Open AccessQuasilinear‐based simulations of bidirectional type III bursts
Author(s) -
Li Bo,
Robinson Peter A.,
Cairns Iver H.
Publication year - 2008
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2008ja013255
Subject(s) - physics , flux (metallurgy) , brightness , computational physics , noise (video) , astrophysics , scattering , plasma , atomic physics , optics , materials science , quantum mechanics , artificial intelligence , computer science , metallurgy , image (mathematics)
Quasilinear‐based simulations are presented of bidirectional type III bursts that originate in the corona and are observed at Earth, assuming plasma emission. By extending a recent simulation model to more realistic three‐dimensional source structures and including Langmuir collisional damping, dynamic spectra of both the normal‐drifting (normal) and the reverse‐slope‐drifting (RS) bursts are simulated and studied in detail for realistic electron‐release and coronal parameters. The radio flux, brightness temperature, frequency drift rate, and time duration of the bursts agree semiquantitatively with typical observations. The flux of 2 f p emission is significantly higher than that of f p emission, which is below the noise thresholds of typical radio instruments. This is mainly because the f p emission is strongly free‐free absorbed and further damped by scattering off density fluctuations. The 2 f p emission is asymmetric between the normal and RS bursts, with the normal burst stronger and lasting longer than the RS burst, consistent with observations. This occurs primarily because of the downgoing beam being weaker, not faster, and narrower in velocity space than the upgoing beam, and because of stronger free‐free absorption for the RS burst than for the normal burst, consistent with a semiquantitative theory. Furthermore, the RS burst terminates at frequencies lower than the maximum simulated, and the normal burst extends to lower frequencies not simulated because of computational limitations. Collisional damping reduces the Langmuir wave levels and consequently suppresses the flux levels and washes out the dynamic spectral structures associated with successive wave‐wave interactions when the damping is switched off.