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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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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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