Interplanetary disturbances caused by the August 1972 solar flares as observed by Pioneer 9
Abstract
Analyses of the dynamical behavior of the interplanetary medium during early August 1972 are carried out with the use of Pioneer 9 plasma and field observations at 0.78 AU. The following studies are discussed: (1) energy and mass estimates for the flares of August 2, 4, and 7 are given; (2) shock wave characteristics are provided; and (3) a numerical simulation of the first two flare-generated disturbances on August 2 as well as of those on August 4 and 7 is demonstrated. The kinetic, magnetic, and thermal energy estimates, corrected for potential energy possessed by the ejected mass at the sun, were obtained by integrating over the surface area of a sphere at 0.78 AU, centered at the sun and subtended by 2π sr. The total energies calculated thereby are as follows: 8.8 × 1031 ergs for the first flare on August 2; 4.6 × 1032 ergs for the second flare on August 2; 1.1 × 1032 ergs for the August 4 flare, which was about 40° to the west of Pioneer 9 at that time; and 3.8 × 1032 ergs for the August 7 flare, which was about 85° to the west of the spacecraft at that time. The ejected mass was in the range 1016-1017 g from each flare. The energy and mass values for the August 7 flare probably represent lower bounds because of the spacecraft's eastward position relative to the flare's central meridian. As a result, the spacecraft probably sampled a relatively weaker portion of the disturbed solar wind. The assumption of the hemispherical disturbance is supported by the independent observations (>160° and ≳50° in longitudinal and latitudinal extent, respectively) of the shock-generated disturbance detected in the August 7 case by interplanetary scintillations. The numerical simulation for the first two flares demonstrates the overtaking of the first shock at approximately 1.16 AU by the shock from the second flare on August 2. This shock interaction was also suggested by the observed average shock trajectories.
- Publication:
-
Journal of Geophysical Research
- Pub Date:
- September 1976
- DOI:
- 10.1029/JA081i025p04651
- Bibcode:
- 1976JGR....81.4651D
- Keywords:
-
- Interplanetary Medium;
- Pioneer 9 Space Probe;
- Plasma-Electromagnetic Interaction;
- Solar Activity Effects;
- Solar Flares;
- Solar Flux;
- Solar Wind;
- Electrostatic Probes;
- Magnetohydrodynamic Flow;
- Mathematical Models;
- Plasma Dynamics;
- Shock Wave Propagation;
- Solar Flux Density;
- Particles and Fields-Interplanetary Space: Shock waves;
- Particles and Fields-Interplanetary Space: Solar wind plasma;
- Particles and Fields-Magnetosphere: Interaction between solar wind and magnetosphere