Solar Flare X?Ray Impacts on Long Subionospheric VLF Paths

Solar flares increase the electron number concentration in daytime ionosphere, potentially affecting radiowave propagation over several frequency ranges. In this study, we use ionospheric observations to determine both peak magnitudes and time variations of solar flare X-rays without using direct measurement from flare. Ground-based VLF transmitter phase perturbations are compared against measured X-ray flux levels during flares. Flare fluxes derived here phases on a west-east subionospheric path with those previously analyzed north-south path. Using wider selection flares, including M-class for first time, best-fit equations root mean square (RMS) errors computed improved standard deviation (SD) uncertainty estimates fluxes. Good agreement is found between long wavelength (XL, 0.1–0.8 nm) X-class by GOES satellites. Linear regression analysis two paths shows uncertainties inverse proportion length. Investigations were made limited set “operational” parameters that could be used derive XL No increases RMS or SD introduced removal satellite-based such as level before onset. As such, these techniques support idea nowcasting entirely ground-based measurements.