LOWER SOLAR CHROMOSPHERE-CORONA TRANSITION REGION .2. WAVE PRESSURE EFFECTS FOR A SPECIFIC FORM OF THE HEATING FUNCTION

Wave pressure effects are incorporated into lower transition region (TR) models in which there is a balance between mechanical heating and radiative losses. The mechanical heating is assumed to be the result of the damping of hydromagnetic waves, which can be described by a wave energy flux density of the simple form F = F0e-s/l, where the damping length l is assumed to be constant. The inclusion of wave pressure in the momentum balance tends to remove the singular requirements on the damping length that were found in Paper I for such a heating function. The ranges in the damping length, the ratio of wave pressure to thermal pressure at the base, and the temperature and pressure dependences of the vertical wave speed are identified for solutions in which the temperature is a monotonically increasing function of height over the temperature range 104 K ≤ T ≤ 105 K. Emission measure (EM) curves are also presented for these solutions. We find that the observations are generally incompatible with both the sound and the Alfvén wave modes. For the sound wave case, models with EM curves not unlike those observed can be produced, but such models require both large damping lengths and large wave fluxes and extend to very large heights (≳ 104 km) because of the outward wave pressure force. Such solutions cannot explain most of the emission observed at lower TR temperatures, but they do suggest that cool material can exist statically at heights far above the gravitational scale height. Solutions have also been analyzed for arbitrary temperature and pressure dependence of the wave speed, and for a particular parameter range in which the wave speed decreases with height, EM curves can be produced which are similar to those observed. These solutions can exist for wave speeds at 104 K on the order of the sound speed and wave fluxes on the order of the radiative flux observed in lower TR lines, and they extend over a total height of the order of 1000 km. We suggest, on the basis of these solutions, that a mixture of fast-mode and slow-mode waves may provide the appropriate heating mechanism in the lower TR, the decline in effective vertical wave speed being due to the refraction and eventual total reflection of the fast-mode waves resulting from the decreasing atmospheric density.