No abstract

We present a self-consistent empirical model for several plasma parameters of a polar coronal hole near solar minimum, derived from observations with the Solar and Heliospheric Observatory Ultraviolet Coronagraph Spectrometer. The model describes the radial distribution of density for electrons, H , and O and the outflow of O are also significantly larger than the corresponding velocities of H . We discuss the constraints and 5ϩ 0 implications on various theoretical models of coronal heating and acceleration.

Abstract. A 1200 km s -• Coronal Mass Ejection wasobserved with the SOHO instruments EIT, LASCO and UVCS on June 11, 1998. Simultaneously, Type I! radio bursts were observed with the WAVES experiment aboard the Wind spacecraft at 4 MHz and by groundbased instruments at metric wavelengths. The density in the shock wave implied by the higher frequency is close to that inferred from the SOHO/UVCS experiment. The drift rates of the Type II radio bursts suggest shock speeds lower than the speed derived from SOHO observations. The SOHO/UVCS spectrum shows enhanced emission in lines of 0 5+ and Si •+, consistent with modest compression in an MHD shock.

We present in this Letter the first coordinated radio occultation measurements and ultraviolet observations of the inner corona below 5.5R s , obtained during the Galileo solar conjunction in 1997 January, to establish the origin of the slow solar wind. Limits on the flow speed are derived from the Doppler dimming of the resonantly scattered component of the oxygen 1032 and 1037.6 Å lines as measured with the ultraviolet coronagraph spectrometer (UVCS) on the Solar and Heliospheric Observatory (SOHO). White light images of the corona from the large-angle spectroscopic coronagraph (LASCO) on SOHO taken simultaneously are used to place the Doppler radio scintillation and ultraviolet measurements in the context of coronal structures. These combined observations provide the first direct confirmation of the view recently proposed by Woo & Martin that the slow solar wind is associated with the axes, also known as stalks, of streamers. Furthermore, the ultraviolet observations also show how the fast solar wind is ubiquitous in the inner corona and that a velocity shear between the fast and slow solar wind develops along the streamer stalks.

The EUV Imaging Telescope (EIT), Large Angle Spectrometric Coronagraph (LASCO), and Ultraviolet Coronagraph Spectrometer (UVCS) instruments aboard the SOHO satellite observed a prominence eruption (coronal mass ejection) on 1997 December 12. Ejected plasma moved at about 130 km s~1 in the plane of the sky and showed Doppler shifts between [350 and ]30 km s~1. The eruption appeared as a strongly curved arch in EIT images low in the corona. Emission in ions ranging from Si III to O VI in the UVCS spectra indicates a temperature range between 104.5 and 105.5 K. The morphology of the bright emission regions seen by all three instruments suggests several strands of a helical structure of moderate pitch angle. A reasonable Ðt to the spatial structure and the velocity evolution measured by UVCS is provided by a left-handed helix untwisting at a rate of about 9 ] 10~4 radians s~1.