  Aims: To study the heating of solar chromospheric magnetic and nonmagnetic
regions by acoustic and magnetoacoustic waves, the deposited acoustic-energy
flux derived from observations of strong chromospheric lines is compared with
the total integrated radiative losses. Methods: A set of 23 quiet-Sun and
weak-plage regions were observed in the Mg II k and h lines with the Interface
Region Imaging Spectrograph (IRIS). The deposited acoustic-energy flux was
derived from Doppler velocities observed at two different geometrical heights
corresponding to the middle and upper chromosphere. A set of scaled nonlocal
thermodynamic equilibrium 1D hydrostatic semi-empirical models (obtained by
fitting synthetic to observed line profiles) was applied to compute the
radiative losses. The characteristics of observed waves were studied by means
of a wavelet analysis. Results: Observed waves propagate upward at supersonic
speed. In the quiet chromosphere, the deposited acoustic flux is sufficient to
balance the radiative losses and maintain the semi-empirical temperatures in
the layers under study. In the active-region chromosphere, the comparison shows
that the contribution of acoustic-energy flux to the radiative losses is only
10 - 30 %. Conclusions: Acoustic and magnetoacoustic waves play an important
role in the chromospheric heating, depositing a main part of their energy in
the chromosphere. Acoustic waves compensate for a substantial fraction of the
chromospheric radiative losses in quiet regions. In active regions, their
contribution is too small to balance the radiative losses and the chromosphere
has to be heated by other mechanisms.
