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* News 04/04/20 * The archive is using a new backend database. This has thrown up a few SQL errors in the last few days. If you have any issues please email adavey@nso.edu with either the number of eprint you are trying to edit or a link to your preprint.

Statistical Study of GOES X-ray Quasi-Periodic Pulsations in Solar Flares  

Laura Hayes   Submitted: 2020-04-26 19:23

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 extit{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.

Authors: Laura A. Hayes, Andrew R. Inglis, Steven Christe, Brian Dennis, Peter T. Gallagher
Projects: None

Publication Status: Accepted The Astrophysical Journal
Last Modified: 2020-04-27 10:45
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Pulsations in the Earth's Lower Ionosphere Synchronized with Solar Flare Emission  

Laura Hayes   Submitted: 2017-10-09 03:09

Solar flare emission at X-ray and extreme ultraviolet (EUV) energies can cause substantial enhancements in the electron density in the Earth's lower ionosphere. It has now become clear that flares exhibit quasi-periodic pulsations with timescales of minutes at X-ray energies, but to date, it has not been known if the ionosphere is sensitive to this variability. Here, using a combination of Very Low Frequency (24 kHz) measurement together with space-based X-ray and EUV observations, we report pulsations of the ionospheric D-region, which are synchronized with a set of pulsating flare loops. Modeling of the ionosphere show that the D-region electron density varies by up to an order of magnitude over the timescale of the pulsations (~ 20 mins). Our results reveal that the Earth's ionosphere is more sensitive to small-scale changes in solar soft X-ray flux than previously thought, and implies that planetary ionospheres are closely coupled to small-scale changes in solar/stellar activity.

Authors: Laura A. Hayes, Peter T. Gallagher, Joseph McCauley, Brian R. Dennis, Jack Ireland, Andrew Inglis
Projects: None

Publication Status: Accepted JGR Space Physics
Last Modified: 2017-10-09 15:58
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Quasi-Periodic Pulsations During the Impulsive and Decay Phases of an X-class Flare  

Laura Hayes   Submitted: 2016-07-26 02:49

Quasi-periodic pulsations (QPP) are often observed in X-ray emission from solar flares. To date, it is unclear what their physical origins are. Here, we present a multi-instrument investigation of the nature of QPP during the impulsive and decay phases of the X1.0 flare of 28 October 2013. We focus on the character of the fine structure pulsations evident in the soft X-ray time derivatives and compare this variability with structure across multiple wavelengths including hard X-ray and microwave emission. We find that during the impulsive phase of the flare, high correlations between pulsations in the thermal and non-thermal emissions are seen. A characteristic timescale of ~20s is observed in all channels and a second timescale of ~55s is observed in the non-thermal emissions. Soft X-ray pulsations are seen to persist into the decay phase of this flare, up to 20 minutes after the non-thermal emission has ceased. We find that these decay phase thermal pulsations have very small amplitude and show an increase in characteristic timescale from ~40s up to ~70s. We interpret the bursty nature of the co-existing multi-wavelength QPP during the impulsive phase in terms of episodic particle acceleration and plasma heating. The persistent thermal decay phase QPP are most likely connected with compressive MHD processes in the post-flare loops such as the fast sausage mode or the vertical kink mode.

Authors: Laura A. Hayes, Peter T. Gallagher, Brian R. Dennis, Jack Ireland, Andrew R. Inglis, Daniel F. Ryan
Projects: None

Publication Status: ApJL Accepted
Last Modified: 2016-07-26 15:00
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Abstracts by Author
Statistical Study of GOES X-ray Quasi-Periodic Pulsations in Solar Flares
Pulsations in the Earth?s Lower Ionosphere Synchronized with Solar Flare Emission
Quasi-Periodic Pulsations During the Impulsive and Decay Phases of an X-class Flare

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