Table 4.
Types of activity in the magnetospheric system
| Type | Explanation |
|---|---|
| Geomagnetic activity | The intensification of one of several current systems in the magnetosphere that can be measured by ground-based magnetometers |
| Dayside reconnection rate | Creation of magnetic connection between solar-wind plasma and the magnetosphere. Highly time variable with solar-wind time variations. Controls the amount of driving of the magnetosphere by the solar wind |
| Magnetotail growth/polar-cap size | Dayside reconnection adds magnetic flux into the magnetotail increasing the magnetic energy of the magnetospheric system |
| Magnetospheric convection | Transport of magnetic flux and plasma from the magnetotail into the dipolar region and then to the dayside magnetopause |
| Ionospheric convection | Horizontal transport of plasma from the dayside of the Earth to the nightside over the polar cap with lower-latitude return flows to the dayside |
| Magnetotail stretching | Intensification and earthward expansion of a cross-tail electrical current as flux is loaded into the magnetotail and as magnetospheric convection intensifies |
| Substorm occurrence | Large-scale morphological instability of the magnetotail. Produces enhanced transport in magnetosphere, injects energetic particles into dipolar region, greatly increases energy dissipation, is driver of enhanced auroral currents and particle precipitation |
| Global sawtooth oscillations | Large-scale morphological instability of the entire magnetosphere, dayside as well as nightside |
| Auroral currents | Field-aligned currents flowing between the nightside magnetosphere and the nightside ionosphere. Important for Joule dissipation of electromechanical energy |
| Auroral particle precipitation | Dissipation of magnetospheric energy. Produces localized enhanced electrical conductivity of the ionosphere |
| Ionospheric outflow | Upflow of ions into the magnetosphere in the cusp and auroral regions. Essential to build magnetospheric plasma populations. Eventually impacts dayside reconnection rate |
| Ring-current enhancement | Diamagnetic distortion of the dipolar magnetosphere caused by the particle pressure of the ion plasma sheet as the plasma-sheet population intensifies and moves into the dipole |
| Radiation-belt dropout | Sudden weakening of the intensity of the electron radiation belt in the early phases of a storm. Temporally correlated with an increase in solar-wind ram pressure |
| Radiation-belt intensification | Slow energization of the electron radiation belt during intervals of sustained magnetospheric driving by the solar wind |
| Storm | A strong elevation of all measures of magnetospheric activity associated with a feature in the solar wind that produces very strong driving of the magnetosphere. Two major types of storms: coronal-mass-ejection-driven and high-speed-stream-driven |
| Calm before the storm | Prior to most high-speed-stream-driven storms, there is a few-day period of anomalously low magnetospheric activity caused by a feature in the solar wind prior to the high-speed stream |