Kinematics of ICMEs Deduced From Remote Radio Observations

Details Kinematics of ICMEs Deduced From Remote Radio Observations Kinematics of ICMEs Deduced From Remote Radio Observations

Dec 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufmsh41a1627r&link_type=abstract

American Geophysical Union, Fall Meeting 2009, abstract #SH41A-1627

Physics

[2101] Interplanetary Physics / Coronal Mass Ejections, [6969] Radio Science / Remote Sensing

Scientific paper

Low-frequency radio emissions, generated at the driven shock wave at the fundamental and harmonic of the plasma frequency, can directly reveal the kinematics of ICMEs as they propagate through the inner heliosphere. The reason is that the frequency of the radio emissions varies in a predictable way as a function of heliocentric distance. Hence, the observed frequency drift of these radio emissions is essentially a plot of the height above the Sun as a function of time. The derivative of the observed frequency-time curve at each point then gives the instantaneous speed of the propagating interplanetary shock. We have used these remote radio observations to determine the speed profiles for some 40 fast CMEs observed during solar cycle 23. The speed profiles for these fast ICMEs were found to imply an initial rapid deceleration at a constant rate, followed by a constant propagation speed to 1 AU (Reiner et al. ApJ 663, 1369, 2007), consistent with some earlier Doppler scintillation measurements (Woo et al., JGR 90, 154, 1985). Because of the large number of CME events for which this analysis was carried out, we were further able to study the correlations of the deceleration parameters of the ICME speed profiles. For most of those remote radio observations, there were no corresponding white-light observations beyond the 32 Rs (0.15 AU) limit of the LASCO coronagraph. After 2003, the all-sky camera SMEI permitted the first direct comparison between the remote radio and the white-light observations in interplanetary space (Reiner et al. JGR 110, A09S14, 2005). The STEREO spacecraft, launched in October of 2006, provide a new and unique opportunity to make direct comparisons between the radio and white-light observations of the ICME kinematics. The STEREO observations also allow the locations of the radio sources along the shock front to be directly deduced from two or three spacecraft triangulation measurement from STEREO and Wind (Reiner et al. Solar Physics 10.1007/s11207-009-9404-z, 2009). However, due to solar minimum, to date no CMEs observed by STEREO were fast enough to produce measurable radio emissions. As we approach solar maximum that situation will surely change. Nevertheless, some height-time data for fast CMEs that were observed in the Heliospheric Imagers on STEREO do seem to confirm the general characteristics of the speed profile previously deduced from radio tracking (Wood et al., ApJ 694, 707, 2009). In this talk, we will summarize our previous remote radio results, and show how they can be used to provide improved algorithms for space weather predictions.

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