Reappraising Transition Region Line Widths in light of Recent Alfvén Wave Discoveries
نویسندگان
چکیده
We provide a new interpretation of ultraviolet transition region emission line widths observed by the SUMER instrument on the Solar and Heliospheric Observatory (SOHO). This investigation is prompted by observations of the chromosphere at unprecedented spatial and temporal resolution from the Solar Optical Telescope (SOT) on Hinode revealing that all chromospheric structures above the limb display significant transverse (Alfvénic) perturbations. We demonstrate that the magnitude, network sensitivity and apparent center-to-limb isotropy of the measured line widths (formed below 250,000K) can be explained by an observationally constrained forward-model in which the line width is caused by the line-of-sight superposition of longitudinal and Alfvénic motions on the small-scale (spicular) structures that dominate the chromosphere and low transition region. Subject headings: waves Sun:atmospheric motions Sun:magnetic fields Sun:chromosphere Sun:transition region Sun:corona
منابع مشابه
Center-to-limb line width measurements of solar chromospheric, transition region and coronal lines
Line widths derived from observational data obtained by SUMER onboard SOHO in August 1996 at disk center and at the limb are used to confront those derived via assuming Alfvén and/or magneto-acoustic wave heating. The observational data clearly shows a center-to-limb variation in the upper chromospheric and transition region lines, with only a marginal difference in the coronal lines in the sen...
متن کاملGeneration of pulsed and continuous-wave squeezed light with 87Rb vapor.
We present experimental studies on the generation of pulsed and continuous-wave squeezed vacuum via nonlinear rotation of the polarization ellipse in a (87)Rb vapor. Squeezing is observed for a wide range of input powers and pump detunings on the D1 line, while only excess noise is present on the D2 line. The maximum continuous-wave squeezing observed is -1.4 +/- 0.1 dB (-2.0 dB corrected for l...
متن کاملProperties of the Lower Transition Region: the Widths of Optically Allowed and Intersystem Spectral Lines
The widths of spectral lines in the ultraviolet (UV) and extreme ultraviolet (EUV) spectral regions that are formed in the solar transition region and corona are usually greater than the optically thin widths due to thermal Doppler broadening calculated under the assumption of ionization equilibrium. Although opacity can explain the widths of some lines, there are a host of optically thin lines...
متن کاملSpectral line width decrease in the solar corona: resonant energy conversion from Alfvén to acoustic waves
Context. Observations reveal an increase with height of the line width of several coronal spectral lines probably caused by outwardly propagating Alfvén waves. However, the spectral line width sometimes shows a sudden decrease at a height ∼ 0.1–0.2 R⊙, where the ratio of sound to Alfvén speeds may approach unity. Aims. To explain the observed line width reduction in terms of the energy conversi...
متن کاملA study of velocity fields in the transition region of ǫ Eri ( K 2 V )
Analyses of the widths and shifts of optically thin emission lines in the ultraviolet spectrum of the active dwarf ǫ Eri (K2 V) are presented. The spectra were obtained using the Space Telescope Imaging Spectrograph on the Hubble Space Telescope and the Far Ultraviolet Spectroscopic Explorer. The line widths are used to find the nonthermal energy density and its variation with temperature from ...
متن کامل