Abstract
In this work, we study the impact of high-energy radiation induced by solar X-ray flares on the determination of the temporal change in precipitable water vapor (ΔPWV) as estimated using the synthetic aperture radar (SAR) meteorology technique. As recent research shows, this radiation can significantly affect the ionospheric D-region and induces errors in the estimation of the total electron content (TEC) by the applied models. Consequently, these errors are reflected in the determination of the phase delay and in many different types of measurements and models, including calculations of meteorological parameters based on SAR observations. The goal of this study is to quantify the impact of solar X-ray flares on the estimation of ΔPWV and provide an estimate of errors induced if the vertical total electron content (VTEC) is obtained by single layer models (SLM) or multiple layer models (MLM) (these models do not include ionosphere properties below the altitude of 90 km as input parameters and cannot provide information about local disturbances in the D-region). The performed analysis is based on a known procedure for the determination of the D-region electron density (and, consequently, the vertical total electron content in the D-region (VTECD)) using ionospheric observations by very low frequency (VLF) radio waves. The main result indicates that if the D-region, perturbed by medium-sized and intense X-ray flares, is not modeled, errors occur in the determination of ΔPWV. This study emphasizes the need for improved MLMs for the estimation of the TEC, including observational data at D-region altitudes during medium-sized and intense X-ray flare events.
Highlights
Earth observations based on remote sensing by synthetic aperture radar (SAR) signals can be applied to different types of detection and modeling
We study how neglecting the D-region electron density temporal variations in the determination of the total electron content by single and multiple layer models affects results in synthetic aperture radar meteorology when this ionospheric region is significantly disturbed
We present an analysis of the correction factors that should be included in the determination of differences in the wet component of tropospheric phase delay and precipitable water vapor obtained by synthetic aperture radar meteorology during a solar X-ray flare event
Summary
Earth observations based on remote sensing by synthetic aperture radar (SAR) signals can be applied to different types of detection and modeling. Even if the temporal sampling frequency of SAR PWV maps is lower than that of the global navigation satellite system (GNSS) PWV measurements, their higher spatial resolution has a positive impact when assimilated in numerical weather prediction (NWP) models [6,7,8,9]. This can enhance the capability of NWP models to compute the propagation delay in the atmosphere [10] with advantages in other InSAR applications (e.g., the measurement of terrain displacements [11,12,13] and snow water equivalent (SWE) [14,15])
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