A statistical study of the interplanetary magnetic field control of sporadic E-layer occurrence in the southern polar cap ionosphere

Details A statistical study of the interplanetary magnetic field control of sporadic E-layer occurrence in the southern polar cap ionosphere A statistical study of the interplanetary magnetic field control of sporadic E-layer occurrence in the southern polar cap ionosphere

Dec 1999

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999jastp..61.1357w&link_type=abstract

Journal of Atmospheric and Solar-Terrestrial Physics, Volume 61, Issue 18, p. 1357-1366.

Physics

6

Scientific paper

The influence of the interplanetary magnetic field (IMF) on the occurrence of sporadic E (Es)-layers in the southern polar cap ionosphere has been investigated. We statistically analysed ionogram and Doppler velocity observations made using a HF digital ionosonde located at Casey, Antarctica (66.3°S, 110.5°E 81°S magnetic latitude) during the two summer campaign intervals 1 January to 18 February, and 1 November to 31 December 1997. The ionogram and Doppler velocity measurements were used to determine the Es-occurrence and electric field vectors (assuming E×B/B2 drift), respectively. Concurrent IMF data were obtained from measurements made on board the Wind spacecraft. First, the gross properties of the IMF dependence of Es-formation were obtained: the occurrence rate was higher for negative By and/or positive Bz, and lower for positive By and/or negative Bz. To reconcile these gross properties with the electric field theory of Es-layer formation, the detailed diurnal variation of both Es-occurrence and the ionospheric electric field were obtained for different orientations of the IMF. The main statistical results are that: (1) the By component mainly controls the occurrence of the midnight Es-layers through its influence on the corresponding South West electric field; and (2) the Bz component mainly controls the occurrence of the evening Es-layers. However, the change in the occurrence rate for evening Es-layers was not related to the strength of the associated North West and North East electric fields. The total occurrence of Es-layers depended more on By than on Bz, owing to the dominance of By-controlled midnight Es-layers in the occurrence distribution. Nevertheless, the dependence of Es-occurrence on Bz was important. We suggest that the increase in Es-occurrence for positive Bz might be explained by the intermittent production of lower F-region ionisation by polar showers and squalls, which also increase in frequency and intensity for positive Bz. The importance of metallic ion transport within the ionosphere is also considered.

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