Plasmapause deformations in the frame of the
interchange instability mechanism
The mechanism of plasmapause formation based on interchange instability and a Kp-dependent magnetospheric electric field model, enables us to determine the position of the plasmapause as a function of Kp and local time. We illustrate here how this physical mechanism is able to account for the formation of shoulders like those observed by the Extreme Ultraviolet (EUV) imager onboard the IMAGE satellite. A wide variety of other structures observed by IMAGE like tails (also called plumes), and notches are also obtained with this mechanism for the formation of a "knee" in the high altitude cross-L distribution of the cold plasma density distribution.
Animation 1: Shoulder created during a sudden decrease of the level of geomagnetic activity as determined by the value of Kp illustrated in the top panel. The shoulder corotates with the plasmasphere. The vestigial plasmapause is still present, so that the cross-L density profile in the post-midnight sector has two separate knees.
Animation 2: Bump created after a sharp increase of the geomagnetic activity as determined by the sudden increase of Kp illustrated in the upper panel. The bump evolves into a plume.
Animation 3: Notch created by a short time burst enhancement in the level of geomagnetic activity determined by the value of Kp illustrated in the upper panel. The notch corotates with the plasmasphere.
The position of the plasmapause given by this model can be simulated on the ESA-SSA web site. The program retrieves the geomagnetic activity level index Kp observed during the date given as input and 24 hours before. Then, it calculates the position of the plasmapause for the required time period, assuming the corotation and using the convection electric field model E5D and the associated magnetic field M2. The mechanism for the formation of the plasmapause is assumed to be the quasi-interchange instability. Finally, the position of the plasmapause is plotted in the geomagnetic equatorial plane as a function of radial distance and MLT with 30 minutes intervals.
Animation A: This simulation shows the equatorial plasmapause during the geomagnetic substorm of 9 and 10 June 2001 found with an interchange simulation using the E5D Kp-dependent E-field model. The upper panels illustrate the Z component of the interplanetary magnetic field (Bz), the disturbed storm time index (Dst) and the geomagnetic activity index Kp. The observed Kp index increases during the geomagnetic substorm. This leads to the formation of a plume in the afternoon sector, rotating with the Earth. After the end of the substorm, a shoulder appears at the plasmapause.
Animation B: This simulation shows the equatorial cross section of the plasmasphere obtained during the same substorm of 9 to 10 June 2001 with a MHD simulation. The convection E-field model is also E5D. In this simulation, plasma elements are continuously released along an equatorial radius and drift as EXB/B². The plume formation is also well visible.
Plasmapause formation by the mechanism of interchange and its deformation
This movie is a digitalized version of a VHS video produced in 1983, at the Belgian Institute for Space Aeronomy (BISA), Brussels. It illustrates the formation of the plasmapause by the mechanism of the interchange motion which is driven convectively unstable in the night side local time sector due to enhanced magnetospheric convection during substorm events.
In this scenario the plasmapause is formed along the surface which is tangent to the Zero-Parallel-Force (ZPF) surface. The time-dependent deformations of the plasmapause displayed in this film are induced by a Kp-dependent convection electric field model, in response to variations of the level of geomagnetic activity. The dynamical development of "Shoulders" and "Tails" in the equatorial cross section of the plasmapause were foreseen in these simulations.
Lemaire's simulation can be accessed by clicking on
http://www.aeronomie.be/dist/lemaire/plasmapause-uk.mov (750 MB!!)
References for interchange simulations:
Lemaire J., The "Roche-Limit" of the ionospheric plasma and the formation of the plasmapause, Planet. Space Sci., 22, 757-766, 1974.
Corcuff Y, P. Corcuff, P and J. Lemaire, Dynamical plasmapause positions during the July 29-31, 1977 storm period: a comparison of observations and time-dependent model calculations, Ann. Geophys., 3, 569-579, 1985.
Lemaire J., The formation plasmaspheric tails, Phys. Chem. Earth (C), 25, 9-17, 2000.
Pierrard V. and J. Lemaire, Development of shoulders and plumes in the frame of the interchange instability mechanism for plasmapause formation, Geophys. Res. Lett., 31, L05809, doi:10.1029/2003GL018919, 2004.
Pierrard V. and J. Cabrera, Comparisons between EUV/IMAGE observations and numerical simulations of the plasmapause formation, Ann. Geophys., 23, 2635-2646, 2005.
Pierrard V. and J. Cabrera, Dynamical simulations of plasmapause deformations, Space Sci. Rev., 122, 119-126, 2006.
Pierrard V. and K. Stegen, A three-dimensional dynamic kinetic model of the plasmasphere, J. Geophys. Res., 113, A10209, doi:10.1029/2008JA013060, 2008.
Reference for MHD simulations compared to interchange simulations:
Lemaire J. and V. Pierrard, Comparison between two theoretical mechanisms of the plasmapause formation and relevant observations, Geomagnetism and Aeronomy, 48(5), 553-570, 2008.
Pierrard V., G. Khazanov, J. Cabrera and J. Lemaire, Influence of the convection electric field models on predicted plasmapause positions during the magnetic storms, J. Geophys. Res., 113, A08212, doi:10.1029/2007JA012612, 2008.