edu.ucar.opensky::articles:23129 UCAR/NCAR - Library OpenSky Support PO Box 3000 Boulder CO 80307-3000 opensky@ucar.edu http://opensky.ucar.edu/ homepage pointOfContact 2025-12-25T15:23:24.028666 ISO 19115-2 Geographic Information - Metadata - Part 2: Extensions for Imagery and Gridded Data ISO 19115-2:2009(E) https://n2t.org/ark:/85065/d7wq070b Some thoughts on emission-line spectroscopy 2019-10-31T00:00:00Z publication https://n2t.org/ark:/85065/d7wq070b https://doi.org/10.1093/mnras/stz3063 Judge, Philip G. author UCAR/NCAR - Library publisher The interpretation of emission lines formed in large astrophysical plasmas such as the solar atmosphere faces many challenges. Relatively simple line-ratio estimates of physical parameters, while appealing, are heavily laden with assumptions. In practical cases, some critical assumptions are neither defensible from first principles, nor testable by experiment. Free parameters and functional forms must be defined, whose numbers of degrees of freedom exceed the number of independent data points. These issues are illustrated in the particular case of using lines of Si IV and O IV formed in the solar transition region, observed for decades, most recently using the IRIS mission. The problems highlighted are in addition to well-known problems of mathematical ill-posedness. UCAR/NCAR - Library OpenSky Support PO Box 3000 Boulder CO 80307-3000 opensky@ucar.edu http://opensky.ucar.edu/ homepage pointOfContact PDF Text theme Resource Type 2016-01-01T00:00:00Z publication Copyright 2020 Oxford University Press. None eng geoscientificInformation