Toroidal‐shaped interplanetary disturbance associated with the halo coronal mass ejection event on 14 July 2000

Interplanetary scintillation (IPS) measurements made with the 327 MHz radio telescopes of the Solar–Terrestrial Environment Laboratory, Nagoya University, have been used to study a three‐dimensional structure of the interplanetary (IP) disturbance associated with the halo coronal mass ejection (CME) event on 14 July 2000 (the so‐called “Bastille Day event”). The IPS observations indicated that the Bastille Day IP disturbance was between 0.3 and 0.7 AU at 17 ± 3 hours after the flare occurrence. A model fitting analysis has been applied here to the IPS observations to reconstruct a global structure of the Bastille Day IP disturbance. As a result, the IP disturbance is found to form a loop‐shaped structure that is significantly longer in the longitudinal (east–west) direction than in latitude. This toroidal‐shaped IP disturbance is found to cross the large‐scale magnetic neutral line almost perpendicularly at its center. Our IPS data also show a nonuniform expansion of the IP disturbance, and the fastest direction is found to lie near above the flare site. Using the best‐fit model determined here and information on the ambient solar wind density from in situ measurements, the mass contained by the IP disturbance has been estimated to be ∼ 5.3 × 10 16 g. The result obtained from the present analysis is consistent with independent observations that suggest the Bastille Day interplanetary CME has decelerated significantly in the solar wind. The radial evolution of the apparent feature of the IP disturbance has been revealed from a model calculation using the best‐fit parameters, and this evolution is consistent with IPS measurements made at Ooty, India, slightly later in time. While an origin of the toroidal‐shaped disturbance is an open question, the compressed plasma between the coronal ejecta and the ambient solar wind or the ejecta itself are considered as a possible one.