摘要:

Annual means of the diurnal anisotropy from 1937 to 1967 are shown to result from the addition of two distinct diurnal components. One component, with maximum in the asymptotic direction 128° east of the sun, contains a well‐determined wave,W, with a period of two solar cycles.Wpasses through zero in 1958 when the sun’s poloidal field reversed. The remaining component withWeliminated, has its maximum in the asymptotic direction 90° east of the sun. Annual means of this component, with maximum at 18.0 hours local asymptotic time, are well correlated (r= +0.75) with magnetic activity and determine a solar cycle variation with minimum near sunspot minimum and amplitude about two‐thirds that ofW. These results derive from a statistical investigation of the variability of annual means of the diurnal variation from ion‐chamber data at Cheltenham‐Fredericksburg, Huancayo, and Christchurch. The absolute, or total, diurnal anisotropy and the atmospheric diurnal temperature effect are in reasonable agreement with those derived independently through a comparison between the diurnal anisotropy from ion‐chamber data and from Simpson's 1953–1966, IGY neutron monitor d

ISSN:0148-0227    

DOI:10.1029/JA074i014p03451

年代:1969

数据来源: WILEY

摘要:

In August‐September 1967 eleven barium vapor clouds were released during evening twilight between invariant magnetic latitudes of 67.3° to 68.1° from Andøya, Norwav. Two flights (8 releases) occurred during moderate negative bays inH, whereas the third flight (3 releases) took place during a positive bay inH. Visual auroral displays were observed in the vicinity during all flights. In the negative bay situation, barium ion cloud motions were eastward and closely parallel to auroral arc alignments. Electric fields transverse to the magnetic field with intensities of 10–130 mv/m directed southward were observed. During the positive bay event the barium clouds spanned the breakup transition region, with the two equatorward clouds moving westward while the poleward cloud went east. Observed reversals in direction were closely correlated with magnetic variations. North‐directed electric fields of up to 50 mv/m were found in the positive bay sector. In all events the ion cloud motions revealed thatEwas perpendicular to the ionospheric current, hence we conclude that the auroral electrojets, both eastward and westward, are essentially Hall currents. The results illustrate that the magnitude ofEdriving ionospheric currents cannot be deduced solely from ground magnetic observations because of the variable ionospheric electrical conductivity. There is evidence that whileEis large near an auroral arc, the field within is very low. Large gradients and/or irregularities in theEfield are found to exist most of the time. These are revealed on three different time‐space scales: from differences in velocity for parallel moving clouds, from velocity changes along the path of a given cloud, and in the form of rayed structure with

ISSN:0148-0227    

DOI:10.1029/JA074i014p03469

年代:1969

数据来源: WILEY

摘要:

A diurnal pair of upper atmosphere composition payloads was launched near 9°30′ south latitude aboard Nike‐Apache rockets on March 11, 1965. Higher O/O2ratios were obtained in the daytime than at night, and the values were approximately equal to those obtained at Wallops Island. The data indicated the existence of atomic nitrogen in the order of 1 to 2% of the molecular species, but the extent of possible instrumental and observational errors precludes a firm conclusion in this respect. Argon‐nitrogen turbopause levels of 101 and 103 km were deduced from the daytime and nighttime data, respectively. No conclusive dependence on time or location was noted in these results or those of other flights. Contrary to expectations, the indicated daytime exospheric temperature of 600°K was lower than the nighttime (

ISSN:0148-0227    

DOI:10.1029/JA074i014p03488

年代:1969

数据来源: WILEY

摘要:

The authors hypothesize that individual flares are not the cause of either Forbush decreases or geomagnetic storms. Evidence supporting this hypothesis is here presented showing that geomagnetic storms and Forbush decreases can be accounted for entirely by the effects of interplanetary ‘streams.’ Major cosmic‐ray variations begin near the time that a flare‐producing region on the sun passes central meridian. This relationship and a similar relationship between geomagnetic storms and flare‐producing regions is shown to exist even during the intervals that include the energetic flares that have produced ground‐level increases in neutron monitor counts. Streams, closely associated with these flare‐producing regions, are usefully described by the structure in the interplanetary magnetic field since fluctuations in the interplanetary field are highly correlated with theKpindex and the interplanetary field strength is inversely correlated with the cosmic‐ray intensity. Such stream structure is used to account for the observed ‘center limb effect.’ It is also shown that when flares of importance 3— or greater occur within a few days of very high geomagnetic activity and at longitudes greater than 25° west, the major geomagnetic activity precedes the flare. This result is not easily explained by the hypothesis that periods of intense geomagnetic activity are due to in

ISSN:0148-0227    

DOI:10.1029/JA074i014p03499

年代:1969

数据来源: WILEY

摘要:

The authors assumed the existence of a long‐lived stream structure in the interplanetary magnetic field during late March 1966. The main feature of this stream was a uniform, high‐field core that passed the earth on March 24. The geomagnetic activity, anisotropy of solar particles over the energy range 0.6 to ∼100 Mev/nucleon, and the anisotropy of the Forbush decrease, which were observed during the event, were analyzed and were all found to be compatible with the proposed stream stru

ISSN:0148-0227    

DOI:10.1029/JA074i014p03512

年代:1969

数据来源: WILEY

摘要:

Simultaneous observations of positive ion composition, VLF earth‐to‐satellite transmission, and whistlers have been obtained from the OGO 2 satellite during October 1965 in a polar, dawn‐dusk orbit. As the satellite moves poleward above about 55° invariant latitude, sudden depletions of the light ion components of the topside ionosphere are observed, wherein the concentrations of H+and He+decrease by as much as an order of magnitude within 3°Λ. The light ion trough correlates with similar rapid reductions in the propagation of both man‐made and natural VLF signals received at the satellite, where signal intensities are observed to decrease by as much as 20 db and where whistler rates decrease abruptly within 3°Λ. Poleward of the trough, the depleted light ion distributions are characterized by rapid fluctuations in concentration, which appear to correlate in some cases with significant enhancements in the VLF noise level. The combined evidence of the light ion depletion and VLF cutoff further identifies the plasmapause as the often abrupt boundary of the plasmasphere. The abruptness of the light ion trough suggests the possibility that the mechanism responsible for the depletion results under certain conditions in a sharply defined heating and upward expansion of the lower atmosphere. Limited evidence of VLF absorption as well as abrupt increases in neutral density near the trough zone appears consistent with this

ISSN:0148-0227    

DOI:10.1029/JA074i014p03517

年代:1969

数据来源: WILEY

摘要:

Approach directions of cosmic rays for quiet times were computed for high latitude stations using a model magnetosphere. This paper describes results obtained for four typical stations: Kiruna (λinv= 64.5°), Byrd (λinv= 68.2°), Churchill (λinv= 70.2°), and Resolute (λinv= 84.2°). Computations included approach directions for vertical incidence, cones for wide ranges of angles of incidence, regions of penetration at the magnetopause for arrival of cosmic rays, all for noon and midnight, and hourly scanning rates. Directions of approach, particularly for medium and low rigidity, present a daily variation, indicating that they do not corotate with the station and that the previous computations based on an internal field model do not accurately present the directions of viewing. A station normally views more easterly directions at noon than at night; this effect is inverted for some very high latitude stations, which, moreover, view at night directions that form small angles with the equator. Cones for low rigidity particles are found to be narrow. A collimated beam of limited rigidity range of cosmic rays coming from the interplanetary medium widens and approaches the station under all pitch angles. The importance of the results for detection of low rigidity galactic cosmic rays and of solar corpuscular events by means of balloons is di

ISSN:0148-0227    

DOI:10.1029/JA074i014p03529

年代:1969

数据来源: WILEY

摘要:

Fifty orbits of Explorer 34 data have been used to study 0.01–0.05 Hz transverse waves in the interplanetary medium region between the bow shock and the spacecraft apogee of 34RE. It is concluded that the waves are associated with the earth's bow shock since they only occur when projection of the interplanetary field observed at the spacecraft intersects the shock. The waves are observed 18.5% of the time when a total of 134 days of interplanetary data is considered, but more than 90% of the time when the field has the proper orientation with respect to the bow shock. On the basis of this result it is suggested that these waves with 20–100 second periods are a permanent feature of the solar wind‐earth interaction. The transverse component of the waves is typically several gammas in amplitude in 4–8 gamma fields. The disturbance vector in theXYplane generally exhibits the same sense of rotation in a coordinate system where the field is oriented along the positivezaxis. Attenuation of wave amplitudes with distance from the bow shock is estimated to be only a factor of 2 when the spacecraft is 15REfrom the bow shock. The absence of waves at particular field orientations, even though the field line intersects the shock, is interpreted as a propagation effect. This observation is the basis for calculations that yield an average velocity in the plasma frame of 2.7 ± 0.4 times the solar wind velocity. Whistler propagation and local generation by two‐stream instability are discussed as alternate theoretical explanations for the presence of the waves. It is suggested that the data favor the latter

ISSN:0148-0227    

DOI:10.1029/JA074i014p03541

年代:1969

数据来源: WILEY

摘要:

The experiment reported here is an attempt to detect effects of a dawn‐to‐dusk electric field of the type implied by recent models of plasma convection in the magnetosphere. Outer radiation zone electron intensities (E>35 kev) measured near dawn and dusk are compared as a function ofLfor three magnetically quiet periods. A requirement of the experiment is to examine the outer‐zone steady state and in particular to avoid local time dependent effects of nonadiabatic acceleration processes. For this reason the quiet periods were selected by choosing intervals of a few days each when the outer‐zone intensity showed a steady decay. AtLvalues greater than 5.5 higher intensities were observed near dawn than near dusk and the dawn‐dusk difference increases with increasingL;atL∼ 7 dawn intensities are approximately 40% higher than dusk intensities. The results are used to place upper limits on the potential drop across the magnetosphere, which are somewhat smaller than implied by plasma convection models. Other possible mechanisms that could account for the observations are als

ISSN:0148-0227    

DOI:10.1029/JA074i014p03554

年代:1969

数据来源: WILEY

摘要:

The spherical Lyman‐β radiative transfer problem is solved for several theoretical models of the hydrogen geocorona. Comparisons of the computed intensities with the experimental observations of Lyman β and Balmer α airglows show that the geocoronal Balmer α contribution is superimposed on a uniform background of about 4 R. The 4 R background is probably galactic (or extra‐galactic) in origin. The column density of hydrogen required to account for the telluric Balmer α component is about 5 × 1013atoms per cm² above 650 km for a 950°

ISSN:0148-0227    

DOI:10.1029/JA074i014p03561

年代:1969

数据来源: WILEY