Abstract. We analyse properties of 58 type II radio bursts recorded in the meter-to-kilometer wavelength range, focusing on episodes of band-split emission. The basic two parameters utilized are the frequency drift D f = d f /dt and the relative band-split BDW = ∆ f / f of type II burst emission lanes. On average, in the meter-to-kilometer wavelength range D f increases with the emission frequency as D f ∝ f 1.83 , revealing that source velocities are smaller at larger heliocentric distances. The relative bandsplit shows a weak but statistically significant dependence on the emission frequency, BDW ∝ f −0.06 , indicating an increase of BDW with the heliocentric distance. Combining the shock velocity estimated from the frequency drift, with the Mach number inferred from the band-split, the Alfvén speed and the magnetic field in the ambient plasma can be estimated as a function of the heliocentric distance r. However, the outcome directly depends on the coronal/interplanetary density model used, which is poorly known in the upper corona and the near-Sun interplanetary space. So, we invert the problem: utilizing the results of the previous paper where it was shown that beyond the heliocentric distance of two solar radii (r/r = R > 2) the average magnetic field decreases approximately as B ∝ R −2 , we infer the density n(R) in the upper corona and near-Sun interplanetary space. The obtained empirical dependence n(R) is presented in the analytical form as a four-degree polynomial of 1/R, and is compared with some theoretical n(R) models, considering also a deviation from the B ∝ 1/R 2 scaling used. The model matches the five-fold Saito density model (representing the active region corona) with the n ∝ R −2 regime in the interplanetary space. Furthermore, it is shown that on average the magnetosonic speed attains a local minimum of v ms ≈ 400 km s −1 around R = 3 and a broad local maximum of v ms ≈ 500 km s −1 in the range R = 4−6, beyond which it gradually decreases to several tens km s −1 at 1 a.u. The local minimum becomes even deeper if the super-radial expansion of the magnetic field is taken into account. The implications regarding the formation and evolution of shocks in the corona and upper corona are discussed in the framework of CME-piston and flare-blast scenarios. The inferred general decrease of type II burst source velocities and broadening of band-splits with distance is interpreted in terms of the deceleration of mass ejections driving the shocks in the decreasing v ms environment.

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Abstract. First time scales of high-frequency (500−1500 MHz) slowly drifting pulsating structures observed during the April 12, 2001 flare by the Ondřejov (800−4500 MHz) and Potsdam (40−800 MHz) radiospectrographs and by the 1420 and 610 MHz Trieste radiopolarimeters (with high time resolution (1 ms)) are studied statistically. The Fourier method reveals periods in the range of 0.9−7.5 s. For shorter periods the power spectra show a power-law form, especially in the interval of about 0.06−0.2 s, where the power-law index is in the 1.3−1.6 range. The results are interpreted using the flare model with plasmoid ejections. For the first time, the multi-scale cascading reconnection process is included in the interpretation. Corresponding time scales are estimated analytically. Further, magnetic reconnection in the bursting regime is simulated in a 2-D MHD model and variations of the dissipation power and radio radiation measure are computed. Fourier spectra of these numerical variations are determined and compared with those obtained from observations.

Abstract. Using both linear and nonlinear methods, narrow band dm-spikes recorded at 1420 and 2695 MHz on June 6, 2000, July 8, 2000, July 12, 2000, July 20, 2000, and March 28, 2001 were analyzed. In particular their time profiles were studied statistically. The mean characteristic times of the ascending and of the decaying parts of their profiles are comparable, even if the dispersion of the values is very broad. For selected spikes at 1420 MHz a more precise fitting technique using exponential profiles was applied. While in the decaying part the exponential trend can be generally found, in the ascending part the exponential form can be confirmed only in few cases. The ascending and decaying phase of spikes presumably correspond to the source instability evolution and the plasma wave absorption. Furthermore, durations and polarization values of both 1420 and 2695 MHz spikes were determined and compared with the results in literature. All the analyzed spike events were located near the solar disk center. The polarization values and their trend in spike groups and the nearly constant duration suggest that the polarization originates at the source itself or near it. Selected time series of spikes were tested with respect to low-dimensional determinism and nonlinearity. We found that spikes recorded at fixed frequencies are not governed by a linear stochastic process, as the underlying physical system contains nonlinear signatures.

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