Persistent long-term (1944-2015) ionosphere-magnetosphere associations at the area of intense seismic activity and beyond

Analysis of the earthquakes catalogues since 1944 reveals the area of the peak global earthquake occurrence in the Pacific Ocean southwards from the magnetic equator, in particular, at Australia. In the present study a long series of geomagnetic aa indices gathered from two antipodal magnetic observatories at Melbourne (Australia) and Greenwich (UK) are compared with the monthly-hourly critical frequency, foF2, from the nearby ionosonde measurements at Canberra and Slough (Chilton) and Moscow (control site) for 1944-2015. The annual percentage occurrence of the positive ionosphere storms W index (pW+) and negative index (pW−) is determined. It is found that the occurrence of the ionosphere plasma depletion pW− of the instant foF2 as compared to the monthly median is well correlated with the aa index at all three sites (cc > 0.85). The positive storm signatures of the plasma density enhancement pW+ show high correlation with the geomagnetic activity aa index at Slough (cc = 0.68) and Moscow (cc = 0.92) but drastic difference of missing correlation at Canberra (cc = 0.06). It has been suggested that the frequent earthquake occurrence over Australia may produce the persistent significant ionosphere plasma enhancements at Canberra which disrupts balance between the ionosphere-magnetosphere activities.