On the nature of magnetic shadows in the solar chromosphere

Recent multi-instrument spacecraft studies of the solar photosphere and chr omosphere have uncovered a feature-a "magnetic shadow" - not previously dis cussed in the literature. A region of the mid-chromosphere neighboring, but not within, a network magnetic element exhibits a suppression of both the mean UV line/continuum intensity and the characteristic 3 minute oscillatio n that is clearly observed elsewhere in apparently similar internetwork reg ions. The clearest cases appear to occur rarely, and their properties stand in obvious contrast to the well-known "aureoles" of enhanced variability s een surrounding some plage regions. It is imperative to understand more cle arly the nature of the shadow region, not least because the suppressed atmo spheric heating within it has implications for heating processes elsewhere in the chromosphere that are dependent on, or at least related to, the 3 mi nute oscillation. Based on the measured photospheric magnetic field, its up ward extrapolation, and the appearance of spectral features formed above th e midchromosphere, we suggest that a shadow occurs when magnetic structures , in a relatively weak background field, "close" locally within the chromos phere, suppressing the upward propagation of magnetoatmospheric waves into the chromosphere.