V. E. Shaposhnikov

Modulation structures in the dynamic spectra of Jovian radio emission obtained with high time-frequency resolution

Aims. The wide-band dynamic spectra of Jovian decameter emission obtained over the last decade with high-frequency and high time resolution equipment on the largest decameter band antenna array, the Ukrainian T-shape Radio telescope (UTR-2), are presented. Methods. We analyzed the data obtained with the Digital SpectroPolarimiter (DSP) and WaveForm Reciever (WFR) installed at UTR-2. The combination of the large antenna and high performance equipment gives the best sensitivity and widest band of analysis, dynamic range, time and frequency resolutions. The wavelet transform method and the Fourier technique was used for further data processing. Results. The main characteristics of already known and newly detected modulation events were investigated and specified. The new receiving-recording facilities, methodology and program of observations are described in detail.

Noise nature investigation of sporadic Jovian decameter emission

The “superfine” time structure of the Jovian S burst decameter emission has been investigated with the aim to clarify the noise nature of the given radiation. The Jovian Io-B noise storm taken for analysis in the paper has been observed on June 8, 1997, with an acousto-optical spectrograph designed at the Observatory Nancay, and incorporated into the giant Kharkov, Ukraine, UTR-2 radio telescope, operating from 10 to 25 MHz. The presence of the flicker noise component in the processed signals has been shown with an application of the wavelet transform and maximum likelihood techniques. The spectral parameters γ characterizing such processes have been calculated for different frequencies and different time intervals. The set of randomly distributed pulses has been considered as one of the possible models of S bursts adiation, capable for producing this noise process.

Origin of ultraviolet emission source in the Jovian ionosphere at the feet of the Io flux tube

A model for an explanation of far ultraviolet (FUV) emissions observed from the Io flux tube footprints at the Jovian ionosphere is presented. An acceleration of electrons and ions of the ionospheric plasma up to sufficient energies for an effective excitation of H2 Lyman and Werner bands is proposed. The neutral particles within the Jovian ionosphere are excited due to their collisions with the charged particles relatively moving to the neutrals in the ionospheric plasma. The motion is induced by the Ampere force which arises due to the interaction between the electric current flowing within the Io magnetic flux tube and its own specific magnetic field. It is established that only a sufficiently strong field-aligned current is capable of providing the required velocity of the relative motion. Our estimates show that in principle the proposed mechanism can provide the level of FUV emissions observed from the Io flux tube footprints.