AMPTE lithium tracer releases in the solar wind: Observations inside the magnetosphere

Abstract

A release of approximately 3.3×1025 lithium atoms was made on September 11 and again on September 20, 1984, by the Active Magnetospheric Particle Tracer Explorers (AMPTE) Ion Release Module (IRM) spacecraft at a geocentric distance of ≈ 18.8 Re in the subsolar direction, creating an ion cloud approximately 4 Re in diameter after one hour. Detailed modeling of ion propagation to the bow shock and transport through the magnetosheath shows that ≳20% (September 11) and ≳50% (September 20) of the ions mapped to a 36‐Re² area around the stagnation point on the magnetopause. The AMPTE Charge Composition Explorer (CCE) satellite, located inside the magnetosphere with an apogee of 8.78 Re and inclination of 4.8°, at a local time of about 1300 MLT, was instrumented to detect lithium ions over the energy range from a few eV to ≳6 MeV. Detailed analysis of the data for the several hours following the lithium releases shows that no measurable lithium ion fluxes reached the location of the CCE; upper limits to the lithium flux at L ≳ 8 are about 50 to 70 (cm2‐sec‐sr)−1 in the range 25–300 keV/e (Li/H ≳ 2×10−5), and about 0.1 to 1 (cm²‐sec‐sr)−1 in the range 45–100 keV/nucleon (Li/H ≈ 1×10−6). The implications of these results are discussed in the context of current theoretical models of plasma entry into and transport within the magnetosphere.