Scales of heliospheric current sheet coherence between 1 and 5 AU

The structure of the heliospheric current sheet (HCS) at Ulysses and at Win d is compared during the period of near-radial alignment in 1998. Electron heat flux and magnetic field data are used to determine true magnetic field polarity. During the solar rotation period surrounding alignment there was considerable disagreement between the HCS crossings at Wind and those pred icted from the corresponding source surface map, both in number and in loca tion, consistent with the disordered, temporally varying solar wind at this ascending phase of the solar cycle. Despite this complexity the four cross ings closest to the time of radial alignment at Wind were successfully iden tified in Ulysses data with use of a one-dimensional hydrodynamic code. Fur ther, minimum variance analysis for the first two crossings, which were sep arated by only 16 hours at Wind, indicated coherent propagation of a large- scale warp in the HCS. Analysis of the local structure of the HCS on the fo ur crossings, however, revealed a high level of variability both from case to case and from one spacecraft to the other. For example, the third crossi ng at Wind was a single-sheet crossing adjacent to structures with fields f olded back on themselves and a brief period of counterstreaming electrons i mplying a transient structure. At Ulysses multiple sheets were encountered. At the fourth crossings Wind passed through a counterstreaming event with a flux rope signature containing a south pointing axis, while Ulysses passe d through a flux tube with little field rotation and northward pointing fie ld. The results are consistent with the view that the heliospheric current sheet is coherent as a global structure but highly variable in local struct ure over angular distances of a few degrees.