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Wind‐Ulysses source location of radio emissions associated with the January 1997 coronal mass ejection
Author(s) -
Hoang S.,
Maksimovic M.,
Bougeret J.L.,
Reiner M. J.,
Kaiser M. L.
Publication year - 1998
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/98gl00571
Subject(s) - physics , coronal mass ejection , interplanetary spaceflight , solar wind , spacecraft , heliosphere , astronomy , coronagraph , ecliptic , astrophysics , interplanetary medium , planet , exoplanet , plasma , quantum mechanics
We investigate the 3‐D source location of interplanetary type Il‐like radio bursts from observations involving two spacecraft. Uncommon type II radio emissions were observed simultaneously on 8 January 1997 by the Wind and Ulysses spacecraft and are believed to be associated with the Interplanetary Coronal Mass Ejection detected on 6–7 January by the LASCO coronagraph on the SOHO spacecraft and on 10–11 January by Wind. Ulysses was located about 4.73 AU from the Sun at 25.6°N ecliptic latitude and 45.1°W of Earth, while Wind was in the solar wind upstream of the Earth. The two spacecraft recorded nearly similar intensity time profiles at the common frequency of 196 kHz. By means of radio triangulation, we locate the 3‐D source region, inferring it to be strongly deviated by several AU from the expected source between the Sun and Earth towards the solar hemisphere opposite Earth. Strong propagation effects, such as scattering and refraction, are suggested as affecting Ulysses observations (both in apparent source size and direction), being due to the presence of interplanetary overdense structures of various scales. We also deduce the source location from the direction as measured at Wind and the difference of the arrival times as measured at both spacecraft. From this latter approach we find that the source location is closer to Wind than the expected source by ∼0.2–0.4 AU, corresponding to an excess travel time of ∼0.55–1.44 min on the radiation path to Ulysses. The excess delay time is found to be about 2.6 times greater for the fundamental emission than for the harmonic emission, and it is found to vary (approximately) inversely as the decay time of the intensity at Ulysses, presuming the existence of scattering.