scholarly journals A new formulation for the ionospheric cross polar cap potential including saturation effects

2005 ◽  
Vol 23 (11) ◽  
pp. 3533-3547 ◽  
Author(s):  
A. J. Ridley

Abstract. It is known that the ionospheric cross polar cap potential (CPCP) saturates when the interplanetary magnetic field (IMF) Bz becomes very large. Few studies have offered physical explanations as to why the polar cap potential saturates. We present 13 events in which the reconnection electric field (REF) goes above 12mV/m at some time. When these events are examined as typically done in previous studies, all of them show some signs of saturation (i.e., over-prediction of the CPCP based on a linear relationship between the IMF and the CPCP). We show that by taking into account the size of the magnetosphere and the fact that the post-shock magnetic field strength is strongly dependent upon the solar wind Mach number, we can better specify the ionospheric CPCP. The CPCP (Φ) can be expressed as Φ=(10-4v2+11.7B(1-e-Ma/3)sin3(θ/2)) {rms/9 (where v is the solar wind velocity, B is the combined Y and Z components of the interplanetary magnetic field, Ma is the solar wind Mach number, θ=acos(Bz/B), and rms is the stand-off distance to the magnetopause, assuming pressure-balance between the solar wind and the magnetosphere). This is a simple modification of the original Boyle et al. (1997) formulation.

2017 ◽  
Vol 44 (23) ◽  
pp. 11,729-11,734 ◽  
Author(s):  
Dong Lin ◽  
Binzheng Zhang ◽  
Wayne A. Scales ◽  
Michael Wiltberger ◽  
C. Robert Clauer ◽  
...  

2012 ◽  
Vol 30 (6) ◽  
pp. 927-928 ◽  
Author(s):  
M. C. Kelley

Abstract. The solar wind inputs considerable energy into the upper atmosphere, particularly when the interplanetary magnetic field (IMF) is southward. According to Poynting's theorem (Kelley, 2009), this energy becomes stored as magnetic fields and then is dissipated by Joule heat and by energizing the plasmasheet plasma. If the IMF turns suddenly northward, very little energy is transferred into the system while Joule dissipation continues. In this process, the polar cap potential (PCP) decreases. Experimentally, it was shown many years ago that the energy stored in the magnetosphere begins to decay with a time constant of two hours. Here we use Poynting's theorem to calculate this time constant and find a result that is consistent with the data.


2017 ◽  
Vol 3 (3) ◽  
pp. 15-19
Author(s):  
Владимир Мишин ◽  
Vladimir Mishin ◽  
Юрий Караваев ◽  
Yuriy Karavaev

From data of three three superstorms we study new features of the saturation process of the polar cap magnetic flux deceleration of its area at strengthening the solar wind (SW). It is shown that the saturation of the polar cap is observed at growth of the SW dynamic pressure and vertical IMF component for both signs. Saturation is realized not only during the passage of interplanetary magnetic clouds, but also at significant enhancement of SW density, when the SW thermal pressure is comparable with the pressure of the interplanetary magnetic field. We assume that at such condiitions the saturation is caused not only by a decrease in the efficiency of reconnection at the dayside magnetopause, but mainly by a finite magnetosphere compressibility –stopping the magnetopause compression due to the rapid Eathward growth of the geomagnetic field, ie, interior magnetospheric structure of the geomagnetic field


1993 ◽  
Vol 98 (A7) ◽  
pp. 11449 ◽  
Author(s):  
A. Nishida ◽  
T. Mukai ◽  
H. Hayakawa ◽  
N. Kaya ◽  
M. Fujimoto

2007 ◽  
Vol 25 (2) ◽  
pp. 533-542 ◽  
Author(s):  
A. J. Ridley

Abstract. A number of recent studies have shown that the upstream Mach number may play a significant role in the energy transfer between the solar wind and the magnetosphere. Magnetohydrodynamic (MHD) simulation results of the magnetosphere-ionosphere system are presented that show the transition from nominal solar wind and interplanetary magnetic field driving to extremely strong driving. One of the predominant features of the magnetosphere that becomes apparent during low Mach number conditions is the formation of Alfvén wings above and below the magnetosphere. Alfvén wing are cavities of low flow, and have been observed at Io and Ganymede, both of which reside in regions of sub-Alfvénic flow. It is shown that Alfvén wings exist even during nominal Mach number time periods – the wings fold over to form what has been classically viewed as the magnetotail. The regions of low flow within the Alfvén wing limit the electric field applied across the ionosphere, hence causing the ionospheric cross polar cap potential to be dependent upon the Mach number, and in turn, causing the saturation of the potential.


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