Saturn's auroral/polar H3+ infrared emission: The effect of solar wind compression

Abstract

Previous investigations into Saturn's aurora have shown that they are strongly controlled by the solar wind. Here, for the first time, we use a combination of ground‐based infrared observations of the aurora and in situ measurements of the magnetosphere in order to better understand this association. We show that large‐scale variability in both the intensity and ion flow velocities can be directly correlated with the solar wind dynamic pressure, with, in particular, the arrival of solar wind compressions. Large compressions in the solar wind trigger the same morphological changes in the auroral structure as have previously been seen in UV images, and these are accompanied by the loss of the open field line corotation region seen in the velocity measurements. This region has been explained as an “old core” of magnetic field lines open to the solar wind, protected from reconnection due to the twisting in the magnetotail, and therefore requires that this region be removed only by major compressions in the solar wind; thus, our observations here generally agree with this model. In addition, we have observed a >8 h delay between the arrival of a major compression and the resulting effect upon the aurora, suggesting that reconnection must either occur well into the tail or that there are other processes in the chain of events that lead to the major dawn brightening seen in both these observations and previously studied UV images.