V. D. Vyakhirev

Ionospheric response to the partial solar eclipse of March 29, 2006, according to the observations at Nizhni Novgorod and Murmansk

The results of observations of the solar eclipse ionospheric effects on March 29, 2006, are presented. The observations were conducted using the partial reflection method near Nizhni Novgorod and the vertical sounding method at the automatic ionospheric station near Murmansk. It has been obtained that the electron density at altitudes of 77 and 91 km decreases by a factor of more than 4; in this case the response of the ionosphere at an altitude of 91 km lags behind the eclipse maximum phase on the Earth by approximately 20 min. It has been established that the eclipse in the E and F1 regions of the polar ionosphere causes a change in the electron density by 15–20%. The delay time of this effect varies from 12 to 24 min depending on the altitude. It has been registered that the reflection virtual altitude at altitudes of the ionospheric F region increases in Murmansk and Nizhni Novgorod.

Studies of the Ionospheric D -Region Using Partial Reflections in Spring 2004 at Middle and High Latitudes

Results of the observations of the ionospheric effects of two solar flares in April 2004 performed using partial reflections are presented. The studies were carried out at the measuring facilities located in different latitudinal regions: at Vasil’sursk station in the Nizhni Novgorod region and at Tumannyi station in the Murmansk region. The quantitative estimates of the electron density in the polar and midlatitude D region under quiet conditions and during solar flares were obtained. The correlation between rapid variations in electron concentration at heights of about 80 km at these stations was found and it was shown that during solar flares the electron density at heights of 60–70 km corresponds to the intensity of the X-ray flux in the range of 0.5–3 Å, which points to the action of the linear law of recombination in the ionospheric D region.

Earth’s lower ionosphere during partial solar eclipses according to observations near Nizhny Novgorod

The results of observations in the Vasil’sursk Laboratory (56.1° N, 46.1° E) of partial solar eclipses of August 11, 1999, August 1, 2008, and March 20, 2015 are discussed. Ionospheric observations in the eclipse periods and on control days were conducted by the method of resonant scatter of radio waves at artificial periodic irregularities of the ionospheric plasma and the partial reflection method based on radio wave scatter by natural irregularities in the D region. The lower ionosphere reaction to solar eclipses, including variations in the electron concentration and characteristics of the signals scattered by APIs, was studied. An intensification of the lower ionosphere turbulization, an increase in the signal amplitudes backscattered by APIs in the E region, stratification of the D region, and the arrival of scattered signals from mesopause heights were observed during the eclipses. A decrease in the electron concentration of the D region up to a factor of 3–5 was found by the partial reflection method. Above 88 km, the ionospheric response was delayed by 20–25 min relative to the moment of the eclipse maximum phase, whereas this delay in the lower part of the D region was 2–4 min.

Vertical Velocities and Temperature of the Neutral Component in the Upper Atmosphere

Results of measurements of the velocity of the vertical plasma motion and the temperature of the neutral component in the upper atmosphere and comparison of variations in these parameters have been described. The measurements have been carried out by the resonance scattering of radio waves by artificial periodic irregularities in the ionospheric plasma. The irregularities arise when the ionosphere is modificated by a powerful high-frequency radio emission from a Sura midlatitude heating facility. Comparison has been conducted using experimental data on altitude- and time-dependent variations in the above parameters obtained in experiments of 2010 and 2014. It has been shown that, above 100 km, wavelike variations in temperature and velocity are commonly observed simultaneously. In the absence of wavelike variations, there is a tendency to an increase in temperature with an increase in the velocity of the vertical plasma motion regardless of direction. This tendency can be attributed to thermal flows directed upward from the turbulent region of the ionosphere.

Studies of the ionospheric D region using partial reflections and radiowave scattering by artificial periodical irregularities

Results of the studies of the ionospheric D region during spring periods of 2004 and 2005 using partial reflections and radiowave scattering by artificial periodical irregularities are presented. It has been found that the vertical profile of the electron density during this period has a local minimum at a height of ∼75 km, which is absent in summer. The causes of the minimum appearance are discussed.

Artificial periodic inhomogeneities and a model for the lower part of theD region

The measured height profiles of the relaxation time and amplitudes of artificial periodic inhomogeneities (API) in the ionospheric D region are compared with the model. It is shown that the height dependences of the relaxation time of APIs and the amplitude of the scattered signal can be explained taking into account the hieght profile of the atmosphere density. Most probably, the upper boundary of APIs in the D region is due to the increase in the atomic oxygen density and can serve as an altitude indicator.