On the short-term relationship between solar soft X-ray irradiances and equatorial total electron content (TEC)

[1] The relationship between total electron content (TEC) and the solar soft X-ray irradiances is presented. Three bands (2–7 nm, 6–19 nm, and 17–20 nm) of solar soft X-ray measurements from the Student Nitric Oxide Explorer (SNOE) satellite are examined and all show a similar relationship with TEC. The TEC data are from a GPS receiver near Ancon, Peru ( 11.78 degrees latitude, 77.15 degrees longitude) from 11 March 1998 to 23 August 1999 and 2 October 1999 to 10 June 2000. During these periods the average TEC measurement was calculated from all observations whose ionospheric pierce point occurred within 12 ± 2 degrees latitude and 77 ± 2 degrees longitude and within the hour selected. TEC shows a more significant correlation with soft X-ray irradiances than with F10.7. The X rays lead the TEC by approximately 0.8–1.3 days, which is consistent with the neutral density affecting the TEC. The magnitude of these short term (27 days or less) changes is approximately 0.18 of the total TEC. During the period examined geomagnetic activity, as represented by Ap, could account for half as much variation in TEC (0.1 of the total TEC) as the solar irradiance.