摘要:

We investigate the two‐dimensional, steady state distributions of solar wind speed and 5‐GeV cosmic ray flux with respect to the heliospheric current sheet and their variation with the solar cycle from late 1964 through mid‐1982. SynopticKcoronameter data are used to locate the current sheet, taken as the center of the “band of coronal streamers,” during years of low and intermediate solar activity. We confirm the conclusion that the profile of the solar wind at 1 AU during these years consists of (1) a minimum in mean speed of ∼400 km s−1at the heliospheric current sheet, (2) a rise to a mean speed of ∼600 km s−1at an angular distance from the current sheet of 20° to 40°, and (3) a plateau of high mean speed of ∼600 km s−1over the polar coronal holes. During those years of moderate solar activity when the current sheet provides a simple organization to the heliosphere, the mean velocities at the current sheet and in the plateau are approximately independent of phase in the solar cycle. The principal change in the profile is that the breadth of the minimum decreases with subsiding solar activity and reaches its narrowest at sunspot minimum. The profile of the flux of 5‐GeV cosmic rays shows a maximum at the current sheet, with a decrease of 2 to 3% out to a displacement in latitude from the current sheet of ∼45°. There is no evidence for change in this gradient with either the level of solar activity or the overall modulation of cosmic ray flux within a given solar cycle. The data are unable to demonstrate the existence of any dependence of either the sign or the magnitude of the gradient with the polarity of the large‐scale heliospheric magnetic field. The observed distribution in cosmic ray flux is compared to the predictions of several theoretical models in an effort to resolve the question of the role played by particle drifts in cosmic ray propagation. Although drift‐dominated models with inclined current sheets naturally produce negative gradients, which could be made to coincide with the observations by a suitable choice of parameters, such models also predict a dramatic dependence of the magnitude of the gradient upon the polarity of the large‐scale heliospheric magnetic field. This dependence is not apparent in the currently available data. Diffusion‐convection models adjusted to yield a constant radial gradient of cosmic ray flux in the ecliptic also produce a negative gradient with displacement in latitude from the current sheet. However, these latter models require considerable arbitrary “tuning” of the latitudinal dependence of the propagation parameters to reproduce the observations. The models which explain recurrent fluctuations in cosmic ray flux as the in‐ecliptic consequences of corotating interaction regions (rather than those of a gradient in displacement in latitude from the current sheet) are shown to produce effects quite contrary to the observations. We conclude that a satisfactory, quantitative explanation of the gradient of cosmic rays with respect

ISSN:0148-0227    

DOI:10.1029/JA090iA04p03391

年代:1985

数据来源: WILEY

摘要:

From measurements on the Pioneer 11 spacecraft, electrons and protons under Saturn's A‐B‐C rings were reported by Simpson et al. (1980) and Chenette et al. (1980) and identified as the secondary products of cosmic ray nucleons with energies ≫10 GeV interacting with ring matter. We have extended their analysis and have also found both secondary gamma ray fluxes with energies ≫15 MeV and fragmentation nuclei (H and heavier nuclei) with energies<10 MeV/nucleon, which are consistent with this interpretation. From a comparison of the measured low‐energy proton and gamma ray fluxes with fluxes from numerical simulations of the secondary particle production and propagation in material slabs (protons) and the Earth's atmosphere (gamma rays) we find that the A‐B‐C ring mean surface density 〈σ〉 (g/cm²) sampled along the trajectory of Pioneer 11 is50−20+30g/cm2. Direct measurement of the A‐B‐C ring surface density 〈σ〉 in radial intervals of ∼300‐1000 km is obtained from the measured higher‐energy secondary particles (electrons ≫25 MeV and protons ≫67 MeV). The surface density of the optically thick B ring is measured for the first time. Two analyses with separate data sets yield surface densities for the B ring of90−46+70and 62 ± 25 g/cm². The latter value yields a B ring mass of 1.0 ± 0.4 × 1022g; we obtain a value for the A‐B‐C ring mass of2.7−0.6+1.0×10−8Ms, whereMs(Saturn';s mass) = 5.7 × 1029g. Our surface density measurements are shown to be consistent with results derived from Voyager ring radio/optical opacity measuremen

ISSN:0148-0227    

DOI:10.1029/JA090iA04p03415

年代:1985

数据来源: WILEY

摘要:

A theory of energetic charged particle absorption by insulating moons is presented that includes gyrophase dependence of the absorption probability when the gyroradius is not small compared to the satellite radius. This effect increases the average lifetime against absorption by factors of approximately 2 to 6 above previous estimates at Saturn. The sweeping lifetime then becomes significantly greater than the strong diffusion lifetime. A rigorous expression for the average lifetime against absorption, appropriate for a drift phase averaged radial diffusion equation, is derived assuming (1) a uniform distribution of gyrocenter equatorial plane crossing points in the sweeping corridor and (2) randomization of gyrophase. The pitch angle and energy dependences of the sweeping lifetime are found to be significantly different from the predictions of previous analytical estimates.

ISSN:0148-0227    

DOI:10.1029/JA090iA04p03428

年代:1985

数据来源: WILEY

摘要:

During periods of low obliquity, previous work has shown that martian CO2partial pressures decreased to 0.1 mbar; CO2partial pressures decreased to 0.02 mbar prior to the formation of the Tharsis bulge. The permanent polar caps act as a cold trap and projected global average water vapor abundances drop to possibly as low as 10−5precipitable µm. As a result, the odd hydrogen catalytic cycle would not be effective at recombining CO and O back into CO2, and as much as 0.12 mbar of CO and 0.06 mbar of O2could exist. These increased abundances would radically affect surface oxidation, change the lower atmospheric thermal structure, and completely alter the upper atmosphe

ISSN:0148-0227    

DOI:10.1029/JA090iA04p03435

年代:1985

数据来源: WILEY

摘要:

We studied the dynamic evolution of the geomagnetic tail in response to a dawn‐to‐dusk electric field Eyapplied at the high‐latitude boundary by means of a two‐dimensional nonlinear MHD code. We found that the electric field propagates inward through the lobes toward the plasma sheet. Only a small fraction, however, penetrates into the interior of the plasma sheet, and eventually an almost linear decrease from the boundary to the equatorial plane is assumed. There was no tendency to evolve toward a steady or nearly steady state which would require Ey≈ const in a larger area. The resulting time‐dependent changes are consistent with quasi‐static analytic models of Schindler and Birn (1982) and Birn and Schindler (1983) and with observed substorm growth phase effects in the near tail. If the external electric field Eyis constant or varies only slightly along the tail, the convection speed within the plasma sheet remains small. A strongly nonuniform external electric field Eyleads to similar spatial and temporal variation of Ey. It does, however, produce a locally much stronger thinning which favors the onset of a tail instability such as the tearing mode. It can also produce stronger flows primarily parallel to the m

ISSN:0148-0227    

DOI:10.1029/JA090iA04p03441

年代:1985

数据来源: WILEY

摘要:

This study presents measurements of group delays, rise times, fall times, frequencies, and effective phase velocities of mid‐latitude (39°–55° geomagnetic latitude) Pi 2's recorded by the Air Force Geophysics Laboratory array of flux gate magnetometers. Measured group delays over the array are sometimes less than 5–10 s, indicating that in some instances Pi 2's can be used to give excellent timing of the onset of substorm expansive phases. Rise and fall times for the envelopes of Pi 2 oscillations are typically 60–100 s, bringing into doubt resonance theories for these types of waves. Most phase velocities indicate westward propagation, particularly near the center of the substorm current wedge, although there is some indication of eastward velocities far to the east of the center. We argue that these observations indicate that the magnetic fields associated with mid‐latitude Pi 2's are due to transient changes in the field‐aligned currents feeding the auroral electrojets at the beginning of the expansive phase of

ISSN:0148-0227    

DOI:10.1029/JA090iA04p03448

年代:1985

数据来源: WILEY

摘要:

For the daytime whistlers frequently observed in the late afternoon at low latitudes, ducted propagation has been experimentally evidenced, and association with the equatorial anomaly has been suggested. It is suggested from the present computations of ray tracing and wave absorption that the ground‐based daytime whistlers may be attributed to propagation trapped in field‐aligned structures of electron density (ducts) with a small dimension of 10–50 km width and a large enhancement factor of 100–300% either present within or superimposed on the high‐latitude flank of the equatorial anomaly. We predict a low‐latitude cutoff of occurrence of the daytime whistlers at a geomagnetic latitude of ∼20°, as experimental

ISSN:0148-0227    

DOI:10.1029/JA090iA04p03457

年代:1985

数据来源: WILEY

摘要:

The transport of ions from the polar ionosphere to the inner magnetosphere during storm time conditions has been computed using a Monte Carlo diffusion code. The effect of the electrostatic turbulence assumed to be present during the substorm expansion phase was simulated by a process that accelerated the ions stochastically perpendicular to the magnetic field with a diffusion coefficient proportional to the rate of energization of the ions by the induced electric field. This diffusion process was continued as the ions were convected from the plasma sheet boundary layer to the double‐spiral injection boundary. Inward of the injection boundary the ions were convected adiabatically. By using as input an O+flux of 2.8×108cm−2s−1(w>10 eV) and an H+flux of 5.5×108cm−2s−1(w>.63 eV) the computed distribution functions of the ions in the ring current were found to be in good agreement, over a wide range inL(4–8), with measurements made with the ISEE 1 satellite during a storm. This O+flux and a large part of the H+flux appear to be consistent with the DE‐1 and DE‐2 satellite measurements of the polar ionospheric outflow durin

ISSN:0148-0227    

DOI:10.1029/JA090iA04p03465

年代:1985

数据来源: WILEY

摘要:

Data from the retarding ion mass spectrometer (RIMS) on Dynamics Explorer 1 are analyzed by means of a thin sheath model to determine ion temperatures. A number of characteristic features of ion temperatures in and near the plasmasphere are presented. Typical H+temperatures in the plasmasphere are found to be 4000 K to 6000 K on the morningside and 2000 K to 4000 K on the eveningside, increasing withLthroughout. In the plasma trough, typical temperatures observed are a few times 104K. In the outer plasmasphere, multiple temperature components are frequently observed. H+and He+ions are found to be very close to thermal equilibrium with each other in all but perhaps the outer part of the plasmasphere. Within the plasmasphere, temperature profiles observed by DE 1/RIMS rarely show small‐scale variation. During geomagnetically active times, high‐altitude temperatures betweenL=2 and 3 appear to be depressed over quiet time values, to the extent that they may be cooler than temperatures at low altitudes along approximately the same field l

ISSN:0148-0227    

DOI:10.1029/JA090iA04p03475

年代:1985

数据来源: WILEY

摘要:

The Plasma Diagnostics Package, which was flown aboard STS 3 as part of the Office of Space Science first shuttle payload (OSS 1), recorded the effects of various chemical releases from the orbiter. Changes in the plasma environment were observed to occur during flash evaporator system releases, water dumps, and maneuvering thruster operations. During flash evaporator operations, broadband orbiter‐generated electrostatic noise was enhanced, and plasma density irregularities (ΔN/N) were observed to increase by 3–30 times with a spectrum which rose steeply and peaked below 6 Hz. Ions with energies up to several hundred eV were also observed during one flash evaporator operation. In the case of water dumps, background electrostatic noise was enhanced at frequencies below about 3 kHz and suppressed at frequencies above 3 kHz during the dump, and ΔN/Nwas also seen to increase by 5–6 times. Various changes in the plasma environment were effected by primary and vernier thruster operations, including increases in electron density by as much as 3 orders of magnitude, neutral pressure increases to as high as 10−4torr from the nominal 10−7torr, and perturbations in the spacecraft potential by several volts, particularly when measured in relation to the plasma potential in the wake. Thruster activity also stimulated electrostatic noise with a spectrum which peaked at approximately 0.5 kHz. In addition, ions with energies up to 1 keV were seen during some thru

ISSN:0148-0227    

DOI:10.1029/JA090iA04p03487

年代:1985

数据来源: WILEY