Search NASA⌕ Search

SEARCH · Search NASA

Results for “solar flares”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

The allowed lines of O IV near 1340 A in high electron density solar flares

Intersystem lines of O IV near 1400 A have long been used as electron density diagnostics for solar plasmas at temperatures of around 160,000 K. In addition, however, several allowed lines of O IV near 1340 A should become visible in conditions of high plasma electron number density (greater than 10(exp 12)/cu cm), such as during a solar flare. We present observations of the 1340 A and 1400 A regions of the solar spectrum for two solar flares, obtained by the SO82B spectrograph on board Skylab. We examine three candidate lines for allowed O IV in the flare spectra which occur at the correct wavelengths, but show that two of these are actually blends dominated by resonantly excited molecular lines of H2. The third candidate line, at 1343.51 A, we identify as the O IV allowd line. We present the density and temperature sensitivity of the ratio of allowed and intersystem O IV lines R = I(1343.51 A)/I(1407.39 A). The 1343.51 A line is clearly present in the first solar flare spectrum, and the ratio value implies an electron density of log N(sub e) = 12.6. The second flare has a much weaker 1343.51 A profile, but again the ratio value implies a high electron density. Both these electron density values are in good agreement with estimates for each flare from independent diagnostic ratios. The simple presence alone of a clearly observed O IV 1343.51 A emission line implies an electron density greater than 10(exp 12)/cu cm.

Cook, J. W.↗
NASA NTRS1992

Imaging solar flares in hard X-rays using Fourier telescopes

The sun emits hard X-rays (above 10 keV) during solar flares. Imaging hard X-ray sources on the sun with spatial resolutions on the order of 1-5 arcsec and integration times of 1 sec will provide greater insight into the energy release processes during a solar flare. In these events, tremendous amounts of energy stored in the solar magnetic field are rapidly released leading to emission across the electromagnetic spectrum. Two Fourier telescope designs, a spatial modulation collimator and a rotating modulation collimator, were developed to image the full sun in hard X-rays (10-100 keV) in an end-to-end simulation. Emission profiles were derived for two hard X-ray solar flare models taken from the current solar theoretical literature and used as brightness distributions for the telescope simulations. Both our telescope models, tailored to image solar sources, were found to perform equally well, thus offering the designer significant flexibility in developing systems for space-based platforms. Given sufficient sensitive areas, Fourier telescopes are promising concepts for imaging solar hard X-rays.

Campbell, Jonathan W.↗
NASA NTRS1975

Studies of solar flares and impact craters in partially protected crystals

Solar-flare track gradients and microcrater densities were determined in two lunar rocks, and it was found that approximately 900 craters greater than or equal to 0.1 microns in diameter and between 10 and 15 times 10 to the minus sixth craters greater than or equal to 500 microns central pit diameter are produced per sq cm per yr per 2-pi steradians on the moon. There is no evidence for a change in the flux of particles producing submicron craters in the last 1,000,000 years. No anisotropy was found between lunar north and the plane of the ecliptic in the directional flux distribution of micrometeoroids producing submicron craters. In contrast to data reported by other investigators, the ratio of solar-flare track densities at 100-micron depth to the abundance of 0.1-micron craters/sq cm is determined to be approximately one for all samples studied.

Morrison, D. A.↗
NASA NTRS2018

Using Machine-Learning Methods and Expert Prediction Probabilities to Forecast Solar Flares

It has long been known that studying connection between solar flares and properties of magnetic field in active regions is very important for understanding the flare physics and developing space weather forecasts. The Helioseismic and Magnetic Imager onboard the Solar Dynamics Observatory (SDO/HMI) obtains tremendous amounts of magnetic field data products. However the operational NOAA Space Weather Prediction Center (SWPC) forecasts of solar flares still represent prediction probabilities issued by the experts. In this research we investigate the possibilities to enhance the daily operational flare forecasts performed at the SWPC by developing a synergy of the expert predictions and physics-based criteria, and by employing machine-learning methods. Among the physics-based criteria we consider the descriptors of the Polarity Inversion Line (PIL) and Space weather HMI Active Region Patches (SHARP), and derive from them daily characteristics of the entire Sun. We also consider the daily descriptors of the GOES Soft X-Ray (SXR) 1-8 Angstroms flux such as the flare history of the previous days and averaged X-Ray flux. We estimate the effectiveness in separation of flaring and non-flaring cases for each characteristic, as well as for the expert prediction probabilities, and find that some PIL, SHARP and SXR descriptors are as effective as the expert prediction probabilities and should be considered to issue the flare forecast. Finally, we train and test several Machine-Learning classification algorithms (Support Vector Classifiers with various kernel functions, k-Nearest Neighbor Classifier, Random Forest Classifier, and Neural Networks) using the most effective descriptors and expert prediction probabilities, and compare the obtained predictions with the current SWPC forecasts.

Machine-Learning↗
NASA NTRS2023

Formation of the Lyman Continuum during Solar Flares

The Lyman continuum (LyC; <911.12 Å) forms at the top of the chromosphere in the quiet Sun, making LyC a powerful tool for probing the chromospheric plasma during solar flares. To understand the effects of nonthermal energy deposition in the chromosphere during flares, we analyzed LyC profiles from a grid of field-aligned radiative-hydrodynamic models generated using the RADYN code as part of the F-CHROMA project. The spectral response of LyC, the temporal evolution of the departure coefficient of hydrogen, b 1 , and the color temperature, T c , in response to a range of nonthermal electron distribution functions, were investigated. The LyC intensity was seen to increase by 4–5.5 orders of magnitude during solar flares, responding most strongly to the nonthermal electron flux of the beam. Generally, b 1 decreased from 10 2 –10 3 to closer to unity during solar flares, indicating a stronger coupling to local conditions, while T c increased from 8–9 to 10–16 kK. T c was found to be approximately equal to the electron temperature of the plasma when b1 was at a minimum. Both optically thick and optically thin components of LyC were found to be in agreement with the interpretation of recent observations. The optically thick layer forms deeper in the chromosphere during a flare compared to quiescent periods, whereas the optically thin layers form at higher altitudes due to chromospheric evaporation, in low-temperature, high-density regions propagating upward. We put these results in the context of current and future missions.

Solar flares↗
NASA NTRS1974

A search for solar neutrons during solar flares

A new upper limit to the 1-20 MeV neutrons produced at the sun during large solar flares was obtained as a result of measurements made by a neutron detector on board the OGO-6 satellite. It was found that the 1-20 MeV solar neutron flux for the Nov. 2, June 13, June 15, Sept. 25, and Dec. 19, 1969, solar flare events cannot be greater than 0.05 n per sq cm per sec at the 95% confidence level. These measurements are consistent with the models proposed by Lingenfelter (1969) and Lingenfelter and Ramaty (1967) for solar neutron production during solar flares.

Ifedili, S. O.↗
NASA NTRS1980

Charge composition and energy spectra of ancient solar flare heavy nuclei

Nuclear tracks in olivine grains from three carbonaceous chondrites are analyzed to determine the energy spectra and charge compositions of solar flare heavy nuclei during the early history of the solar system. Track length measurements of grains irradiated before compaction into meteorites over 4 billion years ago were performed accompanied by calibration experiments using heavy ion beams from an accelerator to identify tracks formed by very heavy (Z between 20 and 28) and very very heavy (Z greater than or equal to 30) groups of nuclei in the Murchison, Murray and Cold Bokkeveld meteorite grains. The time-averaged spectral shape of the solar flare very heavy nuclei is found to be similar to that obtained in lunar sample studies and direct observations. The meteorite grains also reproduce the currently observed enrichment of low-energy heavy ions in solar cosmic rays with respect to photospheric levels, with enhancement factors from 2 to 12 in the energy interval 6-10 MeV/n. Variations of very very heavy/very heavy nuclei abundance ratios within individual kinetic energy intervals are interpreted as representing possible changes of solar flare activity on time scales of 10,000 years.

Goswami, J. N.↗
NASA NTRS1981

Unusual properties of particle events associated with solar flare gamma ray events

An attempt to establish a link between gamma rays observed at the earth with solar flare areas highly enriched with electrons is presented. Two hour averages of the counting rates of 5-100 MeV electrons and 25-145 MeV protons performed on the ISEE-3 spacecraft were correlated with solar flares with a maximum intensity of 6-11 MeV electrons and 25-44 MeV protons recorded by other observers. The coverage was part of the Solar Maximum Mission, which attained a 50 percent coverage. Gamma ray associated events showed high ratios of electrons to protons, about 0.2, and electrons with energies greater than 80 MeV were observed, which are values high enough to produce the highest gamma rays observed, 40 MeV. The available data for electron, proton, and rare isotope fluxes and the time histories of the fluxes are noted to provide a data base for further information on solar flares and particle acceleration mechanisms.

Evenson, P.↗
NASA NTRS1985

The mean ionic charge of silicon in 3HE-rich solar flares

Mean ionic charge of iron in 3He-rich solar flares and the average mean charge of Silicon for 23 #He-rich periods during the time interval from September 1978 to October 1979 were determined. It is indicated that the value of the mean charge state of Silicon is higher than the normal flare average by approximately 3 units and in perticular it is higher then the value predicted by resonant heating models for 3He-rich solar flares.

Luhn, A.↗
NASA NTRS2011

Latest Progress on the Gamma-Ray Imager/Polarimeter for Solar Flares (GRIPS)

We present the latest progress on building the balloon-borne Gamma-Ray Imager/Polarimeter for Solar flares (GRIPS) instrument, including testing and calibration of the detectors and development of the imaging and aspect systems. A continental-US test flight is slated for fall 2012. GRIPS will provide a near-optimal combination of high-resolution imaging, spectroscopy, and polarimetry of solar-flare gamma-ray/hard X-ray emissions from approx.20. keV to > approx.10 MeV. The spectrometer/polarimeter consists of sixteen 3D position-sensitive germanium detectors (3D-GeDs), where each energy deposition is individually recorded with an energy resolution of a few keV FWHM and a spatial resolution to within <0.1 cu mm. Imaging is accomplished by a single multi-pitch rotating modulator (MPRM), a 2.5-cm thick tungsten-alloy grid with pitches that range quasi-continuously from 1 to 13 mm. With the MPRM situated 8 meters from the spectrometer, this instrument will provide excellent image quality and unparalleled angular resolution at gamma-ray energies (12.5 arcsec FWHM), sufficient to separate the 2.2 MeV footpoint sources for almost all flares. Polarimetry is accomplished by analyzing the anisotropy of reconstructed Compton scattering in the 3D-GeDs (i.e. as an active scatterer), with an estimated minimum detectable polarization of a few percent at 150-650 keV in an X-class flare. GRIPS will address questions relevant to particle acceleration and energy release that ha-.e been raised by recent solar flare observations, such as: What causes the spatial separation between energetic electron producing hard X-rays and energetic ions producing gamma-ray lines? How anisotropic are the accelerated electrons, and why do relativistic electron dominate in the corona? How does the composition of accelerated and ambient material vary with space and time, and why?

Shih, Albert Y.↗
NASA NTRS2017

Cloudy with a Chance of Solar Flares: The Sun as a Natural Hazard

Space weather is a naturally occurring phenomenon that represents a quantifiable risk to space- and ground-based infrastructure as well as society at large. Space weather hazards include permanent and correctable faults in computer systems, Global Positioning System (GPS) and high-frequency communication disturbances, increased airline passenger and astronaut radiation exposure, and electric grid disruption. From the National Space Weather Strategy, published by the Office of Science and Technology Policy in October 2015, space weather refers to the dynamic conditions of the space environment that arise from emissions from the Sun, which include solar flares, solar energetic particles, and coronal mass ejections. These emissions can interact with Earth and its surrounding space, including the Earth's magnetic field, potentially disrupting technologies and infrastructures. Space weather is measured using a range of space- and ground-based platforms that directly monitor the Sun, the Earth's magnetic field, the conditions in interplanetary space and impacts at Earth's surface, like neutron ground-level enhancement. The NASA Goddard Space Flight Center's Space Weather Research Center and their international collaborators in government, industry, and academia are working towards improved techniques for predicting space weather as part of the strategy and action plan to better quantify and mitigate space weather hazards. In addition to accurately measuring and predicting space weather, we also need to continue developing more advanced techniques for evaluating space weather impacts on space- and ground-based infrastructure. Within the Earth's atmosphere, elevated neutron flux driven by atmosphere-particle interactions from space weather is a primary risk source. Ground-based neutron sources form an essential foundation for quantifying space weather impacts in a variety of systems.

neutron flux↗
NASA NTRS1985

On reflecting boundary behind the Earth's orbit at propagation of fast particles from solar flares

The flares of solar cosmic rays (SCR) associated with the presence of shocks in interplanetary magnetic field and with their propagation at significant heliocentric distances were always of great interest. Some events and problems concerning the peculiarities of propagation of flare CR in the interplanetary medium are considered. The distinguishing feature of such events is the presence of shock front behind the Earth's orbit having formed either directly in the process of shock generation on the Sun or at large heliocentric distances as a result of the interaction of fast and slow quasistationary recurrent solar wind (SW) streams. Based on the experimental material it is shown that the significant nonlinear disturbances in IMF behind the Earth's orbit can yield the occurrence of the additional SCR flux from shock front region as a result of the interaction of flare flux with shock and a partial reflection from it.

Nishkovskikh, A. S.↗
NASA NTRS1986

On magnetic field stochasticity and nonthermal line broadening in solar flares

Observations of nonthermal line broadening seen in solar flares by the Solar Maximum Mission satellite are discussed in light of recent results on the generation of magnetic field stochasticity. It is shown that a consistent model for the data can be constructed by assuming that the observations signal the destruction of an ambient magnetohydrodynamic equilibrium.

Antonucci, E.↗