Observing the solar chromosphere

Abstract

This review is split into two parts: one on chromospheric line formation in answer to the frequent question ``where is my line formed'', and one presenting state-of-the-art imagery of the chromosphere. In the first part I specifically treat the formation of the Na D lines, Ca II H&K, and Hα. In the second I show DOT, IBIS, VAULT, and TRACE images as evidence that the chromosphere consists of fibrils of intrinsically different types. The straight-up ones are hottest. The slanted ones are filled by shocks and likely possess thin transition sheaths to coronal plasma. The ones hovering horizontally over ``clapotispheric'' cell interiors outline magnetic canopies and are buffeted by shocks, most violently in the quietest regions. In the absence of integral-field ultraviolet spectrometry, Hα remains the principal chromosphere diagnostic. The required fast-cadence profile-sampling imaging is an important quest for new telescope technology.