241 research outputs found
Diamagnetic depression observations at Saturnâs magnetospheric cusp by the Cassini spacecraft
The magnetospheric cusp is a region where shocked solar wind plasma can enter a planetary magnetosphere, after magnetic reconnection has occurred at the dayside magnetopause or in the lobes. The dense plasma that enters the highâlatitude magnetosphere creates diamagnetic effects whereby a depression is observed in the magnetic field. We present observations of the cusp events at Saturnâs magnetosphere where these diamagnetic depressions are found. The data are subtracted from a magnetic field model, and the calculated magnetic pressure deficits are compared to the particle pressures. A high plasma pressure layer in the magnetosphere adjacent to the cusp is discovered to also depress the magnetic field, outside of the cusp. This layer is observed to contain energetic He++ (up to âź100Â keV) from the solar wind as well as heavy water group ions (W+) originating from the moon Enceladus. We also find a modest correlation of diamagnetic depression strength to solar wind dynamic pressure and velocity; however, unlike at Earth, there is no correlation found with He++ counts.Key PointsDiamagnetic depressions are found in the cusp and are observed to continue into the adjacent magnetosphereA heated plasma layer of mixed composition is found to depress the adjacent magnetospheric fieldDiamagnetic depression strength is correlated to solar wind dynamic pressure and velocity but not to the observed He++ counts, like at EarthPeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/137687/1/jgra53517_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/137687/2/jgra53517-sup-0001-supinfo.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/137687/3/jgra53517.pd
Testing the necessity of transient spikes in the storm time ring current drivers
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95070/1/jgra20908.pd
Influence of epoch time selection on the results of superposed epoch analysis using ACE and MPA data
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94710/1/jgra19440.pd
Internally driven large-scale changes in the size of Saturnâs magnetosphere
Saturnâs magnetic field acts as an obstacle to solar wind flow, deflecting plasma around the planet and forming a cavity known as the magnetosphere. The magnetopause defines the boundary between the planetary and solar dominated regimes, and so is strongly influenced by the variable nature of pressure sources both outside and within. Following from Pilkington et al. (2014), crossings of the magnetopause are identified using 7 years of magnetic field and particle data from the Cassini spacecraft and providing unprecedented spatial coverage of the magnetopause boundary. These observations reveal a dynamical interaction where, in addition to the external influence of the solar wind dynamic pressure, internal drivers, and hot plasma dynamics in particular can take almost complete control of the systemâs dayside shape and size, essentially defying the solar wind conditions. The magnetopause can move by up to 10â15 planetary radii at constant solar wind dynamic pressure, corresponding to relatively âplasma-loadedâ or âplasma-depletedâ states, defined in terms of the internal suprathermal plasma pressure
Longâlived plasmaspheric drainage plumes: Where does the plasma come from?
Longâlived (weeks) plasmaspheric drainage plumes are explored. The longâlived plumes occur during longâlived highâspeedâstreamâdriven storms. Spacecraft in geosynchronous orbit see the plumes as dense plasmaspheric plasma advecting sunward toward the dayside magnetopause. The older plumes have the same densities and local time widths as younger plumes, and like younger plumes they are lumpy in density and they reside in a spatial gap in the electron plasma sheet (in sort of a drainage corridor). Magnetosphericâconvection simulations indicate that drainage from a filled outer plasmasphere can only supply a plume for 1.5â2âdays. The question arises for longâlived plumes (and for any plume older than about 2âdays): Where is the plasma coming from? Three candidate sources appear promising: (1) substorm disruption of the nightside plasmasphere which may transport plasmaspheric plasma outward onto open drift orbits, (2) radial transport of plasmaspheric plasma in velocityâshearâdriven instabilities near the duskside plasmapause, and (3) an anomalously high upflux of cold ionospheric protons from the tongue of ionization in the dayside ionosphere, which may directly supply ionospheric plasma into the plume. In the first two cases the plume is drainage of plasma from the magnetosphere; in the third case it is not. Where the plasma in longâlived plumes is coming from is a quandary: to fix this dilemma, further work and probably fullâscale simulations are needed. Key Points Plasmaspheric drainage plumes can persist for weeks The source of the plasma supplying the longâlived plumes is unknown Candidate sources include outflow from the tongue of ionizationPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/108632/1/jgra51234.pd
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