Halpha observations of the August 12, 1975 type III-RS (reverse slope) bursts.

Labonte, B. J., Halpha observations of the August 12, 1975 type III-RS (reverse slope) bursts., Sol. Phys., 50, 201-211 (1976) (ADS)

The cartoon

(click on the image for a larger version)

One of the crucial aspects of the thick-target scenario is that radio type III bursts almost invariably have particle beams that go up, whereas the model wants them to go down. Such downward-moving beams would show themselves as having reverse-slope frequency drift.

      But this is interesting. The Labonte paper studied a swarm of reverse-drift type III bursts, using Big Bear H-alpha data to follow up on the radio description, in terms of the presumed density distribution (and hence radio detectability) of the parent active region. The interpretation of these rare events was that they were the descending legs of U-bursts, rather than reconnection jet products as explored later on in the Aschwanden-Benz description. The thick-target model basically suggets that there should always be up- and down-jets, and perhaps two each for a total of four. Usually there is only one, if any.

Date: 2019 December 16