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Active region oscillations

“…In addition, we found that the Fe xvi and Mg ix lines shared roughly the same frequency bands in both the intensity and the velocity. Unfortunately due to the wavelet filtering applied by us, higher frequencies (>20 mHz) could not be distinguished from noise, and so the lowest periods that could be found by us are at ∼50 s. It is impossible therefore to compare with the lowest periods found in the literature, for example, the 43 s period found by Koutchmy et al (1983) or the values of 25 and 7 s found by Cowsik et al (1999). However, the few frequencies larger than 10 mHz (<100 s periods), found in the high frequency tails of the Mg ix and Fe xvi histograms in Figs.…”

“…From eclipse observations, Singh et al (1997) and Cowsik et al (1999) reported intensity oscillations with periods ∼5-100 s. These were interpreted as compressional magneto-acoustic waves. Furthermore, they showed that the fast mode oscillations in active regions can provide sufficient energy flux for heating of the solar corona, as was concluded earlier by Porter et al (1994).…”

“…McKenzie & Mullan (1997) reported loop oscillations in yohkoh/sxt images, revealing marginal oscillations in brightness with amplitudes of ∼1% and periods of 10-62 s. Ireland et al (1999) presented an analysis of active region oscillations for several transition region and coronal lines as observed by cds on soho. Cowsik et al (1999) reported on high frequency, low-amplitude continuum intensity oscillations in the solar corona during the total solar eclipse of 26 February 1998. Recently, Aschwanden et al (1999) detected spatial oscillations of coronal loops with trace.…”

A wavelet analysis of quasi-periodic variability across a solar coronal hole region

“…They find that short periods are more predominant in C  and suggest that there is even greater power at short periods in O  but the observations are restricted by a high noise level. McKenzie & Mullan (1997) use Yohkoh X-ray light curves obtained from a number of coronal loops and find periods in the range 10-62 s. Koutchmy et al (1983), Rušin & Minarovjech (1991), Cowsik et al (1999), Singh et al (1997) all use off-limb observations of the corona either in the red/green coronal lines or optical continuum and find periods in the range 5-90 s. In the previous work listed above short periods are found predominantly in the high temperature coronal lines with the exception of Hansteen et al (2001) who state that they find power below 100 s in the upper chromospheric C  1334 Å line. It is significant that this current analysis finds short periods in intensity present in lines across the temperature range log T e = 5.3-6.1 K. We find short periods that are not confined to coronal temperatures but are also found in the transition region.…”

“…Region Spectral range Period (s) Ireland (1997) Active Region EUV 300, 900-1200 Ireland et al (1999) Active Region Coronal Loop X-ray 10-62 Aschwanden et al (1999) Coronal Loop EUV ≈280 Koutchmy et al (1983) (Coronagraph) Green coronal line 43, 80, 300 Rušin & Minarovjech (1991) (Coronagraph) Red/Green coronal line 40, 60, 112, 300 Cowsik et al (1999) Off-limb (Eclipse) Optical continuum 7, 25, 90 Singh et al (1997) Off-limb (Eclipse) Optical continuum 5,6,8,14,20,57 the 42 s period then has six data points. All the short periods were still present except for the 59 s period found in Ne .…”