Anomalously low proton temperatures in solar-wind following interplanetary shock waves, evidence for magnetic bottles

Occasionally, anomalously low values of the solar wind proton temperature Tp are observed when the solar wind velocity υ is high. A large fraction of such measurements by the Vela 3 satellites follow the passage of interplanetary shocks by some 20–60 hours. Of 24 postshock events in which υ exceeded 400 km sec−1 and for which Vela 3 measurements are available, 12 exhibited plasma states of anomalously low Tp, high υ. The proton density at the time of these observations typically was depressed below normal, and the velocity tended to be constant or falling. A very strong association with abnormally high (≥15%) concentrations of He++/H+ in the solar wind is noted for these anomalous proton temperatures, the usual temporal sequence of events at 1 AU being: (1) shock wave, (2) helium enrichment, and (3) low Tp, high υ. It is suggested that these observations are consistent with a model for some shock wave disturbances that includes the ejection of new material (distinguished by the helium enrichment at 1 AU) into the solar wind at the time of large solar flares and the formation of a magnetic bottle configuration in the solar wind behind and within the ejecta. The anomalously low proton temperatures then result from the adiabatic cooling of the plasma within the magnetic bottle.