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NASA NTRS1986

Absolute solar flux measurement shortward of 575 A

A rare-gas ionization chamber was used to obtain an accurate measurement of the absolute solar EUV flux in the 50- to 575-A region. The instrument, operating in total and near-total absorption, was flown on a solar-pointing sounding rocket on August 16, 1983. For the day of the flight, the solar activity indices were F sub 10.7 = 132.1 and R sub I = 80, and the integrated solar irradiance at the earth, corrected for atmospheric absorption, was found to be 4.31 + or - 0.31 x 10 to the 10th photons sq cm s. Almost exactly a year earlier (August 10, 1982) the same instrument measured an integrated solar flux of 5.71 + or - 0.42 x 10 to the 10th photons/sq cm s during a time of enhanced solar activity (F sub 10.7 = 209.5 and R sub I = 155).

Ogawa, H. S.↗
NASA NTRS1980

Variability of the solar flux in the far ultraviolet 1175-2100 A

An attempt is made to correlate available observations within the framework of a simple two-component model of the full-disk flux which divides the solar surface into quiet and active areas with a constant average contrast factor for the intensity at a particular wavelength. The expected range of variability over the solar cycle of the far UV flux is examined within the 1175-2100 A wavelength range. Two possible indices of solar variability, the calcium plage index and the Zurich sunspot number, are investigated as guides to the fraction of disk covered by active regions and the possible resulting flux variability. In addition, contrast factors I(plage)/I(quiet region) are determined for various lines and continua, and the fraction of the disk covered by plages at various times is estimated. Results are in good agreement with the L-alpha fluxes of Vidal-Madjar (1975) and the broadband observations by Hinteregger (1979), but disagree with the flux variability reported by Heath and Thekaekara (1977) over the 1700-3000 A range.

Cook, J. W.↗
NASA NTRS2019

Seasonal, Solar Zenith Angle, and Solar Flux Variations of O+ in the Topside Ionosphere of Mars

Using observations from Mars Atmosphere and Volatile EvolutioN's Neutral Gas and Ion Mass Spectrometer, we characterize the seasonal, solar zenith angle (SZA), and solar flux dependent variations of the O+ peak and the O+/O+2 ratio in the topside ionosphere of Mars.We find that the O+ peak is between 220 and 300 km and forms at a roughly constant neutral atmospheric pressure level of 10(−8.7±0.4) Pa. The O+ peak altitude also decreases with increasing SZA near the terminator and varies sinusoidally with an amplitude of 26 km over a period of one Mars year in response to the changing solar insolation. The O+ peak altitude reaches a maximum near Northern Winter solstice and Mars perihelion. The O+ peak density on the dayside has an average value of (1.1 ± 0.5) × 103 cm−3, has no dependence on SZA for SZAs up to ∼90◦, and is mainly controlled by the thermospheric O/CO2 ratio as predicted by photochemical theory. Above the O+ peak, the O+/O+2 ratio in the dayside ionosphere approaches a constant value of 1.1 ± 0.6, decreases with increasing SZA, and is highly variable on timescales of days or less.We discuss why the O+ peak is different than the main (M2) peak at Mars and why it is similar to the F2 peak at Earth.

Girazian, Z.↗
NASA NTRS2007

Orbit Decay Prediction Sensitivity to Solar Flux Variations

It is well known that atmospheric density errors are the main source of uncertainty in orbit decay predictions. Perhaps less well known is the sensitivity of atmospheric density to solar activity. In this paper, we examine the sensitivity of orbit decay predictions to realistic daily variations in solar flux. We present results from analysis of orbit decay prediction for a variety of orbits, initial epochs, and predicted smooth flux profiles. For each set of initial conditions, we simulate multiple sample flux profiles with simulated daily variations, and compute the orbital re-entry date for comparison.

Naasz, Bo J.↗
NASA NTRS1987

The dependence of electroglow on the solar flux

Data from Voyager 2 UV spectrometer observations of electroglow at wavelengths below 110 nm in the atmospheres of Saturn, Jupiter, and Uranus are presented in extensive tables and graphs, analyzed statistically, and compared with the predictions of theoretical models. Findings reported include (1) a dependence (to within 10 percent) of electroglow intensity on the inverse square of heliocentric distance, (2) Uranian electroglow spectra consistent with Rayleigh-Raman scattering of sunlight, and (3) local-time electroglow variations suggesting a solar-flux-dependent excitation mechanism. Mechanisms involving the fluorescence of solar UV radiation in the H2 Lyman and Werner bands or H(-) photolysis are discussed.

Yelle, Roger V.↗
NASA NTRS1985

Photoabsorption cross section of CH3CN - Photodissociation rates by solar flux and interstellar radiation

The photoabsorption cross section of CH2CN vapor was measured in the 106-180 nm region using synchrotron radiation as a light source. The cross section and the quantum yield for the production of CN (A, B-X) fluorescence were measured and were used to infer the photodissociation cross section of CH3CN. The cross sections were used to calculate the photodissociation rates of CH3CN by the solar flux and by the interstellar radiation. In both the stratosphere and the troposphere, the solar photodissociation of CH3CN is negligible in comparison with chemical degradation.

Suto, M.↗
NASA NTRS1992

Detecting and disentangling nonlinear structure from solar flux time series

Interest in solar activity has grown in the past two decades for many reasons. Most importantly for flight dynamics, solar activity changes the atmospheric density, which has important implications for spacecraft trajectory and lifetime prediction. Building upon the previously developed Rayleigh-Benard nonlinear dynamic solar model, which exhibits many dynamic behaviors observed in the Sun, this work introduces new chaotic solar forecasting techniques. Our attempt to use recently developed nonlinear chaotic techniques to model and forecast solar activity has uncovered highly entangled dynamics. Numerical techniques for decoupling additive and multiplicative white noise from deterministic dynamics and examines falloff of the power spectra at high frequencies as a possible means of distinguishing deterministic chaos from noise than spectrally white or colored are presented. The power spectral techniques presented are less cumbersome than current methods for identifying deterministic chaos, which require more computationally intensive calculations, such as those involving Lyapunov exponents and attractor dimension.

Ashrafi, S.↗
NASA NTRS1980

Solar flux variation of the thermospheric molecular oxygen density

The paper presents measurements of the thermospheric molecular oxygen density obtained from the Atmosphere Explorer (AE) satellites and composition data obtained from rocket-based experiments which provide information on the distribution of O2 between 120 and 200 km as a function of solar flux. The rocket experiment data can be analyzed for long-term variations, which show that the O2 density at 200 km shows little variation but at 120 km decreases approximately 30% for the F sub 10.7-cm flux.

Kayser, D. C.↗
NASA NTRS1980

Solar flux incident on an orbiting surface after reflection from a planet

Algorithms describing the solar radiation impinging on an infinitesimal surface after reflection from a gray and diffuse planet are derived. The following conditions apply: only radiation from the sunny half of the planet is taken into account; the radiation must fall on the top of the orbiting surface, and radiation must come from that part of the planet that can be seen from the orbiting body. A simple approximate formula is presented which displays excellent accuracy for all significant situations, with an error which is always less than 5% of the maximum possible reflected flux. Attention is also given to solar albedo flux on a surface directly facing the planet, the influence of solar position on albedo flux, and to solar albedo flux as a function of the surface-planet tilt angle.

Modest, M. F.↗
NASA NTRS2007

An Alternative Interpretation of the Relationship between the Inferred Open Solar Flux and the Interplanetary Magnetic Field

Photospheric observations at the Wilcox Solar Observatory (WSO) represent an uninterrupted data set of 32 years and are therefore unique for modeling variations in the magnetic structure of the corona and inner heliosphere over three solar cycles. For many years, modelers have applied a latitudinal correction factor to these data, believing that it provided a better estimate of the line-of-sight magnetic field. Its application was defended by arguing that the computed open flux matched observations of the interplanetary magnetic field (IMF) significantly better than the original WSO correction factor. However, no physically based argument could be made for its use. In this Letter we explore the implications of using the constant correction factor on the value and variation of the computed open solar flux and its relationship to the measured IMF. We find that it does not match the measured IMF at 1 AU except at and surrounding solar minimum. However, we argue that interplanetary coronal mass ejections (ICMEs) may provide sufficient additional magnetic flux to the extent that a remarkably good match is found between the sum of the computed open flux and inferred ICME flux and the measured flux at 1 AU. If further substantiated, the implications of this interpretation may be significant, including a better understanding of the structure and strength of the coronal field and I N providing constraints for theories of field line transport in the corona, the modulation of galactic cosmic rays, and even possibly terrestrial climate effects.

Riley, Pete↗
NASA NTRS1984

An investigation of the consistency of the ionospheric measurements of the photoelectron flux and solar EUV flux

This paper demonstrates that there is an inconsistency between ionospheric measurements of the photoelectron flux and the solar EUV flux. The problem which occurs for EUV wavelengths near 250 A or photoelectron energies near 35 eV has serious implications for theoretical photoelectron flux calculations and could help to explain up to 40 percent of the difference between calculated and measured photoelectron fluxes for electron energies below 35 eV. It is also shown that: (1) only photons with wavelengths shorter than 310 A are of importance in producing photoelectrons; (2) above 20 eV, the photoelectron flux is controlled by the production of primary photoelectrons, while below 20 eV the flux is controlled by degraded photoelectrons; (3) the calculated cascading production rate is insensitive to the cross sections used for the calculation; and (4) the photoelectron flux is inversely proportional to the total inelastic cross sections.

Richards, P. G.↗
NASA NTRS1981

Estimation of surface temperature variations due to changes in sky and solar flux with elevation

The magnitude of elevation effects due to changes in solar and sky fluxes, on interpretation of single thermal images and composite products such as temperature difference and thermal inertia, are examined. Simple expressions are derived for the diurnal behavior of the two parameters, by fitting field observations in one tropic (Hawaii) and two semi-arid climates (Wyoming and Colorado) (Hummer-Miller, 1981). It is shown that flux variations with elevation can cause changes in the mean diurnal temperature gradient from -4 to -14 degrees C/km, evaluated at 2000 m. Changes in the temperature-difference gradient of 1 to 2 degrees C/km are also produced which is equivalent to an effective thermal-inertia gradient of 100 W s(exp 1/2)/sq m-K-km. An example is presented showing an elevation effect of 12 degrees C on the day and night thermal scenes of a test site in Arizona.

Hummer-Miller, S.↗
NASA NTRS1984

Absolute measurement of the extreme UV solar flux

A windowless rare-gas ionization chamber has been developed to measure the absolute value of the solar extreme UV flux in the 50-575-A region. Successful results were obtained on a solar-pointing sounding rocket. The ionization chamber, operated in total absorption, is an inherently stable absolute detector of ionizing UV radiation and was designed to be independent of effects from secondary ionization and gas effusion. The net error of the measurement is + or - 7.3 percent, which is primarily due to residual outgassing in the instrument, other errors such as multiple ionization, photoelectron collection, and extrapolation to the zero atmospheric optical depth being small in comparison. For the day of the flight, Aug. 10, 1982, the solar irradiance (50-575 A), normalized to unit solar distance, was found to be 5.71 + or - 0.42 x 10 to the 10th photons per sq cm sec.

Carlson, R. W.↗
NASA NTRS1970

Inexpensive net solar flux radiometer

Radiometer measures the absorption and reflection of solar radiation by opaque and translucent surfaces. Surface-coating modifications permit measurements over selected broad wavelength bands within the solar spectrum.

Darkow, G. L.↗
NASA NTRS1974

Solar flux and its variations

Current knowledge of the electromagnetic solar spectrum and radiant energy output for conditions of quiet and active sun is summarized. Discussed are temporal behavior and occurrence of solar phenomena such as active regions, calcium plages and flares, X-rays, UV and other energetic emissions, and their relationships to 11- and 22-year solar cycles.

Smith, E. V. P.↗