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Upper atmosphere temperature variations analysis from satellite drag observations, discussing solar far UV and geomagnetic activity roles
In this study, we compare the SDO/HMI line-of-sight observables (magnetic field, velocity, continuum intensity, and line depth) with the related physical properties for several dynamo simulation runs performed using the "StellarBox" 3D Radiative MHD code. The modeling of the Fe I 6173 A Stokes profiles is performed using the SPINOR radiative transfer code in the LTE approximation. The reproduced SDO/HMI line-of-sight pipeline is applied to the modeled spectra, and the observables are synthesized with high (numerical) and SDO/HMI (instrumental) resolutions. Correlations between the observables and the physical properties at various heights in the atmosphere are studied for a set of view angles (0, 30, 45, 60, 70, and 80 degrees away from the solar disk center). It is found that the SDO/HMI magnetic field and velocity measurements are unambiguously correlated with physical parameters at certain heights of the solar atmosphere. These heights increase from about 100 km above the photosphere for the disk center case to 300-600 km above the photosphere for the 80-degree case. The heights are found to be slightly lower in regions where stronger magnetic fields are found. The comparison of the photospheric magnetic flux and integrated continuum intensity derived from the SDO/HMI observables and high-resolution observations and spectra is discussed. The results of our study improve physics-based interpretations of the SDO/HMI observables and provide a better understanding of the physical properties of the solar atmosphere.
The intensity of He I, 584 A radiation in the night sky was measured from a sounding rocket at altitudes between 160 and 217 km. The results obtained confirm previous measurements of this radiation. The observed intensity and spatial variations can be entirely accounted for by resonance scattering of solar 584 A radiation from interstellar helium. The best fit to the observations in this case is obtained with an interstellar helium model in which the bulk velocity of the gas is 5 km/sec, the temperature is 10,000 K, and the helium number density is 0.032 per cu cm. Even if a geocoronal scattering component is present, the data can be used to set a lower limit to the temperature of the local interstellar medium of 1,500 (plus or minus 500) K, assuming a normal interstellar helium abundance.
A detailed analysis is conducted which shows that signatures in the interplanetary Lyman-alpha emissions observed in three different data sets from Mariner 10 (corresponding to different locations of the spacecraft) provide firm evidence that the intensity departures are correlated with a decrease in solar wind flux with increasing latitude. It is suggested that observations of the interplanetary emission can be used to monitor average solar wind activity at high latitudes. The asymmetry in the solar radiation field as a source of observed departures in L-alpha data is considered and attention is given to the interstellar hydrogen and helium density.
A biophysical process-based model was run using satellite, assimilated and ancillary data for four years (1987-1990) to calculate components of total evaporation (transpiration, interception, soil and snow evaporation), net radiation, absorbed photosynthetically active radiation and net primary productivity over the global land surface. Satellite observations provided fractional vegetation cover, solar and photosynthetically active radiation incident of the surface, surface albedo, fractional cloud cover, air temperature and vapor pressure. The friction velocity and surface air pressure are obtained from a four dimensional data assimilation results, while precipitation is either only surface observations or a blended product of surface and satellite observations. All surface and satellite data are monthly mean values; precipitation has been disaggregated into daily values. All biophysical parameters of the model are prescribed according to published records. From these global land surface calculations results for river basins are derived using digital templates of basin boundaries. Comparisons with field observations (micrometeorologic, catchment water balance, biomass production) and atmospheric water budget analysis for monthly evaporation from six river basins have been done to assess errors in the calculations. Comparisons are also made with previous estimates of zonal variations of evaporation and net primary productivity. Efficiencies of transpiration, total evaporation and radiation use, and evaporative fraction for selected river basins will be presented.
A method of modeling the solar chromosphere is developed, based on submillimeter continuum observations of the solar limb. Submillimeter radiation from the solar limb emanates from the chromosphere in local thermodynamic equilibrium, making it an important chromospheric diagnostic. Also, the use of high-resolution limb profiles allows for atmospheric modeling independent of gravitational hydrostatic equilibrium. The chromospheric model is constructed to match high-resolution solar limb profiles at 30, 50, 100, and 200 microns, determined by an occultation of the solar limb observed from the Kuiper Airborne Observatory during the total solar eclipse of July 31, 1981. This matching is achieved by 'stretching' the solar model atmosphere of Vernazza, Avrett, and Loesser (1981) vertically out of hydrostatic equilibrium, while maintainingn its vertical temperature-optical depth profile.
It is pointed out that the global mean temperature structure of the thermosphere above 120 km is primarily maintained by the absorption of solar extreme ultraviolet (EUV) flux at wavelengths less than 1025 A and solar ultraviolet (UV) flux. A number of previous calculations of the global mean temperature profile have determined that it is not possible to obtain agreement between the calculated global mean exospheric temperature and observed values. Since those studies, a considerable amount of new information on this problem has been obtained, including data obtained with the aid of the Atmospheric Explorer satellites. The present investigation is, therefore, concerned with a reexamination of the question whether there is enough solar UV radiation and auroral energy input to maintain the observed global mean temperature structure of the thermosphere above 120 km. It is found that for solar cycle minimum conditions there is an approximate balance between absorbed solar radiation and downward molecular thermal conduction.
The rate of hydrogen production of Comet West is studied through rocket observation of solar Lyman-alpha radiation resonantly scattered by the escaping hydrogen atoms. Two sets of Lyman-alpha exposure sequences are used to obtain computer-smoothed brightness contour (isophote) maps covering a density range of 100:1. A simple radial outflow model is applied to the contour maps to determine the rate of hydrogen production (3.2 by 10 to the 30th power atoms/sec.) Discrepancies between the observed shape of the outer isophotes and predicted models may be explained by optical depth effects, or by the presence of small pieces of the comet's nucleus distributed along the orbit. Hydrogen, carbon, and oxygen production for Comet West and Comet Kohoutek are compared; differences may be accounted for by variations in the composition or evolution of the two comets.
The characteristics of solar radio emissions at decametric to kilometric wavelengths are reviewed. Special attention is given to the radiation of the quiet sun at several metric and decametric wavelengths and to nonthermal radiation from the active sun, including radio bursts of type III (electron beams), type-III bursts from behind the sun, storms of type III bursts, the flare-associated radio bursts, type II bursts (shock waves), and shock-associated bursts. It is pointed out that almost no observations have been made so far of solar radiation between about 20 MHz and about 2 MHz. Below about 2 MHz, dynamic spectra of flux densities of solar burst have been recorded in space and observations were made of the directions of centroids and characteristic sizes of the emitting sources.
Placed at L4, Sun Chaser is a mission concept that will follow (or chase) high-energy processes around the west limb, combining solar remote sensing & in situ observations, and overseeing the entire solar radiation hemisphere. Sun Chaser’s remote sensing is essential for ~90% of current physics-based and empirical solar energetic particle (SEP) event forecasting techniques. Without Sun Chaser, there cannot be a basis for SEP event all-clear forecasting. It establishes and maintains a space weather (SWx) radiation safe zone that supports all near-term human missions to the Moon and Mars. Sun Chaser latitude in-situ coverage also provides a unique opportunity for solar wind-, interplanetary- and interstellar-dust science. In combination with existing and planned observatories at L1 and L5, the three locations provide 240° longitude coverage of resolving photospheric magnetic field structure and safe Earth-directed CME viewing. A ~14°-inclination of both L4 and L5 out of the ecliptic guarantees continuous viewing of both solar poles and continuous in-situ presence on both sides of the heliographic equator, with >3.6° elevation. Extended observations in both longitude and latitude will revolutionize global solar wind modeling and immediate validation, and enables the development of local helioseismology, with potential for long-term solar activity forecasting.
Global atmospheric energy balance is one of the fundamental processes for the earth's climate system. This study uses currently available satellite data sets of radiative energy at the top of atmosphere (TOA) and surface and latent and sensible heat over oceans for the year 2000 to assess the global annual energy budget. Over land, surface radiation data are used to constrain assimilated results and to force the radiation, turbulent heat, and heat storage into balance due to a lack of observation-based turbulent heat flux estimations. Global annual means of the TOA net radiation obtained from both direct measurements and calculations are close to zero. The net radiative energy fluxes into the surface and the surface latent heat transported into the atmosphere are about 113 and 86 Watts per square meter, respectively. The estimated atmospheric and surface heat imbalances are about -8 ~ 9 Watts per square meter, values that are within the uncertainties of surface radiation and sea surface turbulent flux estimates and likely systematic biases in the analyzed observations. The potential significant additional absorption of solar radiation within the atmosphere suggested by previous studies does not appear to be required to balance the energy budget the spurious heat imbalances in the current data are much smaller (about half) than those obtained previously and debated at about a decade ago. Progress in surface radiation and oceanic turbulent heat flux estimations from satellite measurements significantly reduces the bias errors in the observed global energy budgets of the climate system.
Millimeter wavelength solar radiation consisting of thermal, slowly varying active and burst components and eclipse measurements of brightness distribution
Satellite observation on correlation between outer radiation zone electrons and solar activity cycle
Electron injection and diffusion into electron inner radiation belt after solar flare, measuring electron fluxes by OGO 3 spectrometer
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NASA’s Solar Radiation and Climate Experiment (SORCE) Spectral Irradiance Monitor (SIM) instrument produced about 17 years of daily average Spectral Solar Irradiance ( SSI ) data for wavelengths 240 nm – 2416 nm. We choose a day of minimal solar activity, 2008-08-24, during the 2008 − 2009 minimum between cycles 23 and 24, and compute the brightness temperature (𝑇 o ) from that day’s solar spectral irradiance (𝑆𝑆𝐼 o ). We consider small variations of T and SSI about these reference values, and derive linear and quadratic analytic approximations by Taylor expansion about the reference day values. To determine approximation accuracy, we compare to exact brightness temperatures T computed from the Planck spectrum, by solving analytically for T , or equivalent root-finding in Wolfram Mathematica. We find that the linear analytic approximation overestimates, while the quadratic underestimates the exact result. This motivates search for statistical “fit” models “in between” the two analytic models, with minimum root-mean-square-error RMSE. We make this search using open-source statistical R software, determine coefficients for linear and quadratic fit models, and compare statistical with analytic RMSE’s. When only linear analytic and fit models are compared, the fit model is superior at ultraviolet, visible, and near infrared wavelengths. This again holds true when comparing only quadratic models. Quadratic is superior to linear for both analytic and statistical models, and statistical fits give smallest RMSE’s. Lastly, we use linear analytic and fit models to find an interpolating function in wavelength, useful in case the SIM results need adjustment to another choices of wavelengths, to compare or extend to any other instrument.
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Sources of new measurements of the solar EUV, UV, and visible spectrum are presented together with discussion of formation of the solar spectrum as a problem in stellar atmospheres. Agreement between the data and a modern synthetic spectrum shows that observed radiative variability is a minor perturbation on a photosphere in radiative equilibrium and local thermodynamic equilibrium (LTE). Newly observed solar variability in 1992 defines a magnetic episode on the Sun closely associated with changes in both spectral irradiances and the total irradiance. This episode offers the opportunity to track the relationship between radiation and magnetic flux evolution.