Challenges of standard solar chromospheric models

The core emission of the Ca II H and K lines are one of the important sources of the radiative loss in the solar chromosphere. The H-index is the integrated emission in a 0.1 nm band around the Ca II H line core. We observed a variety of calcium spectra with drastic differences in the emission properties in the core and wing. Ratio of the maximum H-index to the minimum H-index is over 3. There are also "absorption" profiles with no emission peak or bulge in the line core. Our 1-D NLTE radiative transfer calculations show that in presence of a temperature rise, we cannot reproduce an absorption calcium profile. Hence, such profiles challenge models consist of a full time hot chromosphere for the absence of the emission peaks. This supports an inhomogeneous structured chromosphere.