Abstract
Previous models of microwave limb brightening have omitted the alignment of spicules along supergranule boundaries, have neglected the high temperature sheath around spicules, and have assumed an interspicular medium that was averaged over chromospheric network and nonnetwork regions. A model is presented which includes these factors. By constraining the model to conform to results from earlier UV and optical studies, the authors are effectively left with two free parameters: the temperature at the core of the spicules, T sub(c) sub(o) sub(r) sub(e) , and, at solar minimum, the interspicular chromospheric network density model of the lower transition zone. The absence of limb brightening at the short millimeter wavelengths implies T sub(c) sub(o) sub(r) sub(e) < approximately 6000 K. Differences between the model and certain deconvolved observations near 9 mm are expected as a consequence of an extension of emission beyond the optical limb, predicted by the model, which affects the accuracy of the deconvolution technique. Unlike models that assume homogeneous spicules in a random distribution, this one does not require an abnormally high spicule area.