Two models of cross polar cap potential saturation compared: Siscoe‐Hill model versus Kivelson‐Ridley model

Abstract

The cross polar cap potential is considered an instantaneous monitor of the rate at which magnetic flux couples the solar wind to the Earth's magnetosphere‐ionosphere system. Studies have shown that the cross polar cap potential responds linearly to the solar wind electric field under nominal solar wind conditions but asymptotes to the order of 200 kV for large electric field. Saturation of the cross polar cap potential is also found to occur in MHD simulations. Several mechanisms have been proposed to explain this phenomenon. Two well‐developed models are those of Siscoe et al . (2002), herein referred to as the Siscoe‐Hill model, and of Kivelson and Ridley (2008), herein referred to as the Kivelson‐Ridley model. In this study, we compare the mathematical formulas as well as the predictions of the two models with data. We find that the two models predict similar saturation limits. Their difference can be expressed in terms of a factor, which is close to unity during a saturation interval. A survey of the differences in the model predictions show that, on average, the potential of the Kivelson‐Ridley model is smaller than that of the Siscoe‐Hill model by 10 kV. Measurements of AMIE, DMSP, PC index, and SuperDARN are used to differentiate between the two models. However, given the uncertainties of the measurements, it is impossible to conclude that one model does a better job than the other of predicting the observed cross polar cap potentials. Key Points Siscoe‐Hill model and Kivelson‐Ridley model are saturation models. These two models predict similar saturated potentials. It is impossible to prefer one model given the uncertainties in observations.