M. O. Nazarenko

Radiotomography and HF ray tracing of the artificially disturbed ionosphere above the Sura heating facility

We present the results of the radiotomographic imaging of the artificial ionospheric disturbances obtained in the recent experiments on the modification of the midlatitude ionosphere by powerful HF radiowaves carried out at the Sura heater. Radio transmissions from low orbital PARUS beacon satellites recorded at the specially installed network of three receiving sites were used for the remote sensing of the heated ionosphere. We discuss the possibility to generate acoustic-gravity waves (AGWs) with special regimes of ionospheric heating (with the square wave modulation of the effective radiated power at the frequency lower than or of the order of the Brunt-Vaisala frequency of the neutral atmosphere at ionospheric heights during several hours) and present radiotomographic images of the spatial structure of the disturbed volume of the ionosphere corresponding to the directivity pattern of the heater, as well as the spatial structure of the wave-like disturbances, which are possibly heating-induced AGWs, diverging from the heated area of the ionosphere. We also studied the HF propagation of the pumping wave through the reconstructed disturbed ionosphere above the Sura heater, showing the presence of heater-created, field-aligned irregularities that effectively serve as “artificial radio windows.”

Solar flare forcing on ionization of upper atmosphere. comparative study of several major X-class events of 23rd and 24th solar cycles

By analyzing the GNSS (Global Navigational Satellite Systems) signals recorded at the IGS (International GNSS Service) network, we compare the effects of ionization of the upper atmosphere by a series of intense X-class solar flares during the 23rd and 24th solar cycles. We develop the methods for estimating the geo-effectiveness of solar flares from the GNSS data and suggest using the rate of change of the ionospheric total electron content averaged over all the receiving stations located on the sunlit side of the Earth reduced to the solar zenith angle during the flare as the characteristic of the flare’s geo-effectiveness.

Assessing the degree of ionospheric perturbation from radio tomographic data

The methods are suggested for constructing the ionospheric perturbation indices (IPIs) from the empirical electron density distributions retrieved by the ionospheric radio tomography (RT). The indices take into account the specificity of the low- and high-orbiting (LO and HO) RT data, their spatio-temporal resolution and coverage. We consider and analyze various schemes of IPIs construction, calculate the correlation between the IPIs and geomagnetic Kp index, identify the indices that are most sensitive to the geomagnetic activity factor.

Estimation of sea level variations with GPS/GLONASS-reflectometry technique

In the present paper we study GNSS - reflectometry methods for estimation of sea level variations using a single GNSSreceiver, which are based on the multipath propagation effects caused by the reflection of navigational signals from the sea surface. Such multipath propagation results in the appearance of the interference pattern in the Signal-to-Noise Ratio (SNR) of GNSS signals at small satellite elevation angles, which parameters are determined by the wavelength of the navigational signal and height of the antenna phase center above the reflecting sea surface. In current work we used GPS and GLONASS signals and measurements at two working frequencies of both systems to study sea level variations which almost doubles the amount of observations compared to GPS-only tide gauge. For UNAVCO sc02 station and collocated Friday Harbor NOAA tide gauge we show good agreement between GNSS-reflectometry and traditional mareograph sea level data.

Radio tomography imaging based on navigation systems

Methods of radio tomography (RT) based on the low- and high-orbital navigational systems and radio occultation data are considered. Examples of RT imaging of the ionosphere in different regions of the world illustrate the use of low-orbital and high-orbital radio tomography (LORT and HORT, respectively) separately and in combination with each other. RT methods allow studying of various ionospheric structures: troughs, travelling ionospheric disturbances (TIDs), spots of enhanced ionizations, patches, blobs, wavelike structures, manifestations of particle precipitation. The possibilities for the application of RT systems together with other methods of UV and radio sounding are discussed.