Network boundary origins of fast solar wind seen in the low transition region?

Details Network boundary origins of fast solar wind seen in the low transition region? Network boundary origins of fast solar wind seen in the low transition region?

Jul 2004

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004a%26a...421..339p&link_type=abstract

Astronomy and Astrophysics, v.421, p.339-348 (2004)

Astronomy and Astrophysics

Astrophysics

17

Sun: Uv Radiation, Sun: Corona, Sun: Transition Region, Sun: Solar Wind

Scientific paper

We present a study of a high spatial resolution raster acquired on-disk with the SUMER (Solar Ultraviolet Measurements of Emitted Radiation) grating spectrograph on SoHO (the Solar and Heliospheric Observatory) in a polar Coronal Hole (CH) region. We analyse two EUV emission lines, representing the properties of solar plasma in the low transition region (TR), O III 703.87 Å (maximum electron temperature, Te≈ 8× 104 K), as well as in the corona, Mg IX 706.02 Å (Te≈ 106 K). For Mg IX, we find that low CH intensities correspond to negative Doppler velocities (outflows) of ≈5 km s-1. Along the quiet Sun (QS)/CH boundaries, the coronal plasma begins to be more red-shifted. A coronal bright point (BP) located within the CH is blue-shifted in the coronal line. In the TR line, the outer region of the BP is red-shifted at ≈5 km s-1, but, towards its middle, the shift is around zero. The O III line, although it shows predominant downward motion of ≈5.5 km s-1 in the CH and ≈6 km s-1 in the QS, it also has blue-shifts arranged in a small-scale network pattern with average negative values of 3.5 km s-1 in CH and 3 km s-1 in the QS. The blue-shifts are caused either by plasma outflows of a few km s-1, or by transient events such as bi-directional jets which dislocate plasma to upward velocities even higher than 100 km s-1. The outflows originate predominantly from the intersection between the magnetic network and the inter-network cells (network boundaries). The bi-directional jets are found along the CH/QS boundaries, and, moreover, in locations where the plasma seen in the Mg IX line is blue-shifted, but very close to small red-shifted regions. Another interesting change in behaviour is observed at the QS/CH boundaries, in the O III line, where plasma from the network changes its velocity sign, becoming red-shifted. Our results constitute the lowest-in-altitude observed signature of plasma outflows from the chromospheric network boundaries inside a CH. We have derived this conclusion from direct correlation between Doppler velocity and the intensity of the O III 702.87 Åline.

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