Chapter 6 presents an automated wavelet analysis approach to searching for oscillations in intensity in a large number of light curves from both the network and internetwork. This permits a comparison study, in terms of both periodicity and lifetime, of oscillations present in these two regions of the quiet Sun. The network displays a higher peak periodicity ( ~280 s) than the internetwork ( ~250 s). In the lower chromosphere the network also displays a large number of oscillations at higher periods, which may be the signature of kink-mode waves. In both regions, oscillations around these peak values (and with a lifetime of 2-3 cycles) show a tendency to recur in the same spatial position, suggesting a good degree of spatial memory. On the other hand, oscillations with a long lifetime (>8 cycles) do not recur, suggesting the driving source may be expending all its energy in the creation of the initial oscillation.
A study of oscillations in each UV passband shows upwardly-propagating waves in both the network and internetwork. The sudden decrease in oscillation strength (and number) in the 1550 Å band is attributed to waves dissipating, shocking or moving away in the high chromosphere. The cross-over period (i.e., the minimum period at which the network exhibits more oscillatory power than the internetwork) is shown to increase from ~250 s in the low chromosphere to ~300 s in the high chromosphere. The time-localised nature of wavelet analysis is used to show that even in these high-period regimes the internetwork can still exhibit more oscillatory power, but only for oscillations with short lifetimes.
A study into the spatial position of pixels displaying different periodicities and lifetimes may answer some of the questions posed in this chapter. It may be useful to apply this method to higher cadence TRACE quiet-Sun datasets and other instruments. It can also be extended into a third spatial region between the network and internetwork (classified as `intermediate' in Krijger et al. 2001). In a wider context, this technique can be used in other areas of solar physics (e.g., active regions) or astronomy in general where a search for transient, spatially-localised, oscillatory power is required (e.g., multi-target wide-field imaging).
The automated aspect of the wavelet analysis in Chapter 6 is worth discussing. With the large datasets expected from future space missions (e.g., Solar Dynamics Observatory may produce up to 1 terabyte per day), it will impossible to manually inspect every light curve for periodicity. Automated routines must be created to filter through datasets and detect interesting features. In this respect an automated search for both periodicity and possible propagating waves is essential. A search for horizontal flows can also be carried out by detecting the starting time of any oscillations. This may make near real-time detections of solar phenomena a possibility.