“Drift Pair” Solar Bursts at Decameter Wavelengths

Abstract

The solar drift pair bursts observed with the UTR-2 radiotelescope during the noise storm of 13-15 July, 2002 are reported. Using the new back-end facility with high time and frequency resolution has allowed new information on the structure and features of these bursts. More than 700 drift pairs were analyzed statistically separately for the “forward” and “reverse” bursts. Both “forward” and “reverse” drift pairs are noted to have a number of similar characteristics such as the time delay between their elements, the duration of an element, the instantaneous bandwidth. However, they are essentially different, primarily in the average frequency drift rate. Thus, for the “forward” bursts the average frequency drift rate is 0.8 MHz/s, while for the “reverse” ones it equals 2 MHz/s. The obtained empirical dependencies “flux density vs. frequency” and “drift rate vs. frequency” were found to be different from those currently known. Some unusual drift pair variants observed are reported, in particular, the “hook” bursts and drift pairs with fine time and frequency structure. A new generation mechanism of drift pairs is proposed which implies their emission originating in the interaction between the Langmuir waves l and the magneto-sonic waves M having equal phase and group velocities (the processes l+M=t, l+M=t+M.