Phase space variations of near equatorially mirroring ring current ions

<jats:p>We present Isee 1 observations of near equatorially mirroring ring current ions before and after the magnetic storm of November 25–26, 1977. The data are presented as phase space densities, <jats:italic>f</jats:italic> (s³/cm<jats:sup>6</jats:sup>), versus the first adiabatic invariant, µ (MeV/G), for the <jats:italic>L</jats:italic> range ∼2.7–8 <jats:italic>R<jats:sub>E</jats:sub></jats:italic>. The µ range covered varies from ∼50–1000 MeV/G at <jats:italic>L</jats:italic>=8 to ∼1–100 MeV/G at <jats:italic>L</jats:italic>=2.7. The prestorm phase space densities show an intensity peak at a µ value which varies with <jats:italic>L</jats:italic> as µ<jats:sub>peak</jats:sub> ∼38 MeV/G for 5 ≲<jats:italic>L</jats:italic> ≲8 and µ<jats:sub>peak</jats:sub> ∼ 10<jats:italic>e</jats:italic><jats:sup>0.7(<jats:italic>L</jats:italic>−3)</jats:sup> for 2.7 ≲ <jats:italic>L</jats:italic> ≲5. Phase space densities remain nearly constant throughout the storm for µ values greater than µ<jats:sub>peak</jats:sub> and are enhanced for µ values less than µ<jats:sub>peak</jats:sub>. Thus high‐energy ions respond adiabatically to the magnetic field changes caused by the low‐energy ion enhancements. This result agrees with earlier Explorer 45 results (Lyons and Williams, 1976). The Isee 1 data are compared directly with the Explorer 45 data and are found to agree very well. The time difference of ∼6 years and local time separation of ∼12 hours between the two data sets lead to the conclusion that the ring current ion behavior presented here is a characteristic feature of geomagnetic storms.</jats:p>