Ultraviolet Coronagraph Spectrometer Observations of Density Fluctuations in the Solar Wind

Details Ultraviolet Coronagraph Spectrometer Observations of Density Fluctuations in the Solar Wind Ultraviolet Coronagraph Spectrometer Observations of Density Fluctuations in the Solar Wind

Dec 1997

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997apj...491l.111o&link_type=abstract

Astrophysical Journal Letters v.491, p.L111

Astronomy and Astrophysics

Astronomy

112

Sun: Solar Wind, Sun: Corona, Sun: Magnetic Fields, Waves, Magnetohydrodynamics: Mhd

Scientific paper

Recent Ultraviolet Coronagraph Spectrometer (UVCS) white-light channel (WLC) observations on board the Solar and Heliospheric Observatory (SOHO) indicate quasi-periodic variations in the polarized brightness (pB) in the polar coronal holes. This is the first observation of possible signatures of compressional waves high above the limb (at heliocentric distances in the range 1.9-2.45 Rsolar). The Fourier power spectrum of the pB time series at 1.9 Rsolar shows significant peak at about 6 minutes and possible fluctuations on longer timescales (20-50 minutes). The observation at 1.9 Rsolar is the only currently available WLC data set with sufficient cadence to resolve the 6 minute period. These preliminary observations may result from density fluctuations caused by compressional waves propagating in polar coronal holes. We stress that our results are preliminary, and we plan future high-cadence observations in both plume and interplume regions of coronal holes. Recently, Ofman & Davila used a 2.5 D MHD model and found that Alfven waves with an amplitude of 20-70 km s-1 at the base of the coronal hole can generate nonlinear, high-amplitude compressional waves that can contribute significantly to the acceleration of the fast solar wind. The nonlinear solitary-like waves appear as fluctuations in the density and the radial outflow velocity and contribute significantly to solar wind acceleration in open magnetic field structures. The motivation for the reported observations is the MHD model prediction.

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