (2–12 Å), and several microwave frequencies (3–15 GHz).
A small shift in power from low to higher frequencies in the power spectrum of the 2 cm data was found to be correlated with Hα and X-ray activity. This power shift is attributed to a relative increase in chromospheric turbulence at altitudes common to Hα, X-ray, and 2 cm emission.
Consistent statistical analyses of previous works reporting evidence for oscillations at microwave and extreme-ultraviolet frequencies indicate that confidence in these previous results is marginal.
A model for chromospheric oscillation bursts in quiescent supergranules is incorporated into a statistical analysis of the power spectrum detectability of the oscillations to understand the negative results obtained.
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Sentman, D.D., Shawhan, S.D. A search for 5 min periodic structure in solar 2 cm emission. Sol Phys 35, 83–103 (1974). https://doi.org/10.1007/BF00156959
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DOI: https://doi.org/10.1007/BF00156959