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At least 379 records · Page 21
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NASA NTRS1984

Temporal variations in the solar submillimeter continuum

Observations of local intensity variations in the 300-800 micron solar continuum are presented. Two-beam difference observations were used to determine power spectrum statistics of small temporal variations over the frequency range 0.1-20 mHz. A significant enhancement in spectral power (about 5 K rms) is found for frequencies between 3 and 7 mHz. These and higher frequency variations are attributed to adiabatic response of the chromospheric medium to compression waves.

Kaminski, C.↗
NASA NTRS1984

A note on the variational method of Stokes and DeMarcus for radiative transfer in planetary atmospheres

A generalization of the variational principle of Stokes and DeMarcus (1971) by the construction of two bifunctionals is proposed. The equation of radiative transfer is obtained by imposing the stationary condition on such functionals, and the reflectivity and transmissivity at arbitrary angle are given by their extremum values. Further simplification is possible when trail functions are used that are linear in the variational parameters, in which case the source function derived from the method of Stokes and DeMarcus can give the reflectivity at arbitrary emergent angle to second order. The usefulness and limitations of these variational priinciples are explored with extensive numerical results.

Chow, K. S. K.↗
NASA NTRS1984

Explanation of the Normal Winter Anomaly from the Seasonal Variation of Short Wave Absorption

The frequency dependence of the winter anomaly (WA) of radio wave absorption indicates the altitude range where the considered seasonal variation of absorption, L, takes place: 75-95 km. In this height region considerable seasonal variations of ionic composition and effective recombination coefficient, alpha sub e, exist, which can cause seasonal variations of electron concentration, N, and absorption, L. An attempt to render a qualitative estimation of the normal WA, i.e., the increased ratio of winter over summer absorption, L sub w/L sub s, at medium latitudes 40 deg and 50 deg, for solar zenith angles CHi = 60 deg and 75 deg is made. This is compared with existing experimental data.

Velinov, P. J.↗
NASA NTRS1984

NIMBUS-7 SBUV (Solar Backscatter Ultraviolet) observations of solar UV spectral irradiance variations caused by solar rotation and active-region evolution for the period November 7, 1978 - November 1, 1980

Observations of temporal variations of the solar UV spectral irradiance over several days to a few weeks in the 160-400 nm wavelength range are presented. Larger 28-day variations and a second episode of 13-day variations occurred during the second year of measurements. The thirteen day periodicity is not a harmonic of the 28-day periodicity. The 13-day periodicity dominates certain episodes of solar activity while others are dominated by 28-day periods accompanied by a week 14-day harmonic. Techniques for removing noise and long-term trends are described. Time series analysis results are presented for the Si II lines near 182 nm, the Al I continuum in the 190 nm to 205 nm range, the Mg I continuum in the 210 nm to 250 nm range, the MgII H & K lines at 280 nm, the Mg I line at 285 nm, and the Ca II K & H lines at 393 and 397 nm.

Heath, D. F.↗
NASA NTRS1985

11- and 22-year variations of the cosmic ray density and of the solar wind speed

Cosmic ray density variations for 17-21 solar activity cycles and the solar wind speed for 20-21 events are investigated. The 22-year solar wind speed recurrence was found in even and odd cycles. The 22-year variations of cosmic ray density were found to be opposite that of solar wind speed and solar activity. The account of solar wind speed in 11-year variations significantly decreases the modulation region of cosmic rays when E = 10-20 GeV.

Chirkov, N. P.↗
NASA NTRS1985

The effect of the interplanetary magnetic field on sidereal variations observed at medium depth underground detectors

It has been known for some years that the intensity variations in sidereal time observed by muon detectors at moderate underground depths are sensitive to the polarity of the interplanetary magnetic field (ipmf) near the Earth. There are differences in the response to these anisotropies as observed in the Norhtern and southern hemispheres. When fully understood, the nature of the anisotropy seems likely to provide information on the 3-dimensional structure of the heliomagnetosphere, its time variations, and its linking with the local interstellar field. The summation harmonic dials for the sidereal diurnal variation during 1958 to 1982 show that there is a strong dependence on whether the ipmf near the Earth is directed outwards from the Sun or inwards it.

Humble, J. E.↗
NASA NTRS1985

Cosmic ray biannual variation

The study of the cosmic ray (CR) power spectrum has revealed a significant variation with a period around 2 yr that cannot be explained as a high order harmonic of the 11 yr solar cycle. Comparative study of the correlation on different time scales between CR intensity and Rz, aa, high speed streams and polar hole size has put in evidence that a high degree of coherency exists between each couple of variables at 1.58 to 1.64 yr, except between CR and Rz. On the other hand cyclic variation on a short time scale, around 26 months, has been claimed to be present in the neutrino flux. Critical tests of this hypothesis are considered and a preliminary result seems to indicate that the hypothesis of the existence of a 1.6 yr periodicity in the neutrino data during the measurement time interval, has a significance or = 99.9%. The possible origin of this variation as due to a contribution either of CR interactions in the upper atmosphere or to the solar dynamics, are discussed.

Attolini, M. R.↗
NASA NTRS1985

Variations of the cosmic ray general component in Antarctica

A cosmic ray variations, zonal cosmic ray modulation, was found in the lower atmosphere from the sonde measurement results. The variations give rise to anomalies in the latitude distributions of the cosmic ray charged component and the anomalous north-south asymmetry. To find the nature of the variations, the cosmic ray general component was measured with the same detectors as in the sonde measurements gas discharge counters and the counter telescopes with 7-mm Al filters detecting the electrons of energy above 200 keV and 5 MeV. The measurement data obtained in Antarctica in the years 1978 to 1983 are presented and discussed.

Charakhchyan, T. N.↗
NASA NTRS1985

Azimuthal and meridional asymmetries of the solar wind and quasiperiodic variations of intensity of Galactic Cosmic Rays (GCR)

The results of analysis of 27 day, annual and quasi-two year variation of galactic cosmic rays (GCR) are presented. The dependence of the periods of 27 day GCR variation on the energy of initial radiation is discovered, according to the data during 1980 of the World network of station in sufficiently wide range of the observed threshold energy. The dependence of the annual variation of GCR is established, according to the data of the Huancayo station in conforming with the change of the polarity of the General Magnetic Field of the Sun (GMFS).

Shatashvili, L. K.↗
NASA NTRS1985

Dynamics of two-year cosmic ray variations inferred from the data of spacecraft and stratospheric measurements and from the neutron monitor data in 1959-1981

The two year cosmic ray variations are studied using the spacecraft measurements of 1967 to 1976, the sonde measurements at high latitudes in the stratosphere (Murmansk, Mirny), and the neutron monitor data of 1959 to 1981. The two year variations are most pronounced from 1967 to 1975. An anticorrelation is observed between the two year variations in cosmic rays and in geomagnetic activity.

Charakhchyan, T. N.↗
NASA NTRS1985

Solar tri-diurnal variation of cosmic rays in a wide range of rigidity

Solar tri-diurnal variations of cosmic rays have been analyzed in a wide range of rigidity, using data from neutron monitors, and the surface and underground muon telescopes for the period 1978-1983. The rigidity spectrum of the anisotropy in space is assumed to be of power-exponential type as (P/gamma P sub o) to the gamma exp (gamma-P/P sub o). By means of the best-fit method between the observed and the expected variations, it is obtained that the spectrum has a peak at P (=gamma P sub o) approx = 90 GV, where gamma=approx 3.0 and P sub o approx. 30 GV. The phase in space of the tri-diurnal variation is also obtained as 7.0 hr (15 hr and 23 hr LT), which is quite different from that of approx. 1 hr. arising from the axisymmetric distribution of cosmic rays with respect to the IMF.

Mori, S.↗
NASA NTRS1985

Diurnal variations from muon data at Takeyama underground station

An underground station, Takeyama, is introduced, and some results of the solar diurnal and semi-diurnal variations for the period between 1967 and 1984 are presented. There are clear tendencies of double and single solar cycle variations in the daily variations which are in good accord with those detected by other underground and neutron monitor observations.

Takahashi, K.↗
NASA NTRS1985

Magnetic fluctuation and cosmic ray diurnal variations

A unified theory of cosmic ray diurnal variations has been proposed in which the first 3 harmonics of the cosmic ray daily variation all results from a single anisotropy produced by the combined effects of adiabatic focusing and anisotropic pitch angle scattering. The theoretical description of steady state cosmic ray anisotropies are simplified and improved. Preliminary results of a study of correlations between cosmic ray diurnal variations and the fluctuation characteristics of the interplanetary magnetic field are presented and discussed in light of the theory.

Bieber, J. W.↗
NASA NTRS1985

Solar activity beyond the disk and variations of the cosmic ray gradient

Part of galactic cosmic rays (CR) observed near the Earth and on the Earth come from beyond-disk regions of circumsolar space. But CR of those energies which undergo substantial modulation cover too large a path across the lines of force of the interplanetary magnetic field (IMF) in order that they could provide an effective transfer of information about beyond-disk solar activity. And if it is still possible, the most probable channel for transferring such information must be a neutral layer of heliomagnetosphere in which the transverse CR transport is facilitated by their drift in an inhomogeneous magnetic field. A simple diffusion model for an expected CR variation in a neutral layer near the Earth is discussed. It is of importance that variations of the CR gradient are not at all always accompanied by considerable variations of IMF and solar wind velocity at the point of observation.

Belov, A. V.↗
NASA NTRS1985

Diurnal variations of cosmic ray geomagnetic cut-off threshold rigidities

The spectrographic global survey method was used to investigate the rigidity variations Rc of geomagnetic cut-off as a function of local time and the level of geomagnetic disturbance for a number of stations of the world wide network. It is shown that geomagnetic cut-off threshold rigidities undergo diurnal variations. The diurnal wave amplitude decreases with increasing threshold rigidity Rc, and the wave maximum occurs at 2 to 4 hr LT. The amplitude of diurnal variations increases with increasing geomagnetic activity. The results agree with those from trajectory calculations made for an asymmetric model of the magnetosphere during different geomagnetic disturbance conditions.

Dvornikov, V. M.↗
NASA NTRS1985

Magnetic fields on the sun and the north-south component of transient variations of the interplanetary magnetic field at 1 AU

In order to study the relationship between solar magnetic fields and the transient variations of the north-south component B(Z) of the interplanetary magnetic field (IMF) at 1 AU, flares from unusual north-south oriented active regions, large IMF B(Z) events, and large flares with comprehensive flare index higher than 12 were collected. The associated IMF B(Z) changes or the magnetic field of the initiating flares are investigated. For those cases where an association between a transient B(Z) variation and an initiating flare is plausible, it is found that, for a given flare field, the orientation of the corresponding transient variation of B(Z) may be in agreement with the flare field, opposite to it, or more often, fluctuating in both magnitude and direction. Conversely, an IMF B(Z) event may originate in a flare field in the same magnetic orientation, opposite to it, or in the east-west orientation.

Tang, F.↗
NASA NTRS1983

Effect of limb darkening functions variations on deconvolution of wide-field-of-view measurements of earth emitted radiation

A solution is presented to the problem of deconvolving wide field of view measurements of earth-emitted radiation for the case of limb-darkening functions which are geographically dependent. The method of linear perturbations is used and the effects of limb-darkening function variations at various scales are evaluated. A simple model for the geographical variation of the limb-darkening function based on the radiant exitance is introduced. It is shown that the effect of these variations on the global average radiant exitance vanishes identically, and is insignificant for large spatial scales. For wave numbers six through twelve, the limb-darkening effects are small but possibly significant. At wave numbers greater than twelve, the noise due to meteorological variability dominates for an orbit altitude of 1100 km. The smallness of these effects is due to the smoothness of the monthly averaged radiant exitance field.

Smith, G. L.↗
NASA NTRS1985

Seasonal, diurnal, and solar cyclical variations of the limiting H(+) flux in the earth's topside ionosphere

Seasonal and solar cyclical variations in the limiting H(+) flux are compared over the solar minimum-to-maximum interval 1974-80. The comparisons are made on the bases of values derived with the MSIS-83 and -77 models, which in turn are based on Atmospheric Explorer-E O(+) and H(+) data from the ionosphere. The H(+) flux is obtained by integration of the H(+) continuity equation along magnetic flux tubes. The seasonal and cyclical variations are dominated by the neutral hydrogen density, although the O(+) boundary density, scale height and O(+)-H reaction somewhat ameliorate the changes caused by the density variations. Finally, the plasmasphere experienced an order of magnitude decrease in H(+) in going from solar minimum to maximum, which could have been caused by longer limiting flux escapes through more, longer-lived, shorter flux tubes.

Richards, P. G.↗