Search Publications
Helioseismic Studies of Differential Rotation in the Solar Envelope by the Solar Oscillations Investigation Using the Michelson Doppler Imager
Kosovichev, A. G.; Hoeksema, J. T.; Scherrer, P. H. +21 more
The splitting of the frequencies of the global resonant acoustic modes of the Sun by large-scale flows and rotation permits study of the variation of angular velocity Ω with both radius and latitude within the turbulent convection zone and the deeper radiative interior. The nearly uninterrupted Doppler imaging observations, provided by the Solar O…
UVCS/SOHO Empirical Determinations of Anisotropic Velocity Distributions in the Solar Corona
Romoli, M.; Raymond, J. C.; Naletto, G. +28 more
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, H0, and O5+ and the outflow ve…
The Solar Corona Above Polar Coronal Holes as Seen by SUMER on SOHO
Wilhelm, Klaus; Marsch, Eckart; Dwivedi, Bhola N. +4 more
In order to address two of the principal scientific objectives of the Solar and Heliospheric Observatory (SOHO), studies of the heating mechanisms of the solar corona and the acceleration processes of the solar wind, we deduce electron temperatures, densities, and ion velocities in plumes and interplume regions of polar coronal holes using ultravi…
Energy Distribution of Heating Processes in the Quiet Solar Corona
Krucker, Säm; Benz, Arnold O.
We have determined the variations in the emission measure of the solar corona using EUV Imaging Telescope/Solar and Heliospheric Observatory observations of iron lines in a quiet region of the Sun. The emission measure is found to vary significantly in at least 85% of all the pixels within 42 minutes. The variations are interpreted as heating even…
SUMER Measurements of Nonthermal Motions: Constraints on Coronal Heating Mechanisms
Chae, Jongchul; Schühle, Udo; Lemaire, Philippe
We have determined nonthermal velocities in the quiet Sun at temperatures between 104 K and 2 × 106 K by measuring the widths of a number of EUV and far-ultraviolet (FUV) lines taken with SUMER on board the SOHO spacecraft. The broadenings owing to the SUMER instrument and the finite opacity in each line have been carefully e…
Observations of Correlated White-Light and Extreme-Ultraviolet Jets from Polar Coronal Holes
Llebaria, A.; St. Cyr, O. C.; Michels, D. J. +7 more
Time-lapse sequences of white-light images recorded with the Large Angle Spectrometric Coronagraph (LASCO) on the Solar and Heliospheric Observatory (SOHO) frequently show long, narrow structures moving outward over the Sun's polar regions at high apparent speeds. By comparing the LASCO observations with Fe XII λ195 spectroheliograms made with the…
The Effect of Temperature Anisotropy on Observations of Doppler Dimming and Pumping in the Inner Corona
Li, Xing; Habbal, Shadia Rifai; Kohl, John L. +1 more
Recent observations of the spectral line profiles and intensity ratio of the O VI λλ1032 and 1037.6 doublet by the Ultraviolet Coronagraph Spectrometer (UVCS) on the Solar and Heliospheric Observatory (SOHO), made in coronal holes below 3.5 RS, provide evidence for Doppler dimming of the O VI λ1037.6 line and pumping by the chromospheri…
Measurements of Solar Magnetic Element Motion from High-Resolution Filtergrams
Berger, Thomas E.; Title, Alan M.; Löfdahl, Mats G. +1 more
Solar photospheric flowfield properties on sub-0.5" scales are measured using local correlation tracking (LCT) and object tracking of magnetic bright points (MBPs: photospheric bright points associated with magnetic elements). The dataset is a 70 minute time series of cospatial and cotemporal G-band 4305 Å and wideband 4686 Å filtergrams obtained …
Measuring the Sun's Eigenfrequencies from Velocity and Intensity Helioseismic Spectra: Asymmetrical Line Profile-fitting Formula
Kosovichev, A. G.; Nigam, R.
Solar eigenfrequencies are generally determined by fitting a Lorentzian to the spectral lines in the power spectrum. This assumes that the spectral line is symmetric. Recent observations from the Michelson Doppler Imager (MDI) on board the Solar and Heliospheric Observatory have indicated that the power spectra of p-modes show varying amounts of a…
Coronal Composition above the Solar Equator and the North Pole as Determined from Spectra Acquired by the SUMER Instrument on SOHO
Schühle, U.; Feldman, U.; Laming, J. M. +1 more
Using spectra obtained by the SUMER instrument on the Solar and Heliospheric Observatory (SOHO) we have determined the composition of the bulk of the coronal plasma in the vicinity of the solar surface over a polar coronal hole and an equatorial region. Our measurements show that although low first ionization potential (FIP) elements are enriched …