Astronomy and Astrophysics – Astrophysics
Scientific paper
Sep 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006jgra..11109301p&link_type=abstract
Journal of Geophysical Research, Volume 111, Issue A9, CiteID A09301
Astronomy and Astrophysics
Astrophysics
6
Space Weather: Solar Effects, Solar Physics, Astrophysics, And Astronomy: Solar Irradiance, Solar Physics, Astrophysics, And Astronomy: Solar Activity Cycle (2162), Radio Science: Ionospheric Propagation (0689, 2487, 3285, 4275, 4455), Ionosphere: Ionospheric Disturbances
Scientific paper
We investigate the relation between sudden phase anomaly (SPA) amplitudes (Δ$\varphi$) and solar X-ray flares importance and study if it has a solar activity cycle dependence. We find a very significant correlation between Δ$\varphi$ 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 Δ$\varphi$ 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 Δ$\varphi$ versus FX relation is different depending on the epoch within the solar cycle. In particular, a minimum X-ray fluence of 2.5 × 10-6 J m-2 is needed during solar activity minimum to trigger a SPA, while during solar maximum, 7.0 × 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.
Abe Pacini Alessandra
Raulin Jean Pierre
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