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Research progress in particles and fields is summarized, including studies on auroral helium ions and protons, auroral electrons, and OGO-5 data analysis on magnetosphere. Upper atmospheric physics and solar and stellar astronomy are also considered.
A model of the Starfish electrons injected into the radiation belt in July 1962 was determined for epoch September 1964. This model distinguishes between artificial and natural electrons and provides the artificial unidirectional electron flux as a function of equatorial pitch angle, energy, and L value. The model is based primarily upon data from the OGO-1, OGO-3, OGO-5, 1963-38C, and the OV3-3 satellites. Decay times for the Starfish electrons are given as a function of energy and L value. These decay times represent the best compromise between a number of independently determined values. The times at which the artificial Starfish flux component had become insignificant in comparison to the natural flux component are determined as functions of energy and L value. These times are determined by two separate methods, and averaged values are presented. It is shown that Starfish electrons, by the present time, have become insignificant for all energies and L values.
An impulsive burst of 100-400 keV solar X-rays associated with a small solar flare was observed on October 10, 1970 with a large area scintillator aboard a balloon. The X-ray burst was also observed simultaneously in 10-80 keV range by the OGO-5 satellite and in 8-20 A range by the SOLRAD-9 satellite. The event is attributed to an H-alpha subflare located approximately at S13, E88 on the solar disk. The spectral characteristics of this event are examined in the light of the earlier X-ray observations of small solar flares.
Observations of impulsive solar flare X-rays greater than or about equal to 10 keV made with the OGO-5 satellite are compared with ground-based measurements of type III solar radio bursts in 10- to 580-MHz range. It is shown that the times of maxima of these two emissions, when detectable, agree within about 18 sec. This maximum time difference is comparable to that between the maxima of the impulsive X-ray and impulsive microwave bursts. In view of the various observational uncertainties, it is argued that the observations are consistent with the impulsive X-ray, impulsive microwave, and type III radio bursts being essentially simultaneous. The observations are also consistent with 10- to 100-keV electron streams being reponsible for the type III emission. The observations indicate that the non-thermal electron groups responsible for the impulsive X-ray, impulsive microwave, and type III radio bursts are accelerated simultaneously in essentially the same region of the solar atmosphere.
The analysis of type III bursts observed from the OGO-5 satellite between 3.5 MHz and 50 kHz gives an empirical expression for the frequency drift rate as a function of frequency that is valid from 75 kHz to 550 MHz. Using this expression and some simplifying assumptions we obtain indirectly an empirical formula for the electron density distribution of the solar wind to 1 AU which is consistent with published values of electron density and with observed type III burst drift rates.
New details of unsteady magnetospheric convection and gradual erosion of the plasmasphere during a weak magnetic storm are revealed in the light of presented ground data and OGO-4 and OGO-5 data for August 13-15, 1968. These new findings suggest that westward electric fields of the order of 0.5 mv/m were present in the midnight sector during the substorms studied.
Type III bursts were observed between 3.5 MHz and 50 kHz by the University of Michigan radio astronomy experiment aboard the OGO-5 satellite. Decay times were measured and then combined with published data ranging up to about 200 MHz. The observed decay times increase with decreasing frequency, but at a rate considerably slower than that expected from electron-proton Coulomb collisions. At 50 kHz, values differ by about a factor of 100. Using Hartle and Sturrock's solar wind model, Coulomb collisional frequencies were computed and compared with the apparent collisional frequencies deduced from the observations. It was found that the ratio of observed to computed values varies with heliocentric distance according to an inverse 0.71 power.
A search of the 3- to 30-keV data from the NRL proportional counter detector on the Orbiting Geophysical Observatory-5 (OGO-5) satellite has yielded several events which may be nearly completely nonthermal in the e greater than 3 and less than 10 keV range. In each case an impulsive hard X-ray burst accompained by an impulsive microwave burst was associated with a low energy X-ray burst whose profile was a simple rise and fall. The lack of a two component nature in the low energy range argues that the low energy X-ray flux is due to a single physical mechanism, in this case nonthermal bremsstrahlung from accelerated electrons. However, the spectra and time profiles are quite consistent with a thermal interpretation. Polarization measurements are probably necessary to resolve the physical origin of such bursts.
Type 3 solar bursts observed by OGO-5, below 600 kHz, were analyzed. Decay times were measured, and collisional decay times were computed for distances out to 1 AU. By fitting power functions to the computed and observed decay times, and using local plasma hypothesis, it was found that the ratio rho of computed observed values varies with heliocentric radial distance according to a power function rho = 3r to the 0.7th power, assuming fundamental emission, and rho = 2r to the 0.7th power, assuming second harmonic emission.
The solar event of 28 May 1968 is reported using the Goddard Cosmic Ray Telescope on OGO-5. The flare associated with the event occurred at 12:48 on 28 May and had importance 1B. About 600 He-3 were detected in the event and the He-3/He-4 equals 1.52 plus or minus 0.1 in the energy range 4-80 MeV/necleon. This is the highest ratio reported so far for any solar event.
During the flight of Mariner 9 to Mars, the ultraviolet spectrometer on board the spacecraft measured the L-alpha intensity for several points in the sky. These data are compared with a sky map obtained by OGO-5 and the observations of Mariner 6. The absolute calibration of Mariner 9 and Mariner 6 differ by a factor of 1.43 at L-alpha. The low values of the sky brightness measured by Mariner 9 near the sky minimum suggest that the nearby interstellar medium has a kinetic temperature of 200-1100 K and a relative velocity with respect to the sun in the range 13-14 km/sec.
Review of the magnetospheric morphology, using the method of the Delta B topology, where Delta B is the difference between the observed and a reference field. It is confirmed that Delta B continuously decreases inward to close distances from the earth at all local times. Extrapolating the statistical relation between Dst at the ground and the equatorial Delta B obtained from OGO-5 near perigee, it is shown that Dst is 54 gammas, when Delta B is zero at approximately 2 to 3 earth radii. Conversely, for a magnetically quiet condition as defined by Dst = 0, the average equatorial Delta B at these distances is -45 gammas. These results demonstrate the significance of the effects of the magnetospheric equatorial current that exists even at quiet times. A preliminary study of inclination shows that the field lines on the dusk side are more stretched out than on the dawn side. A comparison of declination on both sides indicates that the bending of the field lines toward the tail is greater near dusk than near dawn. These results suggest an appreciable dawn-dusk asymmetry in the configuration of the inner magnetospheric field.
Over the past five years we have measured the energy spectrum of primary cosmic ray electrons with both a balloon-borne and a satellite absorption spectrometer. All of the balloon flights used identical equipment that was launched each summer from Fort Churchill, Manitoba, Canada. The satellite, OGO-5, has been in an eccentric orbit since March 1968. Together these instruments provide the electron spectrum over a range of energy from 20 MeV to 20 GeV. This wide range and the substantial span of time covered by the measurements permit a detailed study of the solar modulation of electrons. These results are compared with the modulation of the nuclear components as observed by a neutron monitor and interpreted using the cosmic ray transport equation.
Experimental results are reported on three energetic particle events with extremely high abundance of He-3. The measurements were taken onboard the OGO-5 satellite. It was shown that the abundance of protons relative to He nuclei were significantly low in these events. Not more than four H-2 and three H-3 were detected during the entire period under study compared to 1110 H-3 nuclei. The limitations these observations place on theoretical models are discussed to explain He-3 flares.
Identical ultraviolet photometer experiments were carried on the eccentric orbiting OGO-5 spacecraft and on the polar orbiting OGO-6 spacecraft. The experiments operated flawlessly and, due to sophisticated electronic design, allowed signals to be processed accurately over a large dynamic range. Scientific results gained from the post-mission data analysis efforts are summarized.
The data from OGO-5 and OSO-7 X-ray experiments have been analyzed to study six chromospheric flares with filament disruption associated with slow thermal X-ray bursts. Filament activation accompanied by a slight X-ray enhancement precedes the first evidence of H alpha flare by a few minutes. Rapid increase of the soft X-ray flux is accompanied by a sudden brightening of the filament when viewed on-band H alpha. Thereafter the bright chromospheric strands reach their maximum brightness with maximum X-ray flux. Any plateau or slow decay phase in the X-ray flux is accompanied by a quieting in filament activity and even by filament re-appearance. The height of the disrupted prominence is proportional to the soft X-ray flux for the August 3, 1970 limb occulted event.
Triaxial electron spectrometer, mounted on OGO-E SPACECRAFT, measures flux and energy distributions of electrons, noting electron multiplier