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At least 883 records · Page 49
All sourcesNASA NTRSDOE OSTI
NASA NTRS2001

Large Solar Flares and Sheared Magnetic Field Configuration

This Comment gives additional information about the nature of flaring locations on the Sun described in the article "Sun unleashes Halloween storm", by R. E. Lopez, et al. What causes the large explosions from solar active regions that unleash huge magnetic storms and adverse space weather? It is now beyond doubt that the magnetic field in solar active regions harbors free energy that is released during these events. Direct measurements of the longitudinal and transverse components of active region magnetic fields with the vector magnetograph at NASA Marshall Space Flight Center (MSFC), taken on a regular basis for the last 30 years, have found key signatures of the locations of powerful flares. A vector magnetograph detects and measures the magnetic shear, which is the deviation of the observed transverse magnetic field direction from the potential field. The sheared locations possess abundant free magnetic energy for solar flares. In addition to active region NOAA 10486, the one that produced the largest flares last October, the NASA/MSFC vector magnetograph has observed several other such complex super active regions, including NOAA 6555 and 6659.

Choudhary, Debi Prasad↗
DOE OSTI2017

The First ALMA Observation of a Solar Plasmoid Ejection from an X-Ray Bright Point

Eruptive phenomena such as plasmoid ejections or jets are important features of solar activity and have the potential to improve our understanding of the dynamics of the solar atmosphere. Such ejections are often thought to be signatures of the outflows expected in regions of fast magnetic reconnection. The 304 Å EUV line of helium, formed at around 10{sup 5} K, is found to be a reliable tracer of such phenomena, but the determination of physical parameters from such observations is not straightforward. We have observed a plasmoid ejection from an X-ray bright point simultaneously at millimeter wavelengths with ALMA, at EUV wavelengths with SDO /AIA, and in soft X-rays with Hinode /XRT. This paper reports the physical parameters of the plasmoid obtained by combining the radio, EUV, and X-ray data. As a result, we conclude that the plasmoid can consist either of (approximately) isothermal ∼10{sup 5} K plasma that is optically thin at 100 GHz, or a ∼10{sup 4} K core with a hot envelope. The analysis demonstrates the value of the additional temperature and density constraints that ALMA provides, and future science observations with ALMA will be able to match the spatial resolution of space-borne and other high-resolution telescopes.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1976

Solar-cycle dependence of galactic cosmic ray flux. II - The correlation between the nucleonic flux and solar indices

To investigate the relationship between solar activity and cosmic-ray modulation, time series of the nucleonic flux and of solar plages, sunspots, centimeter radio noise, and the brightness of the white-light corona at 1.1 and 1.5 solar radii from the center of sun are cross-correlated. Data pertain to the years 1964-1967 during the ascending phase of the current solar cycle. The amplitudes and phases of correlation functions for filtered and unfiltered indices are discussed. The existence of a superior solar index for relating solar activity to long-term modulation is not yet demonstrated conclusively, and the time lag of modulation is too poorly determined to permit its use in estimating the radius of the modulation region.

Parker, G. D.↗
NASA NTRS1986

Heliocentric radius of the cosmic ray modulation boundary

A semiempirical analysis is made of an extensive body of observed cosmic ray intensity data from Pioneers 10 and 11, and related spectral information from other authors, in order to infer the radius R of the modulation region surrounding the sun. During the period 1972-1985, the inferred values of R vary with time systematically and in a manner generally similar to that of sunspot numbers. The range of values of R is from 42 AU at the time of minimum solar activity (circa 1976) to 88 AU about 1.5 yr following the time of maximum solar activity (circa 1980). A specific, testable prediction is that Pioneer 10 will reach the modulation boundary in 1988, and will remain in its vicinity for several years thereafter.

Randall, B. A.↗
NASA NTRS1991

LDEF space environments overview

The Long Duration Exposure Facility (LDEF) was launched into an Earth orbit during a period of minimum solar activity. It was retrieved almost 6 years later during a period of near maximum solar activity. In flight, the LDEF was passively stabilized in three axes and it flew in a near circular orbit having an inclination of 28.5 degs and an initial altitude of approx. 257 nautical miles. When the LDEF was retrieved, the orbit had decayed to an altitude of approx. 180 nautical miles. Specifically, the LDEF flew with one surface always facing the trailing direction, one surface facing Earth, and one surface facing into space. These facts made the LDEF an ideal platform to expose experiments to study the space environments and the effects of these environments on spacecraft materials and systems. An overview is provided of the specific space environments to which the LDEF experiments were exposed. The specific features are also pointed out of the LDEF that allow the effects of different environments to be isolated.

Kinard, William H.↗
NASA NTRS2002

Measuring Solar Radiation Incident on Earth: Solar Constant-3 (SOLCON-3)

Life on Earth is possible because the climate conditions on Earth are relatively mild. One element of the climate on Earth, the temperature, is determined by the heat exchanges between the Earth and its surroundings, outer space. The heat exchanges take place in the form of electromagnetic radiation. The Earth gains energy because it absorbs solar radiation, and it loses energy because it emits thermal infrared radiation to cold space. The heat exchanges are in balance: the heat gained by the Earth through solar radiation equals the heat lost through thermal radiation. When the balance is perturbed, a temperature change and hence a climate change of the Earth will occur. One possible perturbation of the balance is the CO2 greenhouse effect: when the amount of CO2 in the atmosphere increases, this will reduce the loss of thermal infrared radiation to cold space. Earth will gain more heat and hence the temperature will rise. Another perturbation of the balance can occur through variation of the amount of energy emitted by the sun. When the sun emits more energy, this will directly cause a rise of temperature on Earth. For a long time scientists believed that the energy emitted by the sun was constant. The 'solar constant' is defined as the amount of solar energy received per unit surface at a distance of one astronomical unit (the average distance of Earth's orbit) from the sun. Accurate measurements of the variations of the solar constant have been made since 1978. From these we know that the solar constant varies approximately with the 11-year solar cycle observed in other solar phenomena, such as the occurrence of sunspots, dark spots that are sometimes visible on the solar surface. When a sunspot occurs on the sun, since the spot is dark, the radiation (light) emitted by the sun drops instantaneously. Oddly, periods of high solar activity, when a lot of sunspot numbers increase, correspond to periods when the average solar constant is high. This indicates that the background on which the sunspots occur becomes brighter during high solar activity.

Dominique Crommelynck↗
DOE OSTI2016

ENSEMBLE EMPIRICAL MODE DECOMPOSITION OF THE MAGNETIC FIELD OF THE SUN AS A STAR

The ensemble empirical mode decomposition (EEMD) analysis is utilized to extract the intrinsic mode functions (IMFs) of the solar mean magnetic field (SMMF) observed at the Wilcox Solar Observatory of Stanford University from 1975 to 2014, and then we analyze the periods of these IMFs as well as the relation of IMFs (SMMF) with some solar activity indices. The two special rotation cycles of 26.6 and 28.5 days should be derived from different magnetic flux elements in the SMMF. The rotation cycle of the weak magnetic flux element in the SMMF is 26.6 days, while the rotation cycle of the strong magnetic flux element in the SMMF is 28.5 days. The two rotation periods of the structure of the interplanetary magnetic field near the ecliptic plane are essentially related to weak and strong magnetic flux elements in the SMMF, respectively. The rotation cycle of weak magnetic flux in the SMMF did not vary over the last 40 years because the weak magnetic flux element derived from the weak magnetic activity on the full disk is not influenced by latitudinal migration. Neither the internal rotation of the Sun nor the solar magnetic activity on the disk (including the solar polar fields) causes the annual variation of SMMF. The variation of SMMF at timescales of a solar cycle is more related to weak magnetic activity on the full solar disk.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1994

Solar influences on global change

Monitoring of the Sun and the Earth has yielded new knowledge essential to this debate. There is now no doubt that the total radiative energy from the Sun that heats the Earth's surface changes over decadal time scales as a consequence of solar activity. Observations indicate as well that changes in ultraviolet radiation and energetic particles from the Sun, also connected with the solar activity, modulate the layer of ozone that protects the biosphere from the solar ultraviolet radiation. This report reassesses solar influences on global change in the light of this new knowledge of solar and atmospheric variability. Moreover, the report considers climate change to be encompassed within the broader concept of global change; thus the biosphere is recognized to be part of a larger, coupled Earth system. Implementing a program to continuously monitor solar irradiance over the next several decades will provide the opportunity to estimate solar influences on global change, assuming continued maintenance of observations of climate and other potential forcing mechanisms. In the lower atmosphere, an increase in solar radiation is expected to cause global warming. In the stratosphere, however, the two effects produce temperature changes of opposite sign. A monitoring program that would augment long term observations of tropospheric parameters with similar observations of stratospheric parameters could separate these diverse climate perturbations and perhaps isolate a greenhouse footprint of climate change. Monitoring global change in the troposphere is a key element of all facets of the United States Global Change Research Program (USGCRP), not just of the study of solar influences on global change. The need for monitoring the stratosphere is also important for global change research in its own right because of the stratospheric ozone layer.

Source record↗
DOE OSTI2015

THE EFFECT OF A DYNAMIC INNER HELIOSHEATH THICKNESS ON COSMIC-RAY MODULATION

The time-dependent modulation of galactic cosmic rays in the heliosphere is studied over different polarity cycles by computing 2.5 GV proton intensities using a two-dimensional, time-dependent modulation model. By incorporating recent theoretical advances in the relevant transport parameters in the model, we showed in previous work that this approach gave realistic computed intensities over a solar cycle. New in this work is that a time dependence of the solar wind termination shock (TS) position is implemented in our model to study the effect of a dynamic inner heliosheath thickness (the region between the TS and heliopause) on the solar modulation of galactic cosmic rays. The study reveals that changes in the inner heliosheath thickness, arising from a time-dependent shock position, does affect cosmic-ray intensities everywhere in the heliosphere over a solar cycle, with the smallest effect in the innermost heliosphere. A time-dependent TS position causes a phase difference between the solar activity periods and the corresponding intensity periods. The maximum intensities in response to a solar minimum activity period are found to be dependent on the time-dependent TS profile. It is found that changing the width of the inner heliosheath with time over a solar cycle can shift the time of when the maximum or minimum cosmic-ray intensities occur at various distances throughout the heliosphere, but more significantly in the outer heliosphere. The time-dependent extent of the inner heliosheath, as affected by solar activity conditions, is thus an additional time-dependent factor to be considered in the long-term modulation of cosmic rays.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2010

STEREO - The Sun from Two Points of View

NASA's STEREO (Solar TErrestrial RElations Observatory) mission continues its investigations into the three dimensional structure of the sun and heliosphere. With the recent increases in solar activity STEREO is yielding new results obtained using the mission's full array of imaging and in-situ instrumentation, and in February 2011 the two spacecraft will be 180 degrees apart allowing us to directly image the entire solar disk for the first time. We will discuss the latest results from STEREO and how they change our view of solar activity and its effects on our solar system.

Kucera, Therese A.↗
DOE OSTI2015

Local H i emissivity measured with Fermi-LAT and implications for cosmic-ray spectra

Cosmic-ray (CR) electrons and nuclei interact with the Galactic interstellar gas and produce high-energy γ-rays. The γ-ray emission rate per hydrogen atom, called emissivity, provides a unique indirect probe of the CR flux. We present the measurement and the interpretation of the emissivity in the solar neighborhood for γ-ray energy from 50 MeV to 50 GeV. We analyzed a subset of 4 yr of observations from the Large Area Telescope (LAT) aboard the Fermi Gamma-ray Space Telescope (Fermi) restricted to absolute latitudes 10{sup ∘}<|b|<70{sup ∘}. From a fit to the LAT data including atomic, molecular, and ionized hydrogen column density templates, as well as a dust optical depth map, we derived the emissivities, the molecular hydrogen–to–CO conversion factor X{sub CO}=(0.902±0.007)×10{sup 20} cm{sup −2} (K km s{sup −1}){sup −1}, and the dust-to-gas ratio X{sub DUST}=(41.4±0.3)×10{sup 20} cm{sup −2} mag{sup −1}. Moreover, we detected for the first time γ-ray emission from ionized hydrogen. We compared the extracted emissivities to those calculated from γ-ray production cross sections and to CR spectra measured in the heliosphere. We observed that the experimental emissivities are reproduced only if the solar modulation is accounted for. This provides a direct detection of solar modulation observed previously through the anticorrelation between CR fluxes and solar activity. Finally, we fitted a parameterized spectral form to the heliospheric CR observations and to the Fermi-LAT emissivity and obtained compatible local interstellar spectra for proton and helium kinetic energy per nucleon between between 1 and 100 GeV and for electron–positrons between 0.1 and 100 GeV.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRSDate not supplied

Small Energetic Electron Events Observed by Parker Solar Probe/ISOIS

The current understanding of the characteristics of energetic electron events in the inner heliosphere is inferred primarily from observations made by spacecraft located at 1 AU. Previous observations at closer heliocentric distances, by the Helios spacecraft at ∼0.3-1 AU, indicate the presence of electron events that are not detected at 1 AU or that have merged or become smeared out during transport from the Sun. Parker Solar Probe’s proximity to the Sun at perihelion provides an opportunity to make the closest measurements yet of energetic electron events. We present an overview of measurements of energetic electrons between ∼17 keV and ∼1 MeV made by the Parker Solar Probe Integrated Science Investigation of the Sun (ISOIS). The current period of solar activity minimum provides an opportunity to examine small electron events that may be challenging to observe later in the mission when solar activity increases. We examine these events in the context of the electromagnetic and solar wind environment measured by the FIELDS and SWEAP instruments on Parker Solar Probe.

John Grant Mitchell↗
NASA NTRS1981

The O II /7320-7330 A/ airglow - A morphological study

A statistical study of the 7320-30 A airglow arising from the metastable transition between aP and aD states of atomic oxygen ions was conducted by analyzing the data taken from the visible airglow experiment on the Atmosphere Explorer satellites C and E during the time periods between 1974 and 1979. Averaged column emission rate profiles as a function of solar zenith angle and solar activity variation are presented. The galactic background has been carefully subtracted. The result shows that the rate of decreasing emission as a function of solar zenith angle agrees with the theoretical calculation based upon a neutral atmosphere model and the solar spectrum as measured by the EUV spectrometer on the Atmosphere Explorer satellite. Furthermore, an expected increase with solar activity also appeared in a plot of emission brightness versus solar 10.7-cm flux.

Yee, J. H.↗
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 NTRS1993

The production and escape of nitrogen atoms on Mars

Updated rate coefficients and a revised ionosphere-thermosphere model are used to compute the production rates and densities of odd nitrogen species in the Martian atmosphere. Computed density profiles for N(4S), N(2D), N(2P), and NO are presented. The model NO densities are found to be about a factor of 2-3 less than those measured by the Viking 1 mass spectrometer. Revised values for the escape rates of N atoms from dissociative recombination and ionospheric reactions are also computed. Dissociative recombination is found to be comparable in importance to photodissociation at low solar activity, but it is still the most important escape mechanism for N-14 at high solar activity.

Fox, J. L.↗
NASA NTRS2006

Solar Forced Dansgaard/Oeschger Events?

Climate records for the last ice age (which ended 11,500 years ago) show enormous climate fluctuations in the North Atlantic region - the so-called Dansgaard/Oeschger events. During these events air temperatures in Greenland changed on the order of 10 degrees Celsius within a few decades. These changes were attributed to shifts in ocean circulation which influences the warm water supply from lower latitudes to the North Atlantic region. Interestingly, the rapid warmings tend to recur approximately every 1500 years or multiples thereof. This has led researchers to speculate about an external cause for these changes with the variable Sun being one possible candidate. Support for this hypothesis came from climate reconstructions, which suggested that the Sun influenced the climate in the North Atlantic region on these time scales during the last approximately 12,000 years of relatively stable Holocene climate. However, Be-10 measurements in ice cores do not indicate that the Sun caused or triggered the Dansgaard/Oeschger events. Depending on the solar magnetic shielding more or less Be-10 is produced in the Earth's atmosphere. Therefore, 10Be can be used as a proxy for solar activity changes. Since Be-10 can be measured in ice cores, it is possible to compare the variable solar forcing directly with the climate record from the same ice core. This removes any uncertainties in the relative dating, and the solar-climate link can be reliably studied. Notwithstanding that some Dansgaard/Oeschger warmings could be related to increased solar activity, there is no indication that this is the case for all of the Dansgaard/Oeschger events. Therefore, during the last ice age the Be-10 and ice core climate data do not indicate a persistent solar influence on North Atlantic climate.

Muscheler, R.↗
NASA NTRS1972

Description of solar structure and processes.

A general introduction to solar structure and processes is presented. The sun is first viewed as a spherically symmetric steady-state system, and the energy generated in the core is traced as it flows outward. The various forms and manifestations of this energy flow and the resulting uniquely defined characteristics of different atmospheric layers are described. The sources of solar activity are assumed to be differential rotation and solar magnetic fields. The interaction of these sources to produce the observed solar cycle, active regions, the active-sun corona, and solar flares is discussed. In describing solar structure and processes, only elementary physical concepts are utilized.

Gibson, E. G.↗
NASA NTRS1985

Solar neutrino: Flux, cosmic rays and the 11 year solar cycle

It is shown that the results of maximum likelihood treatment of Monte Carlo simulation with constant production rate of 7.6 SNU and 1.Epsilon SNU are consistent with the constant production rate when the tests of hypotheses (e.g., t-test, sigma squared-test, Wilcoxon-Mann-Whitney test, run test, etc.) are applied to the two groups of data formed from sunspot minimum range and sunspot maximum range, whereas the real data pulsates with the solar activity cycle. It is shown that SN flux-change is in opposition phase to the solar activity cycle and lags behind the latter by about one year. A correlation between SN flux and the cosmic rays is suggested.

Raychaudhuri, P.↗