Implosion and Oscillation

From RHESSI Wiki

Introduction

We have many examples now of contracting motions at or before the impulsive phase of a solar flare (see, for example, Ref. [1], for one of the first reports, and an earlier Nugget.) Such an implosion is consistent with the idea of conservation of energy, since flare structures are basically volumes of almost pure magnetism (the plasma beta in the preflare corona is very low), and this implies that the energy storage can be represented by the volume integral of B² as a first approximation. So, to release energy, the volume must shrink at the same time - hence a magnetic implosion. The magnetic structure of a flare also can support oscillatory motions, and these can be excited as a simple mechanical response to the implosion. Another earlier Nugget reports such pulsations detectable even at gamma-ray energies.

This Nugget reports a particularly clear example of implosion and oscillation in flare SOL2012-03-09 (M6.4), observed well by many observatories (including RHESSI, of course). This flare revealed new characteristics of the development of the implosion, and of the nature of the resulting oscillations. We take the opportunity below to speculate a little on the consequences of these newly found properties.

The Flare

Figure 1: Left - an EUV image of the flare, essentially from above, showing the photospheric magnetic field as colored contours (two polarities), plus the line of a slit used to make plots of position vs. time. These are in the middle and right plots on different time scales. The CME-related dimming is very obvious, as are the contracting and oscillating loops. The diagonal line shows a rough guess at the propagation sequence of excitation of the oscillations. Note the different periods for the different loops.

Pulsations seen by GOES

A new interpretation

Conclusion

References

[1] "X-ray sources and magnetic reconnection in the X3.9 flare of 2003 November 3" (.pdf)