Ultra-Long-Period Oscillations in Euv Filaments Near to Eruption: Two-Wavelength Correlation and Seismology

Abstract

We investigate whether or not ultra-long-period oscillations in EUV filaments can be related to their eruption. We report new observations of long-period (∼10-30 hr) oscillatory motions in an apparently quiescent filament, as it crosses the solar disk in a 12 minute cadence SOHO/Extreme-Ultraviolet Imaging Telescope (EIT) 195 Å uninterrupted data set. This data set is chosen to explore characteristics of the filament oscillations depending on its eruptive behavior, which is observed while the filament is still on the disk. The periods are found to increase in a near-stable regime prior to eruption. For the two sequences reported so far, we compare and link the EUV filament oscillations with pulsations in full-disk solar EUV irradiance from SOHO/CELIAS/SEM 304 Å flux measurements. In intervals with stationary periods, we find that the 304 Å pulsations and the 195 Å filament oscillations have similar periodicities, but are phase-shifted by about a quarter of period. The two-wavelength correlation serves to show that, when the filament is the dominant dynamical feature but can no longer be tracked on the disk, the full-disk irradiance may provide a mean to identify the period increase prior to the filament eruption. We use the periods thus obtained to estimate the height increase of filaments' suspending coronal magnetic field lines, based on a magnetohydrodynamic (MHD) wave interpretation of the oscillations. The results are consistent with changes in prominence heights detected off-limb and thus support the seismological tool employed. Other interpretations connected with thermal overstability or MHD piston effect are possible. These theoretical predictions however do not explain the quarter-period shift between the two EUV-wavelength signals. In any case, the detected variations may provide a powerful diagnostic tool for the forecasting of prominence eruptions.

Leakage of long-period oscillations from the chromosphere to the corona

“…Wang et al (2009) reported two significant periodicities of 12 and 25 min in the intensity and Doppler shift variations over a coronal diffuse structure with Hinode/EIS. Prominence oscillations with periods ranging from 20 min up to several hours were reported as well (Foullon et al 2004(Foullon et al , 2009Tripathi et al 2009;Hershaw et al 2011).…”

Oscillatory motions observed in eruptive filaments

“…The dominant period is 12.1 h. Pouget et al (2006) report five to six hour period oscillations detected in the Doppler velocity of a quiescent filament, in He I at 584.33 Å. Foullon et al (2009) show that the long period detected in a quiescent filament, using 195 Å images, increases prior to its eruption.…”

Prominence Oscillations

“…However, this classification (solely based on the period value) is far from complete: Balthasar et al (1993) observed a prominence simultaneously with the GCT and VTT telescopes in Tenerife to remove doubts about the instrumental or atmospheric origin of prominence oscillations and obtained strong power in the Doppler shift from both telescopes with period around 30 s; hence, very short-period small amplitude oscillations also exist. Furthermore, a few works in which prominences have been observed from space during extended time intervals show that very long-period oscillations also exist: Pouget et al (2006) detected periodicities of 5 -6 h, while Foullon et al (2004) and Foullon et al (2009) have observed variations in EUV filaments with periods around 12 h, and 10 -30 h, respectively. Although the classification in terms of shortperiod, long-period, etc.…”