Effects of interplanetary shocks on kilometric type III radio bursts

Abstract

Interplanetary (IP) type III bursts that undergo sudden intensity changes when their electron beams traverse the vicinity of an IP shock are examined. Three types of intensity changes are discussed: cutoffs in which the type III intensity is abruptly reduced and remains at the reduced level for all lower frequencies, narrow-band intensifications that frequently occur on the high-frequency edge of a cutoff, and narrow-band intensity reductions. Pitch angle scattering of the beam electrons in the enhanced magnetic turbulence downstream of shocks is proposed as a principal cause of the intensity cutoffs and, possibly, the intensifications. These observations suggest that one type III emission mode (fp or 2fp) is frequently at least 10 times more intense than the other mode. 10 times above the background level.-(Lin-et ai., 1986). Enhanced background levels m•y reduce the Langmuir wave amplification by diminishing the.. velocity extent of the' bUmp-on-tail. Turning to the NBI's, it seems .pro.bable •that the region in which they occur has an angular extent COrresponding t ø tha t'•of no. rmal•: • .:ype. Ill ß 'emission and a radial extent of order 0.1 •o 0.3 of the distance R to the Sun. If the enh'•inced emission came from a• region significantly narrower '(or, wider• '• than the normal" type III -angUlar Wid•hi one would detect changes in position a'nd.søUrc• size, which are not observed (MacDowall; 1988). "Normal" type III emission in a bandwidth-•M/f of" order 0.3 would be produced in a region of radial extent fiR/R~0.3 due to the approximate inverse re-Phys., 46, 461-464, 1976. Fainberg, J., S. Hoang, and R. Manning, Measurements of distributed polarized radio sources from spinning spacecraft; effect of a tilted axial antenna. ISEE-3 application and results, Astron. Astrophys., 153, 145-150, 1985. Kennel, C.F., et al., N'•'•ocal plasma turbulence associated with interplanetary shocks, J. Geophys. Res., 87, 17-34, 1982. Knoll, R., et al., The 3-dimensional radiomapping experiment (SBH) on ISEE-C, Trans. Geosci. Electronics, GE-16, 199-204, 1978. Lacombe, C. and B. Moller-Pedersen, Interaction of a collisionless shock wave and a stream of particles in the upper solar corona, Astron. Astrophys., 15, 406-418, 1971. Lengyel-Frey, D. and R.G. Stone, Characteristics of interplanetary type II radio emission and the relationship to shock and plasma parameters, Geophys. Res., 94, 159-167, 1989. Lin, R.P., Energetic solar electrons in the interplanetary medium, Solar Phys., 100, 537-561, 1985. Lin, R.P., et al., Evidence for nonlinear wave-wave interactions in solar type III radio bursts, Astrophys. J., 308, 954-965, 1986. MacDowall, R.J., Kilometric type III radio bursts and interplanetary transients, Ph.D. dissertation, 145 pp., Melrose, D.B., Plasma Astrophysics -Nonthermal processes in Diffuse Magnetized Plasmas, Vol. 2, 423 pp., Gordon and Breach, New York, 1980. Reiner, M.J. and R.G. Stone, Model interpretation of type III radio burst characteristics I. Spatial aspects, Astron. Astrophys., 206, 316-335, 1988. Sawant,...

Imprints of coronal temperature disturbances on type III bursts

“…MacDowall (1989) observed that the flux of IP type IIIs changed suddenly as beams neared shocks. He suggested that the changes are caused by the scattering of beam electrons by magnetic turbulence.…”

The 17 January 2005 Complex Solar Radio Event Associated with Interacting Fast Coronal Mass Ejections

“…The type-III bursts (III 1 ) might then not start near the CME front, but at higher frequencies, and be interrupted by interactions of the electron beams with the turbulence near the front of CME 1 . This is a frequently quoted interpretation of complex features in type-III bursts, both at kilometric (MacDowall, 1989) and decametric wavelengths (e.g. Reiner and Kaiser, 1999).…”

Quantitative prediction of type II solar radio emission from the Sun to 1 AU

“…This event also had local harmonic radio emission, Langmuir waves, and accelerated electrons observed upstream of the shock crossing at STEREO A [Graham and Cairns, 2015]. Produced by electron beams accelerated in solar flares, type IIIs can intensify as the beams cross the shock [Lacombe and Moller Pedersen, 1971;MacDowall, 1989;Li and Cairns, 2012], based on radio telescope triangulation measurements and theory. Interference from type III bursts, the almost vertical frequency-time signals in Figure 1, is apparent.…”