Ulysses observations of wave activity at interplanetary shocks and implications for type II radio bursts

Journal Article · Sat Feb 01 04:00:00 EST 1997 · Journal of Geophysical Research

DOI:https://doi.org/10.1029/96JA02871· OSTI ID:491850

Lengyel-Frey, D ^[1]; Thejappa, G ^[1]; MacDowall, R J; Stone, R G ^[2]; Phillips, J L ^[3]

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1. Department of Astronomy, University of Maryland, College Park, Maryland (United States)
2. NASA Goddard Space Flight Center, Greenbelt, Maryland (United States)
3. Los Alamos National Laboratory, Los Alamos, New Mexico (United States)

We present the first quantitative investigation of interplanetary type II radio emission in which in situ waves measured at interplanetary shocks are used to compute radio wave intensities for comparison with type II observations. This study is based on in situ measurements of 42 in-ecliptic forward shocks as well as 10 intervals of type II emission observed by the Ulysses spacecraft between 1 AU and 5 AU. The analysis involves comparisons of statistical properties of type II bursts and in situ waves. Most of the 42 shocks are associated with the occurrence of electrostatic waves near the time of shock passage at Ulysses. These waves, which are identified as electron plasma waves and ion acoustic-like waves, are typically most intense several minutes before shock passage. This suggests that wave-wave interactions might be of importance in electromagnetic wave generation and that type II source regions are located immediately upstream of the shocks. We use the in situ wave measurements to compute type II brightness temperatures, assuming that emission at the fundamental of the electron plasma frequency is generated by the merging of electron plasma waves and ion acoustic waves or the decay of electron plasma waves into ion acoustic and transverse waves. Second harmonic emission is assumed to be produced by the merging of electron plasma waves. The latter mechanism requires that a portion of the electron plasma wave distribution is backscattered, presumably by density inhomogeneities in regions of observed ion acoustic wave activity. The computed type II brightness temperatures are found to be consistent with observed values for both fundamental and second harmonic emission, assuming that strong ({approx_equal}10{sup {minus}4}V/m) electron plasma waves and ion acoustic waves are coincident and that the electron plasma waves have phase velocities less than about 10 times the electron thermal velocity. (Abstract Truncated)

• OSTI ID: 491850
• Journal Information: Journal of Geophysical Research, Journal Name: Journal of Geophysical Research Journal Issue: A2 Vol. 102; ISSN JGREA2; ISSN 0148-0227
• Country of Publication: United States
• Language: English

Related Subjects

66 PHYSICS
CORONA DISCHARGES
ELECTRON PLASMA WAVES
INTERPLANETARY SPACE
RADIOWAVE RADIATION
SHOCK WAVES
SOLAR ACTIVITY
SOLAR ATMOSPHERE
SOLAR CORONA
SOLAR WIND
SPECTRA