Spectral diagnostics of chromospheres - A signature of emergent magnetic flux

The chromospheres of the Sun and solar-like stars respond to the underlying magnetic activity. The spectral lines of singly ionized calcium (e.g., Ca II K at 3933 Angstrom) exhibit single or double reversals and serve as diag nostic tools for the magnetic activity. We present observations showing tha t the Ca II K spectral Line may exhibit reversals in addition to the well-k nown K1, K2, and K3 components, when observed with high angular and spectra l resolution. These Ca II K spectral line anomalies occur when small-scale, subarcsecond magnetic fields emerge through the chromosphere. The anomalou s profiles originate at locations that are cospatial with H alpha brighteni ng at footpoints of dark active region fibrils, or active region filaments. The photospheric magnetic field is bipolar (small opposite polarity magnet ic nodules) or has neutral lines at cospatial locations where the spectral lines are anomalous. Small-scale reconnective processes can cause these ano malous profiles. From a simultaneous time series of magnetic field data, we find that the emerging magnetic flux is associated with these profiles. Th e additional reversals primarily occur redward of the familiar K3 absorptio n trough, implying chromospheric downflow velocities that lead to the forma tion of shocks. The magnitude of the Doppler shift is of the order 40-50 km s(-1). We present evidence to suggest that a combination of subresolution elements, each of which has regular profiles with large relative Doppler sh ifts could explain the formation of some of these profiles. A heuristic mod el that combines buoyant magnetic fields, convective collapse, gas evacuati on, shock formation, heating, and a multicomponent model atmosphere can rep roduce these profiles.