Chapter 6

Oscillations in TRACE Observations of the Quiet-Sun Chromosphere

Quiet-Sun oscillations in the four TRACE ultraviolet passbands centred on 1700 Å, 1600 Å, 1216 Å and 1550 Å are studied using a wavelet-based technique. Both network and internetwork regions show oscillations with a variety of periods and lifetimes in all passbands. The most frequent network oscillation has a period of 283 s with a lifetime of 2-3 cycles in all passbands. These oscillations are discussed in terms of upwardly-propagating magnetohydrodynamic wave models. The most frequent internetwork oscillation has a period of 252 s, again with a lifetime of 2-3 cycles, in all passbands. The tendency for these oscillations to recur in the same position is discussed in terms of `persistent flashers'. The network contains greater oscillatory power than the internetwork at periods longer than 300 s in the low chromosphere. This value is shown to decrease to 250 s in the high chromosphere. The internetwork also displays a larger number of short-lifetime, long-period oscillations than the network, especially in the low chromosphere. Both network and internetwork regions contain a small number of non-recurring long-lifetime oscillations.