Non-Uniqueness of Atmospheric Modeling

Abstract

We focus on the deceptively simple question: how can we use the emitted photons to extract meaningful information on the transition region and corona? Using examples, we conclude that the only safe way to proceed is through forward models. In this way, inherent non-uniqueness is handled by adding information through explicit physical assumptions and restrictions made in the modeling procedure. The alternative, ‘inverse’ approaches, including (as a restricted subset) many standard ’ ‘spectral diagnostic techniques’, rely on more subjective choices that have, as yet, no clear theoretical support. Emphasis is on the solar transition region, but necessarily discussing the corona, and with implications for more general problems concerning the use of photons to diagnose plasma conditions.

As in all other astronomical endeavors where the subject is not directly retrievable, the study of the transition region ranges from purely ab-initio physical models to semi-empirical conclusions drawn more directly from observational data. I have used the expression ‘semi-empirical’ because any conclusions concerning the state of the transition region material must rely on physical models and implicit assumptions. Only the photons are directly observable.

L. S. Anderson-Huang (1998)

Also with the Advanced Study Program of NCAR.