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At least 1,099 records · Page 61
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

Geomagnetic activity and local modulations of cosmic rays circa 1 GV

Solar-sector synchronous modulations of the particulate cosmic radiation reaching the earth's atmosphere have been studied using low altitude satellite and surface data. The flux in the broad maximum of the galactic cosmic ray differential spectrum (near GV rigidity) exhibits an intermittent north-south asymmetry (NSA) in mid and high geomagnetic latitudes. During the 1964 and 1965 years of sunspot minimum, this modulation had a negative rigidity dependence and strong correlations with geomagnetic disturbance index (ap) and interplanetary magnetic field direction. Taken together with other features, this ap dependence is consistent with the hypothesis that reconnection of the interplanetary and geomagnetic fields should produce a local NSA independent of much larger scale NSAs associated with cosmic ray gradients in the heliosphere. This finding is also consistent with suggestions that solar activity influence on atmospheric processes may be mediated by the resulting modulations of upper tropospheric ionization.

Ely, J. T. A.↗
NASA NTRSDate not supplied

MaGIXS 2: Preparations for the Second Flight of the Marshall Grazing Incidence X-ray Spectrometer

Overview MaGIXS is a slitless soft X-ray (SXR) imaging spectrometer designed to observe solar active regions. - The instrument produces spatially resolved SXR spectra, known as “overlappograms.” (Athiray et al. 2019 & Champey et al., 2022) The first sounding rocket flight of the Marshall Grazing Incidence X-ray Spectrometer occurred on July 30, 2021 from the White Sands Missile Range, New Mexico. - Spectrally pure images of X-ray bright points were obtained through the inversion of overlappograms, e.g. Fig. 3 (Savage et al., 2022). MaGIXS 2 is a simplified version of the original design, less the spectrometer mirror pair. - Eliminating the spectrometer mirror pair improves spatial resolution, increases effective area and the field of view (Table 1). No field stop in this design, data will be an overlappogram with the same spatial and spectral plate scale.

x-ray spectrometer, x-ray optics, solar corona, so↗
NASA NTRSDate not supplied

An Overview of MaGIXS-2, The Second Flight of the Marshall Grazing Incidence X-ray Spectrometer

MaGIXS is a slitless soft X-ray (SXR) imaging spectrometer designed to observe solar active regions. - The instrument produces spatially resolved SXR spectra, known as “overlappograms.” (Athiray et al. 2019 & Champey et al., 2022) The first sounding rocket flight of the Marshall Grazing Incidence X-ray Spectrometer occurred on July 30, 2021 from the White Sands Missile Range, New Mexico. - Spectrally pure images of X-ray bright points were obtained through the inversion of overlappograms, e.g. Fig. 3 (Savage et al., 2022). MaGIXS 2 is a simplified version of the original design, less the spectrometer mirror pair. - Eliminating the spectrometer mirror pair improves spatial resolution, increases effective area and the field of view (Table 1). No field stop in this design, data will be an overlappogram with the same spatial and spectral plate scale.

x-ray spectrometer, x-ray optics, solar corona, so↗
NASA NTRS1984

Modulation of solar irradiance by active regions

Hoyt and Eddy (1983) have modeled solar irradiance by accounting for active regions. It is presently noted, however, in contradiction to this model, that in active region modeling of solar irradiance care should be taken to not merely employ average contrasts of faculae. This caveat is especially applicable if the model proceeds to ignore the active region facular areas when their contrasts are low, since this doubly devalues the faculae contribution relative to that of sunspots.

Schatten, K. H.↗
DOE OSTI2016

The effects of the ionosphere on ground-based detection of the global 21 cm signal from the cosmic dawn and the dark ages

Detection of the global H i 21 cm signal from the Cosmic Dawn and the Epoch of Reionization is the key science driver for several ongoing ground-based and future ground-/space-based experiments. The crucial spectral features in the global 21 cm signal (turning points) occur at low radio frequencies ≲100 MHz. In addition to the human-generated radio frequency interference, Earth’s ionosphere drastically corrupts low-frequency radio observations from the ground. In this paper, we examine the effects of time-varying ionospheric refraction, absorption, and thermal emission at these low radio frequencies and their combined effect on any ground-based global 21 cm experiment. It should be noted that this is the first study of the effect of a dynamic ionosphere on global 21 cm experiments. The fluctuations in the ionosphere are influenced by solar activity with flicker noise characteristics. The same characteristics are reflected in the ionospheric corruption to any radio signal passing through the ionosphere. As a result, any ground-based observations of the faint global 21 cm signal are corrupted by flicker noise (or 1/f noise, where f is the dynamical frequency) which scales as ν{sup −2} (where ν is the frequency of radio observation) in the presence of a bright galactic foreground (∝ν{sup −s}, where s is the radio spectral index). Hence, the calibration of the ionosphere for any such experiment is critical. Any attempt to calibrate the ionospheric effects will be subject to the inaccuracies in the current ionospheric measurements using Global Positioning System (GPS) ionospheric measurements, riometer measurements, ionospheric soundings, etc. Even considering an optimistic improvement in the accuracy of GPS–total electron content measurements, we conclude that Earth’s ionosphere poses a significant challenge in the absolute detection of the global 21 cm signal below 100 MHz.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

ARGO-YBJ OBSERVATION OF THE LARGE-SCALE COSMIC RAY ANISOTROPY DURING THE SOLAR MINIMUM BETWEEN CYCLES 23 AND 24

This paper reports on the measurement of the large-scale anisotropy in the distribution of cosmic-ray arrival directions using the data collected by the air shower detector ARGO-YBJ from 2008 January to 2009 December, during the minimum of solar activity between cycles 23 and 24. In this period, more than 2 × 10{sup 11} showers were recorded with energies between ∼1 and 30 TeV. The observed two-dimensional distribution of cosmic rays is characterized by two wide regions of excess and deficit, respectively, both of relative intensity ∼10{sup −3} with respect to a uniform flux, superimposed on smaller size structures. The harmonic analysis shows that the large-scale cosmic-ray relative intensity as a function of R.A. can be described by the first and second terms of a Fouries series. The high event statistics allow the study of the energy dependence of the anistropy, showing that the amplitude increases with energy, with a maximum intensity at ∼10 TeV, and then decreases while the phase slowly shifts toward lower values of R.A. with increasing energy. The ARGO-YBJ data provide accurate observations over more than a decade of energy around this feature of the anisotropy spectrum.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2001

Radiation transport modeling and assessment to better predict radiation exposure, dose, and toxicological effects to human organs on long duration space flights

NASA is very interested in improving its ability to monitor and forecast the radiation levels that pose a health risk to space-walking astronauts as they construct the International Space Station and astronauts that will participate in long-term and deep-space missions. Human exploratory missions to the moon and Mars within the next quarter century, will expose crews to transient radiation from solar particle events which include high-energy galactic cosmic rays and high-energy protons. Because the radiation levels in space are high and solar activity is presently unpredictable, adequate shielding is needed to minimize the deleterious health effects of exposure to radiation. Today, numerous models have been developed and used to predict radiation exposure. Such a model is the Space Environment Information Systems (SPENVIS) modeling program, developed by the Belgian Institute for Space Aeronautics. SPENVIS, which has been assessed to be an excellent tool in characterizing the radiation environment for microelectronics and investigating orbital debris, is being evaluated for its usefulness with determining the dose and dose-equivalent for human exposure. Thus far. the calculations for dose-depth relations under varying shielding conditions have been in agreement with calculations done using HZETRN and PDOSE, which are well-known and widely used models for characterizing the environments for human exploratory missions. There is disagreement when assessing the impact of secondary radiation particles since SPENVIS does a crude estimation of the secondary radiation particles when calculating LET versus Flux. SPENVIS was used to model dose-depth relations for the blood-forming organs. Radiation sickness and cancer are life-threatening consequences resulting from radiation exposure. In space. exposure to radiation generally includes all of the critical organs. Biological and toxicological impacts have been included for discussion along with alternative risk mitigation methods--shielding and anti-carcinogens. c 2001. Elsevier Science Ltd. All rights reserved.

STS-91 Shuttle Project↗
NASA NTRS1980

Radio physics of the sun; Proceedings of the Symposium, University of Maryland, College Park, Md., August 7-10, 1979

Papers are presented in the areas of the radio characteristics of the quiet sun and active regions, the centimeter, meter and decameter wavelength characteristics of solar bursts, space observations of low-frequency bursts, theoretical interpretations of solar active regions and bursts, joint radio, visual and X-ray observations of active regions and bursts, and the similarities of stellar radio characteristics to solar radio phenomena. Specific topics include the centimeter and millimeter wave characteristics of the quiet sun, radio fluctuations arising upon the transit of shock waves through the transition region, microwave, EUV and X-ray observations of active region loops and filaments, interferometric observations of 35-GHz radio bursts, emission mechanisms for radio bursts, the spatial structure of microwave bursts, observations of type III bursts, the statistics of type I bursts, and the numerical simulation of type III bursts. Attention is also given to the theory of type IV decimeter bursts, Voyager observations of type II and III bursts at kilometric wavelengths, radio and whitelight observations of coronal transients, and the possibility of obtaining radio observations of current sheets on the sun.

Kundu, M. R.↗
DOE OSTI2015

Interstellar flow and temperature determination with IBEX: Robustness and sensitivity to systematic effects

The Interstellar Boundary Explorer (IBEX) samples the interstellar neutral (ISN) gas flow of several species every year from December through late March when the Earth moves into the incoming flow. The first quantitative analyses of these data resulted in a narrow tube in four-dimensional interstellar parameter space, which couples speed, flow latitude, flow longitude, and temperature, and center values with approximately 3° larger longitude and 3 km s{sup −1} lower speed, but with temperatures similar to those obtained from observations by the Ulysses spacecraft. IBEX has now recorded six years of ISN flow observations, providing a large database over increasing solar activity and using varying viewing strategies. In this paper, we evaluate systematic effects that are important for the ISN flow vector and temperature determination. We find that all models in use return ISN parameters well within the observational uncertainties and that the derived ISN flow direction is resilient against uncertainties in the ionization rate. We establish observationally an effective IBEX-Lo pointing uncertainty of ±0.°18 in spin angle and confirm an uncertainty of ±0.°1 in longitude. We also show that the IBEX viewing strategy with different spin-axis orientations minimizes the impact of several systematic uncertainties, and thus improves the robustness of the measurement. The Helium Warm Breeze has likely contributed substantially to the somewhat different center values of the ISN flow vector. By separating the flow vector and temperature determination, we can mitigate these effects on the analysis, which returns an ISN flow vector very close to the Ulysses results, but with a substantially higher temperature. Due to coupling with the ISN flow speed along the ISN parameter tube, we provide the temperature T{sub VISN∞}=8710+440/−680 K for V{sub ISN∞}=26 km s{sup −1} for comparison, where most of the uncertainty is systematic and likely due to the presence of the Warm Breeze.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Properties of the suprathermal heavy ion population near 1 AU during solar cycles 23 and 24

Using measurements from the Advanced Composition Explorer/Ultra-Low Energy Isotope Spectrometer (ACE/ULEIS) near 1 AU, we surveyed the composition and spectra of heavy ions (He-through-Fe) during interplanetary quiet times from 1998 January 1 to 2014 December 31 at suprathermal energies between ∼0.11 and ∼1.28 MeV nucleon{sup −1}. The selected time period covers the maxima of solar cycles 23 and 24 and the extended solar minimum in between. We find the following: (1) The number of quiet-hours in each year correlates well with the sunspot number, year 2009 was the quietest for about 90% of the time; (2) The composition of the quiet-time suprathermal heavy ion population ({sup 3}He, C-through-O, and Fe) correlates well with the level of solar activity, exhibiting SEP-like composition signatures during solar maximum, and CIR- or solar wind-like composition during solar minimum; (3) The heavy ion spectra at ∼0.11-0.32 MeV nucleon{sup −1} exhibit suprathermal tails with power-law spectral indices ranging from 1.4 to 2.7. (4) Fe spectral indices get softer (steeper) from solar minimum of cycle 23 to solar cycle 24 maximum. These results imply that during IP quiet times and at energies above ∼0.1 MeV nucleon{sup −1}, the IP medium is dominated by material from prior solar and interplanetary events.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2017

Origin and Properties of Quiet-time 0.11–1.28 MeV Nucleon{sup −1} Heavy-ion Population Near 1 au

Using measurements from the Advanced Composition Explorer /Ultra-Low Energy Isotope Spectrometer near 1 au, we surveyed the composition and spectra of heavy ions (He-through-Fe) during quiet times from 1998 January 1 to 2015 December 31 at suprathermal energies between ∼0.11 and ∼1.28 MeV nucleon{sup −1}. The selected time period covers the maxima of solar cycles 23 and 24 and the extended solar minimum in between. We find the following. (1) The number of quiet hours in each year correlates well with the sunspot number, year 2009 was the quietest for about 82% of the time. (2) The composition of the quiet-time suprathermal heavy-ion population ({sup 3}He, C-through-Fe) correlates well with the level of solar activity, exhibiting SEP-like composition signatures during solar maximum, and CIR- or solar wind-like composition during solar minimum. (3) The heavy-ion (C–Fe) spectra exhibit suprathermal tails at energies of 0.11–0.32 MeV nucleon{sup −1} with power-law spectral indices ranging from 1.40 to 2.97. Fe spectra soften (steepen, i.e., spectral index increases) smoothly with increasing energies compared with Fe, indicating a rollover behavior of Fe at higher energies (0.45–1.28 MeV nucleon{sup −1}). (4) Spectral indices of Fe and O do not appear to exhibit clear solar cycle dependence. (2) and (3) imply that during IP quiet times and at energies above ∼0.1 MeV nucleon{sup −1}, the IP medium is dominated by material from prior solar and interplanetary events. We discuss the implications of these extended observations in the context of the current understanding of the suprathermal ion population near 1 au.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Variations in Solar Parameters and Cosmic Rays with Solar Magnetic Polarity

The sunspot number varies with the 11-year Schwabe cycle, and the solar magnetic polarity reverses every 11 years approximately at the solar maximum. Because of polarity reversal, the difference between odd and even solar cycles is seen in solar activity. In this study, we create the mean solar cycle expressed by phase using the monthly sunspot number for all solar cycles 1–23. We also generate the mean solar cycle for sunspot area, solar radio flux, and cosmic ray flux within the allowance of observational range. The mean solar cycle has one large peak at solar maximum for odd solar cycles and two small peaks for most even solar cycles. The odd and even solar cycles have the statistical difference in value and shape at a confidence level of at least 98%. For solar cycles 19–23, the second peak in the even solar cycle is larger than the first peak. This result is consistent with the frequent solar events during the declining phase after the solar maximum. The difference between odd and even solar cycles can be explained by a combined model of polarity reversal and solar rotation. In the positive/negative polarity, the polar magnetic field introduces angular momentum in the same/opposite direction as/to the solar rotation. Thus the addition/subtraction of angular momentum can increase/decrease the motion of plasma to support the formation of sunspots. Since the polarity reverses at the solar maximum, the opposite phenomenon occurs in the declining phase.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1978

A new use of high resolution magnetograms

Ground-based solar magnetograms are frequently in error by as much as twenty percent and contribute to the poor correlation between magnetic changes and solar flares. High resolution measurement of the magnetic field component, which is normal to the photosphere and measured at photospheric height, can be used to construct a magnetic flux partition function F. Therefore, dF/dt is an EMF which drives atmospheric currents in reconnecting solar active regions. With a high quality magnetograph, the solar probe can be used to obtain good estimates of F and dF/dt and thereby the energy stored as induced solar atmospheric currents during quiescent interflare periods. Should a flare occur during a favorable observing period, the present method of analysis should show characteristic signatures in F, DF/dt, and especially, in the stored flux computed from dF/dt.

Baum, P. J.↗
NASA NTRS1981

Solar wind electron densities from Viking dual-frequency radio measurements

Simultaneous phase coherent, two-frequency measurements of the time delay between the earth station and the Viking spacecraft have been analyzed in terms of the electron density profiles from 4 solar radii to 200 solar radii. The measurements were made during a period of solar activity minimum (1976-1977) and show a strong solar latitude effect. The data were analyzed with both a model independent, direct numerical inversion technique and with model fitting, yielding essentially the same results. It is shown that the solar wind density can be represented by two power laws near the solar equator proportional to r exp -2.7 and r exp -2.04. However, the more rapidly falling term quickly disappears at moderate latitudes (approximately 20 deg) leaving only the inverse-square behavior.

Muhleman, D. O.↗
NASA NTRS1983

SAFE II: Large systems space plasma evaluation experiment

A shuttle flight experiment, the purpose of which is to obtain space data on the interaction of a high voltage solar array with the ambient space plasma is addressed. This flight experiment is a reflight of the solar array flight experiment, SAFE, except that three active solar array panels, electron release devices and plasma diagnostics are added. This experiment, SAFE 2, evaluates power loss due to parasitic current collected by the solar array, arcing on the solar array and perturbations to the plasma which may increase power loss and disturb plasma and charged particle science acquisition.

Carruth, M. R., Jr.↗
NASA NTRS1982

Solar variability

The variability in the total radiant energy flux, or solar irradiance, is discussed. Direct techniques of measuring irradiance, including ground-based, balloon and rocket-borne, and spacecraft-based measurements are compared; the latter type has led to dramatic advances in accuracy since it eliminates the need for corrections for atmospheric absorption. Correlations of the measured irradiance with solar activity are described. Indirect techniques that monitor other solar parameters such as photospheric conditions or the solar diameter are reviewed, and theoretical studies which attempt to interpret the measurements are discussed. Physical mechanisms which can lead to changes in the solar luminosity are addressed, as is global time-dependent modeling of the response of the sun to structural perturbations. Finally, findings from all techniques are summarized, their weak and strong points are assessed, and suggestions for future research are made.

Sofia, S.↗
NASA NTRS1985

On the retention of high-energy protons and nuclei with charges Z or equal to 2 in large solar flares after the process of their acceleration

Data which suggest that the protons with energies of up to several GeV should be retained on the Sun after the process of their acceleration are presented. The protons are on the average retained for 15 min, irrespectively of the solar flare heliolatitude and of the accelerated particle energy ranging from 100 MeV to several GeV. It is suggested that the particles are retained in a magnetic trap formed in a solar active region. No Z or = 2 nuclei of solar origin during large solar flares. The absence of the 500 MeV/nucleon nuclei with Z or = 2 may be due to their retention in the magnetic trap which also retains the high-energy protons. During the trapping time the approx. 500 MeV/nucleon nuclei with Z or = 2 may escape due to nuclear interactions and ionization loss.

Volodichev, N. N.↗