Long-period intensity pulsations in the solar corona during activity cycle 23

Abstract

We report on the detection (10 σ) of 917 events of long-period (3 to 16 hours) intensity pulsations in the 19.5 nm passband of the SOHO Extreme ultraviolet Imaging Telescope. The data set spans from January 1997 to July 2010, i.e the entire solar cycle 23 and the beginning of cycle 24. The events can last for up to six days and have relative amplitudes up to 100%. About half of the events (54%) are found to happen in active regions, and 50% of these have been visually associated with coronal loops. The remaining 46% are localized in the quiet Sun. We performed a comprehensive analysis of the possible instrumental artifacts and we conclude that the observed signal is of solar origin. We discuss several scenarios which could explain the main characteristics of the active region events. The long periods and the amplitudes observed rule out any explanation in terms of magnetohydrodynamic waves. Thermal nonequilibrium could produce the right periods, but it fails to explain all the observed properties of coronal loops and the spatial coherence of the events. We propose that moderate temporal variations of the heating term in the energy equation, so as to avoid a thermal nonequilibrium state, could be sufficient to explain those long-period intensity pulsations. The large number of detections suggests that these pulsations are common in active regions. This would imply that the measurement of their properties could provide new constraints on the heating mechanisms of coronal loops.

Above the Noise: The Search for Periodicities in the Inner Heliosphere

“…In addition, recovery of four-hour and nine-hour periods in the o1 box (in Figure 3) and the qs1 box (in Figure 5b) lie at the edges of the typical range of periods reported in Telloni et al (2013), but all are well within the range of periods previously recovered for a range of solar coronal structures (e.g. Ivanov, 1983;Foullon, Verwichte, and Nakariakov, 2004;Smirnova et al, 2013;Auchère et al, 2014). Furthermore, the o1 and qs1 detections are both marginally above global confidence levels and rely on the form of the fitted background power derived from Equation 1.…”

“…Periods of the order of an hour or longer have been recovered for several decades across a range of coronal instruments (e.g. by Ivanov, 1983;Foullon, Verwichte, and Nakariakov, 2004;Popescu et al, 2005;Auchère et al, 2014). The Solar Dynamics Observatory (SDO: Pesnell, Thompson, and Chamberlin, 2012) allows for continuous high-resolution and high-cadence measurements across a suite of instruments; this observatory has also contributed significantly to studies of long-period oscillatory features in recent years.…”

Closed-Field Coronal Heating Driven by Wave Turbulence

“…There are also indicators that hydrodynamic evolution along coronal loops can be quite common, especially for active regions. These include observations of coronal rain and catastrophic cooling cycles (Schrijver 2001;Antolin & Rouppe van der Voort 2012;Antolin et al 2015), as well as pervasive cooling signatures observed in extreme ultraviolet (Viall & Klimchuk 2011Auchère et al 2014;Froment et al 2015) and soft X-Ray imaging (Ugarte- Urra et al 2006). A successful heating model should be plausibly consistent with such observations.…”

The Coronal Monsoon: Thermal Nonequilibrium Revealed by Periodic Coronal Rain

“…Processing more than 13 years of quasi-continuous 12 minute-cadence observations with the 19.5nm passband of the Solar and Heliospheric Observatory (Domingo et al 1995) Extreme-ultraviolet Imaging Telescope (Delaboudinière et al 1995), we discovered 499 periodic (3-16 hr) intensity pulsation events in on-disk active regions, 268 of which are clearly associated with loops, and some lasting for up to six days (Auchère et al 2014). Froment (2016) found more than 2000 similar events in six years of images taken in the six coronal passbands of the Solar Dynamics Observatory (SDO; Pesnell et al 2012) Atmospheric Imaging Assembly (AIA; Lemen et al 2012).…”