Geos 2 identification of rapidly moving current structures in the equatorial outer magnetosphere during substorms

摘要: The ULF magnetic and the dc electric antennas operating onboard GEOS have been used to study origin characteristics of short irregular pulsations (SIP's). Strong SIP's are always observed during substorm “onsets”, which characterized by an abrupt change field from a taillike configuration more dipolar one is known be associated with rapid poleward displacement aurorals forms in vicinity line. By applying three-component signal complex processing it possible demonstrate that most fact signatures localized current structures passing spacecraft at high velocity. Very intense spikes (E ≃ 3–25mV/m) connection over such satellite location, but these E generally 10–20 s earlier than SIP's. On average direction earthward smaller component towards dusk. Provided duration signature (2τ) enough (less 2 s) show they correspond aligned tubes (FACT's) spacecraft. When 2τ > s, SIP still consistent field-aligned tube, this cannot assessed without ambiguity experiment alone. Nevertheless, velocity moving structure can deduced signature. For detected onsets (within 40°) drift as determined × B. This situation occurs for 28 events out total 42, were analyzed detail. events, assuming amplitude given B/B², compute characteristic parameters structure: density J, radius R (by cyclindrical simplification), v. thus obtained 6.10−9 < J 3.10−7 A/m², 20 900 km, 15 v 170 km/s, following values: 8×10−8 215 70 km/s. transposed ionospheric altitudes values those found ground or low orbiting observations. nature discussed. A simple theory based on MHD stability proposed explain why hardly exceed equatorial plane critical value order 10−7 A/m².