Neutral densities from GRACE at 20:01 LT (left) and GOCE at 06:50 LT (right) as functions of time along the X axis, and latitude along the Y axis, measured during the August 2011 magnetic storm. At left, the GRACE data are shown as residuals (ρ/ρ_quiet), with K_p shown as the heavy black line. TADs were reported in the GRACE data (Huang et al. 2014a). The inset to left of the GOCE data panel is an expanded view of the initial response to the storm onset. The higher densities (in red) indicated by arrows are detected at decreasing latitude at later times, corresponding to the TAD.