# A Multiscale Approach to Geomagnetic Storm Morphology Analysis Based on DMA Activity Measures
## 3 Results and Discussion
### General Information on the Analyzed Geomagnetic Storms  
The first storm on 15-19 May 2005 was the one of the largest of the 23 rd solar cycle, with a Dst index reaching \(-263\) nT right on the first day of the storm. The IMF plots (Figure 2b,c) show the major \(B_{z}\) and \(B_{y}\) disturbances, and the SSC signal is seen on the \(X\) component data on 02:40 UT, 15 May 2005 (Figure 2a). This is the time moment when the \(B_{z}\) component turned southward first for a relatively small period. Next it returned to low positive values for a while, turned north, reaching even up to 35 nT, and then its rapid decrease began, which nearly matched the main phase of the geomagnetic storm (seen on the \(X\) component plot). The disturbances corresponding to the storm generation are also seen on the solar wind flux speed and proton density plots (Figure 2b,c, respectively). The next one of the geomagnetic storms we selected for the research was the storm on 14-16 December 2006. At the beginning of 14 December, the \(B_{z}\) (Figure 3c) southward direction did not last for long periods, and the \(B_{y}\) component (Figure 3b) was also close to zero. However, the solar wind speed was relatively high right at the beginning of the day (more than 600 km/s). Around 14:14 UT, there was an abrupt \(B_{z}\) decrease to \(-10\) nT and \(B_{y}\) increase to 6 nT. The storm onset is also seen on the proton density (Figure 3e) and flux speed (Figure 3d) plots as an increase from 2 to 6 n/cc and from 600 to nearly 1000 km/s, respectively. The SSC signal is seen on the \(X\) observatory data component (Figure 3a) clearer than on the IMF plots. The proton density reached its maximum of about 25n/cc by the end of 14 December and returned to low (undisturbed) values the next day as well as the flux speed that decreased slowly over the next two days. In addition, there was a sudden disturbance during the main phase of the storm which is seen as abrupt \(B_{z}\) and \(B_{y}\) increases and relatively small increases in solar wind plots. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Storm** & **Solar** & **Start Date and Time** & **End Date and Time** & **min Dst** & **SSC Time** \\
**Number** & **Cycle** & **(UTC)** & **(UTC)** & **(nT)** & **(UTC)** \\ \hline
1 & 23 & 2005-05-15 06:00 & 2005-05-19 06:00 & \(-263\) & 02:38 \\
2 & 23 & 2006-12-14 23:00 & 2006-12-16 17:00 & \(-146\) & 14:14 \\
3 & 24 & 2015-06-22 19:00 & 2015-06-29 01:00 & \(-204\) & 18:33 \\
4 & 24 & 2018-08-25 19:00 & 2018-08-28 21:00 & \(-174\) & No SSC \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Main features of the geomagnetic storms selected for analysis. Figure 2: The geomagnetic data and solar wind parameters during a geomagnetic storm of May 2005: HON observatory \(X\) component **(a)**, IMF \(B_{y}\) **(b)** and \(B_{z}\) **(c)** components, solar wind flux speed **(d)** and proton density **(e)**. The magnetic storm on 22-29 June 2015 (Figure 4) was one of the strongest in the 24 th solar cycle (minimum Dst index reached \(-\)204 nT by the end of the main storm phase). The interplanetary conditions were initially calm, but on 22 June at 18:33 UT, the \(B_{z}\) component of the IMF (Figure 4c) turned to the south, reaching the local peak value of \(-\)40 nT. At the same time, the \(B_{y}\) component (Figure 4b) changed first to \(-\)25 nT and then to 32 nT. This IMF disturbance was caused by the CME arrival to the magnetosphere frontal part, characterized by the plasma flux speed increase to more than 700 km/s (as seen in Figure 4d) and the proton density increase from 11 to 60-70 n/cc (Figure 4e). The simultaneous abrupt increases in the mentioned IMF and plasma parameters indicate a SSC at 18:33 UT, which is also clearly seen on the \(X\) component observatory data plot (Figure 4a).