## 3 Results
### Ionospheric Response to the Storm of 30 September to 3 October 2012  
The sudden storm commencement (SSC) of the 30 September to 3 October storm occurred at 1300 UT, on 30 September. This storm developed in two steps with the first step having a minimum _Dst_ index of \(-\)39 nT at 2000 UT and the second step (main phase) with a minimum _Dst_ index of \(-\)122 nT at 0400 UT on 1 October, as shown in panel a of Figures 1-3. Variations in the _fo_F2, _Af_oF2%, and _h'F_ for this storm at three stations are shown in Figures 1-3, respectively. Figure 1b (Darwin station) showed a sharp increase in the _fo_F2 for 4-5 h, with a maximum increase from the median value of 12.6 to 17.1 MHz at 0500 UT, on 1 October giving _Af_oF2% of +35.7% (Figure 1c). The _f_oF2 values available online are with scaling up by a factor of 10, so the values shown here are scaled down by a factor of 10 (MHz \(\times\) 10\({}^{-1}\)) (also shown in y-axis of panel b) to indicate the actual values. As shown in Figure 1d, to this positive effect in _fo_F2, _h'F_ showed no significant change during the storm main phase, but an increase in the _h'F_ between the SSC and main phase of the storm from 240 to 297 km occurred at 1900 UT on 30 September. The _fo_F2 and _h'F_ variations approached the median value around 0800-0900 UT on 1 October. Thereafter, during the recovery phase of the storm _fo_F2 decreased from 1400-2100 UT on 1 and 2 October and this decrease was accompanied by an increase in the _h'F_ with a maximum decrease from 242 to 319 km at 2000 UT on 2 October. At Townsville station (Figure 2b), the _fo_F2 variation during the main phase of the storm showed an increase (maximum, 10.0-13.3 MHz, at 0600 UT) during 0200-0700 UT on 1 October. Together with the increase in _fo_F2 of about 33% as shown in Figure 2d, there was a short duration increase in the _h'F_ on 1 October. On 1 October between 0900-1000 UT, the _fo_F2 and _h'F_ approached median values showing the storm effect for about 6 h. A decrease in the _fo_F2 from median was observed during 1300-1900 UT, on 1 October, with a simultaneous increase in the _h'F_ with a maximum of about 24%. Another decrease in the _fo_F2 occurred from 0800-2000 UT on 2 October, which was accompanied by an increase in the _h'F_ (maximum, 264-326 km, at 1900 UT). As shown in Figure 3b-d, at Canberra station this particular storm produced an increase in _fo_F2 (maximum 8.0-11.7 MHz at 0500 UT) from 2100 UT on 3 September to 0600 UT on 1 October (about 9 h) with a maximum _Af_oF2% of +45.3% (Figure 3c) at 0500 UT on 1 October relative to the median value. There was no significant change in the _h'F_ (Figure 3d) during the increase in _fo_F2. As _fo_F2 approached the median value at around 0800-0900 UT on 1 October during the recovery phase of the storm, a large and long duration decrease in the _fo_F2 was observed (Figure 3b) with a maximum _Af_oF2% of \(-\)63.5% at 1600 UT on 1 October. This decrease in the _fo_F2 occurred between 1200-2000 UT on 1 October-2 October giving a long duration negative ionospheric storm. This storm produced positive/negative ionospheric effects during its main/recovery phase. Both positive and negative ionospheric storms at Canberra station were stronger and of longer duration as compared to Townsville and Darwin stations showing latitude dependence of the geomagnetic storm effect.