STREAM INTERFACES AND ENERGETIC IONS CLOSER THAN EXPECTED - ANALYSES OF PIONEER-10 AND PIONEER-11 OBSERVATIONS

An empirical study of corotating interaction regions (CIRs) observed b etween 3.9 AU and 5.9 AU on Pioneers 10 and 11 shows that the main cor otation energetic ion population (CEIP), which is associated with the trailing reverse shock, terminates within the CIR at a definite, struc tural boundary, which we show here is the stream interface. This new r esult has significant implications for solar wind and energetic partic le modeling. In particular it implies either that the reverse shock fo rms closer to the stream interface than models suggest or that the the ories that treat the generation and transport of these energetic ions, such as preshock Fermi acceleration and cross-field diffusion must be combined or extended. We test these scenarios by comparing the CEIP i ntensity profiles on the two sides of the stream interface. We find th at while each automatically accounts for one or two aspects of the res ults none of them alone can account for all of our empirical results.