A statistical investigation of dayside magnetosphere erosion showing saturation of response


We present a statistical investigation of dayside magnetospheric erosion based on a survey of 316 cases in 1996–2004. We monitor erosion through the depression in the strength of the terrestrial magnetic field at geostationary heights using magnetic field observations acquired by four GOES spacecraft 2 hours on either side of local magnetic noon. The southward component of the interplanetary magnetic field (IMF) and the solar wind dynamic pressure, quantities which are responsible for opposing effects on the geostationary field, are obtained from the Wind and ACE spacecraft. We extend our previous work to encompass the Bz range [0, −35] nT. We find that dayside erosion saturates when IMF Bz is in the range [−12, −16] nT. This result is consistent with global simulations. With the measured solar wind velocity, this corresponds to an interplanetary electric field (IEF) of 6.2 ± 1.6 mV m−1. We discover that the maximum depression of the geostationary field at saturated erosion is ∼26 nT. In addition, we reveal a direct relation between the saturation of flux erosion of the dayside magnetosphere and that of the cross-polar cap potential (CPCP), both of which occur at approximately the same electric field. For the latter, we apply the Hill-Siscoe model for the calculation of CPCP to our data set. We find the CPCP to deviate from a linear increase with IEF at ∼4 and 7 mV/m, which correspond closely to the IEF range at which we find saturation of dayside erosion to start to manifest itself.

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JGR: Space Physics



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