Modeling the Ionosphere with GPS and Rotation Measure Observations

TL;DR

This study assesses the accuracy of ionospheric models used to correct Faraday Rotation in radio signals, finding that local TEC measurements outperform global models for precise ionospheric RM correction.

Contribution

The paper evaluates and compares the accuracy of different ionospheric models using new pulsar observations, highlighting the superiority of local TEC measurements over global models.

Findings

Models show substantial disagreement in RM predictions.

Local high-cadence TEC measurements outperform global models.

Corrections are needed to reconcile model differences.

Abstract

The ionosphere contributes time-varying Faraday Rotation (FR) to radio signals passing through it. Correction for the effect of the ionosphere is important for deriving magnetic field information from FR observations of polarized cosmic radio sources, as well as providing valuable diagnostics of the structure of the ionosphere. In this paper, we evaluate the accuracy of models commonly used to correct for its effects using new observations of pulsars at low frequencies, which provide total rotation measures (RM) at better precision than previously available. We evaluate models of the ionosphere derived from modern digital ionosondes that provide electron density information as a function of height, as well as GPS-derived Total Electron Content (TEC) measurements. We combine these density models with reference global magnetic field models to derive ionospheric RM contributions. We find that the models disagree substantially with each other and seek corrections that may explain the differences in RM prediction. Additionally we compare these models to global TEC models and find that local high-cadence TEC measurements are superior to global models for ionospheric RM correction.