Generation of intermediate drift bursts in solar type IV radio continua through coupling of whistlers and Langmuir waves |
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| Authors: | Jan Kuijpers |
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| Institution: | 1. Sterrekundig Instituut, Utrecht, The Netherlands
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| Abstract: | The possible generation of intermediate drift bursts in type IV dm continua through coupling between whistler waves, traveling along the magnetic field, and Langmuir waves, excited by a loss-cone instability in the source region, is elaborated. We investigate the generation, propagation and coupling of whistlers. It is shown that the superposition of an isotropic background plasma of 106K and a loss-cone distribution of fast electrons is unstable for whistler waves if the loss-cone aperture 2α is sufficiently large (sec α?4); a typical value of the excited frequencies is 0.1 ω ce (ω ce is the angular electron cyclotron frequency). The whistlers can travel upwards through the source region of the continuum along the magnetic field direction with velocities of 21.5–28 v A (v A is the Alfvén velocity). Coupling of the whistlers with Langmuir waves into escaping electromagnetic waves can lead to the observed intermediate drift bursts, if the Langmuir waves have phase velocities around the velocity of light. In our model the instantaneous bandwith of the fibers corresponds to a frequency of 0.1–0.5 ω ce and leads to estimates of the magnetic field strength in the source region. These estimates are in good agreement with those derived from the observed drift rate, corresponding to 21.5–28 v A, if we use a simple hydrostatic density model. |
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