Similarity and difference of the durations of the small-scale solar wind structure boundaries by multipoint observations

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This report presents observations of very fast (from a few seconds to a hundred seconds) and large (from 50% up to several hundred percents) changes in the solar wind ion flux. These changes are connected with the sharp boundaries of solar wind small-scale and middle-scale structures that may be as thin as tens of proton gyroradii. These observations of solar wind plasma and magnetic field changes were performed aboard the Interball-1 satellite with very high time resolution (1 s or 60 ms) and “simultaneously” by the WIND spacecraft with a time resolution of 3 s and in some cases also by the Geotail satellite with resolution of 12 s. We found some events in which boundaries of the very fast changes of the solar wind ion flux and magnetic field have similar thicknesses and amplitudes over the hour it takes the solar wind to propagate from WIND to Interball-1 and Geotail. In many cases, we find that event boundaries which have durations of 20–100 s at WIND 50–200 R E upstream of Earth are steeper, with durations of 3–10 s, at Interball-1 and Geotail near Earth. These differences result from local irregularities along the disturbance fronts or from the steepening of these boundaries as they move together with the solar wind.