Astronomy and Astrophysics – Astrophysics
Scientific paper
Mar 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004a%26a...416..749a&link_type=abstract
Astronomy and Astrophysics, v.416, p.749-758 (2004)
Astronomy and Astrophysics
Astrophysics
27
Sun: Corona, Sun: Uv Radiation, Sun: Solar Wind
Scientific paper
A new spectroscopic method, aimed to derive the plasma electron density and outflow velocity in expanding solar coronal regions, is discussed in this paper. The method is based on the analysis of a pair of coronal lines emitted via collisional and radiative excitation by the same ion, such as the O VI 1032, 1037 Å, doublet. The merit of this technique consists in allowing us to derive at the same time electron density and outflow velocity of the coronal plasma from nearby lines detectable with the same instrument, provided the constraint on mass flux conservation along the flow tube connecting solar corona and heliosphere is taken into account. The results obtained from the analysis of the OVI emission imply that the physical conditions of a polar coronal hole plasma, observed during minimum activity, are the following. The electron density decreases from 4× 105 cm-3 at 1.7 R&sun; to 2-4× 104 cm-3 at 3.1 R&sun;, whereas the outflow velocity of the oxygen ions is monotonically increasing to reach 350-500 km s-1 at 3.1 R&sun;, depending on the assumptions on the degree of anisotropy of the velocity distribution of the ions. These results of the velocity of expansion of the fast wind confirm those obtained with Doppler dimming techniques when assuming the lowest observed density values for the coronal hole plasma. This implies that, for a rarified corona, the outflow velocity of the fast solar wind in polar holes can be traced by the motion of the O VI ions at least up to 2.4 R&sun;. The analysis also shows that the degree of anisotropy of the oxygen ions, due to the acceleration of the ions across the magnetic field in a coronal hole, exhibits a steep increase and that the geometry of the flow tube diverges very rapidly low down in the inner corona/transition region. The observations of the extended corona analysed in this paper are obtained with the Ultraviolet Coronagraph Spectrometer of the SOHO space mission.
Antonucci Ester
Dodero Maria Adele
Giordano Stefano
Krishnakumar V.
Noci Giancarlo
No associations
LandOfFree
Spectroscopic measurement of the plasma electron density and outflow velocity in a polar coronal hole does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Spectroscopic measurement of the plasma electron density and outflow velocity in a polar coronal hole, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Spectroscopic measurement of the plasma electron density and outflow velocity in a polar coronal hole will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1620045