Statics and dynamics of Giacobini‐Zinner magnetic tail

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Abstract
We subject the data ICE collected in its traverse of the tail of Giacobini‐Zinner to the requirements of stress balance. The result provides estimates for unmeasured quantities. We note that unlike planetary magnetotails, the comet's tail is embedded in an ionosheath that has a static pressure nearly equal to the solar wind stagnation pressure. This leads to a large lobe field strength. Transverse pressure balance reveals a systematic variation in the ion temperature across the tail which in turn tells how the pick‐up velocity of new ions varies across the pick‐up region. We find the pick‐up velocity increases from 14 km s−1 in the plasma sheet to 46 km s−1 in the ionosheath. This is the same velocity shear that stretches the magnetic field to form the tail. Imposing axial stress balance leads to an expression for the strength of the lobe field which reveals that it varies weakly with axial distance. The expression also gives an estimate of 24 km s−1 for the plasma sheet velocity at ICE's location. We find that the plasma takes between 7 and 13 minutes to flow through the coma to the position of ICE in the plasma sheet.