### Direct Observations of Traveling Ionospheric Disturbances as  Focusers of Solar Radiation: Spectral Caustics by A. Koval et al*

2019-08-27

The solar radiation focusing effect is related to the specific phenomenon of propagation of the Sun-emitted HF and VHF waves through the terrestrial ionosphere. This natural effect is observed with ground-based radio instruments running within the 10-200 MHz range, as distinctive patterns – the Spectral Caustics (SCs) – on the solar dynamic spectra. On the spectrograms they exhibit unusual morphology and specific time-frequency features (CESRA nugget by Koval et al., […]

### The effect of scattering on the apparent positions of solar radio sources observed by LOFAR by Mykola Gordovskyy

2019-05-21

Radio sources observed in the decametric range during type II and type III solar radio bursts are believed to be produced by coherent plasma emission due to electrostatic plasma oscillations induced by propagating suprathermal electrons (e.g. Ginzburg & Zhelezniakov 1958). This type of emission is a valuable tool for observational diagnostics of the upper corona. Produced at the local plasma frequency, $f_{pe}\rm{[kHz]}= 8.93 (n_e\rm{[cm}^{-3}\rm{]})^{-1/2}$ or its harmonic, plasma emission can reveal […]

### High‐Frequency Communications Response to Solar Activity in September 2017 as Observed by Amateur Radio Networks by Nathaniel A. Frissell

2019-05-07

Long before satellite communications, high frequency (HF, 3–30 MHz) radio was the primary method for long distance, over-the-horizon wireless communications. HF signals are able to travel long distances by refracting off of the ionosphere in what is known as “skip” or “skywave” propagation. Aside from a transmitter and receiver, no additional technological infrastructure is needed. Because of this, even in the modern age of space‐borne relays and widely distributed Internet availability, […]

### Simulation of Focusing Effect of Traveling Ionospheric Disturbances on Meter-Decameter Solar Dynamic Spectra by A. Koval et al*

2019-01-02

Traveling ionospheric disturbances (TIDs) are one particular type of the Earth’s ionosphere irregularities (Hunsucker, 1982). They represent wave-like electron density structures propagating in the ionosphere. The motion of TIDs modulates the electron density distribution in space. It leads to a modification of plasma parameters, namely the refractive index, and affects the propagation of radio waves. In particular cases, the variations of plasma parameters strongly affect the lower-frequency electromagnetic waves that […]