Simultaneous in situ magnetospheric and ionospheric detection of detached plasmas

On January 19, 1972, in situ measurements by Explorer 45, orbiting in the magnetosphere near the equatorial plane, and ISIS 2, in a circular polar orbit at 1400 km, simultaneously detected patches of enhanced ionization outside the main body of the plasmasphere. The magnetospheric plasma region extended between (geomagnetic latitude) L values 3.4-4.8 and the ionospheric electron density enhancement extended between L values 3.6-4.4. The two plasma features were detected near 22 hours magnetic local time (MLT). Based on a number of observations, it is inferred that the plasma density enhancement persisted for more than 5 hours and extended over at least 2 hours in MLT near L = 5. These results provide experimental evidence that some detached magnetospheric plasma regions are signatures of a flux tube containing enhanced ionization throughout a volume extending from the topside ionosphere out to the equator.