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Spatial model of geomagnetic field of effective solar corpuscular flux based on mariner ii measurements
The physical implications of the existence at about 1 AU of a quiet solar wind particle flux about 90 percent larger than that suggested in the past is investigated within the framework of the two-fluid solar wind model equations. During the spherically symmetric radial expansion of the quiet solar wind, the particle flux is conserved quantity. It is found that a pure collisional two-fluid model provides good particle density and streaming velocity at 1 AU, but predicts too large an electron temperature and too small a proton temperature. When noncollisional contributions to the transport coefficients are incorporated in the model equations, a complete satisfactory agreement with the available observations is obtained. Upper limits to the effective coupling between electrons and protons, as well as to the effective proton thermal conductivity, and both upper and lower limits to the effective electron thermal conductivity in the quiet solar wind, required to provide agreement with observations, are given.
The Mariner 10 H (1216-A) interplanetary observations are examined by using models that consider anisotropies in the solar fluxes. It is verified that the dominant contribution to asymmetric structure in the Mariner 10 H (1216-A) data is a latitudinal variation of the solar-wind flux and of the solar wind velocity, leading to a hydrogen atom lifetime that is latitude dependent. The average lifetime at 1 AU is found to increase from the solar equator to the solar poles by about 25%. This allows interstellar hydrogen to penetrate closer to the solar poles than to the equator. A general analytic model is constructed for evaluating the neutral hydrogen density distribution in interplanetary space. This model takes into account the latitude-dependent ionization rate. When this model is applied to the Mariner 10 H (1216-A) data, it is shown to be capable of matching the observations with a statistical accuracy of 5%. The effect of this latitudinal variation on H (1216-A) sky background maps is to produce a latitudinal shift in the maximum toward the north ecliptic pole.
A coupled high and low latitude radiative-dynamical model of the annual mean northern hemisphere has been constructed in order to study the interactions of the vertical and meridional heat fluxes and their feedback effect on model climate sensitivity. The model's climate sensitivity to solar constant changes and CO2 increases is investigated, and the effect of feedback in the dynamical fluxes on model climate sensitivity is examined. Nonlinear interactions between heat fluxes and other feedbacks such as radiation-temperature, ice albedo, and humidity are also discussed.
Total solar irradiance (TSI), normalized to the mean earth-sun distance, is analyzed to assess long-term solar variability which may affect climate. TSI data sets are reviewed primarily from the 1984-1999 Earth Radiation Budgets Satellite (ERBS), 1978-1993 Nimbus7, 1980-1989 Solar Maximum Mission (SMM), 19911998 Upper Atmospheric Research Satellite (UARS), and 1996-1998 Solar and Heliospheric Observatory (SOHO)/ Variability of solar IRradiance and Gravity Oscillations (VIRGO) Spacecraft missions. The data sets indicate that 1365 W/sq m [Watts per meter square] is the most likely TSI amplitude at minimum solar magnetic activity as indicated by minimum sunspot numbers. The TSI long-term variability component was found to vary with a period of approximately 10 years and with an amplitude of 2 W/sq m. An empirical TSI fit model, based upon 10.7-cm solar radio fluxes and prompt photometric sunspot indices, was used to characterize TSI variability. Comparisons among TSI measurements and empirical fit trends are reviewed as well as inconsistencies among current spacecraft TSI data set trends. The 1996-1998, SOHO/VIRGO measurement indicate stronger TSI increasing trends than those suggested by the corresponding ERBS and UARS measurement and by the empirical model fit. 1978-1999 TSI data sets are analyzed to identify the probable existence of another long-term TSI variability component.
Techniques for the determination of leaf area index or leaf angle distribution from remote-sensing canopy-reflectance (CR) measurements are developed on the basis of empirical models relating CR to parameters such as soil and vegetation spectral properties, solar flux, and viewing angle. A general procedure for inverting CR models is presented and applied to the models of Suits (1972), Verhoef and Bunnik (1981), and Norman (1979) in the IR range. Numerical results for a soybean canopy are compared in a table, and the error sensitivity of the inverted models is shown to be relatively high, requiring the use of ancillary data such as soil reflectance, leaf reflectance, and leaf transmittance.
Several physical models of the high-latitude ionosphere have been developed that describe the time-dependent evolution of the E- and F-region plasma density. The models require a variety of inputs, including solar EUV fluxes, magnetospheric convection, auroral precipitation, and neutral atmosphere. Of specific relevance to this study is how the neutral atmosphere is incorporated into the ionospheric models. For the USU ionospheric model, the neutral atmosphere is the MSIS 1986 empirical model, while for the UCL-Sheffield coupled thermospheric-ionospheric model the neutral atmosphere is computed simultaneously with the ionosphere. Both models were run for similar solar and magnetospheric conditions (solar maximum, moderate geomagnetic activity, and winter solstice). Solar maximum conditions ensured a strong coupling between the ionosphere and thermosphere, which provided the possibility of a large ionospheric difference between the two physical models. This was further enhanced by choosing winter conditions so that the densities were not dominated by sunlight. The comparison of the two models indicated that both models predict the same morphological features with similar ionospheric densities, generally within about 30 percent.
There exists a growing need to improve the accuracy of measurement of the absolute solar flux within the wavelength range 120-400 nm. Although full-disk solar fluxes and variations thereof in the 120-400 nm region are required to model the solar atmosphere, current increased interest in the measurements arises from their importance in modeling the terrestrial atmosphere. The Solar Ultraviolet Spectral Irradiance Monitor (SUSIM) experiment under development for flight aboard the Space Shuttle and the Upper Atmospheric Research Satellite is described. SUSIM will monitor the solar flux in the 120-144 nm region with high precision, using an in-flight calibration system to reduce absolute error to less than 10%, and error relative to the 400 nm continuum to less than 1%.
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.
A 3-D electron fluid model has been developed as a steping stone to fully describe the electron current flow across magnetic fields inside a vacuum chamber and to provide electron flux to solar arrays for spacecraft surface charging model. A detailed description of the numerical treatment of the electric potential solver, including finite-volume formulation, implementation, and the treatment of boundary conditions, are presented in this paper. Verification tests of the model are presented.
A 3-D electron fluid model has been developed as a stepping stone to fully describe the electron current flow across magnetic fields inside a vacuum chamber and to provide electron flux to solar arrays for spacecraft surface charging model. A detailed description of the numerical treatment of the electric potential solver, including finite-volume formulation, implementation, and the treatment of boundary conditions, are presented in this paper. Verification tests of the model are presented.
A 3-D electron fluid model has been developed as a steping stone to fully describe the electron current flow across magnetic fields inside a vacuum chamber and to provide electron flux to solar arrays for spacecraft surface charging model. A detailed description of the numerical treatment of the electric potential solver, including finite-volume formulation, implementation, and the treatment of boundary conditions, are presented in this paper. Verification tests of the model are presented.
An analysis is presented for evaluation of equilibrium temperature distribution on radiatively adiabatic, adjoint planes which are uniformly irradiated by a collimated solar flux. The analysis employs a semigrey spectral model. Radiation properties for surface emitted radiation are obtained from the expressions of electromagnetic theory for smooth surfaces. Rough surface properties for solar radiation are given by the Beckmann bidirectional reflectance model. Numerical solutions to the governing equations yield equilibrium temperature distributions for a range of the influencing parameters. Surface roughness has little influence on equilibrium temperature for materials with high values for solar absorptance. However, for low or intermediate values of solar absorptance, roughness effects on the spatial distribution of reflected solar radiation can significantly alter equilibrium temperature particularly at surface elements where radiant interaction is small.
During solar flares plasma is typically heated to very high temperatures, and the resulting redistribution of energy via thermal conduction is a primary mechanism transporting energy throughout the flaring solar atmosphere. The thermal flux is usually modeled using Spitzer’s theory, which is based on local Coulomb collisions between the electrons carrying the thermal flux and those in the background. However, often during flares, temperature gradients become sufficiently steep that the collisional mean free path exceeds the temperature gradient scale size, so that thermal conduction becomes inherently non-local. Further, turbulent angular scattering, which is detectable in nonthermal widths of atomic emission lines, can also act to increase the collision frequency and so suppress the heat flux. Recent work by Emslie & Bian (2018) extended Spitzer’s theory of thermal conduction to account for both non-locality and turbulent suppression. We have implemented their theoretical expression for the heat flux (which is a convolution of the Spitzer flux with a kernel function) into the RADYN flare-modeling code and performed a parameter study to understand how the resulting changes in thermal conduction affect flare dynamics and hence the radiation produced. We find that models with reduced heat fluxes predict slower bulk flows, less intense line emission, and longer cooling times. By comparing features of atomic emission lines predicted by the models with Doppler velocities and nonthermal line widths deduced from a particular flare observation, we find that models with suppression factors between 0.3 to 0.5 relative to the Spitzer value best reproduce observed Doppler velocities across emission lines forming over a wide range of temperatures. Interestingly, the model that best matches observed nonthermal line widths has a kappa-type velocity distribution function
The Nowcast of Aerospace Ionizing RAdiation System (NAIRAS) predicts dosimetric quantities for quantifying human radiation exposure and differential/integral flux/fluence quantities for assessing single event effects (SEE) in avionic systems from galactic cosmic rays (GCR), trapped inner belt protons, and solar energetic particle (SEP) events from the Earth’s surface to the space environment. Real-time predictions of the aviation radiation environment are available at NASA Goddard Space Flight Center’s Community Coordinated Modeling Center (CCMC) integrated Space Weather Analysis (iSWA) data feeds and cygnets, and a run-on-request (RoR) capability has also been deployed at CCMC. Recent model improvements include a more accurate atmospheric ionizing radiation transport methodology and more robust and reliable SEP nowcast dose predictions. In addition, preliminary results of SEP dose forecasts are shown by coupling the University of Malaga Solar Energetic Particle (UMASEP) model of integral proton flux forecasts with the NAIRAS model. These model updates and improvements are presented, and results are shown for aircraft, high-latitude balloon, and low-Earth orbit flights during quiescent and solar-geomagnetic disturbed conditions. Model comparisons with flight measurements are also shown.
We present a new quantitative model for detailed solar-pumped fluorescent emission of the main isotopologue of CN. The derived fluorescence efficiencies permit estimation and interpretation of ro-vibrational infrared line intensities of CN in exospheres exposed to solar (or stellar) radiation. Our g-factors are applicable to astronomical observations of CN extending from infrared to optical wavelengths, and we compare them with previous calculations in the literature. The new model enables extraction of rotational temperature, column abundance, and production rate from astronomical observations of CN in the inner coma of comets. Our model accounts for excitation and de-excitation of rotational levels in the ground vibrational state by collisions, solar excitation to the A(sup 2)Pi(sub I) and B(sup 2)Sum(sup +) electronically excited states followed by cascade to ro-vibrational levels of X(sup 2)Sum(sup +), and direct solar infrared pumping of ro-vibrational levels in the X(sup 2)Sum(sup +) state. The model uses advanced solar spectra acquired at high spectral resolution at the relevant infrared and optical wavelengths and considers the heliocentric radial velocity of the comet (the Swings effect) when assessing the exciting solar flux for a given transition. We present model predictions for the variation of fluorescence rates with rotational temperature and heliocentric radial velocity. Furthermore, we test our fluorescence model by comparing predicted and measured line-by-line intensities for X(sup 2)Sum(sup +) (1-0) in comet C/2014 Q2 (Lovejoy), thereby identifying multiple emission lines observed at IR wavelengths.
The interaction of solar p-modes with a sunspot magnetic flux tube is investigated theoretically by means of two simple models. An increase in horizontal wavelength between the nonmagnetic and magnetic regions, due to the different characteristic wave speeds in the two regions, explains the corresponding observed wavelength shift of powe in the umbral k-omega power spectrum. The variation of the transmission coefficient with wavenumber along the p-mode diagnostic curves, due to resonant transmission, is responsible for the observed selective filtering of the p-modes by the sunspot.
The rotation of erupting filaments in the solar corona is addressed through a parametric simulation study of unstable, rotating flux ropes in bipolar force-free initial equilibrium. The Lorentz force due to the external shear-field component and the relaxation of tension in the twisted field are the major contributors to the rotation in this model, while reconnection with the ambient field is of minor importance, due to the field's simple structure. In the low-beta corona, the rotation is not guided by the changing orientation of the vertical field component's polarity inversion line with height. The model yields strong initial rotations which saturate in the corona and differ qualitatively from the profile of rotation vs. height obtained in a recent simulation of an eruption without preexisting flux rope. Both major mechanisms writhe the flux rope axis, converting part of the initial twist helicity, and produce rotation profiles which, to a large part, are very similar within a range of shear-twist combinations. A difference lies in the tendency of twist-driven rotation to saturate at lower heights than shear-driven rotation. For parameters characteristic of the source regions of erupting filaments and coronal mass ejections, the shear field is found to be the dominant origin of rotations in the corona and to be required if the rotation reaches angles of order 90 degrees and higher; it dominates even if the twist exceeds the threshold of the helical kink instability. The contributions by shear and twist to the total rotation can be disentangled in the analysis of observations if the rotation and rise profiles are simultaneously compared with model calculations. The resulting twist estimate allows one to judge whether the helical kink instability occurred. This is demonstrated for the erupting prominence in the "Cartwheel CME" on 9 April 2008, which has shown a rotation of approximately 115 deg. up to a height of 1.5 Solar R above the photosphere. Out of a range of initial equilibria which include strongly kink-unstable (Phi = 5 pi), weakly kink-unstable (Phi = 3.5 pi), and kink-stable (Phi = 2.5 pi) configurations, only the evolution of the weakly kink-unstable flux rope matches the observations in their entirety.