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Document title
Solar X-ray flares and ionospheric sudden phase anomalies relationship : A solar cycle phase dependence

Author(s)
ABE PACINI Alessandra (1 2) ; RAULIN Jean-Pierre (1) ;
Author(s) Affiliation(s)

(1) Centro de Radioastronomia e Astrofisica Mackenzie, Universidade Presbiteriana Mackenzie, São Paulo, BRESIL

(2) Instituto Nacional de Pesquisas Espaciais, São José dos Campos, BRESIL

Abstract

[1] We investigate the relation between sudden phase anomaly (SPA) amplitudes (?f) and solar X-ray flares importance and study if it has a solar activity cycle dependence. We find a very significant correlation between ?f and the X-ray fluences, FX (time-integrated photon fluxes) in the range 0.5-2 Å. Compared with earlier works, the improvements of the ?f versus FX relation allow us to study separately solar events as a function of their occurrence in the solar activity cycle, and we find that the ?f versus FX relation is different depending on the epoch within the solar cycle. In particular, a minimum X-ray fluence of 2.5 x 10-6J m-2 is needed during solar activity minimum to trigger a SPA, while during solar maximum, 7.0 x 10-6 J m-2 is required. Similarly, a solar flare will produce a SPA during solar minimum that is greater by ~2.6° M m-1 than would a flare of the same size during solar maximum. These results confirm recent findings about the dependence with the solar activity of the ionospheric undisturbed D region sensitivity.

A possible consequence would be the monitoring of the long-term solar irradiance, which maintains the D region, through measurements of VLF wave propagation properties.

Journal Title
Journal of geophysical research ISSN 0148-0227
Source
2006, vol. 111, noA9, [Note(s): A09301.1-A09301.4] (20 ref.)

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Title: On the relation between ionospheric winter anomalies and solar wind
Authors: Rumi, G. C.*
Keywords: Ionospheric winter anomalies solar wind

Issue Date: Jun-2001

Series/Report no.: 44/3

Abstract: There are two different winter anomalies. A small one that appears in connection with ionization at relatively low latitudes in the bottom of the D-region of the ionosphere. There, the electron densities in the winter happen to be less than should be expected. On the other hand, the classic winter anomaly is present when in the winter the upper D-region, again at relatively low latitudes, has more ionization than should be expected. Both these effects are due to the slant compression of the geomagnetic field produced by the solar wind in the winter season (which is, of course, the summer season when reference is made to events in the other hemisphere). It is shown that the small winter anomaly is a consequence of a hemispheric imbalance in the flux of galactic cosmic rays determined by the obliquely distorted geomagnetic field. It is shown that the standard winter anomaly can be ascribed to the influx of a super solar wind, which penetrates into the Earth’s polar atmosphere down to E-region heights and, duly concentrated through a funneling action at the winter pole of the distorted geomagnetic field, slows down the winter polar vortex. An equatorward motion of the polar air with its content of nitric oxide brings about the excess of ionization in the upper D-region at lower latitudes. The experimentally observed rhythmic recurrence of the upper winter anomaly is correlated to a possible rhythmic recurrence of the super solar wind. The actual detection of the upper winter anomaly could yield some information on the velocity of the basic solar wind. A by-product of the present analysis, the determination of à , the coefficient of collisional detachment of the electrons from the O2 ions, is presented in the Appendix.
URI: http://hdl.handle.net/2122/1198
Appears in Collections: Annals of Geophysics

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