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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
NASA NTRS1975

Observations at 6 cm of the solar active region

Preliminary results are reported for the synthesis of a solar active region from observations with a synthesis radio telescope at a wavelength of 6 cm. Several individual sources are observed in the total-intensity and circular-polarization maps. These are shown to correspond to two large sunspots, two groups of small sunspots, and a plage. A magnetogram indicates that this active region had a bipolar structure with positive polarity concentrated on the main sunspots and negative polarity scattered over the plage and some of the small sunspots. It is noted that several radio bursts were recorded during the observation period and that one corresponded to a H-alpha flare near one of the sunspot groups.

Kundu, M. R.↗
NASA NTRS1983

VLA observations of a solar active region and coronal loops

In May 1981, observations of a solar active region at 6 cm and 20 cm were conducted with the aid of a Very Large Array (VLA). It was found that the 6 cm emission was associated with sunspots and transverse magnetic fields between spots. The 20 cm emission came from elongated sources connecting regions of opposite magnetic polarity. The sources of the emission at 20 cm could be identified as coronal loops. A model for hydrostatic loops proposed by Rosner et al. (1978) was employed to determine a likely mechanism for the emission at 20 cm. It was found that a two-component model of bremsstrahlung emission from the feet and gyroresonance emission from the top of the loops can satisfactorily explain the observations.

Mcconnell, D.↗
NASA NTRS1995

Periodogram analysis of sunspot numbers and the relation with solar activities

The time series of average monthly sunspot numbers during 1900-1992 is studied by using power spectral analysis. This prediction method is used to study the sunspot periodicities relations between its, and with the other periodicities by solar activities. There are periodicities (between few days and 5 years) overwhelm on the mean solar cycle. ( 11 year cycle). These periodicities have the same relation with variations of solar constant and solar radiation reaching the Earth's atmosphere in the last solar cycle. These periods are related to the solar magnetic activity and to the modulation of solar features due to solar rotation.

Hady, Ahmed A.↗
NASA NTRS1974

Relationships between solar activity and climate change

Recurrent droughts are related to the double sunspot cycle. It is suggested that high solar activity generally increases meridional circulations and blocking patterns at high and intermediate latitudes, especially in winter. This effect is related to the sudden formation of cirrus clouds during strong geomagnetic activity that originates in the solar corpuscular emission.

Roberts, W. O.↗
NASA NTRS1975

Solar activity and the motions of the upper atmosphere

A possible mechanism for the action of solar radiation on the motion of the upper atmosphere is considered that includes the time dependent interplanetary field contour line and its effect on zonal wind velocity. A strong correlation is reported between this induction mechanism and those indices of solar activity that characterize the magnetic fields of the solar plasma.

Dmitriyev, A. A.↗
DOE OSTI2025

Scaler Rates from the Pierre Auger Observatory: A New Proxy of Solar Activity

The modulation of low-energy galactic cosmic rays reflects interplanetary magnetic field variations and can provide useful information on solar activity. An array of ground-surface detectors can reveal the secondary particles, which originate from the interaction of cosmic rays with the atmosphere. In this work, we present an investigation of the low-threshold rate (scaler) time series recorded in 16 yr of operation by the Pierre Auger Observatory surface detectors in Malargüe, Argentina. Through an advanced spectral analysis, we detected highly statistically significant variations in the time series with periods ranging from the decadal to the daily scale. We investigate their origin, revealing a direct connection with solar variability. Thanks to their intrinsic very low noise level, the Auger scalers allow a thorough and detailed investigation of the galactic cosmic-ray flux variations in the heliosphere at different timescales and can, therefore, be considered a new proxy of solar variability.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2009

The Updated Solar Activity Prediction during the MAVEN Mission, but Should We Believe It?

Mars atmospheric processes are very dependent not only on the absolute level of the solar irradiance but also the changes in solar irradiance. Correlated with many of these irradiance changes, especially during solar flares, are large particle events called coronal mass ejections that themselves significantly drive processes in the Martian atmosphere. The NOAA Space Weather Prediction Center has issued a consensus solar cycle activity prediction for the upcoming solar cycle 24 maximum, and this maximum period of solar activity will be during the prime MAVEN science mission. This 'consensus' prediction calls for lower activity than the previous solar cycle maximum that occurred during the years 2001-2002, but looking at the wide spread of peer-reviewed predictions there is little faith that can be taken in any one prediction. This drives the importance of real-time measurements from the LPW/EUV diodes and the measurement and modeling results that will be improved upon using results from the Solar Dynamics Observatory (SDO).

Chamberlin, Philip↗
NASA NTRS1978

The relationship between solar activity and coronal hole evolution

The relationship between coronal hole evolution and solar active regions during the Skylab period is examined. A tendency is found for holes to grow or remain stable when the activity nearby, seen as calcium plages and bright regions in X-rays, is predominantly large, long-lived regions. It is also found that there is a significantly higher number of small, short-lived active regions, as indicated by X-ray bright points, in the vicinity of decaying holes than there is near other holes. This is interpreted to mean that holes disappear at least in part because they become filled with many small scale, magnetically closed, X-ray emitting features. This interpretation, together with the observation that the number of X-ray bright points was much larger near solar minimum than it was during the Skylab period, provides a possible explanation for the disappearance of the large, near-equatorial coronal holes at the time of solar minimum.

Nolte, J. T.↗
NASA NTRS2004

How Large Scale Flows in the Solar Convection Zone may Influence Solar Activity

Large scale flows within the solar convection zone are the primary drivers of the Sun s magnetic activity cycle. Differential rotation can amplify the magnetic field and convert poloidal fields into toroidal fields. Poleward meridional flow near the surface can carry magnetic flux that reverses the magnetic poles and can convert toroidal fields into poloidal fields. The deeper, equatorward meridional flow can carry magnetic flux toward the equator where it can reconnect with oppositely directed fields in the other hemisphere. These axisymmetric flows are themselves driven by large scale convective motions. The effects of the Sun s rotation on convection produce velocity correlations that can maintain the differential rotation and meridional circulation. These convective motions can influence solar activity themselves by shaping the large-scale magnetic field pattern. While considerable theoretical advances have been made toward understanding these large scale flows, outstanding problems in matching theory to observations still remain.

Hathaway, D. H.↗
NASA NTRS1987

Simultaneous SMM flat crystal spectrometer and Very Large Array observations of solar active regions

High-resolution images of the quiescent emission from two solar active regions at 20 cm (VLA) and soft X-ray (SMM FCS) wavelengths are compared. There are regions where the X-ray coronal loops have been completely imaged at 20 cm wavelength. In other regions, the X-ray radiation was detected without detectable 20 cm radiation, and vice versa. The X-ray data were used to infer average electron temperatures of about 3-million K and average electron densities of about 2.5 x 10 to the 9th/cu cm for the X-ray emitting plasma in the two active regions. The thermal bremsstrahlung of the X-ray emitting plasma is optically thin at 20 cm wavelength. The 20 cm brightness temperatures were always less than T(e), which is consistent with optically thin bremsstrahlung. The low T(B) can be explained if a higher, cooler plasma covers the hotter X-ray emitting plasma. Thermal gyroresonance radiation must account for the intense 20 cm radiation near and above sunspots where no X-ray radiation is detected.

Lang, Kenneth R.↗
NASA NTRS1994

Patterns of helicity in solar active regions

Using 46 vector magnetograms from the Stokes Polarimeter of Mees Solar Observatory (MSO), we studied patterns of local helicity in three diverse solar active regions. From these magnetograms we computed maps of the local helicity parameter alpha = J(sub z)/B(sub z). Although such maps are noisy, we found patterns at the level approximately 2 to 3 sigma(sub J(sub z)), which repeat in successive magnetograms for up to several days. Typically, the alpha maps of any given active region contain identifiable patches with both positive and negative values of alpha. Even within a single sunspot complex, several such alpha patches can often be seen. We followed 68 alpha patches that could be identified on at least two successive alpha maps. We found that the persistence fraction of such patches decrease exponentially, with a characteristic time approximately 27 hr.

Pevtsov, Alexei A.↗
NASA NTRS1980

Solar activity during the past 10,000 years from radionuclides in lunar samples

The radionuclides Ar-37, Ar-39, H-3, and C-14 in lunar samples are related to solar activity during time periods corresponding to their mean lives. The Ar-37 activities at shallow depths vary with each Apollo mission according to the intensities of the large solar flares preceding the mission. At large depths, the Ar-37 activities are independent of solar flares and decrease with an attenuation length that is in accord with the energy spectrum of the galactic cosmic rays. The Ar-39 depth-profile differs somewhat from galactic cosmic-ray expectation; the difference may be caused by solar modulation during Maunder Minima periods. The H-3 and C-14 activities at shallow depths are considerably higher than expected from galactic cosmic rays. The high H-3 is explained by solar-flare interactions during the past 60 years. The high C-14 activities at shallow depths are caused in part by solar-flare interactions during the past 10,000 years and in part by solar-wind implantations. Solar wind-implanted C-14 is indicated by the grain-size and temperature-release dependence of C-14 in surface soil.

Fireman, E. L.↗
NASA NTRS1973

Test for planetary influences on solar activity

A method due to Schuster is used to test the hypothesis that solar activity is influenced by tides raised in the sun's atmosphere by planets. We calculate the distribution in longitude of over 1000 flares occurring in a 6 1/2 yr segment of solar cycle 19, referring the longitude system in turn to the orbital positions of Jupiter and Venus. The resulting distributions show no evidence for a tidal effect.

Dingle, L. A.↗
NASA NTRS1989

Physical mechanisms of solar activity effects in the middle atmosphere

A great variety of physical mechanisms of possibly solar induced variations in the middle atmosphere has been discussed in the literature during the last decades. The views which have been put forward are often controversial in their physical consequences. The reason may be the complexity and non-linearity of the atmospheric response to comparatively weak forcing resulting from solar activity. Therefore this review focuses on aspects which seem to indicate nonlinear processes in the development of solar induced variations. Results from observations and numerical simulations are discussed.

Ebel, A.↗