Coronal Radio Sounding with MEX, VEX and Rosetta

Details Coronal Radio Sounding with MEX, VEX and Rosetta Coronal Radio Sounding with MEX, VEX and Rosetta

Dec 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufmsh44a..03b&link_type=abstract

American Geophysical Union, Fall Meeting 2009, abstract #SH44A-03

Astronomy and Astrophysics

Astrophysics

[6964] Radio Science / Radio Wave Propagation, [7509] Solar Physics, Astrophysics, And Astronomy / Corona, [7599] Solar Physics, Astrophysics, And Astronomy / General Or Miscellaneous

Scientific paper

Coronal radio sounding experiments were carried out with the S-band (2.3 GHz) and X-band (8.4 GHz) signals of the ESA spacecraft Mars Express (MEX), Venus Express (VEX) and Rosetta. The Mars Express Radio Science experiment (MaRS) was carried out during three superior conjunctions in 2004, 2006 and 2008/2009. One coronal occultation opportunity was available for the analogous experiments on Rosetta (RSI) and Venus Express (VeRa), both occurring in 2006. Differential frequency and propagation delay (ranging) observations were recorded during an extended period of low solar activity, yielding information on the large-scale structure of the coronal electron density distribution and its variations, including turbulent fluctuations on time scales from seconds to hours. In all cases, the conjunction geometry constrains the radio propagation paths to the low heliolatitude regions of the corona (predominantly slow solar wind). Several Coronal Mass Ejection (CME) events were identified in the data, some of which were observed in white light by the LASCO instrument on SOHO. The mean frequency fluctuation and power law index of the frequency fluctuation temporal spectra are determined as a function of heliocentric distance. In agreement with previous experiments on Ulysses and Galileo, the mean frequency fluctuation follows a power-law function of the solar distance and the frequency fluctuation spectra become flatter in the solar wind acceleration region, i.e. for heliocentric distances less than 15 solar radii. Detailed spectral analysis of the MaRS data implies the occasional presence of a quasi-periodic component (QPC) at small heliocentric distances, which we interpret as a signature of MHD waves in the corona. The sporadic QPC typically appears as a broad peak at temporal frequencies near 4 mHz and a power level as much as four times higher than the background power-law spectrum. We interpret these data as a signature of MHD waves in the solar wind acceleration region, which are continuously present and can be occasionally detected in radio sounding data under favorable conditions.

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