Correction to “Evolution of auroral asymmetries in the conjugate hemispheres during two substorms”

Authors


[1] In the paper “Evolution of auroral asymmetries in the conjugate hemispheres during two substorms” by Østgaard et al. (Geophysical Research Letters, 38, L03101, doi:10.1029/2010GL046057, 2011), the geometry presented in Figure 3b is not correct. Instead, the geometry first suggested by Stenbaek-Nielsen and Otto [1997] and shown here in Figure 1 should be used. For Interplanetary Magnetic Field (IMF) By < 0, Stenbaek-Nielsen and Otto [1997] derived, according to Ampere's law, a north-to-south inter-hemispheric field aligned current (FAC) in the region of auroral arcs and a south-to-north FAC at the inner edge of the plasma sheet that maps to the region of region 2 currents (Figure 1). Applying this geometry to the case study presented by Østgaard et al. [2011] would imply that a net FAC from the north to the south in the region of auroral arcs and the rest of the argument based on integrating the Faraday's law along a loop of two closed field is still valid.

Figure 1.

Sketch of how IMF By < 0 will penetrate the magnetosphere and extend to close field lines, similar to Figure 4 in Stenbaek-Nielsen and Otto [1997]. In this sketch, the entire By component is shown in the equatorial plane to make our point clearer. The penetration has a maximum in the region of discrete aurora and decreases towards the tail and at the inner edge of plasma sheet, giving a south-to-north current at the inner edge of the plasma sheet and a north-to-south current in the auroral region for IMF By < 0.