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Astron. Astrophys. 364, 785-792 (2000)

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4. Conclusion and discussion

Low-frequency nonlinear plasma currents could be excited by high-frequency oscillation via wave-wave and the wave-particle interactions, leading to excitation of a very low-frequency magnetic field. It is shown that the dynamic behavior and configuration for the self-generated field is determined by Eqs. (29) and (30). If we take [FORMULA] initially, then

[EQUATION]

i.e., the turbulent electric field in dimension is [FORMULA] V/m; the period and width are chosen as [FORMULA] and [FORMULA]. Fig. 2 gives the resulting field strength and the characteristic size as [FORMULA] and [FORMULA], respectively, and using Eqs. (32) and (33) yields

[EQUATION]

If we take [FORMULA] initially, i.e., [FORMULA] V/m, and take [FORMULA] and [FORMULA], the resulting field strength and characteristic size are [FORMULA] and [FORMULA] (see Fig. 3), i.e.,

[EQUATION]

If we take [FORMULA] initially, i.e., [FORMULA] V/m, and take [FORMULA] and [FORMULA], Fig. 4 gives the resulting field strength and characteristic size as [FORMULA] and [FORMULA], i.e.,

[EQUATION]

It is worth noting that Mckean et al. (1990, 1989) proposed a model for microwave spike bursts. In this model, the formation of fine structure is dependent on the existence of an intermittent magnetic field in coronal active regions. They inferred that the field would have a characteristic scale of 0.02 - 0.03 km (corresponding to [FORMULA]) and a strength of 250 - 500 Gauss (corresponding to [FORMULA]), which are similar to our results. In addition, it should be noted that the collapse tendency of self-generation magnetic fields is about the same for the three different initial values, although the resulting strength and characteristic size of such magnetic fields have slight difference in detail. This is a better result, which is not sensitive to the initial values.

On the other hand, the results of numerical analyses have shown that when [FORMULA] increases while [FORMULA] remains unchanged, the collapse of self-magnetic fields become fast; when [FORMULA] increases while [FORMULA] remains unchanged, the collapse of the self-magnetic fields becomes slow.

When the time scales are [FORMULA] (see Fig. 2), [FORMULA](see Fig. 3) and [FORMULA](see Fig. 4) respectively, the field collapses rapidly and leads to a very strong field. [FORMULA] and in this case the expansion Eq. (7) is no longer valid.

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© European Southern Observatory (ESO) 2000

Online publication: January 29, 2001
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