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In the equatorial ionosphere of the Earth , the wind driven currents coupled with the Earth's primarily
horizontal magnetic field produce the EEF. The EEF is known to be highly variable from day to day, primarily
as a result of solar wind electric fields penetrating from high latitudes to the equator, in addition to
variabilities in the neutral winds coming from below. Around 30% of the EEF variability can be attributed to
the effect of solar wind on the Earth’s magnetosphere. The interplanetary electric fields (IEF) ,
generated by the convection movement of the solar wind across the interplanatry magnetic field (E = -V x B)
appear instantaneously in the magnetosphere and ionosphere. This process is called prompt penetration of the
solar-wind electric fields. The strikingly linear relationship between IEF and EEF was used to develop a
frequency dependent model of the prompt penetration effect. The transfer function was derived from 8 years of
IEF data from the ACE satellite, radar data from JULIA, and magnetometer data from the CHAMP satellite.
Using the real-time data from ACE, the transfer function models the current variations in the equatorial
ionospheric electric fields. In addition, the propagation delay from L1 point to the Earth allows for more
than 1 hour advance prediction of the EEF.
References:
Manoj, C., S. Maus, and P. Alken (2013), Long-period prompt-penetration electric fields derived from CHAMP satellite magnetic measurements, J. Geophys. Res. Space Physics, 118, 5919–5930, doi:10.1002/jgra.50511.
Manoj, C., and S. Maus (2012), A real-time forecast service for the ionospheric equatorial zonal electric field, Space Weather, 10, S09002, doi:10.1029/2012SW000825.
Manoj, C., S. Maus, H. Lühr, and P. Alken (2008), Penetration characteristics of the interplanetary electric field to the daytime equatorial ionosphere, J. Geophys. Res., 113, A12310, doi:10.1029/2008JA013381.
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