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At least 901 records · Page 50
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

Analysis of solar spectral irradiance measurements from the SBUV/2-series and the SSBUV instruments

The measurements of the solar ultraviolet spectral irradiance by the two Upper Atmosphere Research Satellite (UARS) solar instruments are validated to agree within their 2-Sigma calibration uncertainties of about 7 percent, as well as with measurements from the two solar instruments on the Shuttle Atmospheric Laboratory for Applications and Science (ATLAS) missions. Additionally, the precision of the two UARS data sets is better than the original 2 percent goal, especially at wavelengths greater than 160 nm. This excellent agreement can be credited to accurate pre-flight calibrations, comprehensive in-flight calibrations to track instrument degradation, and a coordinated validation program among the UARS and ATLAS solar instrument teams. The solar irradiance results presented here include those derived from UARS SUSIM, UARS SOLSTICE, ATLAS SUSIM and ATLAS SSBUV measurements on 29 March 1992 during the ATLAS-1 mission and on 15 April 1993 during the ATLAS-2 mission. Two ultraviolet spectra from 119 to 410 nm are derived as the weighted average of the UARS SOLSTICE and SUSIM measurements and are recommended as representative solar spectra for the period of the ATLAS-1 and ATLAS-2 missions. The ATLAS-1 mission occurred during the initial phase of the solar cycle 22 decline when solar activity was moderately high. The ATLAS-2 mission occurred later during the declining phase of the solar cycle 22 when solar activity was more moderate.

Cebula, Richard P.↗
NASA NTRS2010

A New Way that Planets can Affect the Sun

As planets orbit the Sun, the Sun also has to move to keep the total momentum of the solar system constant. The Sun's small orbital motion plus its 25 day rotation about its axis combine to invigorate some solar instabilities. Occasional convection cells at the proper phase in their short life can be strengthened by factors of two or more. This local burst of extra kinetic energy eventually reaches the surface where it can increase the intensity of solar activity. It might explain some reports in the last century of how planetary positions correlate with solar activity. This is the first effect of planets that is large enough to cause a significant response on the Sun.

Wolff, Charles↗
NASA NTRS1979

Coupling processes related to the Sun-weather problem

Physical mechanisms for coupling the energetics of solar activity to meteorological responses are reviewed. Although several hypotheses have been advanced, none can be said to be sufficiently complete to be applied to weather or climate prediction. Solar activity indicators potentially useful for forecasting are identified, including sunspots, solar flares, and magnetic sector boundary crossings. Additional experiments, studies, and analyses are required before Sun-weather concepts can be utilized for predicting meteorological responses.

Goldberg, R. A.↗
DOE OSTI2012

Development and assessment of solar-thermal-activated fuel production: Phase 1, summary

Sandia National Laboratories has for many years been engaged in investigating and developing the science and technology of solar thermochemistry for solar fuel applications under the banner “Sunshine to Petrol.” This report summarizes BP‐funded solar thermochemical work performed from November 2011 through May 2012. This “phase one” effort centered on performance mapping of the Counter‐Rotating‐Ring Receiver Reactor Recuperator (CR5) prototype, a thermochemical heat engine for splitting CO 2 (and/or H 2 O) to produce CO (H 2 ) and O 2 . The bulk of the on‐sun testing effort was performed with 8 ceria‐finned rotating rings. During operation, argon is injected into the reduction side of the CR5 while CO 2 is provided to the oxidation side.

Miller, James Edward↗
NASA NTRS1994

Solar proton effects on austral ozone during the final months of 1989

Intense solar activity during 1989 prompted six major particle events. Four of these occurred between August and December. Energetic solar protons are a natural source of ozone depletion due to the nitric oxides they produce in the polar atmospheres. In particular, modelling (Reid et al., 1991) of an event that peaked on October 20 (with greater than 10 MeV proton flux of 73000 particles sq cm s(exp -1) ster(exp -1) yields 55 percent column density enhancements of NO over the southern polar cap. Total column ozone data from the total ozone ,mapping spectrometer (TOMS) instrument aboard the Nimbus 7 satellite used at times when solar illumination facilitates measurements by TOMS over the entire southern polar regions. The impact of odd nitrogen enhancements on the spatial extent of low total column ozone and of the total ozone mass, over a region August to December. Comparisons are made with previous years (1984 to 1988) of moderate solar activity. The effect, if any, of these events on ozone during times of heterogeneous chlorine chemistry and dynamic processes is discussed.

Stephenson, Judy A. E.↗
NASA NTRS1995

Pole-equator difference and the variability of the brightness of the chromospheric CaII-K-network elements in quiet regions over the solar cycle

The dependence of the brightness of chromospheric network elements on latitude was investigated for quiet solar regions. Calibrated photographic CaII K-spectroheliograms were used to compare the variation in brightness at the center of the disk with higher latitude of chromospheric network elements in a quiet region as a function of solar activity. It was found that there was no significant difference in brightness between the center of the solar disk and higher latitude. It is concluded that the brightness of the chromospheric network elements in a quiet region does not depend on the latitude, but that the variation in the intensity enhancement is related to the level of solar activity.

Kariyappa, R.↗
NASA NTRS2003

ISS FPP Ionospheric Electron Density and Temperature Measurements: Results, Comparison with the IRI-90 Model, and Implications for ISS Charging

We give measurement results of electron temperature and electron density from the Floating Potential Probe (FPP) on the International Space Station (ISS), and relate them to the electron current collection of the ISS solar arrays and the degree of charging of ISS when its Plasma Contacting Units (PCUs) are not operating. We show that on days of high solar activity index Kp, high levels of ISS charging are significantly more probable than on days of low solar activity, due to some abnormally low morning electron temperatures. Although the FPP electron temperatures measured are almost always higher than predicted by the International Reference Ionosphere 90 model (IRI-90), it is shown that the CHAMP satellite Langmuir Probe (PLP) also shows low dawn electron temperatures on the same day as those found by FPP. It is further shown that similar high levels of predicted charging, accompanied by vxB charging on the ISS structure, could exceed the -40 V specification on ISS charging, and could be dangerous to ISS astronauts if the PCUs fail to operate.

Ferguson, D. C.↗
NASA NTRS1990

A Solar-luminosity Model and Climate

Although the mechanisms of climatic change are not completely understood, the potential causes include changes in the Sun's luminosity. Solar activity in the form of sunspots, flares, proton events, and radiation fluctuations has displayed periodic tendencies. Two types of proxy climatic data that can be related to periodic solar activity are varved geologic formations and freshwater diatom deposits. A model for solar luminosity was developed by using the geometric progression of harmonic cycles that is evident in solar and geophysical data. The model assumes that variation in global energy input is a result of many periods of individual solar-luminosity variations. The 0.1-percent variation of the solar constant measured during the last sunspot cycle provided the basis for determining the amplitude of each luminosity cycle. Model output is a summation of the amplitudes of each cycle of a geometric progression of harmonic sine waves that are referenced to the 11-year average solar cycle. When the last eight cycles in Emiliani's oxygen-18 variations from deep-sea cores were standardized to the average length of glaciations during the Pleistocene (88,000 years), correlation coefficients with the model output ranged from 0.48 to 0.76. In order to calibrate the model to real time, model output was graphically compared to indirect records of glacial advances and retreats during the last 24,000 years and with sea-level rises during the Holocene. Carbon-14 production during the last millenium and elevations of the Great Salt Lake for the last 140 years demonstrate significant correlations with modeled luminosity. Major solar flares during the last 90 years match well with the time-calibrated model.

Perry, Charles A.↗
NASA NTRS1988

The regimes of the east-west and the radial anisotropies of cosmic rays in the heliosphere

Observations dating back to 1957 are used to show that there are two distinct physical states of the heliosphere. From 1957-1970 the diurnal anisotropy consisted of the azimuthal component only. This period is defined as the regime of the east-west anisotropy. The period 1971-1979 is characterized by the appearance of a radial anisotropy which attained a maximum amplitude in 1976, when the solar activity was minimum. It is suggested that there is an inverse correlation between the amplitude of the radial anisotropy and solar activity. The physical state of the heliosphere is very stable during the regime of east-west anisotropy and extremely dynamic during the radial anisotropy regime. It is suggested that the heliosphere switches from one physical state to another following the onset of the solar polar field reversal.

Ahluwalia, H. S.↗
DOE OSTI2016

WHY IS A FLARE-RICH ACTIVE REGION CME-POOR?

Solar active regions (ARs) are the major sources of two of the most violent solar eruptions, namely flares and coronal mass ejections (CMEs). The largest AR in the past 24 years, NOAA AR 12192, which crossed the visible disk from 2014 October 17 to 30, unusually produced more than one hundred flares, including 32 M-class and 6 X-class ones, but only one small CME. Flares and CMEs are believed to be two phenomena in the same eruptive process. Why is such a flare-rich AR so CME-poor? We compared this AR with other four ARs; two were productive in both and two were inert. The investigation of the photospheric parameters based on the SDO /HMI vector magnetogram reveals that the flare-rich AR 12192, as with the other two productive ARs, has larger magnetic flux, current, and free magnetic energy than the two inert ARs but, in contrast to the two productive ARs, it has no strong, concentrated current helicity along both sides of the flaring neutral line, indicating the absence of a mature magnetic structure consisting of highly sheared or twisted field lines. Furthermore, the decay index above the AR 12192 is relatively low, showing strong constraint. These results suggest that productive ARs are always large and have enough current and free energy to power flares, but whether or not a flare is accompanied by a CME is seemingly related to (1) the presence of a mature sheared or twisted core field serving as the seed of the CME, or (2) a weak enough constraint of the overlying arcades.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1989

Periodic behaviors in the observed vertical column abundances of atmospheric hydroxyl

OH vertical column abundances measured at Fritz Peak Observatory, Colorado, from 1977 through 1988 reveal semi-annual and annual cycles which are amplitude modulated over the 11-year data base. The modulation of the OH seasonal behavior is in phase with solar activity as described by the sunspot number index. No mechanism for the observed covariance of this OH behavior with solar activity has yet been identified.

Burnett, Elizabeth Beaver↗
NASA NTRS1993

The interplanetary magnetic field from 1 to 5 AU - Ulysses observations

Observations of the IMF carried out from October 1990 to February 1992 during the in-ecliptic phase of the Ulysses mission are presented. The observations were made between 1 and 5.4 AU during a different phase of the solar cycle from previous missions. The large-scale reorganization of the solar coronal fields following the maximum in Solar Cycle 22 generated numerous transient events, causing large-scale disturbances in interplanetary space, particularly during the first half of 1991. From about the middle of 1991, solar activity apparently decreased, resulting in fewer transient events, allowing the formation of corotating interaction regions (CIRs) recurring in successive solar rotations. Observations of the IMF reflect this temporal evolution in solar activity. However, the average orientation of the IMF, the observed sector structure, and the evolution of the CIRs show that the dynamic interaction of transient events with evolving stream-stream structures in this heliocentric distance range results in significant deviations from the expected IMF topology, even when signature of the transients is less apparent.

Balogh, A.↗
NASA NTRS1996

Radio Emissions from the Outer Heliosphere

For nearly fifteen years the Voyager 1 and 2 spacecraft have been detecting an unusual radio emission in the outer heliosphere in the frequency range from about 2 to 3 kHz. Two major events have been observed, the first in 1983-84 and the second in 1992-93. In both cases the onset of the radio emission occurred about 400 days after a period of intense solar activity, the first in mid-July 1982, and the second in May-June 1991. These two periods of solar activity produced the two deepest cosmic ray Forbush decreases ever observed. Forbush decreases are indicative of a system of strong shocks and associated disturbances propagating outward through the heliosphere. The radio emission is believed to have been produced when this system of shocks and disturbances interacted with one of the outer boundaries of the heliosphere, most likely in the vicinity of the the heliopause. The emission is believed to be generated by the shock-driven Langmuir-wave mode conversion mechanism, which produces radiation at the plasma frequency (f(sub p)) and at twice the plasma frequency (2f(sub p)). From the 400-day travel time and the known speed of the shocks, the distance to the interaction region can be computed, and is estimated to be in the range from about 110 to 160 AU.

Gurnett, D. A.↗
NASA NTRS1992

Revised predictions of LDEF exposure to trapped protons

Initial estimates of LDEF exposure to the trapped proton environment were reported previously to aid in the interpretation dosimetry data and in conjunction with dosimetry response predictions. These previous estimates were made using the standard NASA AP8 trapped proton models for two sets of assumed conditions: (1) the omnidirectional flux spectra were calculated with the LDEF altitude and solar activity variations taken into account; and (2) the NASA Marshall anisotropy model was applied to obtain directional spectra, but only for solar minimum conditions and at a single altitude. Herein, the directional trapped proton fluence spectra is calculated considering both the altitude variation and solar activity during the LDEF mission. These additional results represent an extension of previous calculations to provide a more definitive description of the LDEF trapped proton exposure.

Watts, J. W., Jr.↗
NASA NTRS1981

Large-scale variations of the interplanetary magnetic field: Voyager 1 and 2 observations between 1-5 AU

Observations by the Voyager 1 and 2 spacecraft of the interplanetary magnetic field between 1 and 5 AU were used to investigate the large scale structure of the IMF in a period of increasing solar activity. The Voyager spacecraft found notable deviations from the Parker axial model. These deviations are attributed both to temporal variations associated with increasing solar activity, and to the effects of fluctuations of the field in the radial direction. The amplitude of the latter fluctuations were found to be large relative to the magnitude of the radial field component itself beyond approximately 3 AU. Both Voyager 1 and Voyager 2 observed decreases with increasing heliocentric distance in the amplitude of transverse fluctuations in the averaged field strength (B) which are consistent with the presence of predominantly undamped Alfven waves in the solar wind, although and necessarily implying the presence of them. Fluctuations in the strength of B (relative to mean field strength) were found to be small in amplitude, with a RMS which is approximately one third of that for the transverse fluctuations and they are essentially independent of distance from the Sun.

Burlaga, L. F.↗
NASA NTRS1979

Solar-induced variations of environment affecting manned space flight and spacecraft operations

Estimates of short and long term solar activity are required for calculating variations in the environment with regard to spacecraft charging, radiation effects, and orbital lifetime. Correlations appear to exist between the time of solar activity and the time of operational anomalies due to electrical discharges when the dielectric surfaces of geosynchronous spacecraft are charged by interaction with the ambient plasma to levels above breakdown voltage. An ability to predict the solar induced variation variability of the plasmas could permit refinement of design criteria. The influence of the radiation on spacecraft materials, systems, and manned operations is summarized. Solar radition effects on the orbital altitude atmospheric density environment and spacecraft lifetimes are also considered.

Johnson, W. G.↗
NASA NTRS2007

Four-Formation In-Track Configuration Maintenance Strategy

The aim of this paper is to present the analysis conducted by CNES for the maintenance of a formation made of several LEO satellites (typically 4) in several planes (typically 2), 100 km or so apart from each other. The along-track separations between the satellites have to be controlled to within 15 km thanks to orbit correction maneuvers supposed to be performed every 2 weeks. The main difficulty is related to solar activity which is expected to be close to its maximum for the entire mission s lifespan. As a matter of fact, a high solar activity makes orbit prediction harder, and makes it impossible to keep the altitude of the formation constant. Thus, a specific relative maintenance strategy had to be devised in order to meet the mission's requirements. The first part provides a few elements on the mission analysis process that has taken place. The method used for the evaluation of the maneuver frequency is detailed, based on the evaluation of the effects of atmospheric drag on the orbit. The second part is dedicated to the maintenance strategy that has been designed, and particularly to the computation of the reference orbits and of the velocity increments that enable the in-track inter-satellite distances to be maintained within the desired bounds. Finally a few simulation results are presented; they enable the performance of the maintenance strategy to be checked in a more realistic context.

Lamy, Alain↗