Cassini plasma observations of Saturn's magnetospheric cusp

Abstract

The magnetospheric cusp is a funnel‐shaped region where shocked solar wind plasma is able to enter the high‐latitude magnetosphere via the process of magnetic reconnection. The plasma observations include various cusp signatures such as ion energy dispersions and diamagnetic effects. We present an overview analysis of cusp plasma observations at the Saturnian magnetosphere from the Cassini spacecraft era. A comparison of the observations is made as well as classification into groups due to varying characteristics. The locations of the reconnection site are calculated and shown to vary along the subsolar magnetopause. We show the first in situ evidence for lobe reconnection that occurred at nearly the same time as dayside reconnection for one of the cusp crossings. Evidence for “bursty” and more “continuous” reconnection signatures is observed at different cusp events. The events are compared to solar wind propagation models, and it is shown that magnetic reconnection and plasma injection into the cusp can occur for a variety of upstream conditions. These are important results because they show that Saturn's magnetospheric interaction with the solar wind and the resulting cusp signatures are dynamic and that plasma injection in the cusp occurs due to a variety of solar wind conditions. Furthermore, reconnection can proceed at a variety of locations along the magnetopause.

Diamagnetic depression observations at Saturn's magnetospheric cusp by the Cassini spacecraft

“…The injected plasma displays various signatures, such as ion energy dispersions and depressions of the local magnetic field. This process and the associated cusp signatures have been observed at the Earth (see recent reviews by Smith and Lockwood [1996] and Cargill et al [2005]), Mercury [e.g., Winslow et al, 2012;Raines et al, 2014], and Saturn [Jasinski et al, 2014[Jasinski et al, , 2016aArridge et al, 2016].…”

Energetic Electron Periodicities During the Cassini Grand Finale

“…The mass from the solar wind would presumably enter the high‐latitude magnetosphere through the cusps in some reconnective process. However, a recent study of Saturn's high‐latitude cusps indicates that the region is highly variable, and steady reconnection does not occur (e.g., Jasinski et al, ). Given this variability, any transfer of mass should also be variable, so the ionosphere would not be smoothly loaded and the consequent periodicity would not be as stable as observed.…”

Saturn's Open‐Closed Field Line Boundary: A Cassini Electron Survey at Saturn's Magnetosphere

“…There is a clear boundary between the two plasma regimes, which identifies the boundary between magnetospheric field lines that are open to the solar wind (magnetic field is tethered to the ionosphere in one hemisphere) and fields that are closed (both footpoints of the magnetic field are tethered to the ionosphere), otherwise known as the OCB. This boundary contains Saturn's magnetospheric cusp (Jasinski et al, ; Jasinski, Arridge, et al, ; Jasinski, Arridge, et al, ; Arridge et al, ).…”

“…At the dayside magnetopause and the magnetotail, Dungey‐type magnetic reconnection occurs to open and close magnetospheric flux, respectively. On the dayside, this involves injecting plasma from the magnetosheath into the high‐latitude open magnetosphere and into the region called the cusp (Jasinski et al, ; Jasinski, Arridge, et al, ). Both the northern and southern cusp have been measured at Saturn's magnetosphere (Arridge et al, ; Jasinski, Arridge, et al, ).…”