Cosmic noise absorption pulsations
thesisposted on 2023-05-27, 16:44 authored by Reid, JS
The fast cosmic noise absorption (c.n.a.) pulsations observed with fast response riometers at Macquarie Island in the southern auroral zone are discussed in relation to the parameters of the lower ionosphere. The pulsations which are similar to and associated. with pulsations in aurora luminosity (at ˜í¬™ 4278‚àövñ), Pi2 micropulsations and fast bremmstrahlung X-ray pulsations are unique in that they exhibit a time asymmetry or relaxation time which is believed to be a consequence of the relatively slow rate of removal of secondary electrons in the ionosphere. The relaxation time, T is defined as ˜ìvë = - A/ (¬ªvü) max where A is the amplitude of the pulse,above background and (¬ªvü)max is the Maximum (negative) slope of the relaxation part of the pulse. Measured values of ˜ìvë varied between 1 and 30 seconds and scatter diagrams of ˜ìvë versus A indicate a strong tendency for ˜ìvë to increase with increasing pulse amplitude. The properties and anomalies of the D-region of the ionosphere are discussed, as is the applicability of the Bates and Massey rate equations to fluctuations in electrons density in this region. A computer model was constructed in which the rate equations were numerically integrated using a variety of values of the parameters involved and for a variety of primary spectrum e-folding energies in an attempt to simulate the observed pulsations. Relaxation times as small as some of those observed were not obtained from the model. A new approximation formula for relaxation time as a function of height was derived. The possibility that the observed positive relationship between relaxation time and pulse amplitude is due to the chemical dynamics of a situation in which electrons recombine with positive ions of widely differing reaction rates is discussed and dismissed. It is concluded that the observed c. n. a. pulsations are an E-region phenomenon associated with quasi monoenergetic peaks in the background primary flux with energies somewhere in the range of from 4 to 10 keV. The pulsations are believed to be due to fluctuations in the energy of this peak or to pulsations in primary particle flux on the high energy side of the -peak.
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