Ionospheric response to the solar storm on 15th – 18th February 2011
Solar storms may cause significant perturbations in the ionosphere even under low solar activity conditions. On 15th February the NOAA Space Weather Prediction Center (SWPC) announced a coronal mass ejection (CME) propelled toward Earth by the X2-flare in the early morning hours of 15 February 2011 (see animation below).
Solar flares may be detected easily by measuring the signals of VLF (very low frequency) transmitters propagating in the wave guide between the Earth surface and the ionosphere. Since X-rays enhance the ionization in the bottom side ionosphere, solar flares modify the propagation conditions of VHF signals visible as strength changes.
This is clearly seen in lower panel of the subsequent left Figure.
Whereas the solar flare at 01:44 UT recorded onboard GOES as strong enhancement of X ray fluxes, it could not be detected by the Sun & Ionosphere MONitoring Network (SIMONE) in Germany because of night time hours in the monitoring region. However, the second flare at 14:32 UT was clearly recorded. SIMONE is a student’s project well established at several schools in the federal states Mecklenburg-Vorpommern and Niedersachsen. The Figure shows the plots obtained at the Gymnasium Walsrode and at the Ernst Moritz Arndt Gymnasium Bergen.
Changes of the interplanetary magnetic field, measured onboard the solar wind satellite ACE satellite (Bz- component) indicate the arrival of a solar storm effect on 18th February 2011. Due to the coupling of the CME plasma cloud with the Earth’s magnetosphere an enhanced geomagnetic activity is indicated by geomagnetic indices such as the hemispheric power index, Dst and Kp on 18th February 2011.
Based on coupling processes mapped down to the ionosphere, the total electron content (TEC) was also strongly changed at the same day as shown in the subsequent figure and TEC movie.
For comparison, the lower panel shows the TEC behaviour under unperturbed conditions represented by the median values of the last 27 days.
To see the movie, please click here.