The Seasonal Dependence of Saturn's Apparent Rotation Period

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Abstract Brooks et al. (2019), https://doi.org/10.1002/2019ja026870 developed a model to explain the observed dual‐periodicity observed in Saturn's magnetosphere. They posited that the northern and southern neutral thermospheres have different angular velocities because of unequal conductances leading to unequal coupling with the magnetosphere. In particular, currents to the hemisphere with stronger conductance should be higher than those to the other hemisphere. To do so, they applied a model developed previously to explain the relative insensitivity of the Io plasma torus at Jupiter to short‐period temporal fluctuations in the magnetosphere. In response, Cowley et al. (2020), https://doi.org/10.1029/2020ja028247 provided a valuable analysis of Cassini magnetometer data that calculated the torques exerted in each hemisphere as a function of latitude. In contrast to the predictions of Brooks et al., Cowley et al. found that the torque imbalance in the auroral zone was quite modest. In this paper we resolve the matter by solving time‐dependent versions of the original equations and arrive at results that are quite similar to the data presented by Cowley et al. A key step is removing the influence of currents that cross the auroral zone without diverging.

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