MESSENGER Observations of Magnetohydrodynamic Waves in the Solar Corona from Faraday Rotation
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MESSENGER Observations of Magnetohydrodynamic Waves in the Solar Corona from Faraday Rotation E.A. Jensen · M. Nolan · M.M. Bisi · I. Chashei · F. Vilas
Received: 26 March 2012 / Accepted: 8 October 2012 / Published online: 7 December 2012 © Springer Science+Business Media Dordrecht 2012
Abstract During the declining phase of the longest solar minimum in a century, the arrival of the MESSENGER spacecraft at superior conjunction allowed the measurement of magnetohydrodynamic (MHD) waves in the solar corona with its 8 GHz radio frequency signal. MHD waves crossing the line of sight were measured via Faraday rotation fluctuations (FRFs) in the plane of polarization (PP) of MESSENGER’s signal. FRFs in previous observations of the solar corona (at greater offset distances) consisted of a turbulent spectrum that decreased in power with increasing frequency and distance from the Sun. Occasionally a spectral line, a distinct peak in the power spectral density spectrum around 4 to 8 mHz,
Observations and Modelling of the Inner Heliosphere Guest Editors: Mario M. Bisi, Richard A. Harrison, and Noé Lugaz E.A. Jensen () · F. Vilas Planetary Science Institute, 1700 E. Ft. Lowell, Ste. 106, Tucson, AZ 85719-2395, USA e-mail: [email protected] F. Vilas e-mail: [email protected] E.A. Jensen ACS Consulting/ACS Engineering & Safety, 40 Cypresscreek Pkwy, PMB 370, Houston, TX 77090, USA e-mail: [email protected] M. Nolan NAIC/Arecibo Observatory, HC-3 Box 53995, Arecibo, PR 00612, USA e-mail: [email protected] M.M. Bisi Institute of Mathematics and Physics, Physical Sciences Building, Aberystwyth, Ceredigion SY23 3BZ, UK e-mail: [email protected] I. Chashei Lebedev Institute of Physics, Pushchino Radio Astronomy Observatory, 142290 Pushchino, Russian Federation e-mail: [email protected]
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was also observed in these early data sets at offset distances of about 5 to 10 solar radii. The MESSENGER FRF data set shows a spectral line at an offset distance between 1.55 to 1.85 solar radii with a frequency of 0.6 ± 0.2 mHz. Other possible spectral lines may be at 1.2, 1.7, and 4.5 mHz; MHD waves with these same frequencies have been observed in X-ray data traveling along closed coronal loops at lower offset distances. An initial analysis of the MESSENGER spectral line(s) shows behavior similar to turbulent spectra: decreasing power with increasing frequency and distance from the Sun. Here we detail the steps taken to process the MESSENGER change in PP data set for the MHD wave investigation. Keywords Solar cycle · Spacecraft · Magnetohydrodynamic waves · Solar corona · Radio frequency · Polarization · Faraday rotation · Faraday rotation fluctuations · Turbulence · Spectral lines · Alfvén waves · Magnetic field
1. Introduction The solar wind drives Earth’s space weather through a variety of mechanisms, including ram pressure when it interacts with the stationary geomagnetic field at supersonic, superAlfvénic speeds and mixing (via reconnection) as a function of magnetic field strength and direction. The resulting geo
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