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Register a new userQuasi-periodic pulsation detected in Lyman-alpha emission during solar flares
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We investigated the quasi-periodic pulsation (QPP) in Lyman-alpha, X-ray and extreme-ultraviolet (EUV) emissions during two solar flares, i.e., an X-class (SOL2012-01-27T) and a C-class (SOL2016-02-08T). The full-disk Lyman-alpha and X-Ray flux during these solar flares were recorded by the EUV Sensor and X-Ray Sensor on board the Geostationary Operational Environmental Satellite. The {deg}are regions were located from the EUV images measured by the Atmospheric Imaging Assembly. The QPP could be identified as a series of regular and periodic peaks in the light curves, and its quasi-periodicity was determined from the global wavelet and Fourier power spectra. A quasi-periodicity at about 3 minutes is detected during the impulsive phase of the X-class flare, which could be explained as the acoustic wave in the chromosphere (e.g., Milligan et al. 2017). Interestingly, a quasi-periodicity at roughly 1 minute is discovered during the entire evolutionary phases of solar flares, including the precursor, impulsive, and gradual phases. This is the first report of 1-minute QPP in the Lyman-alpha emission during solar flares, in particular during the flare precursor. It may be interpreted as a self-oscillatory regime of the magnetic reconnection, such as magnetic dripping.
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We report quasi-periodic pulsations (QPPs) with double periods during three solar flares (viz. SOL2011-Feb-15T01:44, SOL2011-Sep-25T04:31, SOL2012-May-17T01:25). The flare QPPs were observed from light curves in Ly$alpha$, hard X-ray (HXR) and microwave emissions, with the Ly$alpha$ emission recorded by the Geostationary Operational Environmental Satellite, the HXR emission recorded by the Reuven Ramaty High-Energy Solar Spectroscopic Imager and the Fermi Gamma-ray Burst Monitor, and the microwave emission recorded by the Nobeyama Radio Polarimeters and Radioheliograph. By using the Markov chain Monte Carlo (MCMC) method, QPPs with double periods of about two minutes and one minute were first found in the Ly$alpha$ emission. Then using the same method, a QPP with nearly the same period of about two minutes was also found in HXR and microwave emissions. Considering the possible common origin (nonthermal electrons) between Ly$alpha$ and HXR/microwave emission, we suggest that the two-minute QPP results from the periodic acceleration of nonthermal electrons during magnetic reconnections. The ratio between the double periods in the Ly$alpha$ emission was found to be close to two, which is consistent with the theoretical expectation between the fundamental and harmonic modes. However, we cannot rule out other possible driving mechanisms for the one-minute QPPs in HXR/microwave emissions due to their relatively large deviations.
The chromospheric Lyman-alpha line of neutral hydrogen (lya; 1216AA) is the strongest emission line in the solar spectrum. Fluctuations in lya are known to drive changes in planetary atmospheres, although few instruments have had the ability to capture rapid lya enhancements during solar flares. In this paper we describe flare-associated emissions via a statistical study of 477 M- and X-class flares as observed by the EUV Sensor on board the 15th Geostationary Operational Environmental Satellite, which has been monitoring the full-disk solar lya irradiance on 10~s timescales over the course of Solar Cycle 24. The vast majority (95%) of these flares produced lya enhancements of 10% or less above background levels, with a maximum increase of $sim$30%. The irradiance in lya was found to exceed that of the 1-8 AA X-ray irradiance by as much as two orders of magnitude in some cases, although flares that occurred closer to the solar limb were found to exhibit less of a lya enhancement. This center-to-limb variation was verified through a joint, stereoscopic observation of an X-class flare that appeared near the limb as viewed from Earth, but close to disk center as viewed by the MAVEN spacecraft in orbit around Mars. The frequency distribution of peak lya was found to have a power-law slope of $2.8pm0.27$. We also show that increased lya flux is closely correlated with induced currents in the ionospheric E-layer through the detection of the solar flare effect as observed by the Kakioka magnetometer.
We report a quasi-periodic pulsation (QPP) event simultaneously detected from the spatial displacements of coronal loop at both EUV images and microwave emission during the preflare phase of a C1.1 flare on 2016 March 23. Using the motion magnification technique, a low-amplitude transverse oscillation with the growing period is discovered in a diffuse coronal loop in Atmospheric Imaging Assembly (AIA) image sequences at wavelength of 171 A, and the initial oscillation period is estimated to be ~397 s with a slow growth rate of 0.045. At the same time, a QPP with growing periods from roughly 300 s to nearly 500 s is discovered in the microwave flux in the same active region. Based on the imaging observations measured at EUV wavelengths by the AIA and at microwave 17 GHz by Nobeyama Radioheliograph, the diffuse coronal loop and the microwave radiation source are found to be connected through a hot loop seen in AIA images at wavelength of 94 A. The growing period of the QPP should be related to the modulation of LRC-circuit oscillating process in a current-carrying plasma loop. The existence of electric currents may imply the non-potentialities in the source region during the preflare phase.
Small amplitude quasi-periodic pulsations (QPPs) detected in soft X-ray emission are commonplace in many flares. To date, the underpinning processes resulting in the QPPs are unknown. In this paper, we attempt to constrain the prevalence of textit{stationary} QPPs in the largest statistical study to date, including a study of the relationship of QPP periods to the properties of the flaring active region, flare ribbons, and CME affiliation. We build upon the work of cite{inglis2016} and use a model comparison test to search for significant power in the Fourier spectra of lightcurves of the GOES 1--8~AA channel. We analyze all X-, M- and C- class flares of the past solar cycle, a total of 5519 flares, and search for periodicity in the 6-300~s timescale range. Approximately 46% of X-class, 29% of M-class and 7% of C-class flares show evidence of stationary QPPs, with periods that follow a log-normal distribution peaked at 20~s. The QPP periods were found to be independent of flare magnitude, however a positive correlation was found between QPP period and flare duration. No dependence of the QPP periods to the global active region properties was identified. A positive correlation was found between QPPs and ribbon properties including unsigned magnetic flux, ribbon area and ribbon separation distance. We found that both flares with and without an associated CME can host QPPs. Furthermore, we demonstrate that for X- and M- class flares, decay phase QPPs have statistically longer periods than impulsive phase QPPs.
Recent studies of interstellar neutral (ISN) hydrogen observed by the Interstellar Boundary Explorer (IBEX) suggested that the present understanding of the radiation pressure acting on hydrogen atoms in the heliosphere should be revised. There is a significant discrepancy between theoretical predictions of the ISN H signal using the currently used model of the solar Lyman-alpha profile by Tarnopolski et al. 2009 (TB09) and the signal due to ISN H observed by IBEX-Lo. We developed a new model of evolution of the solar Lyman-alpha profile that takes into account all available observations of the full-disk solar Lyman-alpha profiles from SUMER/SOHO, provided by Lemaire et al. 2015 (L15), covering practically the entire 23rd solar cycle. The model has three components that reproduce different features of the profile. The main shape of the emission line that is produced in the chromosphere is modeled by the kappa function; the central reversal due to absorption in the transition region is modeled by the Gauss function; the spectral background is represented by the linear function. The coefficients of all those components are linear functions of the line-integrated full-disk Lyman-alpha irradiance, which is the only free parameter of the model. The new model features potentially important differences in comparison with the model by TB09, which was based on a limited set of observations. This change in the understanding of radiation pressure, especially during low solar activity, may significantly affect the interstellar H and D distributions in the inner heliosphere and their derivative populations.
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