摘要:

Amplitude and polarization measurements of structured Pc 1 micropulsations obtained in Alaska and in Finland imply that the Pc 1 source lines are near or inside the plasmapause. The measurements give the source lines significantly closer to the earth than are given by Pc 1 dispersion calculations. Specific Pc 1 events are compared with plasmapause positions determined by the Ogo 3 and Ogo 5 satellites. We present some evidence that implies that structured Pc 1 source lines corotate with the earth.

ISSN:0148-0227    

DOI:10.1029/JA076i001p00100

年代:1971

数据来源: WILEY

摘要:

The loss and replenishment of electrons (E>0.3 Mev andE>0.5 Mev) in the inner zone were studied during 1965, 1966, and 1967 by electron spectrometers on the Pegasus A and B spacecrafts. Several featuers were apparent from the data: (a) The magnitude of the trapped flux and its decay time are related to the state of solar activity. (b) Large increases in flux follow large magnetic storms. The fractional increase is largest at highLvalues (L=2.0) and is observable belowL=1.25. (c) The rise time of the flux increase is shortest at highL, and the decay times after storms are complex. (d) The increased flux is accompanied by a softening of the electron spectrum between 300 and 500 kev. (e) The increase in the flux of trapped electrons atL=1.8–2.2 is accompanied by a large flux of precipitating electrons observed within the loss cone. (f) The precipitating flux decreases with decreasingL; it is also highly variable, usually ranging within one day from background to 106electrons/cm2sec. (g) The precipitated fluxe‐folding energy is 41±3 kev, roughly similar to thee‐folding energy of the trapped flux atL=1.8–2.2. (h) The precipitation period and maximum precipitated flux depend not only on the magnitude of magnetic activity index,Ap, but also on the length of time the activity continues. We conclude that the exponential decay time of the inner radiation zone is a variable, dependent on the interval of time over which the decay is measured. We suggest that the source of the precipitated electrons atL=2 and of the increased electron flux observed atL=1.25 is the same. The evidence for this suggestion is the similarity in behavior of the trapped and precipitated flux with magnetic activity, the similarity of thee‐folding energy between the trapped and precipitated flux atL=2, and the softening of the spectrum associated with the observed flux increases at the

ISSN:0148-0227    

DOI:10.1029/JA076i001p00110

年代:1971

数据来源: WILEY

摘要:

Simultaneous observations of λ5577 O I and X‐ray bremsstrahlung reveal that postbreakup quasiperiodic 5‐ to 15‐sec pulsations in these two phenomena are positively correlated. Cross‐correlation analysis of the fluctuations shows that λ5577 O I pulses lag corresponding X‐ray pulses by ∼0.5–1 sec, a value consistent (within experimental uncertainties) with the effective lifetime of oxygen atoms in the 21Sstate. The percentage modulation of X rays>25 kev was usually 2–5 times larger than the percentage modulation of auroral light. Estimates of the energy distribution in the primary electron precipitation pulsations indicate that at times as much as 50% of the energy needed to account for the luminosity variations may be carried by electrons with energies greater than 25 kev. It is concluded that pulsating auroras and X rays result from a single process modulating both the low‐energy (25 kev) primary electron flux. From these observations, gross intensity changes of a slowly varying nature appear to be largely unrelated, in agreement with the majority

ISSN:0148-0227    

DOI:10.1029/JA076i001p00122

年代:1971

数据来源: WILEY

摘要:

Analytic formulas are given for inelastic cross sections for collisions of protons and hydrogen atoms with atomic and molecular gases in the energy range 0.5 kev to 5 Mev. They are convenient interpolation formulas that span the broad energy region important in atmospheric physics, astrophysics, radiation physics, and plasma physics. The asymptotic form of the analytic expressions is shown to be equivalent in appropriate cases to theoretical results obtained with the well‐known Born approximation. The parameters of the formulas are evaluated for noble gases and for diatomic atmospheric gases with the aid of electron impact data and recent results of proton and hydrogen atom impact experiments. The systematics of the parameters are discusse

ISSN:0148-0227    

DOI:10.1029/JA076i001p00133

年代:1971

数据来源: WILEY

摘要:

Retarding potential analysis of photoelectrons created by the earth's EUV airglow has permitted us to measure the height profile of the He I 584‐A and H I 1216‐A dayglow lines from 400 to 1016 km. Maximum 584‐A emission occurred at 500 km during rocket ascent and amounted to 0.7±0.3 kR. The large uncertainty reflects several experimental difficulties, one of which was the presence of a large and variable background signal. This backgorund is believed to have been caused by photoelectrons produced at the instrument baffles by direct sunlight. We have concluded that there is no important contribution to the signal from ionospheric electrons. The height profile of the 584‐A line was consistent with that expected for resonance scattering of solar 584‐A radiation by telluric helium in diffusive equilibrium at 927°K. The helium density required was 6.5±0.7×106cm−3at 176 km. However, the very large emission rates observed demand that the solar 584‐A (full) line width be 0.023±0.007 A if the flux was 109photons cm−2sec−1. Lyman α airglow (14 kR at 1000 km) varied in a way consistent with expectations for resonance scattering in an atmosphere containing 3×107H atoms cm−3at 100 km. There is some evidence in the Lyman α data for a rather strong dependence of exospheric hydrogen abundanc

ISSN:0148-0227    

DOI:10.1029/JA076i001p00145

年代:1971

数据来源: WILEY

摘要:

Solar‐stimulated fluorescence by photoelectric ionization in the earth's upper atmosphere generates fluxes of up to 9×104photons cm−2sec−1ster−1at 110 km for nitrogenK‐α emission. The corresponding maximum flux for oxygen is 1×104photons cm−2sec−1ster−1at approximately the same altitude. Recent observations have confirmed the fluorescence at a somewhat lower level than that computed here. This flux may place some limitations on low‐energy (0.1–1 kev) X‐ray astronomy experiments performed during the daytime a

ISSN:0148-0227    

DOI:10.1029/JA076i001p00163

年代:1971

数据来源: WILEY

摘要:

Earlier studies of ionospheric scintillations outlined the lower boundary of the high‐latitude region where intense scintillations at 40 MHz were observed. The quiet‐day scintillation boundary reached a lower position of 57° invariant latitude at 2200 LT. Dyson's (1969) recent observations with a Langmuir probe have verified the existence of a lower latitude boundary of small‐scale irregularities. The boundary concept has been extended to include the effects of magnetic storms. Observations of satellite beacon signals at 40 and 54 MHz during 1961 to 1966 indicate that the mean change in the lower boundary latitude of the irregularity region is a decrease of approximately 1.6° per unit change in localKindex. This is quite similar to the change of 1.8° per unit change inKpnoted for the trough position by Rycroft and Thomas (1970). In examining the data available from high‐inclination and synchronous satellites, it was noted that the change in latitude withKindex is a function of time. The maximum change of latitude as a function ofKindex, approximately 2° to 3° per unitK, occurred between 0300 and 0600 LT; the minimum change, about 1° per unitK, occurred over a broad interval from 1600 to 0200 LT. If the irregularity structure is produced by an interaction of the plasmapause with the ionosphere, the morphologic behavior of this region of the magnetosphere can be studied by reviewing the large inventory of scintillation and spreadFdata that has been amassed in the course of ionosph

ISSN:0148-0227    

DOI:10.1029/JA076i001p00170

年代:1971

数据来源: WILEY

摘要:

A technique to measure the direction of the geomagnetic field by using incoherent scatter techniques is described. The technique has been used to measure the inclination of the magnetic field at the Jicamarca Radar Observatory with an accuracy of the order of 1 minute of arc in the height range from 200 to 800 km. The corresponding inclinations obtained from the Goddard Space Flight Center (12/66) and the International Geomagnetic Reference Field (10/68) models are found to be about 1° in error

ISSN:0148-0227    

DOI:10.1029/JA076i001p00178

年代:1971

数据来源: WILEY

摘要:

Series of high‐resolution electron and ion temperature and electron density measurements at Arecibo have been used to derive profiles of the neutral temperature from 116 km to 400 km throughout the day. In this technique, least squares fitting is used to calculate a smooth temperature profile and a neutral atmospheric model. The availability of a complete profile allows calculation of the thermal energy storage and downward heat conduction throughout the day. Two methods have been employed to calculate the density profile. The first assumes that the density at 120 km is known and solves for the diffusion equilibrium model that best fits the data. The second method requires only the assumption of the relative densities of the neutral constituents at the lower boundary but has a somewhat higher experimental variance. It is shown that density and temperature do not generally peak at the same time, though current atmospheric models such as Cira 1965 suggest that they do. These models are based mainly on satellite orbital decay measurements and indicate a density maximum around 1400 hours. Neutral temperatures derived from incoherent sounding have indicated a temperature maximum near 1600 hours. It is now suggested that these two phenomena may be self consistent when the entire temperature profile affecting the neutral density is considere

ISSN:0148-0227    

DOI:10.1029/JA076i001p00185

年代:1971

数据来源: WILEY

摘要:

A drag analysis using high‐accuracyC‐band radar‐transponder data has yielded densities at heights between 135 and 195 km at approximately 1‐day intervals over a 4‐month period in 1968. On the average, the results were in reasonable agreement with currently used model atmospheres, but the variability of the density was found to be much larger than was predicted by the models. Density variations of the order of 10%–20% at 170 km were observed to correlate with moderate geomagnetic activity and the semiannual effect. A large increase of about 35% at 140 km was observed during a major geomagnetic storm. Increases in the density at times of geomagnetic activity were significantly larger in the northern auroral region than elsewhere. The effects of solar activity, the diurnal bulge, and latitude were not apparent in the data. The atmospheric rotation rate at 175 km was found to be higher than that of the earth by a factor o

ISSN:0148-0227    

DOI:10.1029/JA076i001p00197

年代:1971

数据来源: WILEY