Radio evidence for an expanding magnetic arch beyond 20 solar radii
✍ Scribed by R. G. Stone; Joseph Fainberg
- Book ID
- 104645147
- Publisher
- Springer
- Year
- 1975
- Tongue
- English
- Weight
- 165 KB
- Volume
- 42
- Category
- Article
- ISSN
- 0038-0938
No coin nor oath required. For personal study only.
✦ Synopsis
A magnetic loop located beyond 20 R| appears to be the later evolution of an expanding magnetic arch observed at 2 R o. The expansion speed is of the order of 100 km s -a.
A magnetic loop located at a height greater than 20 R o has been deduced from longwavelength solar radio observations . The purpose of this note is to suggest that the loop is a later stage of an expanding magnetic arch observed at 2R o on the previous day . The long-wavelength observations also constitute an example of the interplanetary manifestation of a moving type IV solar radio event.
Spacecraft observations of solar radio bursts in the frequency range from 10 kHz to 10 MHz correspond in general to radio emission from phenomena occurring at distances from the Sun of 5 R o to 1 AU and beyond . The overwhelming majority of observed events are type lII bursts produced by superthermal electrons propagating along open field lines over this distance range. Type III burst dynamic spectra are characterized by a fast drift from high to lower frequencies as the exciter moves outward. There have been a few rare instances in which the dynamic spectrum at low frequencies shows a burst drifting from high to lower frequencies, followed by a subsequent drift back to higher frequencies, leading to its classification as a 'U' burst. The analysis of approximately one year of data from the RAE-1 satellite has revealed less than a dozen U bursts in the low-frequency range . These bursts are an indication that the exciter particles are confined to move along a magnetic loop type configuration (e.g. The observation of a U burst on 1968 November 23 ) by the RAE-1 spacecraft between 5 and 0.7 MHz is shown in Figure . The coronal levels in the figure were obtained from the emission level scale determined from a statistical study of type III bursts observed from RAE-1 (Fainberg and Stone, 1971, 1974). From an initial analysis of the U burst, estimated the height of the magnetic loop to be of the order of 35 R o. Further analysis suggests that the height may be more nearly 25 Ro, as suggested from the turning frequency in Figure . There is difficulty in selecting the turning point because during the down-frequency phase of the event, both a U burst and a conventional type III burst (drifting to still lower frequencies) were observed (see Figure ; .