The lifetime of a depression in the plasma density over Jicamarca produced by space shuttle exhaust in the ionosphere

Abstract

When the Space Shuttle Orbiting Maneuver Subsystem (OMS) engines bum in the ionosphere, a plasma density depression or "hole" is produced. Charge exchange between the exhaust molecules and the ambient o+-ions yields molecular ions beams that eventually recombine with electrons. The resulting plasma hole in the ionosphere can be studied with ground based, incoherent-scatter radars (ISR' s ). This type of ionospheric modification is being studied during the Shuttle Ionospheric Modification with Pulsed Localized Exhaust (SIMPLEX) series of experiments over ISR systerns located around the globe. The SIMPLEX I experiment occurred over Jicamara, Peru in the aftemoon on 4 October 1997 during the Shuttle Mission STS-86. An electron density depression was produced at 359-km altitude on the rnid-point of a magnetic field line. The experiment was scheduled when there were no zonal drifts of the plasma so the modified field-line remained fixed over the 50 MHz, Jicamarca radar. The density depression was filled in by plasma flowing along the magnetic field line with a time constant of 4.5 minutes. The density perturbation has completely vanished 20 minutes after the engine bum. The experimental measurements were compared with two models: (1) SAMI2 a fully numerical model of the F­region, and (2) an analytic representation of field-aligned transport by arnbipolar diffusion. The computed recovery time from each model is much longer than the observed recovery time. The theory of arnbipolar diffusion currently used in ionospheric models seems to be inadequate to describe the SIMPLEX I observations. Several possible sources for this discrepancy are discussed. The SIMPLEX I active experiment is shown to have the potential for testing selected processes in ionospheric models.