Penetration of Solar Wind and Magnetospheric Electric Fields to the Inner Magnetosphere

Details Penetration of Solar Wind and Magnetospheric Electric Fields to the Inner Magnetosphere Penetration of Solar Wind and Magnetospheric Electric Fields to the Inner Magnetosphere

Dec 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agufmsa44a..02k&link_type=abstract

American Geophysical Union, Fall Meeting 2006, abstract #SA44A-02

Physics

2411 Electric Fields (2712), 2415 Equatorial Ionosphere, 2736 Magnetosphere/Ionosphere Interactions (2431), 7904 Geomagnetically Induced Currents, 7954 Magnetic Storms (2788)

Scientific paper

Almost 40 years ago Nishida showed that magnetic field fluctuations measured in the solar wind were sometimes highly correlated with magnetic fields measured near the magnetic equator. With the development of electric field measurements, tracking the chain of events from the solar wind to the inner magnetosphere is now possible. Here we present several case studies illustrating this chain. We often find almost identical waveforms for the dawn-to-dusk component of the interplanetary electric field (IEF) and the zonal component of the ionospheric field at latitudes from the auroral zone to the equator. The response is symmetric in that the inner magnetosphere responds to both IEF increases and decreases, implying that an energy storage element in the system can be traced to inductance of the ring current. Thus, when the IEF abruptly turns toward the dusk-to-dawn direction, the inner magnetospheric current system (region 2 currents) continues to flow, with a portion closing in the ionosphere. Likewise, when the IEF dawn-to-dusk component increases, region 1 currents intensify but region 2 currents cannot change immediately. Again, this imbalance is associated with currents in the inner ionosphere. To study the temporal response of this system, four years of electric field data were compared to the IEF using ACE data. The ratio of these parameters is like a transfer function (TF) between the interplanetary and ionospheric systems, which is a function of frequency. Using the average of many such TFs revealed a distinct logarithmic dependence on Kp with a 16 db difference between low and high values. The average TF is significant for periods from 30 min. to 6 hours and displays a small peak near a 1 hour period, suggesting that some capacitance exists in the system and possibly a weak resonance. The average TF indicates that about 3% of the IEF appears in the equatorial ionosphere whereas case studies indicate values as high as 10%. Case studies also show a higher frequency response than the average TF since sharp transitions in the IEF are also seen in equatorial fields, suggesting that wavelet analysis might be more accurate than Fourier methods. We have studied penetration events from widely different longitudes and are building a better understanding of this world-wide effect.

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