Characteristics of interplanetary type II radio emission and the relationship to shock and plasma properties

Abstract

We present the first detailed study of the properties of the radio emission of interplanetary type II bursts, based on a large sample of type II events. From an analysis of 33 bursts, a data base of more than 600 flux density versus frequency spectra has been developed and used to determine statistical properties of type II bursts, as well as to study the evolution of the emission of individual events. From this analysis the following results have been obtained: (1) The type II spectra appear to be composed of fundamental and harmonic components of plasma emission. The intensity of the fundamental component increases relative to the harmonic as the burst evolves with heliocentric distance. (2) The average flux density of a type II burst increases as a power of the average velocity of the associated shock. (3) As the shock propagates outward, the observed flux density at the peak of a type II spectrum remains relatively constant. The flux density integrated over frequency, however, generally decreases with distance because of a decrease in the bandwidth of the type II emission. (4) It is likely that solar wind density structures has a significant influence on type II bandwidths, and it may be responsible for differences between coronal and interplanetary type II spectral features.