# A Multiscale Approach to Geomagnetic Storm Morphology Analysis Based on DMA Activity Measures
## 3 Results and Discussion
### Initial Geomagnetic and Interplanetary Data  
To display the possibilities of the method in the analysis of geomagnetic storm features, we applied it to several strong storms that took place at the ends of the 23 rd and 24 th solar cycles. It is known that during the final period of an 11-year solar cycle, the solar flare activity often increases. For instance, in the 23 rd cycle [19], the most flare-active periods (leading to geoeffective coronal mass ejections) took place in 2003-2005, and in the 24 th cycle in 2015-2020 (after the solar maximum in 2014).  
We selected the Honolulu (HON) geomagnetic observatory data for the tests. Due to its latitudinal position being close to equatorial, during geomagnetic storms, the equatorial ring current contributes fully to the geomagnetic data recorded by this observatory. Therefore, in these data, the global geomagnetic activity is fully represented, and the impact of local geomagnetic disturbances occurring in higher latitudes and driven by ionospheric currents is almost absent. The data from the HON observatory were used for \(Dst\) geomagnetic index calculation [20]. Horizontal components of the magnetic field of the Earth are usually under the most powerful influence of a geomagnetic storm, and their records clearly display the storm evolution and its phases. Thus, to display the storm dynamics using activity measures, we selected the northward (\(X\)) component of the total geomagnetic field from the definitive geomagnetic data [12] of the HON observatory.  
Initially about 10 storms were studied. However, in order not to overload the article with excessive material and charts, here we focus on 4 strong storms, which we consider the most representative and suitable to highlight the possibilities of the method in the analysis of the features of storms during their different phases. The analyzed storms are listed in Table 1. These storms are not the strongest in the mentioned cycles, as we did not analyze some of the most extreme and well-studied events, such as the storm on 20-24 November 2003, or the St. Patrick's Day storm on 17-18 March 2015 [21] that appeared to be the most intense geomagnetic storm in the 24 th cycle (\(Dst\) index \(\leq-230\) nT).  
Prior to three of these eight storms, storm sudden commencements (SSC) occurred, which can be clearly seen on the magnetic variation data. Storm sudden commencements occur due to the magnetohydrodynamic shockwave impact on the Earth's magnetosphere prior to geomagnetic storm onset. The SSC signal can often be clearly identified on \(X\) or \(H\) magnetic component data. However, sometimes it is not so possible to recognize it. Therefore, as an additional reference, we used the SSC database from the International Service on Rapid Magnetic Variation [22].  
The method was applied first to the data describing the space weather conditions during storms--the interplanetary magnetic field (IMF) \(B_{z}\) and \(B_{y}\) components, the solar wind speed and density, extracted from the NASA/GSFC OMNI data set through OMNIWeb [23] and 1 min averaged. Changes in the direction of \(B_{z}\) IMF component are a key factor in the geomagnetic storm onset and generation [24]. The solar wind speed data were registered by the ACE spacecraft. Solar wind speed and proton density are the characteristics displaying the energy of the coronal mass ejection, as the high-density and high-speed solar wind plasma also affects the storm behavior and possible enhancements [25]. Next, we applied the method to the observatory geomagnetic data to see the geomagnetic storm response on the Earth's surface and juxtaposition between the ground-based and interplanetary measurements.