Dynamics of the solar chromosphere. II. Ca II H_2v and K_2v grains versus internetwork fields

We use the Advanced Stokes Polarimeter at the NSO/Sacramento Peak Vacuum Tower Telescope to search for spatio-temporal correlations between enhanced magnetic fields in the quiet solar internetwork photosphere and the occurrence of Ca II H_2V grains in the overlying chromosphere. We address the question of whether the shocks that produce the latter are caused by magnetism-related processes, or whether they are of purely hydrodynamic nature. The observations presented here are the first in which sensitive Stokes polarimetry is combined synchronously with high-resolution Ca II H spectrometry. We pay particular attention to the nature and significance of weak polarization signals from the internetwork domain, obtaining a robust estimate of our magnetographic noise level at an apparent flux density of only 3 Mx cm^-2. For the quiet Sun internetwork area analyzed here, we find no direct correlation between the presence of magnetic features with apparent flux density above this limit and the occurrence of H_2V brightenings. This result contradicts the one-to-one correspondence claimed by Sivaraman & Livingston. We also find no correspondence between H_2V grains and the horizontal-field internetwork features discovered by Lites et al.