Physics
Scientific paper
Dec 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003agufmsh11b..01c&link_type=abstract
American Geophysical Union, Fall Meeting 2003, abstract #SH11B-01
Physics
2149 Mhd Waves And Turbulence, 2164 Solar Wind Plasma, 2194 Instruments And Techniques, 7513 Coronal Mass Ejections
Scientific paper
Intensity scintillations (IPS) have been used to measure the velocity and the micro-structure of the solar wind for many years. Observations with a single antenna are simple and easily arranged, but they provide only one-dimensional information on the microstructure and they are subject to bias if the microstructure is anisotropic or the scattering becomes ``strong.'' Observations with two or more antennas provide a two-dimensional measure of the microstructure; a vector velocity; and they are more robust in the onset of strong scattering. However there are few suitable arrays and they are difficult to schedule. In either case a reliable estimate requires that many time scales be observed - typically about 10 minutes of observation. Here we report a robust new method which requires only one antenna, but is not sensitive to either anisotropic structure or strong scattering. Furthermore a reliable speed estimate can be made in about 2 s. The method obviously requires additional data - the intensity must be measured with a multi-channel spectrometer. Fortunately such spectrometers are standard equipment at radio observatories. The resulting dynamic spectra can be processed to show the 2-dimensional microstructure and the flow speed. Theory, simulations, and observations will be presented to demonstrate the method. It appears particularly suitable for measuring transients such as coronal mass ejections (CME's) in the interplanetary medium. It will be possible to track many sources with a single antenna, spending only a few seconds on each source, and thus to map the space-time evolution of the CME in turbulence level, flow speed, and anisotropy.
Coles William A.
Harmon John K.
Rickett Barney J.
Venkataraman Anand
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