If an infinitely long, straight, cylindrical thread model, with the tube fully filled with cool and dense material (Figure 31), is assumed, a comparison between the observed wave properties and the theoretical prediction can be made. This enabled Lin et al. (2009) to obtain estimates for some physical parameters of interest, namely the Alfvén speed and the magnetic field strength in the studied threads. To this end, the observed phase velocity was directly associated to the kink speedet al. (2009) assumed that thread oscillations observed from the H sequences were the result of a propagating kink mode, which implies that the measured phase velocity, , is equal to the kink speed. Then, the thread Alfvén speed can be computed from
The inferred values of for the ten selected threads are displayed in Table 2 in Lin et al. (2009). The results show a strong dispersion, suggesting that the physical conditions in different threads were very different in spite of belonging to the same filament. This result clearly reflects the highly inhomogeneous nature of solar prominences. Once the Alfvén speed in each thread was determined, the magnetic field strength could be computed after a value for the thread density was assumed. For the analyzed events, and considering a typical value = 5 × 10–11 kg m–3, magnetic field strengths in the range 0.9 – 3.5 G were obtained (see Figure 63b).
Living Rev. Solar Phys. 9, (2012), 2
This work is licensed under a Creative Commons License.