# Modulation of Solar Wind Impact on the Earth's Magnetosphere during the Solar Cycle
## 3 Results and Discussion
A slow wind plasma with speed \(250\leq V\leq 300\) km s\({}^{-1}\) (corresponding to a stable region with respect to magnetospheric ring currents expected for \(Dst=20\) on quiet days [34]) fills a portion of the plane with energies spanning the range \(0.01\leq E_{t}\leq 0.3\) and with positive or close to zero \(Dst\). This indicates that low-speed flows have a negligible impact on the geomagnetic field, regardless of the kinetic energy levels transported. Stronger geomagnetic activity is observed for high speed streams, where the \(Dst\) index reaches extreme values of the order of \(Dst<-100\) nT. In such conditions, the SW average bulk speed lies in the range \(V\in[500,800]\) km s\({}^{-1}\), and higher kinetic energy levels \(5<E\leq 10\) are present. This is probably associated with compressive regions generated at the interface between fast and slow flows, where CMEs are more geo-effective drivers. The same trend is also observed for the distribution of the kinetic and magnetic energy (Figure 4 second and third row, left column). During the minimum activity period (right column), the distribution presents a rather simple shape, stretched along the energy direction in the energy range \(E\in[0.02,10]\) and compressed in a small region of \(Dst\) values in the range \(Dst\in[20,-50]\). All distributions present a neat separation in terms of wind velocity around \(Dst\approx 0\), as shown by the fact that the plane is divided into two portions. Positive \(Dst\) are characterized by low speed streams \(V\in[250,500]\) km s\({}^{-1}\). For \(Dst<0\), only higher speed streams are recorded, characterized by a mean bulk speed \(V>500\) km s\({}^{-1}\), and the wind is always able to trigger moderate disturbances in the \(Dst\) index. Figure 3: Bivariate histograms of the \(Dst\) index measurements as a function of the SW energy total energy (**first row**), kinetic energy (**second row**), magnetic energy (**third row**), respectively, for maximum (**left column**) and minimum (**right column**) solar activity periods. The black solid line represents the most probable \(Dst\) value at each energy level, within the 68% confidence bounds indicated by the shaded gray area. The bottom row of Figure 4 shows the bivariate distribution of \(Dst\) and residual energy, \(E_{r}=E_{v}-E_{b}\). During both maxima and minima, higher values of residual energy are accompanied by stronger perturbations in the \(Dst\) indexes (higher geo-effectiveness), showing that \(E_{v}\) is a stronger driver for \(Dst\) disturbances. Moreover, the enhanced role of the \(Dst\) disturbances in the \(Dst\) and \(Dst\) disturbances are also observed in the \(Dst\) and \(Dst\) cases. Figure 4: 2D histogram of the median value of the solar wind bulk speed \(V\) in the \(E-Dst\) plane observed during the maximum (**left panels**) and minimum (**right panels**) activity periods. First row: kinetic energy \(E_{v}\), second row: magnetic energy \(E_{b}\), third row: total energy \(E_{t}\), and fourth row: residual energy \(E_{r}=E_{v}-E_{b}\). of the solar wind bulk speed during minima is evident; conversely, at maxima, the geo-effectiveness is similar for all wind speeds.