Reach out, touch space

A quick look at the stellar week of outreach activitites that formed part of NAM202

Prevalence of non-stationarity in quasi-periodic pulsations (QPPs) associated with M- and X- class solar flares

Quasi-periodic pulsations (QPPs) are frequently observed in solar and stellar flare emission, with recent studies suggesting that an increasing instantaneous period is a common characteristic of QPPs. Determining the prevalence of non-stationarity in QPPs contributes to a better understanding of which mechanism(s) is (are) responsible in QPP generation. We obtain the rate of period evolution from QPPs in 98 M- and X- class flares from Solar Cycle 24 with average periods between 8-130 s and investigate the prevalence of QPP non-stationarity. We also investigate whether the presence of a Coronal Mass Ejection (CME) impacts the period evolution of QPPs. We analyse soft X-ray lightcurves obtained from GOES- X-Ray Sensor (XRS) and assess the dominant periods in the impulsive and decay phases of the flares using the Fast Fourier Transform. We relate the rate of period evolution to flare duration, peak flare energy, and average QPP period. We find evidence of non-stationarity in 81% of the flares assessed, with most QPPs exhibiting a period evolution of ≤10 s between the impulsive and decay phases, of which 66% exhibited an apparent period growth and 14% showed an apparent period shrinkage. We find a positive correlation between the absolute magnitude of period evolution and the duration of the flare and no correlation between the period evolution of the QPPs and flare energy or CME presence. Furthermore, we conclude that non-stationarity is common in solar QPPs and must be accounted for in flare analysis

Cycle dependence of a quasi-biennial variability in the solar interior

We investigated the solar cycle dependence on the presence and periodicity of the Quasi-Biennial Oscillation (QBO). Using helioseismic techniques, we used solar oscillation frequencies from the Global Oscillations Network Group (GONG), Michelson Doppler Imager (MDI), and Helioseismic and Magnetic Imager (HMI) in the intermediate-degree range to investigate the frequency shifts over Cycles 23 and 24. We also examined two solar activity proxies, the F10.7 index and the Mg ii index, for the last four solar cycles to study the associated QBO. The analyses were performed using Empirical Mode Decomposition (EMD) and the Fast Fourier Transform (FFT). We found that the EMD analysis method is susceptible to detecting statistically significant Intrinsic Mode Functions (IMFs) with periodicities that are overtones of the length of the data set under examination. Statistically significant periodicities, which were not due to overtones, were detected in the QBO range. We see a reduced presence of the QBO in Cycle 24 compared to Cycle 23. The presence of the QBO was not sensitive to the depth to which the p-mode travelled, nor the average frequency of the p-mode. The analysis further suggested that the magnetic field responsible for producing the QBO in frequency shifts of p-modes is anchored above approximately 0.95 R⊙

A blueprint of state-of-the-art techniques for detecting quasi-periodic pulsations in solar and stellar flares

Quasi-periodic pulsations (QPPs) appear to be a common feature observed in the light curves of both solar and stellar ares. However, their quasi-periodic nature, along with the facts that they can be small in amplitude and short-lived, make QPPs difficult to unequivocally detect. In this paper, we test the strengths and limitations of state-of-the-art methods for detecting QPPs using a series of hare-and-hounds exercises. The hare simulated a set of ares, both with and without QPPs of a variety of forms, while the hounds attempted to detect QPPs in blind tests. We use the results of these exercises to create a blueprint for anyone who wishes to detect QPPs in real solar and stellar data. We present eight, clear recommendations to be kept in mind for future QPP detections, with the plethora of solar and stellar are data from new and future satellites. These recommendations address the key pitfalls in QPP detection, including detrending, trimming data, accounting for coloured noise, detecting stationary-period QPPs, detecting QPP with non-stationary periods, and ensuring detections are robust and false detections are minimized. We find that QPPs can be detected reliably and robustly by a variety of methods, which are clearly identied and described, if the appropriate care and due diligence is taken

A study of solar quasi-oscillatory signals

We observe quasi-oscillatory behaviour frequently in solar data, for example in the quasi-biennial oscillation visible in magnetic activity proxies and quasi-periodic pulsations in flares. These behaviours have to be fully understood in order for our solar models to be complete. We can assess these behaviours using a host of analysis techniques that are capable of tracking the quasi-periodicities inherent in these data. In this thesis we use Empirical Mode Decomposition on helioseismic data to examine the quasi biennial oscillation and establish that there is a significant risk of spurious detections when used on short duration data. We also use a combination of the Fast Fourier Transform and Wavelet analysis to obtain the prevalence of non-stationarity in quasi-periodic pulsations using GOES data. We find that quasi-periodic behaviours are extremely common in solar data. We determine that the relative amplitude of the quasi-biennial oscillation is correlated with the amplitude of the solar cycle. We obtain evidence of low magnitude non-stationarity in the majority of quasi-periodic pulsations. Finally we conclude that understanding quasi-oscillatory behaviour is essential to form a complete understanding of the Sun, its dynamo, its magnetic field, and all associated behaviours

Reconnection microjets in the pre-eruption phase of a prominence/coronal rain complex

Coronal rain is known to be one of the highest resolution tracers of the coronal magnetic field. In this work the dynamics of a prominence/coronal rain complex are analysed based on imaging and spectroscopic observations with IRIS. Prior to eruption, the loop-like magnetic field arcade hosting the rain is observed to slowly expand in height. This movement is accompanied by several small (~1 arsec) and short (<20 sec) bursts of plasma perpendicular to the field, captured in the Si IV and Mg II lines. The line profiles are broad and asymmetric with long tails above ~100 km/s. These microjets are accompanied with strong intensity enhancements along the loop in most of the AIA channels, indicating significant energy release. We interpret these microjets as reconnection outflows, produced by component reconnection as the magnetic structure expands transversely. The originally cold conditions of the rain allows in this case a unique high resolution glance at the reconnection dynamics in low beta plasmas

A Blueprint of State-of-the-art Techniques for Detecting Quasi-periodic Pulsations in Solar and Stellar Flares

status: publishe