Low and Mid Latitude Ionospheric and Thermospheric Storm Dynamics During the September 2011 Geomagnetic Storm

We provide ionospheric storm timing from multiple topside satellites (four DMSP spacecraft) along with a vast database of ionospheric and thermospheric measurements, allowing comprehensive investigation of the timing and response of the ionosphere and thermosphere to the ionospheric storm associated with the geomagnetic storm of 26 September 2011. Such a comprehensive study of ionosphere storm timing and dynamics has not been reported previously. The positive phase of the ionospheric storm peaked near the end of the geomagnetic storm growth phase and continued several hours into the recovery phase before entering the negative phase. During the positive phase, neutral heating and vertical motion at high latitudes led to dramatic decreases in the O/N 2 ratio that extended well into the mid‐latitudes in both hemispheres and lasted throughout the storm recovery phase. The ion temperature in the topside decreased during the positive phase and increased during the negative phase as a result of vertical ion velocities that extended into the mid‐latitudes during the positive phase, leading to adiabatic cooling and movement of the O + /H + transition height to higher altitudes, followed by vertically downward velocities and adiabatic heating. Density increases at the equator early in the positive phase are attributed to vertical drifts associated with the eastward zonal electric field driven by a penetration electron field while the merging of the Appleton peaks observed in the vTEC data is attributed to the reverse fountain effect associated with a change in the zonal electric field from eastward to westward and downward ion drifts.