Christian Beck

The signature of chromospheric heating in Ca II H spectra

Context. The heating process that balances the solar chromospheric energy losses has not yet been determined. Conflicting views exist on the source of the energy and the influence of photospheric magnetic fields on chromospheric heating. Aims. We analyze a 1-h time series of cospatial Call H intensity spectra and photospheric polarimetric spectra around 630 nm to derive the signature of the chromospheric heating process in the spectra and to investigate its relation to photospheric magnetic fields. The data were taken in a quiet Sun area on disc center without strong magnetic activity. Methods. We have derived several characteristic quantities of Call H to define the chromospheric atmosphere properties. We study the power of the Fourier transform at different wavelengths and the phase relations between them. We perform local thermodynamic equilibrium (LTE) inversions of the spectropolarimetric data to obtain the photospheric magnetic field, once including the Ca intensity spectra. Results. We find that the emission in the Call H line core at locations without detectable photospheric polarization signal is due to waves that propagate in around 100 s from low forming continuum layers in the line wing up to the line core. The phase differences of intensity oscillations at different wavelengths indicate standing waves for v < 2 mHz and propagating waves for higher frequencies. The waves steepen into shocks in the chromosphere. On average, shocks are both preceded and followed by intensity reductions. In field-free regions, the profiles show emission about half of the time. The correlation between wavelengths and the decorrelation time is significantly higher in the presence of magnetic fields than for field-free areas. The average Call H profile in the presence of magnetic fields contains emission features symmetric to the line core and an asymmetric contribution, where mainly the blue H 2 v emission peak is increased (shock signature). Conclusions. We find that acoustic waves steepening into shocks are responsible for the emission in the Call H line core for locations without photospheric magnetic fields. We suggest using wavelengths in the line wing of Call H, where LTE still applies, to compare theoretical heating models with observations.

Relation between photospheric magnetic field and chromospheric emission

Aims. We investigate the relationship between the photospheric magnetic field and the emission of the mid chromosphere of the Sun. Methods. We simultaneously observed the Stokes parameters of the photospheric iron line pair at 630.2 nm and the intensity profile of the chromospheric

Magnetic loop emergence within a granule

\ion{Ca}{ii}

Temporal evolution of the Evershed flow in sunspots. I. Observational characterization of Evershed clouds

 H line at 396.8 nm in a quiet Sun region at a heliocentric angle of 53°. Various line parameters have been deduced from the

A 3D sunspot model derived from an inversion of spectropolarimetric observations and its implications for the penumbral heating

\ion{Ca}{ii}

The magnetic flux of the quiet Sun internetwork as observed with the Tenerife infrared polarimeter

 H line profile. The photospheric magnetic field vector has been reconstructed from an inversion of the measured Stokes profiles. After alignment of the Ca and Fe maps, a common mask has been created to define network and inter-network regions. We perform a statistical analysis of network and inter-network properties. The H -index is the integrated emission in a 0.1 nm band around the Ca core. We separate a non-magnetically,

Small-scale chromospheric jets above a sunspot light bridge

H_{{\rm non}}

The Chromospheric Telescope

, and a magnetically,

Formation of a penumbra in a decaying sunspot

H_{{\rm mag}}

Near-infrared spectropolarimetry of a delta-spot

, heated component from a non-heated component,