Sharp boundaries of small- and middle-scale solar wind structures

[1] This work reviews the characteristics of sharp ( less than 10 min) and large (> 0.5 x 10(8) cm(-2) s(-1)) solar wind ion flux changes which are not due to shocks. These changes are boundaries of small- and middle-scale solar wind plasma structures. We present examples and statistical results from simultaneous plasma and magnetic field measurements by Interball-1 and Wind from 1996 to 1999. The behavior of the solar wind bulk velocity, temperature, and interplanetary magnetic field ( IMF) during these changes is described. We show that in many cases pressure balance is not maintained across these structures and discuss possible implications. In 50% of the events the sharp boundaries are pressure balanced structures; these events are probably tangential discontinuities. We use multipoint measurements of the sharp discontinuities to determine the orientation of the plasma fronts; many fronts are at large angles to the solar wind flow direction. We show that these events can be geoeffective and produce sharp changes in the magnetic field at geosynchronous orbit and on the ground.