摘要:

The trajectory‐tracing technique was used to obtain the angles of incidence, and hence ‘intensities,’ of negatively charged 0.88‐GV particles reentrant at Palestine, Texas. Splash albedo trajectories were traced from the conjugate point, and also from Palestine itself, for those trajectories that were unable to complete a full gyration before reentry into the shadow cone at Palestine. Both isotropic and anisotropic ejection configurations were used at these two locations. These simulations predict a north‐south anisotropy (hence also a zenithal anisotropy) for reentrant albedo, with a dearth of trajectories incident from the south. The anisotropy is large enough to explain experimentally determined north‐south anisotropies for lower‐energy particles, as observed by other groups in the Northern Hemisphere. The results are in agreement with measurements and simulations previously obtained in the Southe

ISSN:0148-0227    

DOI:10.1029/JA086iA02p00515

年代:1981

数据来源: WILEY

摘要:

The fallout rates of radionuclides,7Be and22Na, in rainwater collected at Tokyo were measured monthly during the period from February 1975 to February 1977, using a low‐background dual NaI(T1) coincidence gamma ray spectrometer. It is found that the contribution from nuclear weapon tests to these nuclides is negligibly small. Therefore these activities (7Be and22Na) are attributed to the cosmic ray produced nuclides in the atmosphere. The average fallout rates of7Be and22Na measured at ground level of Tokyo are 118±13 and (1.66±0.24) × 10−2pCi/m²/d, respectively. These values are in agreement with values estimated by Lal and Peters, within the experimental error. Using the observed fallout rate of22Na, the global average fallout rate of26Al produced in the atmosphere is estimated to be 5.4 × 10−8pCi/m²/d, which is higher by about a factor of ten than the influx rate of cosmic dust bearing26Al estimated by Reyss et al. Therefore most of the26Al activity contained in the terrestrial sample seems to be originated from the26Al produced by cosmic rays in the

ISSN:0148-0227    

DOI:10.1029/JA086iA02p00520

年代:1981

数据来源: WILEY

摘要:

The dynamic behavior of flare‐associated disturbances has been investigated using a time‐dependent two‐dimensional MHD numerical model for a one‐fluid solar wind with adiabatic expansion. Simulations of the development and propagation of perturbations have been performed between 18Rsand 226Rs(whereRs= solar radius) in an angular sector of the equatorial plane of the sun 90° wide. Several test computations have been carried out with different initial pulse characteristics. These pulses are set arbitrarily at the inner boundary assuming that a shock wave is already formed. The parameters are the velocity of the shock front, the angular width of the perturbation, and its time duration at 18Rs. It is shown that in every case the time delay between 18Rsand 226Rsdepends on the total amount of energy released by the prototype flare (hence in the pulse). This dependence is stronger with the initial velocity than with the angular width. Also it appears that the shock wave propagates according to a power law of time:R=atb. After a relatively short time the expansion of the wave is dominated by the internal energy so that the longitudinal extent of the perturbation at 1 AU seems to be only a function of the time elapsed after the arrival of the front shock at this distance. The existence of a reverse shock which is formed after a few hours is shown to last a time long enough to reach 1 AU. Its longitudinal extension is limited to the area around the flare central meridian where the pressure gradient induced by the initial condition is stron

ISSN:0148-0227    

DOI:10.1029/JA086iA02p00525

年代:1981

数据来源: WILEY

摘要:

The nonlinear evolution of linearly polarized, hydromagnetic waves propagating along the initial radial magnetic field in the solar wind is considered. Numerical solutions of the dissipationless, time‐dependent equations of motion are used to study the steepening of the waves into hydromagnetic shocks and the subsequent propagation of the shocks. If the shocks propagate into a region in which the plasma beta (ratio of thermal to magnetic pressure) is greater than one, each shock splits into a second shock and a rotational discontinuity. It is shown that these secondary hydromagnetic shocks readily propagate through the rotational discontinuities without altering their structure. With increasing time the secondary hydromagnetic shocks propagate out ahead of the rotational discontinuities and become hydrodynamic shocks. Hence an initial packet of linearly polarized hydromagnetic waves ultimately evolves into a packet of rotational discontinuities preceeded by a packet of hydrodynamic shocks. The conditions for which the waves steepen into shocks, the time required for shock formation, and further implications of the results in the solar wind are discusse

ISSN:0148-0227    

DOI:10.1029/JA086iA02p00535

年代:1981

数据来源: WILEY

摘要:

Two factors which can contribute to proton anisotropy in the high‐speed solar wind are investigated. We present evidence that observed protonT⊥>T∥anisotropies are maintained locally by plasma instabilities driven by proton and helium beams. The transfer of beam energy toT⊥by means of these instabilities is shown to be sufficient to account for the aforementioned proton temperature ani

ISSN:0148-0227    

DOI:10.1029/JA086iA02p00541

年代:1981

数据来源: WILEY

摘要:

Data from the Los Alamos Scientific Laboratory/Max‐Planck‐Institut fast plasma experiment on Isee 2 have been combined with data from the European Space Agency/Imperial College/Space Research Laboratory low‐energy proton experiment on Isee 3 to obtain for the first time an ion velocity distribution functionf(ν) extending from solar wind energies (∼1 keV) to 1.6 MeV during the postshock phase of an energetic storm particle (ESP) event. This study reveals thatf(ν) of the ESP population is roughly isotropic in the solar wind frame from solar wind thermal energies out to 1.6 MeV. Emerging smoothly out of the solar wind thermal distribution, the ESPf(ν) initially falls with increasing energy asE−2.4in the solar wind frame. Above about 40 keV no single power law exponent adequately describes the energy dependence off(ν) in the solar wind frame. Above ∼200 keV in both the spacecraft frame and the solar wind frame,f(ν) can be described by an exponential in speed (f(ν) ∝e−ν/ν0) with ν0=1.05 × 108 cm s−1. The ESP event studied (August 27, 1978) was superposed upon a more energetic particle event which was predominantly field‐aligned and which was probably of solar origin. Our observations suggest that the ESP population is accelerated directly out of the solar wind thermal population or its quiescent suprathermal tail by a stochastic process associated with the shock wave disturbance. The acceleration mechanism is sufficiently efficient that ∼1% of the solar wind population is accelerated to suprathermal energies. These suprathermal particles have an

ISSN:0148-0227    

DOI:10.1029/JA086iA02p00547

年代:1981

数据来源: WILEY

摘要:

The solar spectrum in the range 2000–3100 Å has been observed in 0.12‐Å resolution in the stratosphere by means of a balloon‐borne spectrometer. Two flights are reported, on April 21, 1977, and April 19, 1978, and the data from the two flights agree within 4% in the spectral regions of most accurate measurement. Absolute irradiance values at 40‐km altitude are presented. By extrapolation to zero optical depth, comparisons are made to two other recent mea

ISSN:0148-0227    

DOI:10.1029/JA086iA02p00555

年代:1981

数据来源: WILEY

摘要:

The thermal response of the nighttimeFregion ionosphere to local heating by HF radio waves has been observed with the incoherent scatter radar at Arecibo, Puerto Rico. The observations consist of high‐resolution space and time variation of the electron temperature as a high‐power HF transmitter is switched on and off with a period 240 s. As soon as the HF transmitter is turned on, the electron temperature begins to rise rapidly in a narrow altitude region near 300 km, below theF2layer peak. The electron temperature perturbation subsequently spreads over a broader altitude region. The observations are compared with the anticipated thermal response of the ionosphere based on numerical solutions of the coupled time‐dependent heat conduction equations for the electron and composite ion gases and are found to be in good agreement over the entire altitude region covered by the observations. The calculations show that heat conduction is responsible for the spreading of the electron temperature enhancement outside the region where the radio wave energy is deposited. They also show that a smaller, but experimentally observable, ion temperature enhancement takes place while electron temperatures are enhanced by 40% or more of their equilibrium values. For the data presented they also show ionospheric absorption of roughly half the radiated HF energy, with anomalous absorption roughly equal to deviation absorption he

ISSN:0148-0227    

DOI:10.1029/JA086iA02p00561

年代:1981

数据来源: WILEY

摘要:

With an extensive array of particle sensors the plasma environment surrounding the Echo III accelerator payload is studied. From measurements of the thermal ion spectrum, negative payload potentials referenced to the unperturbed ionospheric plasma are obtained. Multiple detectors determined the electron population from a fraction of an eV up to 40‐keV energy. An intense electron population extending up to the energy of injected electrons by the accelerator is produced when the acceleration is turned on. The energetic tail of this population is returned to the payload principally from directions in which the beam was fired, with the most intense fluxes coming from the atmosphere for downward injections of the beam. The atmospheric‐scattered beam and secondary electrons are called ‘quick echoes.’ Electrons of energy less than several keV down to the detector threshold (0.1 eV) are called the suprathermal component. These electrons are produced isotropically around the payload during gun firings and decay away in approximately 32 ms. The largest directional intensities of this component are observed at the higher altitudes. Quick echo electrons are also observed to produce suprathermal electrons when they encounter the payload. The mechanism by which the suprathermal electrons are produced is discussed but remains unknown at the present time. The hot electrons surrounding the accelerator payload during gun injections bring sufficient charge to the payload to neutralize it provided the loss of charge by secondary production on the payload skin is small, presumably owing to a positive payload floating potential during injection. Since the hot population exists for tens of milliseconds after the gun turn off, it results in driving the payload up to 4 volts negative during this time. Secondary production on the payload skin apparently prevents much larger negative potentials after gun turnoff when the payload is immersed in the hot population. Quick echo electrons creating suprathermal electrons around the payload also drive the payload to a few volts negative. This is an important consideration when discussing the origin of the suprathermal electrons, since electrical discharge and beam plasma discharge mechanisms do not apply to the quick ech

ISSN:0148-0227    

DOI:10.1029/JA086iA02p00575

年代:1981

数据来源: WILEY

摘要:

An analysis and evaluation are presented of a technique for extracting information on neutral thermospheric temperature from satellite measurements of the relative abundances of H+and O+ions in theFregion. Charge‐exchange equilibrium in the neighborhood of 320 km relates the observed altitude distribution of this ion concentration ratio directly to that of the associated neutral species and thus to the neutral temperature. The method has been applied to an extensive set of ion concentration data acquired with the Atmosphere Explorer C and D satellites, and evaluated through direct comparison of these ‘ion‐ratio’ temperatures with other concurrent in situ measurements. A comprehensive orbit‐by‐orbit comparison is presented with both ion temperature data and with calculations from the MSIS model. Select comparisons are also available with direct temperature measurements from the Nate instrument, and with temperatures derived from height distributions of observed neutral particle densities. Statistical analyses emphasize random and systematic differences between these several alternative types of temperature data. Sources and estimates of possible uncertainties unique with the ion‐ratio method are also discussed. Excellent agreement has been achieved between the ion‐ratio and the ion temperatures from the AE‐D satellite; the analysis is, however, unable to account for a small systematic difference between corresponding measurements from AE‐C. A random uncertainty of ∼5% must also be associated with neutral temperatures derived from the ion‐ratio method. Otherwise, a general consistency is demonstrated between the various forms of temperature data. All classes of measurements indicate that nighttime thermospheric temperatures are lower than pred

ISSN:0148-0227    

DOI:10.1029/JA086iA02p00585

年代:1981

数据来源: WILEY