摘要:

A full analysis of radar‐determined meteor rates from New Zealand, involving 3,085,574 meteors recorded over a total of 3½ years, and 12,391,976 meteors recorded by the National Research Council of Canada in 8½ years confirms an inverse relationship between meteor rates and solar activity as measured by sunspot numbers. The relationship, significant at the 1% level, appears in the Canadian annual average when the abnormal 1963 increase is removed, in monthly and ⅓‐monthly results for the total Canadian period, and in monthly intervals for 1 year of the New Zealand data. This proven relationship of meteor rates with the solar cycle calls for a significant density gradient change over the solar cycle in the 70‐ to 120‐km height range. Although some definite negative results have been reported, no unambiguous positive results are yet available supporting such a density gradient change. It is possible that density variations due to annual, semiannual, diurnal, and latitudinal changes obscure any 11‐year density gradient change occurring at these heights. It is uncertain whether the 1963 increase represents density gradient changes in the meteor ablation region regularly brought about 1–2 years before each sunspot minimum or is a special event due to volcanic dust. The following additional facts have emerged from the present analysis. (1) Within a 1‐year period the seasonal rate change of astronomical origin overrides any density gradient change in controlling the meteor rates in one of the two hemispheres. (2) The earth's daily rotation alters rates in phase with probable diurnal density gradient changes. (3) An effect due toDregion absorption has been observed in the Canadian data. (Such absorption can alter radar meteor rates appreciably in the lower t

ISSN:0148-0227    

DOI:10.1029/JA082i010p01455

年代:1977

数据来源: WILEY

摘要:

We report here measurements of the terrestrial and extraterrestrial 0.511‐MeV gamma rays with a collimated high‐resolution gamma ray spectrometer which was flown on a balloon over Palestine, Texas, on June 10, 1974. The instrument consists of four 40‐cm³ Ge(Li,) crystals surrounded by a CsI(Na) shield. The angular resolution of the instrument is 30° full width at half maximum, and the energy resolution is 2.3 keV at 0.511 MeV. Our measurements of the atmospheric fluxes are consistent with reported fluxes measured with omnidirectional scintillation detectors and with angular distributions and depth variations of the intensities derived from a semiempirical model after allowance is made for a component of the background rate due to β+decays produced by neutron‐ and proton‐initiated interactions with materials near the detectors. Our 2σ upper‐limit measurement of the cosmic diffuse flux from the galactic anticenter direction is 9.2 × 10−3photon/(cm² s sr), and the 2σ upper‐limit flux from the Crab Nebula and the quiet sun at the too of the atmosphere is 4.

ISSN:0148-0227    

DOI:10.1029/JA082i010p01463

年代:1977

数据来源: WILEY

摘要:

Aerodynamic drag and lift effects on the inclination of the orbit of the S3‐1 satellite (1974‐85D) have been used to infer atmospheric zonal wind speeds at an altitude of 175 km and to estimate the satellite surface thermal accommodation coefficient. The unusually high quality of the orbital and attitude data permitted the 7‐month data span to be analyzed in six nonoverlapping subintervals, thereby resulting in finer local time and spatial resolution than is normally obtained in such studies. The aerodynamic lift force was found to be quite sensitive to the assumed value of the thermal accommodation coefficient, a quantity that is neither well known nor well understood. The inclination data were best fit (in a least squares sense) when the accommodation coefficient was greater than 0.95. Best agreement with theoretical models in terms of wind speed and direction was obtained when the accommodation coefficient was taken to be nearly 1.0. In this case the inferred wind was ∼400 m/s eastward at 1900–2100 LT and ∼200 m/s westward at 0700–0900 LT. The study indicates that if accurate zonal wind velocities are to be derived from satellite orbital inclination changes, care must be taken to ensure that the shape and orientation of the satellite are such that the lift forces generated are sufficiently small that the resulting uncertainty due to inadequate knowledge of the accommodation coefficient does not cause sign

ISSN:0148-0227    

DOI:10.1029/JA082i010p01474

年代:1977

数据来源: WILEY

摘要:

From solar spectra obtained during the reentry of Calroc 4 the optical depth of the atmosphere in the wavelength interval 1213–1219 Å has been obtained for altitudes between ∼120 and ∼70 km. The data are consistent with the interpretation that molecular oxygen is the primary absorbing species under these conditions if the values of the O2cross section in the 1216.2‐ to 1217.2‐Å region are approximately those of Ogawa (1968) and the O2column densities in the 80‐km region are approximately those derived from the 8‐0 and 11‐0 Schumann‐Runge bands observed dur

ISSN:0148-0227    

DOI:10.1029/JA082i010p01481

年代:1977

数据来源: WILEY

摘要:

A statistical study has been made of the variability of the basic solar wind flow parameters in high‐ and low‐speed flows. Care was taken to exclude data taken during positive speed gradients, where dynamical effects severely alter the flow parameters. The study reveals that other than the bulk velocity the flow parameters within high‐speed streams are steadier and more uniform from stream to stream than they are within low‐speed flows, by a factor of 3. Comparison of simple models of the structure‐free solar wind with average high‐speed flow parameters should therefore be more meaningful than comparison with low‐speed parameters. Of particular importance to models of the lower corona and chromosphere‐corona transition region are the particle and energy fluxes carried by the solar wind. If we assume that all of the solar wind originates in coronal holes, our best estimates of these fluxes at 1Rsare 1.2 × 1014cm−2s−1and 6.4 × 105ergs cm−2s−1, respectively, with an uncertainty of ±40%. Interestingly, the He abundance is observed to be nearly uniform within high‐speed flows at 1 AU. Thus it seems unlikely that a steady state fractionation of heavy elements occurs in those open field regions of the low corona from which the high‐speed solar wind originates. The high‐speed solar wind He abundance may therefore be a faithful measure of the He abundance of the outer layer of the sun. Our best estimate isNα/Np= 0.048 ± 0.005, whereNαandNpare the densities of the alpha particle a

ISSN:0148-0227    

DOI:10.1029/JA082i010p01487

年代:1977

数据来源: WILEY

摘要:

A data set containing merged plasma and magnetic field measurements obtained aboard several spacecraft is presented. By using simple formulas resulting from the constant velocity approximation the field magnitude and direction and the plasma density at 0.3 AU are calculated from this data set. This is possible in about three quarters of the cases from June 1967 to July 1968 with the use of 6‐hour averages. The relation between streams and sectors is examined. The cross correlation between the various parameters is calculated. It is found that the directional fluctuations of the magnetic field on this time scale are mainly due to interplanetary processes; however, the amplitude fluctuations of the magnetic field are decreased by interplanetary processes. The high‐speed portions of interplanetary streams arise in regions of low plasma density. Since the data are at solar maximum, the implication is that the Skylab results for the relation between coronal holes and solar wind sources may hold for the entire solar cy

ISSN:0148-0227    

DOI:10.1029/JA082i010p01493

年代:1977

数据来源: WILEY

摘要:

In order to reduce the discrepancy between solar wind measurements at 1 AU and the corresponding predictions of the basic two‐fluid model a nonthermal heating of solar wind protons in the outer corona up to distances of about 0.1 AU from the sun was postulated. In the absence of thermal energy transfer to an anisotropic plasma the quantitiesc∥=T∥B²/n² andc⊥=T⊥/B(whereT∥andT⊥denote proton temperature components parallel and perpendicular to the magnetic field with intensityBandndenotes the proton number density) constitute adiabatic invariants. Accepting the hypothesis that damping of fast‐mode hydromagnetic waves near the sun strongly dominates the heating and acceleration of the solar wind, we argue thatc∥is increased thereby. Depending on the coupling between parallel and perpendicular degrees of freedom in the turbulent solar envelope,c⊥will be raised to some extent too. If we may neglect interplanetary irreversible processes, these values are transported to the earth and may give some direct information on the turbulent outer corona. We therefore invokec⊥as a new natural ordering parameter instead of the customarily employed bulk velocity in a statistical presentation of solar wind data measured on the earth‐orbiting satellite Heos 2. This choice reveals completely novel features that have been missed in the conventional presentation. We interpret these features as a signature of an extended heating process which survives the transit of the solar wind plasma to 1 AU. We note that the purely wave‐heated two‐fluid model of Barnes and co‐workers was unable to reach flow velocities exceeding 450 km/s. Our data consistently indicate that for larger flow velocities additional heating and acceleration processes (e.g., nonspherically symmetric outflow from coronal holes) come into play. We suggest that a suitable combination of a corotating model and the wave‐heated two‐fluid model should be able to predict both the observed macroscale relation between proton temperature and bulk velocity and the dynamic effects in the moderately active solar wind. Further, we propose that proton double streams and related deformations of the proton distribution functions might be a relic of the interaction with a fast‐mode hydromagnetic wave field w

ISSN:0148-0227    

DOI:10.1029/JA082i010p01503

年代:1977

数据来源: WILEY

摘要:

The electric fields engendered by winds of gravity wave origin are theoretically calculated for the dynamo region of the equatorial ionosphere. A general expression for the efficiency parameter, which is a measure of the effectiveness in producing the total electric field, is derived for a two‐dimensional case, and the results are compared with those obtained from the one‐dimensional treatment of the problem by Kato (1973). The efficiency parameter evaluated by Kato (1973) at the center of the electrojet is higher by about a factor of 5 than that computed here, owing to some approximations made by him. The dependence of the efficiency parameter on the horizontal scale size of the gravity wave wind and the effectiveness of the east‐west wind shear in producing the electron density stratifications are disc

ISSN:0148-0227    

DOI:10.1029/JA082i010p01510

年代:1977

数据来源: WILEY

摘要:

The magnetometer on the Isis 2 satellite is used to study a number of magnetic field perturbations which are interpreted as being due to field‐aligned currents whose directions are opposite to the direction usually observed. The perturbations are observed mainly on the dawn side of the earth and can be interpreted as a result of two adjacent and oppositely directed current sheets in which the equatorward current is into the atmosphere and the poleward current out of the atmosphere. These perturbations are observed only at times when the interplanetary magnetic field (IMF) has a strong northerly component, and they are found at latitudes above those usually associated with field‐aligned currents. The locations of the magnetic field perturbations are compared with simultaneous particle measurements, and the results are discussed in relation to what might be expected from field line merging mod

ISSN:0148-0227    

DOI:10.1029/JA082i010p01513

年代:1977

数据来源: WILEY

摘要:

Enhanced fluxes of electrons precipitating over middle latitudes (L∼ 3–4) were detected by the polar‐orbiting satellite 1971‐089A following a period of magnetic activity starting on December 16, 1971. The electron fluxes measured in 256 differential channels between 130 and 2800 keV have been coordinated with phase observations of VLF radio waves propagating in the earth‐ionosphere wave guide. The VLF paths in question, NLK (near Seattle, Washington) and GBR (at Rugby, England) to APL (near Washington, D. C.), cover ≈120° in longitude and range fromL∼ 2.5 toL∼ 4.0 in invariant latitude. These paths showed marked daytime and nighttime phase advances from 1650 UT on December 17 (in excess of 10 µs during maximum disturbance). The phase values did not return to prestorm levels before December 22–23. The unusual presence of these daytime VLF disturbances is offered as evidence for the widespread precipitation at lowLshell values of nearly relativistic electrons (Ee≳ 200 keV) which would be required to penetrate below ∼70‐km altitude to affect the daytime VLF transmissions. Wave guide mode calculations usingDregion electron density profiles deduced from the satellite particle data predict phase advances which agree reasonably well with the observed values. It is concluded that the observed long‐lived VLF phase disturbances can be explained by excessDregion ionization caused by energetic electrons precipitating from the earth's radiation belt following their injection deep into the magnetospher

ISSN:0148-0227    

DOI:10.1029/JA082i010p01519

年代:1977

数据来源: WILEY