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 721 records · Page 40
All sourcesNASA NTRSDOE OSTI
DOE OSTI2011

PHOTOSPHERIC SIGNATURES OF GRANULAR-SCALE FLUX EMERGENCE AND CANCELLATION AT THE PENUMBRAL BOUNDARY

We studied flux emergence events of sub-granular scale in a solar active region. The New Solar Telescope (NST) of the Big Bear Solar Observatory made it possible to clearly observe the photospheric signature of flux emergence with very high spatial (0.''11 at 7057 A) and temporal (15 s) resolution. From TiO observations with the pixel scale of 0.''0375, we found several elongated granule-like features (GLFs) stretching from the penumbral filaments of a sunspot at a relatively high speed of over 4 km s{sup -1}. After a slender arched darkening appeared at the tip of a penumbral filament, a bright point (BP) developed and quickly moved away from the filament, forming and stretching a GLF. The size of a GLF was approximately 0.''5 wide and 3'' long. The moving BP encountered nearby structures after several minutes of stretching, and the well-defined elongated shape of the GLF faded away. Magnetograms from the Solar Dynamics Observatory/Helioseismic and Magnetic Imager and NST/InfraRed Imaging Magnetograph revealed that those GLFs are photospheric indicators of small-scale flux emergence, and their disappearance is related to magnetic cancellation. From two well-observed events, we describe detailed development of the sub-structures of GLFs and different cancellation processes that each of the two GLFs underwent.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2004

What the Sunspot Record Tells Us About Space Climate

The records concerning the number, sizes, and positions of sunspots provide a direct means of characterizing solar activity over nearly 400 years. Sunspot numbers are strongly correlated with modem measures of solar activity including: 10.7-cm radio flux, total irradiance, x-ray flares, sunspot area, the baseline level of geomagnetic activity, and the flux of galactic cosmic rays. The Group Sunspot Number provides information on 27 sunspot cycles, far more than any of the modem measures of solar activity, and enough to provide important details about long-term variations in solar activity or Space Climate. The sunspot record shows: 1) sunspot cycles have periods of 131 plus or minus 14 months with a normal distribution; 2) sunspot cycles are asymmetric with a fast rise and slow decline; 3) the rise time from minimum to maximum decreases with cycle amplitude; 4) large amplitude cycles are preceded by short period cycles; 5 ) large amplitude cycles are preceded by high minima; 6) although the two hemispheres remain linked in phase, there are significant asymmetries in the activity in each hemisphere; 7) the rate at which the active latitudes drift toward the equator is anti-correlated with the cycle period, 8) the rate at which the active latitudes drift toward the equator is positively correlated with the amplitude of the cycle after the next; 9) there has been a significant secular increase in the amplitudes of the sunspot cycles since the end of the Maunder Minimum (1715); and 10) there is weak evidence for a quasi-periodic variation in the sunspot cycle amplitudes with a period of about 90 years. These characteristics indicate that the next solar cycle should have a maximum smoothed sunspot number of about 1.45 plus or minus 30 in 2010 while the following cycle should have a maximum of about 70 plus or minus 30 in 2023.

Hathaway, David H.↗
NASA NTRSDate not supplied

Impact of Solar Cycle Variation on Space Weather

We report on the solar cycle variation of solar eruptions and their space weather consequences during solar cycles 23-25. While the solar activity cycle is primarily expressed in terms of the Sunspot number (SSN), coronal mass ejections (CMEs) provide a different perspective on the solar cycle owing to their origin in sunspot regions as well as other non-spot magnetic regions such as quiescent filament regions. Weak solar activity observed in solar cycle 24 has been found to result in a weak heliospheric state, which backreacted on CME properties. The cycle resulted in mild space weather in that the number of large solar energetic particle events and geomagnetic storms decreased significantly. The occurrence of intense geomagnetic storms and high-energy SEP events was drastically reduced, much more than the reduction in the solar activity. The current status of solar cycle 25 indicates that it will be similar to solar cycle 24 or slightly stronger, which means a mild space weather in this cycle as well. We illustrate this using the data obtained during the rise phase of solar cycle 25 in comparison with the corresponding phases in cycles 23 and 24.

Nat Gopalswamy↗
NASA NTRS1987

Solar EUV induced variations in the thermosphere

The effects of solar activity on the thermosphere are reviewed. The neutral total density, temperature, and electron density increase with solar activity, and their variations are fairly well correlated with variations in solar 10.7-cm flux. The electron temperature, by contrast, has a complex behavior with solar activity, depending on altitude and season, as increased heat input is balanced by increased cooling provided by the enhanced electron density. Also, individual neutral species do not all increase in step but are influenced by dissociation and dynamical processes. The increased ion drag at higher solar activities inhibits the neutral wind from increasing in the same proportion as the neutral temperatures and densities.

Hedin, A. E.↗
NASA NTRS1990

A Probable Approx. 2400 Year Solar Quasi-cycle in Atmospheric Delta C-14

A 2200 to 2600 year quasi-periodicity is present in atmospheric delta C-14 records after removal of long-term trends due to the geomagnetic dipole amplitude variation. This periodicity consists of both a long-term variation of the mean and a superposed, approximately recurring pattern of century-scale variations. The strongest of these latter variations occur near maxima of the approx. 2400 year delta C-14 cycles. The residual record can be modeled to first order as an amplitude modulation of a century-scale periodic forcing function by a approx. 2400 year periodic forcing function. During the last millennium, the largest century-scale variations (occurring near the most recent 2400 year delta C-14 maximum) are known to be mainly a consequence of the pronounced Maunder, Sporer, and Wolf solar activity minima, as verified by independent proxy solar activity records. Therefore, during this period, amplitude modulation has been occurring primarily in the sun and not in the terrestrial radiocarbon system. It is therefore inferred that the approx. 2400 year forcing function is mainly solar although some secondary terrestrial feedback into the delta C-14 record is likely. This conclusion has implications for the predictability of future pronounced solar activity minima and for the interpretation of certain minor Holocene climatic variations.

Hood, L. L.↗
NASA NTRS1980

On lunar evidence for a possible large increase in solar flare activity approximately 2 x 10 to the 4th years ago

Data from lunar materials which may be interpreted as suggesting an increase in solar cosmic ray activity approximately 20,000 years ago is examined. The evidence includes the iron track within pit data of Hartung and Storzer (1974), the lunar whole rock pit and track data, lunar C-14 radioactivity data, lunar Ni-59 radioactivity data, the impact pit and iron track data of Morrison and Zinner (1975, 1977) and the lunar thermoluminescence data. While numerous explanations are possible for each set of data, it is shown that the first four data sets may be explained by a past increase in solar cosmic ray activity, and the remaining data sets are not necessarily incompatible with solar activity a factor of 20 to 40 times higher than at present for several thousand years prior to about 20,000 years ago.

Zook, H. A.↗
DOE OSTI2011

THE ACOUSTIC CUTOFF FREQUENCY OF THE SUN AND THE SOLAR MAGNETIC ACTIVITY CYCLE

The acoustic cutoff frequency-the highest frequency for acoustic solar eigenmodes-is an important parameter of the solar atmosphere as it determines the upper boundary of the p-mode resonant cavities. At frequencies beyond this value, acoustic disturbances are no longer trapped but are traveling waves. Interference among them gives rise to higher-frequency peaks-the pseudomodes-in the solar acoustic spectrum. The pseudomodes are shifted slightly in frequency with respect to p-modes, making possible the use of pseudomodes to determine the acoustic cutoff frequency. Using data from the GOLF and VIRGO instruments on board the Solar and Heliospheric Observatory spacecraft, we calculate the acoustic cutoff frequency using the coherence function between both the velocity and intensity sets of data. By using data gathered by these instruments during the entire lifetime of the mission (1996 until the present), a variation in the acoustic cutoff frequency with the solar magnetic activity cycle is found.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

A STATISTICAL SURVEY OF DYNAMIC PRESSURE PULSES IN THE SOLAR WIND BASED ON WIND OBSERVATIONS

Solar wind dynamic pressure pulse (DPP) structures, across which the dynamic pressure changes abruptly over timescales from a few seconds to several minutes, are often observed in the near-Earth space environment. The space weather effects of DPPs on the magnetosphere–ionosphere coupling system have been widely investigated in the last two decades. In this study, we perform a statistical survey on the properties of DPPs near 1 AU based on nearly 20 years of observations from the WIND spacecraft. It is found that only a tiny fraction of DPPs (around 4.2%) can be regarded as interplanetary shocks. For most DPPs, the total pressure (the sum of the thermal pressure and magnetic pressure) remains in equilibrium, but there also exists a small fraction of DPPs that are not pressure-balanced. The overwhelming majority of DPPs are associated with solar wind disturbances, including coronal mass ejection-related flows, corotating interaction regions, as well as complex ejecta. The annual variations of the averaged occurrence rate of DPPs are roughly in phase with the solar activity during solar cycle 23, and during the rising phase of solar cycle 24.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

ELECTRON CYCLOTRON MASER EMISSIONS FROM EVOLVING FAST ELECTRON BEAMS

Fast electron beams (FEBs) are common products of solar active phenomena. Solar radio bursts are an important diagnostic tool for understanding FEBs and the solar plasma environment in which they propagate along solar magnetic fields. In particular, the evolution of the energy spectrum and velocity distribution of FEBs due to the interaction with the ambient plasma and field during propagation can significantly influence the efficiency and properties of their emissions. In this paper, we discuss the possible evolution of the energy spectrum and velocity distribution of FEBs due to energy loss processes and the pitch-angle effect caused by magnetic field inhomogeneity, and we analyze the effects of the evolution on electron-cyclotron maser (ECM) emission, which is one of the most important mechanisms for producing solar radio bursts by FEBs. Our results show that the growth rates all decrease with the energy loss factor Q , but increase with the magnetic mirror ratio σ as well as with the steepness index δ . Moreover, the evolution of FEBs can also significantly influence the fastest growing mode and the fastest growing phase angle. This leads to the change of the polarization sense of the ECM emission. In particular, our results also reveal that an FEB that undergoes different evolution processes will generate different types of ECM emission. We believe the present results to be very helpful for a more comprehensive understanding of the dynamic spectra of solar radio bursts.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1980

Orbiting solar observatory 8 high resolution ultraviolet spectrometer experiment

Oscillations, physical properties of the solar atmosphere, motions in the quiet solar atmosphere, coronal holes, motions in solar active regions, solar flares, the structure of plage regions, an atlas, and aeronomy are summarized. Photometric sensitivity, scattered light, ghosts, focus and spectral resolution, wavelength drive, photometric sensitivity, and scattered light, are also summarized. Experiments are described according to spacecraft made and experiment type. Some of the most useful data reduction programs are described.

Source record↗
NASA NTRS1984

Analysis of the Earth's variable rotation

The objective was to analyze the Earth's rotation, and to compare the observations with the atmospheric and seismic excitation functions. The variation in the Earth's rotation can be separated into the length-of-day (LOD) variation and the polar motion. Possible driving mechanisms include: atmospheric/oceanic circulations, seismic activities, solar-lunar tides, mantle convection, core-mantle coupling, and solar activities. The major problem of concern was the identification of these dynamical processes as primary driving mechanisms for the various features in the variation of the Earth's rotation.

Chao, B. F.↗
NASA NTRS1984

The Solar Wind at 20-30 AU

Pioneer 10 sampled the interplanetary plasma over the range 20 to 30 astronomical units, during the period 1979-1983. The median flow speed is about 400 km/s, and at 20 AU the median density, proton temperature and dynamic pressure are, respectively, 0.025 cm-3, 10(4) K, and 6x10-11 dyne cm-2. It is shown that the average solar wind flow speed does not vary significantly with increasing heliocentric distance, and the density falls off as R-2, as predicted by simple solar wind models. The day-to-day variations in solar wind parameters are smaller at larger distance. Very large shocks however, were detected beyond 25 AU. Comparison of Pioneer 10 and 11 observations at similar distances but different phases of the solar activity cycle shows that solar wind dynamic pressure varies over a wider range during epochs of high solar activity. The variation near 20 AU is likely to be smaller at Voyager 2 Uranus encounter than observed by Pioneer 10 in the 1979-80 period.

Barnes, A.↗
NASA NTRS1985

The study of the physics of cometary nuclei

The development and utilization of an optimized computer program to analyze orbital stabilization by repeated calculations is presented. The stability of comets in the Opik-Oort Cloud about the Sun against perturbations by the Galactic center involve the same basic type of calculation. The supposed persistence of these bodies in orbits over the life of the solar system, depends upon the stability of bodies of negligible mass in orbits around a body whose mass is small compared to the central mass about which they revolve. The question remains of preferential orientation of extremely eccentric comet orbits, possibly to explain the asymmetry observed among new comet motions. A third application of the computing programs is suited to meteoroids that may exist in orbits about asteroids and that may endanger science spacecraft making flybys too near to asteroids. As in the double-comet case, solar activity and solar gravitational perturbations limit the attendance to an asteroid by small meteroids in their orbits. It is found that the mass distances planned for asteroid fly-bys are adequate.

Whipple, F. L.↗
NASA NTRS1988

The solar wind control of Jupiter's broad-band kilometric radio emission

Observations of the solar wind close to Jupiter are compared with the broad-band kilometric radio emission (bKOM), using data recorded by Voyager 1 and Voyager 2 during 1979. The lower bKOM frequencies, less than about 300 kHz, are found to correlate with the solar wind density and pressure and with the interplanetary magnetic field (IMF) magnitude during periods when there is a well-defined magnetic sector structure. The results suggest that lower frequency bKOM events are most likely to occur after a sector boundary has passed Jupiter during the period when the solar wind density and the IMF magnitude are increasing towards the sector center. The average bKOM energy per Jovian rotation tends to have lower values soon after the sector center has passed. Higher-frequency/higher-energy bKOM emission may be contaminated by hectometric emission (HOM) and differently correlated with solar activity. The solar wind control may also be obscured by some stronger control. It is suggested that electron density fluctuations in the Io torus, where the source is believed to be located, may be responsible for variations in the beaming and hence variations in the observed emission.

Barrow, C. H.↗
NASA NTRS1991

Solar irradiance variability from modern measurements

Direct measurements from satellites of the solar 'constant' (the total irradiance at mean sun-earth distance) during more than ten years show variations over time scales from minutes to years and decades. At high frequencies, solar oscillations contribute to the variance. The most important influences are related to solar activity: during the passage of active regions on the solar disk (sunspots and faculae) changes of a few 0.1 percent lasting for several days are observed. The effects of spots can be well reproduced by the projected sunspot index, whereas the influence of faculae have to be modeled from proxy data like the Ca-K plage index or the He I index. Long-term trends are detected which are connected to the 11-yr solar activity cycle.

Froehlich, C.↗
NASA NTRS1993

Continued Development of an Ultra-Narrow Bandpass Filter for Solar Research

The objective of work under this task was to develop ultranarrow optical bandpass filters and related technology necessary for construction of a compact solar telescope capable of operating unattended in space. The scientific problems to which such a telescope could be applied include solar seismology, solar activity monitoring, solar irradiance variations, solar magnetic field evolution, and the location of targets for narrow-field specialized telescopes. We have demonstrated a Y-cut lithium-niobate Fabry-Perot etalon. This filter will be used on the Flare Genesis Experiment. We also obtained solar images with a Z-cut etalon. The technical report on etalon filters is attached to this final report. We believe that work under this grant will lead to the commercial availability of a universal optical filter with approximately 0.1 A bandwidth. Progress was made toward making a suitable 1-2 A tunable blocker filter, but it now appears that the best approach is to make a double-cavity etalon that will not require such a narrow blocker. Broader band blockers are commercially available.

Rust, David M.↗
NASA NTRS1995

The Heliosphere During the Declining Solar Cycle; Symposium D1.1 of COSPAR Scientific Assembly, 30th, Hamburg, Germany, July 11-21, 1994

The conference discussed the heliosphere during the declining solar cycle. Topics covered included: manifestations of solar activity, the solar wind, ion pick-up and anomalous cosmic rays, the interplanetary magnetic field, cosmic ray modulation, co-rotating interaction regions, and the heliosphere boundary, as well as several related topics.

Shea, M. A.↗