Millisecond pulsations of solar radio emission:
New possibilities of plasma diagnostics

V. F. Melnikov
Radiophysical Research Institute, Nizhnii Novgorod, Russia
G. D. Fleishman
Physico-Technical Institute, St Petersburg, Russia
Q. J. Fu
National Astronomical Observatories, Beijing, China
G. L. Huang
Purple Mountain Observatory, Nanjing, China

Narrowband millisecond pulsations of microwave solar radio emission with oscillations of both intensity and polarization are studied. Large delays between R- and L- polarized components are found. The pulsating radio emission is proved to be generated by nonlinear plasma mechanism at the second harmonics of local upper-hybrid frequency. The observed oscillations of the polarization degree arise due to difference in the group velocities of ordinary and extraordinary waves along the line of sight. The frequency dependence of the delay is in excellent agreement with theoretical prediction. Moreover, the dependences of the delays on frequency contain information on both wave dispersion in the magnetized plasma and effect of source inhomogeneity, both of them are studied. In particular, the gradients of plasma density and/or magnetic field are found to be enhanced in the radio source cite, providing preferable conditions for the upper-hybrid wave instability to operate.


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