Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Solar Activity”

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 955 records · Page 53
All sourcesNASA NTRSDOE OSTI
NASA NTRS1975

Project SOLWIND: Space radiation exposure

A special orbital radiation study was conducted for the SOLWIND project to evaluate mission-encountered energetic particle fluxes. Magnetic field calculations were performed with a current field model, extrapolated to the tentative spacecraft launch epoch with linear time terms. Orbital flux integrations for circular flight paths were performed with the latest proton and electron environment models, using new improved computational methods. Temporal variations in the ambient electron environment are considered and partially accounted for. Estimates of average energetic solar proton fluences are given for a one year mission duration at selected integral energies ranging from E greater than 10 to E greater than 100 MeV; the predicted annual fluence is found to relate to the period of maximum solar activity during the next solar cycle. The results are presented in graphical and tabular form; they are analyzed, explained, and discussed.

Stassinopoulos, E. G.↗
NASA NTRS1974

Skylab contributions to the future

Skylab showed that a multidisciplinary manned space station is practical and can be highly productive. Quality data was produced concerning earth resources (mineral resources, agriculture, climatology, etc.), solar astronomy (solar activity, magnetic fields, and solar winds), materials sciences (e.g., zero-gravity crystal growth), and astronomy and astrophysics (including observations of comet Kohoutek). Two types of astronaut maneuvering unit were tested. Medical data are applicable to adaptational environmental physiology.

Schneider, W. C.↗
NASA NTRS1976

Galactic cosmic-ray intensity 0.99 to 5.26 astronomical units from the sun

The intensity of galactic cosmic radiation in interplanetary space has been observed over the heliocentric radial range 0.99 to 5.26 AU with five Geiger-Mueller tubes on Pioneer 10 and over the range 1.00 to 3.59 AU with three similar tubes on Pioneer 11. The observations span the time period 1972 March 3 to 1974 April 29, near the epoch of minimum solar activity. The contributions of solar energetic particles are eliminated. The effect of temporal trends is removed in a variety of ways - by comparison of simultaneous measurements on the two spacecraft; by comparison with data from Explorer 35 at 1.0 AU; and by comparison with terrestrial neutron monitor data. The radial gradient of the intensity of particles with energies greater than 80 MeV/nucleon is zero to within an experimental uncertainty of less than 2 per cent per AU over the range 0.99 to 5.26 AU. Hence, it is less than the theoretically expected value by at least a factor of 5.

Thomsen, M. F.↗
NASA NTRS1982

Statistical aspects of the 1980 solar flares. 2: Solar cycle activity relationships and additional remarks

Based on 1349 hydrogen alpha flares with X-ray counterparts, an investigation into the relationship between the rise time, decay time, duration, latitude, hydrogen alpha importance, and X-ray class with 2800 MHz radio emission (F2800) was accomplished. An important finding is that during 1980 both the number of hydrogen alpha importance class 1 and number of X-ray class M (and M+X) flares appeared to be rather strongly related to F2800, in a positive sense; i.e., number of class 1 and class M events increased as F2800 increased.

Wilson, R. M.↗
NASA NTRS1984

Line width of the solar EUV He I resonance emissions at 584 and 537 A

Instrumentation was carried aloft on a Black Brant rocket in August 1982 to gather spectrometry on the solar He I resonance lines. The payload consisted of a He spectrometer which furnished 11 readings at FWHM of close to 97 and 132 mA for the 584 and 537 a lines, respectively. The results indicated a variation of the solar line width that was inversely correlated with solar activity and with the solar EUV flux. Further studies of the 522 A line are recommended to detect any unidentified first order solar emissions close to or within the absorption profile of the 537 A line that contributed to the observed line width.

Ogawa, H. S.↗
NASA NTRS1985

Solar and interplanetary particles at 2 to 4 MEV during solar cycles 21, solar cycle variations of event sizes, and compositions

In This paper 2 to 4 MeV/nucleon protons, alpha particles, and medium (CNO) nuclei in the near-Earth interplanetary medium during the years 1974 to 1981 are studied. This period contains both the solar activity minimum in 1976, and the very active onset phase of Solar Cycle 21. Characteristic compositional differences between the solar minimum and solar maximum ion populations have been investigated. Previous studies of interplanetary composition at these energies have concentrated on well-defined samples of the heliospheric medium. During flare particle events, the ambient plasma is dominated by ions accelerated in specific regions of the solar atmosphere; observation of the proton/alpha and alpha/medium ratios for flare events shows that there is marked compositional variability both during an event and from event to event suggesting the complicated nature of flare particle production and transport.

Armstrong, T. P.↗
NASA NTRS1986

Studies of the aurorally-induced ultraviolet emissions on the nightside of Venus

The effect of a monoenergetic flux of electrons on a model atmosphere of the nightside thermosphere of Venus was examined. The neutral model chosen is that of Hedin for high solar activity and l65 degrees solar zenith angle. The model is based on measurements made by the Pioneer Venus Orbiter Neutral Mass Spectrometer. Four species were included in the calculation: CO2, O, CO, and N2. The numerical method that was chosen for energy deposition of the primary electrons is the continuous slowing down approximation. The secondary electron distribution was computed using the empirically determined shape of the differential cross section.

Fox, J. L.↗
NASA NTRS1985

Coronal X-ray activity preceding solar flares

The characteristics of coronal emplacements preceding solar flares were investigated based on a comprehensive survey of Skylab soft X-ray images. A search interval of 30 min before flare was used in the X-ray observations. X-ray images with preflare enhancements were compared with high resolution H-alpha images and photospheric magnetograms and preflare enhancements were found in a statistically significant number of the observed preflare intervals. The enhancement events consisted of loops, kernels, and sinuous features with one to three separate preflare structures appearing in each interval. Typical gas pressures in the preflare X-ray features were estimated on the order of a few dyne per sq cm and densities were 4-10 x 10 to the -9th per cu cm for assumed average temperatures. H-alpha brightenings in the form of knots and patches were found in conjunction with the X-ray preflare features in nearly all of the intervals. It is concluded that H-alpha emission is characteristic of preflare emission processes. The observational data are interpreted within the framework of existing loop preheating models, and the results are discussed in detail.

Webb, D. F.↗
NASA NTRS1984

Pinhole Occulter Facility

The Pinhole Occulter Facility (POF) is designed for X-ray observations of solar activity, coronal structure and solar wind generation, and coronal transients. The four telescopes or positioning counters, the self-deployable 32-m boom, and the pointing-control actuator of the POF are described. The development of the facility is discussed. The configuration of the POF and means of maintaining its attitude control are examined.

Dabbs, J. R.↗
NASA NTRS1987

A study of solar preflare activity using two-dimensional radio and SMM-XRP observations

A study of type III activity at meter-decameter wavelengths in the preflare phase of the February 3, 1986 flare is presented, using data obtained with the Clark Lake Multifrequency Radioheliograph. This activity is compared with similar type III burst activity during the impulsive phase, and it is found that there is a displacement of burst sources between the onset and end times of the activity. A comparison of this displacement at three frequencies suggests that the type III emitting electrons gain access progressively to diverging and different field lines relative to the initial field lines. The energetics of the type III emitting electrons are inferred from observations and compared with those of the associated hard X-ray emitting electrons. The soft X-ray data from SMM-XRP show enhanced emission measure, density, and temperature in the region associated with the preflare type III activity.

Kundu, M. R.↗
NASA NTRS2000

Solar Physics

The areas of emphasis are: (1) develop theoretical models of the transient release of magnetic energy in the solar atmosphere, e.g., in solar flares, eruptive prominences, coronal mass ejections, etc.; (2) investigate the role of the Sun's magnetic field in the structuring of solar corona by the development of three-dimensional numerical models that describe the field configuration at various heights in the solar atmosphere by extrapolating the field at the photospheric level; (3) develop numerical models to investigate the physical parameters obtained by the ULYSSES mission; (4) develop numerical and theoretical models to investigate solar activity effects on the solar wind characteristics for the establishment of the solar-interplanetary transmission line; and (5) develop new instruments to measure solar magnetic fields and other features in the photosphere, chromosphere transition region and corona. We focused our investigation on the fundamental physical processes in solar atmosphere which directly effect our Planet Earth. The overall goal is to establish the physical process for the Sun-Earth connections.

Wu, S. T.↗
NASA NTRS2007

Solar Modulation of Low-Energy Antiproton and Proton Spectra Measured by BESS

The spectra of low-energy cosmic-ray protons and antiprotons have been measured by BESS in nine high-latitude balloon flights between 1993 and 2004. These measurements span a range of solar activity from the previous solar minimum through solar ma>:im%am and the onset of the present solar minimum, as well as a solar magnetic field reversal from positive to negative in 2000. Because protons and antiprotons differ only in charge sign, these simultaneous measurements provide a sensitive probe of charge dependent solar modulation. The antiproton to proton ratio measured by BESS is consistent with simple spherically symmetric models of solar modulation during the Sun's positive polarity phase, but favor charge-sign-dependent drift models during the negative phase. The BESS measurements will be presented and compared to various models of solar modulation.

Mitchell, John W.↗
NASA NTRS2014

GCR Environmental Models III: GCR Model Validation and Propagated Uncertainties in Effective Dose

This is the last of three papers focused on quantifying the uncertainty associated with galactic cosmic rays (GCR) models used for space radiation shielding applications. In the first paper, it was found that GCR ions with Z>2 and boundary energy below 500 MeV/nucleon induce less than 5% of the total effective dose behind shielding. This is an important finding since GCR model development and validation have been heavily biased toward Advanced Composition Explorer/Cosmic Ray Isotope Spectrometer measurements below 500 MeV/nucleon. Weights were also developed that quantify the relative contribution of defined GCR energy and charge groups to effective dose behind shielding. In the second paper, it was shown that these weights could be used to efficiently propagate GCR model uncertainties into effective dose behind shielding. In this work, uncertainties are quantified for a few commonly used GCR models. A validation metric is developed that accounts for measurements uncertainty, and the metric is coupled to the fast uncertainty propagation method. For this work, the Badhwar-O'Neill (BON) 2010 and 2011 and the Matthia GCR models are compared to an extensive measurement database. It is shown that BON2011 systematically overestimates heavy ion fluxes in the range 0.5-4 GeV/nucleon. The BON2010 and BON2011 also show moderate and large errors in reproducing past solar activity near the 2000 solar maximum and 2010 solar minimum. It is found that all three models induce relative errors in effective dose in the interval [-20%, 20%] at a 68% confidence level. The BON2010 and Matthia models are found to have similar overall uncertainty estimates and are preferred for space radiation shielding applications.

Slaba, Tony C.↗
NASA NTRS2001

Developments and activities in solar sail propulsion

NASA's drive to reduce mission costs and accept the risk of incorporating innovative, high payoff technologies into its missions while simultaneously undertaking ever more difficult missions has sparked a greatly renewed interest in solar sails. This paper summarizes these on-going developments in solar sails.

solar↗
NASA NTRS2005

Simulation of the October-November 2003 solar proton event in the CMAM GCM: Comparison with observations

The FTS instrument on SciSat-I observed a very large NO(x) anomaly in mid February of 2004 near 80 N in the lower mesosphere. It has been proposed that the most likely origin of the lower mesosphere anomaly in February is transport, from the lower thermosphere or upper mesosphere, of high levels of NO(x) associated with high levels of solar activity in 0ct.-Nov. 2003. There was no major solar flare activity during January and February to cause ionization in the mesosphere. Using a middle atmosphere GCM we investigate whether the NO(x) produced directly by the 0ct.-Nov. 2003 solar flares or indirectly via enhanced auroral ionization as a result of magnetospheric precipitation can explain the ACE observations. We find that the solar proton events associated with the solar explosions in 0ct.-Nov. 2003 produce insufficient amounts of NO(x), in the mesosphere and thermosphere (less than 2 ppm at 90 km) to give rise to the observed anomaly. However. there is evidence that intense aurorae caused by the 0ct.-Nov. 2003 solar storms produced thermospheric values of NO(x) reaching hundreds of ppm. The NO(x) created by the auroral particles appears to have lasted much longer than the immediate period of the 0ct.-Nov. 2003 solar storms. It appears that NO(x) rich air experienced confined polar night descent into the middle mesosphere during November and December, prior to the onset of the strong mesospheric vortex in January 2004.

Semeniuk, K.↗
DOE OSTI2017

Polarization of Coronal Forbidden Lines

Since the magnetic field is responsible for most manifestations of solar activity, one of the most challenging problems in solar physics is the diagnostics of solar magnetic fields, particularly in the outer atmosphere. To this end, it is important to develop rigorous diagnostic tools to interpret polarimetric observations in suitable spectral lines. This paper is devoted to analyzing the diagnostic content of linear polarization imaging observations in coronal forbidden lines. Although this technique is restricted to off-limb observations, it represents a significant tool to diagnose the magnetic field structure in the solar corona, where the magnetic field is intrinsically weak and still poorly known. We adopt the quantum theory of polarized line formation developed in the framework of the density matrix formalism, and synthesize images of the emergent linear polarization signal in coronal forbidden lines using potential-field source-surface magnetic field models. The influence of electronic collisions, active regions, and Thomson scattering on the linear polarization of coronal forbidden lines is also examined. It is found that active regions and Thomson scattering are capable of conspicuously influencing the orientation of the linear polarization. These effects have to be carefully taken into account to increase the accuracy of the field diagnostics. We also found that linear polarization observation in suitable lines can give valuable information on the long-term evolution of the magnetic field in the solar corona.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1984

Solar-terrestrial research opportunities - A look to the future

Recent and proposed research programs and their impact on the understanding of solar-terrestrial interactions, the processes driving solar activity, and the propagation of the solar wind are outlined. The magnetospheres of the earth and major planets have been mapped and their interactions with the solar wind modeled. MHD activity has been identified as the driving force for stellar surface activity, and Pioneer data are permitting a mapping of the outer areas of the heliosphere. Further studies are required to understand solar magnetic field-earth magnetosphere, ionosphere-atmosphere interactions, the effects of solar heating on earth atmosphere ozone levels, and the effects of solar transient events on the earth atmosphere. The initiation of an International Geosphere-Biosphere Program is now under study and several satellites for solar-terrestrial research are under development as cooperative efforts among the U.S., Japanese, and European agencies.

Intriligator, D. S.↗
NASA NTRS1983

Solar wind disturbances in th outer heliosphere caused by successive solar flares from the same active region

Solar wind disturbances caused by successive flares from the same active region are traced to about 20 AU, using the modeling method developed by Hakamada and Akasofu (1982). It is shown that the flare-generated shock waves coalesce with the co-rotating interaction region of the interplanetary magnetic field, resulting in a large-scale magnetic field structure in the outer heliosphere. Such a structure may have considerable effects on the propagation of galactic cosmic rays.

Akasofu, S. I.↗