The Non-magnetic Solar Chromosphere

We summarizerecent results from self-consistent non-LTE radiation hydrodynamicssimulations of the propagation of acoustic waves through the non-magnetic solar chromosphere. References to more detailed write-ups of the work are given. The simulations closely match the observed behaviour of Ca II H 2 V bright grains. Observations of CO-lines, that are problematicto explain in semi-empiricalone-componentmodels, are consistent with the simulations. Recent observations of UV continua with the SOHO satellite are also well explained. The simulations show that for regions of the chromosphere whose structure is not obviously controlled by magnetic elds, a dynamic and not static picture is needed to describe the structure and the emitted spectrum. The whole foundation for using spectral features in static models to infer physical properties of the chromosphere must be called into question. It is found that enhancedchromospheric emission, which correspondsto an outwardly increasing semi-empirical temperature structure, can be produced by wave motions without any increase in the mean gas temperature. Thus, despite long held beliefs, the sun may not have a classical chromosphere in magnetic eld free internetwork regions at heights below 1Mm. Lines formed above 1 Mm height show emission all the time in observations from the SOHO satellite in contrast with what is expected from the simulations. Thus, something important is missing from the calculations { perhaps concerning the fate of shock waves propagating upwards into a magnetic \canopy", perhaps concerning diierent propagation modes (MHD eeects), or energetically non-connected material lying along the line of site (like magnetic ux-tubes).