Abstract
SUMMARY We have analyzed IMD bursts recorded in the decimetric frequency band (- 1000 - 2500 MHz) for the first time with high time resolution of 20 - 50 ms and frequency less than 10 MHz. The main characteristics determined for the individual IMD bursts are: (i) the total duration is N 200 - 2000 ms; (ii) the frequency bandwidth, Av 1~ 50 - 150 MHz; (iii) the instantaneous bandwidth, Au/v N 2 - 12 %; (iw) all individual IMD bursts show negative frequency drift rate as ti 21 -30 - -270 MHz s-l; and (u) the ratio b/u ” -0.20 - -0.02 s-l. We discussed the application of Alfven wave models based on plasma emission and electron cyclotron maser emission mechanisms to IMD bursts observations. We find that the model with plasma emission can satisfy the requirements on the density and the magnetic field of the emission region for generation of the decimetric IMD bursts. The magnetic field strength in the source was estimated as N 30 ~ 150 G. Finally, we concluded that the maser model is not operative in the frequency range of our observations and also the whistler wave model predicts a dependence between ti and Y that does not agree with the present observations. ACKNOWLEDGEMENTS The BSS project is supported by INPE, CNPq and FAPESP. F.C.R. Fernandes and V. Krishan ac- knowledge receiving scholarship from MCT-CNPq (PCI-382499/2002-06) and FAPESP (01/06031-8), respec- tively. The participation of H.S. Sawant in 34th COSPAR Scientific Assembly was supported by FAPESP (01/00056-9). Thanks are due to the referees for suggestions and comments. REFERENCES Aurass, H., G. P. Chernov, M. Karlicky, et al., On a sequence of remarkable fine structures in the type IV burst of 24 April, 1985, Solar Phys., 112, 547-357, 1987. Benz, A. O., and G. Mann, Intermediate drift bursts and the coronal magnetic field, As&on.
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