Observations of Powerful Type III Bursts in the Frequency Range 10 – 30 MHz

Abstract

The properties of powerful (flux > 10 −19 W m −2 Hz −1 ) type III bursts observed in July -August 2002 by the radio telescope UTR-2 at frequencies 10 -30 MHz are analyzed. Most bursts have been registered when the active regions associated to these bursts were located near the central meridian or at 40°-60°to the East or West from it. All powerful type III bursts drift from high to low frequencies with frequency drift rates 1 -2.5 MHz s −1 . It is important to emphasize that according to our observations the drift rate is linearly increasing with frequency. The duration of the bursts changes mainly from 6 s at frequency 30 MHz up to 12 s at 10 MHz. The instantaneous frequency bandwidth does not depend on the day of observations, i.e. on the disk location of the source active region, and is increasing with frequency.The results of observational properties are discussed in the frame of the standard plasma model of type III bursts radio emission.

Large-scale simulations of solar type III radio bursts: flux density, drift rate, duration, and bandwidth

“…with A ∼ 0.1 and B ∼ 1 MHz is found by Melnik et al (2011) between 10 and 30 MHz similar to that found by Wild (1950) of…”

Properties of Decameter IIIb–III Pairs

“…In these cases IIIb-III pairs have the same properties as III-III pairs except for the fine frequency structure of Type IIIb bursts in the form of stria-bursts (Abranin et al, 1976(Abranin et al, , 1979. Decame-ter IIIb-III pairs observed in July -August 2002 were discussed by Melnik et al (2011). Their main properties were the same as for fundamental-harmonic pairs.…”

“…It is six times smaller than for the harmonic at 38 MHz (Dulk, Suzuki, and Sheridan, 1984). Drift rates of decametre fundamentals and harmonics are mainly close and equal to 2 -4 MHz s −1 (Melnik et al, 2011). Heights and apparent source sizes of fundamentals and harmonics (both components are Type III bursts) are practically the same and both increase with wavelengths (Dulk, Suzuki, and Sheridan, 1984).…”

“…However, the situation is different. Usually the frequency dependences of burst durations are approximated by a power law (Elgaroy and Lyngstad, 1972, Suzuki and Dulk, 1985, Melnik et al, 2011, Rutkevych and Melnik, 2012)…”

Revisiting the Frequency Drift Rates of Decameter Type III Solar Bursts Observed in July – August 2002

“…In a very recent work Reid and Kontar (2018), using a selection of type III bursts observed in the frequency range 30-70 MHz by LOFAR between April-September 2015, have shown that the drift rate of the bursts can also be fitted by a power-law function of frequency. On the other hand, Melnik et al (2011) note that the connection between drift rate and frequency for powerful solar type III bursts for each day of observations in July-August 2002 is linear, df /dt = −Af + B, where A and B are constants varying from day to day, and the contribution of B in df /dt attains 33.3 % in 10 MHz and 12.2 % in 30 MHz. It should be noted that this study was carried out at the mean frequencies 11.5,14,17.5,22.5 and 27.5 MHz. In this way 163 bursts of July 2002 and 231 bursts of August 2002 have been analyzed.…”