Average configuration of the distant (<220 R_e) magnetotail: Initial ISEE‐3 magnetic field results

Abstract

Magnetic field measurements from the first two passes of the ISEE‐3 GEOTAIL Mission have been used to study the structure of the trans‐lunar tail. Good agreement was found between the ISEE‐3 magnetopause crossings and the Explorer 33,35 model of Howe and Binsack. Neutral sheet location was well ordered by the hinged current sheet models based upon near earth measurements. Between X=−20 R e and −120 R e the radius of the tail increases by about 30% while the lobe field strength decreases by approximately 60%. Beyond X=−100 to −120 R e the tail diameter and lobe field magnitude become nearly constant at terminal values of approximately 60 R e and 9 nT, respectively. These results are consistent with pressure balance across the distant magnetopause equating lobe field pressure, B² L /8π, and external solar wind thermal and magnetic pressure, nk(T e +T i ) + B²/8π. The distance at which the tail was observed to cease flaring, 100‐120 R e , is in close agreement with the predictions of the analytic tail model of Coroniti and Kennel. Overall, the findings of this study suggest that the magnetotail retains much of its near earth structure out to X=−220 R e .