DP3 system, available under conditions of northward IMF, consists of two current vortices of opposite polarity disposed in the limited near-pole area. The DP3 disturbances are typical of the summer sunlit polar cap; intensity of the DP3 disturbances in winter season is usually negligible. The current system of DP4 disturbances related to the IMF BY component includes currents flowing in the day-time cusp region along geomagnetic latitudes Φ ~ 78-80°, the current direction, opposite in summer and winter polar caps, being dependent on the IMF BY sign.
DP4 magnetic disturbances were separated originally as related to the IMF sector structure. The term “sector structure” (SS) denotes separation of the large-scale solar wind structure on an even number of sectors with opposite polarity of the radial BX IMF component. The SS periodicity is determined by the solar corona magnetic field extending into the space and can remain unchanged during solar rotation period of ~ 27 days. The SS polarity is defined by the sign of the IMF radial (BX) component in GSM coordinate system. The SS effect is positive if BX>O (usually, in combination with the negative tangential IMF component BY<0) and it is negative if BX<0 (and BY>0). Later it has been shown that the SS-associated magnetic disturbances are determined by variations of the IMF azimuthal component. Analysis has revealed that the polar cap magnetic disturbances are related to the BZ and BY IMF components, whereas the radial BX component is almost ineffective.
Author(s) Details:
A. Troshichev
Arctic and Antarctic Research Institute, Russia.
Recent Global Research Developments in DP3 and DP4 Magnetic Disturbances: Influence of IMF Components and Sector Structure
The Polar Cap Magnetic Activity (PC Index):
- The PC index serves as a valuable tool for monitoring and nowcasting magnetospheric disturbances. Initially introduced as a characteristic of polar cap magnetic activity resulting from geoeffective solar wind coupling with the magnetosphere, subsequent research revealed interesting relationships.
- The PC index closely follows changes in the solar wind electric field (EKL) through the field-aligned current system (R1 FAC). Variations in solar wind parameters influence the PC index value, which typically has a threshold level of around 1.5 ± 0.5 mV/m.
- Appearance of magnetospheric disturbances is associated with the PC index value and its growth rate. Interestingly, the progression of disturbances correlates linearly with the PC magnitude, impacting substorms (AL) and magnetic storms (Dst).
- Statistically, the PC index now serves as a proxy for solar wind energy input into the magnetosphere. Unlike satellite-based methods, the PC index provides real-time information on magnetic activity in both the northern (PCN) and southern (PCS) polar caps, aiding in monitoring and predicting magnetic disturbances [1].
DP3 and DP4 Disturbances:
- DP3 disturbances occur in the sunlight summer polar cap under conditions of northward interplanetary magnetic field (IMF). These disturbances are characterized by variations in the near-pole magnetic field.
- DP4 disturbances, on the other hand, are related to azimuthal IMF components. They exhibit a combined effect with DP2 or DP3 current systems, leading to deformation of the DP2 (or DP3) current vortex in the northern polar cap. Specifically, the evening DP2 current vortex expands into the dawn sector under certain B Y conditions [2].
References
- Troshichev, O. A. (2022). The Polar Cap Magnetic Activity (PC Index) as a Tool of Monitoring and Nowcasting the Magnetospheric Disturbances. In Magnetosphere and Solar Winds, Humans and Communication. IntechOpen. https://www.intechopen.com/chapters/81259
- Troshichev, O., Janzhura, A. (2012). Physical background (historical outline). In: Space Weather Monitoring by Ground-Based Means. Springer Praxis Books(). Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-642-16803-1_2
- Troshichev OA (2022) PC index as a ground-based indicator of the solar wind energy incoming into the magnetosphere: (1) relation of PC index to the solar wind electric field EKL. Front. Astron. Space Sci. 9:1069470. doi: 10.3389/fspas.2022.1069470