Winter anomaly of the E-layer critical frequency in the nighttime auroral zone

Abstract
<p>Analysis of the annual variation of the <em>E</em>-layer critical frequency median <em>foE</em> in the nighttime (22-02 LT) auroral zone by the data of several stations of the Northern Hemisphere has shown the median maximum in winter and minimum in summer, even though the summer contribution of solar radiation to <em>foE</em> is greater. Thus, a new phenomenon was discovered\textemdashan <em>foE</em> median winter anomaly in the nighttime auroral zone. Its amplitude (ratio of winter to summer <em>foE</em> figures) can reach 10\textendash15\%; however, this anomaly was weakly expressed and statistically insignificant at particular stations located in the auroral zone. The winter anomaly is more distinct for <em>foE</em> <sub>avr</sub>, the median of the <em>E</em>-layer critical frequency <em>foE</em> caused by the auroral source of atmospheric ionization, i.e., excluding the solar radiation contribution to <em>foE</em>. For <em>foE</em> <sub>avr</sub>, the amplitude of the winter anomaly can reach 15\textendash20\%. Based on the qualitative analysis, it has been found that <em>foE</em> winter anomaly is stipulated by the winter/summer asymmetry of energy flow of accelerated electrons, which induce discrete aurorae in the nighttime auroral zone.</p>
Year of Publication
2017
Journal
Geomagnetism and Aeronomy
Volume
57
Number of Pages
584-590
Date Published
10/2017
ISSN Number
0016-7932
URL
http://link.springer.com/10.1134/S0016793217050061
DOI
10.1134/S0016793217050061