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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 289 records · Page 16
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NASA NTRS2017

Detection and Interpretation of Long-lived X-Ray Quasi-Periodic Pulsations in the X-Class Solar Flare on 2013 May 14

Quasi-periodic pulsations (QPP) seen in the time derivative of the GOES soft X-ray light curves are analyzed for the X3.2 event on 2013 May 14. The pulsations are apparent for a total of at least two hours from the impulsive phase to well into the decay phase, with a total of 163 distinct pulses evident to the naked eye. A wavelet analysis shows that the characteristic timescale of these pulsations increases systematically from approx. 25 s at 01:10 UT, the time of the GOES peak, to approx. 100 s at 02:00 UT. A second ridge in the wavelet power spectrum, most likely associated with flaring emission from a different active region, shows an increase from approx. 40 s at 01:40 UT to approx. 100 s at 03:10 UT. We assume that the QPP that produced the first ridge result from vertical kink-mode oscillations of the newly formed loops following magnetic reconnection in the coronal current sheet. This allows us to estimate the magnetic field strength as a function of altitude given the density, loop length, and QPP timescale as functions of time determined from the GOES light curves and Ramaty High Energy Solar Spectroscopic Imager (RHESSI) images. The calculated magnetic field strength of the newly formed loops ranges from approx. 500 G at an altitude of 24Mm to a low value of approx. 10 G at 60 Mm, in general agreement with the expected values at these altitudes. Fast sausage-mode oscillations are also discussed and cannot be ruled out as an alternate mechanism for producing the QPP.

Dennis, Brian R.↗
NASA NTRS2017

Modeling and Measuring Charge-Sharing in Hard X-ray Imagers Using HEXITEC CdTe Detectors

The Rutherford Appleton Laboratory's HEXITEC ASIC has been designed to provide fine pixelated X-ray spectroscopic imaging in combination with a CdTe or CZT detector layer. Although HEXITEC's small pixels enable higher spatial resolution as well as higher spectral resolution via the small-pixel effect, they also increase the probability of charge sharing, a process which degrades spectral performance by dividing the charge induced by a single photon among multiple pixels. In this paper, we investigate the effect of this process on a continuum X-ray spectrum below the Cd and Te fluorescence energies (23 keV). This is done by comparing laboratory measurements with simulations performed with a custom designed model of the HEXITEC ASIC. We find that the simulations closely match the observations implying that we have an adequate understanding of both charge sharing and the HEXITEC ASIC itself. These results can be used to predict the distortion of a spectrum measured with HEXITEC and will help determine to what extent it can be corrected. They also show that models like this one are important tools in developing and interpreting observations from ASICs like HEXITEC.

Ryan, Daniel F.↗
NASA NTRS2017

Energy Release in the Solar Atmosphere from a Stream of Infalling Prominence Debris

Recent high-resolution and high-cadence extreme-ultraviolet (EUV) imaging has revealed a new phenomenon, impacting prominence debris, where prominence material from failed or partial eruptions can impact the lower atmosphere, releasing energy. We report a clear example of energy release and EUV brightening due to infalling prominence debris that occurred on 2011 September 7-8. The initial eruption of material was associated with an X1.8-class flare from AR 11283, occurring at 22:30 UT on 2011 September 7. Subsequently, a semicontinuous stream of this material returned to the solar surface with a velocity v greater than 150 km/s, impacting a region remote from the original active region between 00:20 and 00:40 UT on 2011 September 8. Using the Solar Dynamics Observatory/Atmospheric Imaging Assembly, the differential emission measure of the plasma was estimated throughout this brightening event. We found that the radiated energy of the impacted plasma was L(sub rad) approx. 10(exp 27) erg, while the thermal energy peaked at approx.10(exp 28) erg. From this we were able to determine the mass content of the debris to be in the range 2 x 10(exp 14) less than m less than 2 x 10(exp 15) g. Given typical prominence masses, the likely debris mass is toward the lower end of this range. This clear example of a prominence debris event shows that significant energy release takes place during these events and that such impacts may be used as a novel diagnostic tool for investigating prominence material properties.

Inglis, A. R.↗
NASA NTRS2018

Coronal Hard X-Ray Sources Revisited

This paper reports on the re-analysis of solar flares in which the hard X-rays (HXRs) come predominantly from the corona rather than from the more usual chromospheric footpoints. All of the 26 previously analyzed event time intervals, over 13 flares, are re-examined for consistency with a flare model in which electrons are accelerated near the top of a magnetic loop which has a sufficiently high density to stop most of the electrons by Coulomb collisions before they can reach the footpoints. Of particular importance in the previous analysis was the finding that the length of the coronal HXR source increased with energy in the 20–30 keV range. However, after allowing for the possibility that footpoint emission at the higher energies affects the inferred length of the coronal HXR source, and using analysis techniques that suppress the possible influence of such footpoint emission, we conclude that there is no longer evidence that the length of the HXR coronal sources increase with increasing energy. In fact, for the six flares and 12 time intervals that satisfied our selection criteria, the loop lengths decreased on average by 1.0 ± 0.2 arcsec between 20 and 30 keV, with a standard deviation of 3.5 arcsec. We find strong evidence that the peak of the coronal HXR source increases in altitude with increasing energy. For the thermal component of the emission, this is consistent with the standard CHSKP flare model in which magnetic reconnection in a coronal current sheet results in new hot loops being formed at progressively higher altitudes. The explanation for the nonthermal emission is not so clear.

Gamma rays↗
NASA NTRS2018

Determining the Mode, Frequency, and Azimuthal Wave Number of ULF Waves During a HSS and Moderate Geomagnetic Storm

Ultralow frequency (ULF) waves play a fundamental role in the dynamics of the inner magnetosphere and outer radiation belt during geomagnetic storms. Broadband ULF wave power can transport energetic electrons via radial diffusion, and discrete ULF wave power can energize electrons through a resonant interaction. Using observations from the Magnetospheric Multiscale mission, we characterize the evolution of ULF waves during a highspeed solar wind stream (HSS) and moderate geomagnetic storm while there is an enhancement of the outer radiation belt. The Automated Flare Inference of Oscillations code is used to distinguish discrete ULF wave power from broadband wave power during the HSS. During periods of discrete wave power and utilizing the close separation of the Magnetospheric Multiscale spacecraft, we estimate the toroidal mode ULF azimuthal wave number throughout the geomagnetic storm. We concentrate on the toroidal mode as the HSS compresses the dayside magnetosphere resulting in an asymmetric magnetic field topology where toroidal mode waves can interact with energetic electrons. Analysis of the mode structure and wave numbers demonstrates that the generation of the observed ULF waves is a combination of externally driven waves, via the KelvinHelmholtz instability, and internally driven waves, via unstable ion distributions. Further analysis of the periods and toroidal azimuthal wave numbers suggests that these waves can couple with the core electron radiation belt population via the drift resonance during the storm. The azimuthal wave number and structure of ULF wave power (broadband or discrete) have important implications for the inner magnetospheric and radiation belt dynamics.

Murphy, Kyle R.↗
NASA NTRS2019

The Refractive Index of Amorphous and Crystalline Water Ice in the UV-vis

Amorphous solid water (ASW) is found on icy dust grains in the interstellar medium (ISM), as well as on comets and other icy objects in the outer solar system. The optical properties of ASW are thus relevant for many astrophysical environments, but in the ultraviolet–visible (UV–vis), its refractive index is not well constrained. Here, we introduce a new method based on UV–vis broadband interferometry to measure the wavelength dependent refractive index n(λ) of amorphous water ice from 10 to 130 K, i.e., for different porosities, in the wavelength range of 210–757 nm. We also present n(λ) for crystalline water ice at 150 K, which allows us to compare our new method with literature data. Based on this, a method to calculate n(λ, ρ) as a function of wavelength and porosity is reported. This new approach carries much potential and is generally applicable to pure and mixed ice, both amorphous and crystalline. The astronomical and physical–chemical relevance and future potential of this work are discussed.

Kofman, Vincent↗
NASA NTRS2019

FOXSI-2 Solar Microflares: Multi-Instrument Differential Emission Measure Analysis

Outline: Overview of FOXSI-2 (Focusing Optics X-ray Solar Imager) coordinated microflare observations with Hinode/XRT (X-Ray Telescope) and SDO/AIA (Solar Dynamics Observatory/Atmospheric Imaging Assembly); Temperature response functions for FOXSI-2, XRT and AIA; Combined Differential Emission Measure (DEM) analysis - to determine the amount of plasma in the line of sight that emits the radiation as a function of temperature; Thermal energy released during the microflares; Summary.

Athiray, P. S.↗
NASA NTRS2019

Persistent Quasi-Periodic Pulsations During a Large X-Class Solar Flare

Solar flares often display pulsating and oscillatory signatures in the emission, known as quasi-periodic pulsations (QPP). QPP are typically identified during the impulsive phase of flares, yet in some cases, their presence is detected late into the decay phase. Here, we report extensive fine structure QPP that are detected throughout the large X8.2 flare from 2017 September 10. Following the analysis of the thermal pulsations observed in the Geostationary Operational Environmental Satellite/X-ray sensor and the 131 Å channel of Solar Dynamics Observatory/Atmospheric Imaging Assembly, we find a pulsation period of ~65 s during the impulsive phase followed by lower amplitude QPP with a period of ~150 s in the decay phase, up to three hours after the peak of the flare. We find that during the time of the impulsive QPP, the soft X-ray source observed with the Reuven Ramaty High Energy Solar Spectroscopic Imager rapidly rises at a velocity of approximately 17 km/s following the plasmoid/coronal mass ejection eruption. We interpret these QPP in terms of a manifestation of the reconnection dynamics in the eruptive event. During the long-duration decay phase lasting several hours, extended downward contractions of collapsing loops/plasmoids that reach the top of the flare arcade are observed in EUV. We note that the existence of persistent QPP into the decay phase of this flare are most likely related to these features. The QPP during this phase are discussed in terms of magnetohydrodynamic wave modes triggered in the post-flaring loops.

Hayes, Laura A.↗
NASA NTRS2019

AWARE: An Algorithm for the Automated Characterization of EUV Waves in the Solar Atmosphere

Conference Poster-Introduction Extreme ultraviolet (EUV) waves are large-scale propagating disturbances observed in the solar corona, frequently associated with coronal mass ejections and flares (Thompson et al., 1999, Thompson & Myers 2009). They appear as faint, extended structures propagating from a source region across the structured solar corona, making them difficult to isolate and measure. To further the understanding of EUV waves, we have constructed the Automated Wave Analysis and REduction (AWARE) algorithm for the measurement of EUV waves (Ireland et al, submitted). AWARE is implemented using the persistence transform, simple image processing operations and the RANSAC algorithm.

Ireland, Jack↗
NASA NTRS2019

Characteristics of Ephemeral Coronal Holes

Small-scale ephemeral coronal holes may be a recurring feature on the solar disk but have received comparatively little attention. These events are characterized by compact structures and short total lifetimes, which are substantially less than a solar disk crossing. We present a systematic search for these events, using Atmospheric Imaging Assembly extreme ultraviolet image data from the Solar Dynamics Observatory, covering the time period of 2010–2015. Following strict criteria, this search yielded four clear examples of the ephemeral coronal hole phenomenon. The properties of each event are characterized, including their total lifetime, growth and decay rates, and areas. The magnetic properties of these events are also determined using Helioseismic and Magnetic Imager data. Based on these four events, ephemeral coronal holes experience rapid initial growth of up to ∼3000 Msq.m/hr, while the decay phases are typically more gradual. Like conventional coronal holes, the mean magnetic field in each ephemeral coronal hole displays a consistent polarity, with mean magnetic flux densities generally <10 G. No evidence of a corresponding signature is seen in solar wind data at 1 au. Further study is needed to determine whether ephemeral coronal holes are under reported events or are truly rare phenomena.

Inglis, A. R.↗
NASA NTRS2019

AWARE: an Algorithm for the Automated Characterization of EUV Waves in the Solar Atmosphere

Extreme ultraviolet (EUV) waves are large-scale propagating disturbances observed in the solar corona, frequently associated with coronal mass ejections and flares. They appear as faint, extended structures propagating from a source region across the structured solar corona. To measure these waves, we have constructed the Automated Wave Analysis and REduction (AWARE) algorithm. AWARE is implemented in two stages. In the first stage, we use simple image processing techniques to isolate the propagating, brightening wave fronts as they move across the corona. In the second stage, AWARE measures the distance, velocity and acceleration of that wave front across the Sun. We explore the use of the Huygens principle, dynamic time warping and a simple parametric representation of the wave front as potential methods for detecting and tracking non-radial EUV wave propagation.

Ireland, Jack↗
NASA NTRS2022

Requirements for Progress in Understanding Solar Flare Energy Transport: The Impulsive Phase

Solar flares are a fundamental component of solar eruptive events (SEEs), along with solar energetic particles (SEPs) and coronal mass ejections (CMEs). Flare emission is the first component of a SEE to impact the Earth’s ionosphere which can set the stage for the later effects of the space weather event. Magnetic reconnection drives SEEs by restructuring the solar coronalmagnetic field, liberating a tremendous amount of energy which is partitioned into various physical manifestations: particle acceleration,mass and magnetic-field eruption, atmospheric heating, and the subsequent emission of radiation as solar flares. In this white paper we discuss the observational and theoretical advances required in order to make substantial progress in understanding the physical processes acting during the impulsive phase of a flare. That is, the initial rapid and intense period in which a tremendous amount of energy is released over the span of several minutes, resulting in the dramatic broadband increase to the solar radiative output. A second white paper by us covers the flare’s gradual phase, that is the decay phase where processes occur over longer timescales.

Graham S. Kerr↗
NASA NTRS2022

Requirements for Progress in Understanding Solar Flare Energy Transport: The Gradual Phase

Solar flares are a fundamental component of solar eruptive events (SEEs), along with solar energetic particles (SEPs) and coronal mass ejections (CMEs). Flare emission is the first component of a SEE to impact the Earth’s atmosphere which can set the stage for the later arrival of the associated SEPs, CME, and space weather event. Magnetic reconnection drives SEEs by restructuring the solar coronal magnetic field, liberating a tremendous amount of energy which is partitioned into various physical manifestations: particle acceleration, mass and magnetic-field eruption, atmospheric heating, and the subsequent emission of radiation as solar flares. In this white paper we discuss the observational and theoretical advances required in order to make substantial progress in understanding the physical processes acting during the gradual phase of a flare. That is, the decay period, following the initial rapid release of energy during the impulsive phase (see our other white paper). In particular we want to address the unknown processes that sustain the long decay phase of flares and identify the unknown mechanism and magnitude of continued energy injection during the gradual phase.

Graham S Kerr↗
NASA NTRS2022

Searching for Quasi-periodic Oscillations in Astrophysical Transients Using Gaussian Processes

Analyses of quasi-periodic oscillations(QPOs)are important to understanding the dynamic behavior in manyastrophysical objects during transient events like gamma-ray bursts, solarflares, magnetarflares, and fast radiobursts. Astrophysicists often search for QPOs with frequency-domain methods such as(Lomb–Scargle)periodograms, which generally assume power-law models plus some excess around the QPO frequency. Time-series data can alternatively be investigated directly in the time domain using Gaussian process(GP)regression.While GP regression is computationally expensive in the general case, the properties of astrophysical data andmodels allow fast likelihood strategies. Heteroscedasticity and nonstationarity in data have been shown to causebias in periodogram-based analyses. GPs can take account of these properties. Using GPs, we model QPOs as astochastic process on top of a deterministicflare shape. Using Bayesian inference, we demonstrate how to infer GPhyperparameters and assign them physical meaning, such as the QPO frequency. We also perform model selectionbetween QPOs and alternative models such as red noise and show that this can be used to reliablyfind QPOs. Thismethod is easily applicable to a variety of different astrophysical data sets. We demonstrate the use of this methodon a range of short transients: a gamma-ray burst, a magnetarflare, a magnetar giantflare, and simulated solarflare data.

Moritz Hubner↗
NASA NTRS2023

Global and Zonal-Mean Hydrological Response to Early Eocene Warmth

Earth's hydrological cycle is expected to intensify in response to global warming, with a “wet-gets-wetter, dry-gets-drier” response anticipated over the ocean. Subtropical regions (∼15°–30°N/S) are predicted to become drier, yet proxy evidence from past warm climates suggests these regions may be characterized by wetter conditions. Here we use an integrated data-modeling approach to reconstruct global and zonal-mean rainfall patterns during the early Eocene (∼56–48 million years ago). The Deep-Time Model Intercomparison Project (DeepMIP) model ensemble indicates that the mid- (30°–60°N/S) and high-latitudes (>60°N/S) are characterized by a thermodynamically dominated hydrological response to warming and overall wetter conditions. The tropical band (0°–15°N/S) is also characterized by wetter conditions, with several DeepMIP models simulating narrowing of the Inter-Tropical Convergence Zone. However, the latter is not evident from the proxy data. The subtropics are characterized by negative precipitation-evaporation anomalies (i.e., drier conditions) in the DeepMIP models, but there is surprisingly large inter-model variability in mean annual precipitation (MAP). Intriguingly, we find that models with weaker meridional temperature gradients (e.g., CESM, GFDL) are characterized by a reduction in subtropical moisture divergence, leading to an increase in MAP. These model simulations agree more closely with our new proxy-derived precipitation reconstructions and other key climate metrics and imply that the early Eocene was characterized by reduced subtropical moisture divergence. If the meridional temperature gradient was even weaker than suggested by those DeepMIP models, circulation-induced changes may have outcompeted thermodynamic changes, leading to wetter subtropics. This highlights the importance of accurately reconstructing zonal temperature gradients when reconstructing past rainfall patterns.

Margot J. Cramwinckel↗
NASA NTRSDate not supplied

Solar Flare Catalog for SPICE Instrument on the Solar Orbiter

Studying the solar corona, the outermost layer of solar atmosphere, is a pivotal part of understanding the dynamic relations between solar activity and the solar wind, which can disrupt the near-Earth environment. Solar flares emit electromagnetic radiation in the solar corona, capable of releasing large amounts of energy in a matter of minutes. Flares can also be associated with Coronal Mass Ejections (CMEs) and affect Earth’s ionosphere. One instrument that can be used to study flares is the Spectral Imaging of the Coronal Environment (SPICE) instrumentaboard the Solar Orbiter (SolO). SPICE is a high-resolution extreme ultraviolet stigmatic slit spectrometer that covers emission lines formed from the solar chromosphere to corona. Since SPICE is a stigmatic slit spectrometer, the instrument can only take in data from a small spatial area on the Sun at a time. Due to the fast and unpredictable nature of flare events, it can be difficult to determine if and when SPICE has observed a flare. For this reason, we have created a catalog of flares observed by SPICE. This catalog of observational data was assembledby cross referencing data between different solar missions, including data from SolO’s E xtreme Ultraviolet Imager (EUI) and Spectrometer Telescope for Imaging X-rays (STIX), Solar Dynamics Observatory’s Atmospheric Imaging Assembly (SDO/AIA) instrument, and the Geostationary Operational Environmental Satellite (GOES-R). Supplemental analysis of the SPICE solar flare data includes Gaussian line fitting for flares of particular interest. The catalog can be utilized to locate and study coronal loop structures and flare ribbons. This SPICE solar flare catalog and additional supplemental analysis allows for the ease of identification of useful SPICE spectral data and multi-instrument analysis in order to study solar flare activity. It will be open for use by the Solar Orbiter and broader Heliophysics communities.

Anneliese L. Schmidt↗