摘要:

The characteristics of quasi‐periodic (QP) ELF‐VLF emissions with periods of 10–150 s and their relationships to magnetic pulsations are studied by using data obtained from Syowa and Mizuho Stations in Antarctica and at Husafell in Iceland, which is located near the geomagnetic conjugate point of Syowa. From the coherency analysis between QP emissions and Pc 3–4 magnetic pulsations it is found that the coherency between theDcomponent of magnetic pulsations and the intensity fluctuations of QP's is much higher than that between theHcomponent of magnetic pulsations and QP's. It is also found that the propagation time of magnetic pulsations (HM waves) from the interaction region between magnetic pulsations and QP's in the magnetosphere to the ground is 20–30 s. These properties are observed at conjugate‐pair stations with good conjugacy. The results strongly suggest that QP emissions are modulated by compressional mode Pc 3–4 magnetic pulsations near the equatorial plane in the outer

ISSN:0148-0227    

DOI:10.1029/JA085iA01p00101

年代:1980

数据来源: WILEY

摘要:

We investigate the relationship of local daytime geomagnetic energy (measured in the period range ∼30–300 s at a mid‐latitude ground‐based station) to interplanetary parameters during two time intervals when the solar wind/interplanetary field conditions were quite different. We find that the geomagnetic energy levels in the entire period band are consistent with production by a Kelvin‐Helmholtz instability source at the earth's magnetopause. We further find that at the shorter periods (∼30–60 s) the energy may also have a source contribution from the mechanism proposed by Greenstadt, which involves wave energy transfer from the earth's bow shock to the magnetopause. This result represents the first evidence of frequency dependencies in the interplanetary source mechanisms for hydromagnetic energy production in the

ISSN:0148-0227    

DOI:10.1029/JA085iA01p00114

年代:1980

数据来源: WILEY

摘要:

All‐sky camera photographs from flights of the Air Force Geophysics Laboratory (AFGL) airborne ionospheric observatory have been used to investigate discrete auroras in the midnight sector of the auroral oval. The photographs were taken at intervals of 1 min throughout flight durations of 5–10 hours near 69° (±4°) corrected geomagnetic latitude; the 12 flights totaling 93 hours provide ∼5600 frames. For each flight the photographs have been assembled into a montage format which permits perception of individual frames and also, in the aggregate, reveals individual events of auroral activation with measurable lifetimes. The discrete auroras observed in this way, when classified into four categories of activity, active (A), moderate (M), quiet (Q), and no discrete aurora visible (N), exhibit frequencies of occurrence of 22, 37, 24, and 17%, respectively. The lifetimes of auroras in categories A, M, and Q occur predominantly in a group which maximizes between 10 and 20 min with another lesser group which maximizes near 2 hours. Ten to 20 min is also characteristic of the duration of plasma flows observed in the plasma sheet, and thus it is suggested that discrete auroras may be associated with the

ISSN:0148-0227    

DOI:10.1029/JA085iA01p00119

年代:1980

数据来源: WILEY

摘要:

Pararesonance (PR) whistlers observed in the topside ionosphere by the Dartmouth receiver on Ogo 6 are examined. The study extends that of Walter and Angerami (1969) to higher frequencies and shows that the upper cutoff frequency of PR whistlers closely follows a 1/L4dependence from 6 to 100 kHz (atL=2.90 and 1.37, respectively). Most PR whistlers are attached to paralongitudinal (PL) whistlers due, presumably, to intermode coupling. The ‘walking trace,’ or unattached PR whistler, reported by Walter and Angerami is evidently unusual. The upper cutoff frequency follows 1/L4whether attachment occurs or not. Rising sawtooth appendages starting at the upper cutoff frequency are frequently seen on PR whistlers. The required multivalued extensions, of the theoretical isofrequency curves plotted in travel time versus observing latitude by Walter and Angerami, to produce these appendages are given in the appendix, but their physical implication has not been investigated. The terms pararesonance (PR) and paralongitudinal (PL) are suggested as preferable to proresonance and prolongitudinal which have been previously u

ISSN:0148-0227    

DOI:10.1029/JA085iA01p00130

年代:1980

数据来源: WILEY

摘要:

Using scintillation observations from a series of equatorial propagation paths as well as backscatter and airglow data, the development, motion, and decay of equatorial irregularity patches have been studied. Assembling the results of earlier studies in the field with our observations, we find the following: the patch has limited east‐west dimensions with a minimum of 100 km. Several patches may be melded together to reach an extent of 1500 km. Its magnetic north‐south dimensions are often greater than 2000 km; the most intense irregularities (as evidenced by the Jicamarca radar at the dip equator) are from 225 to 450 km in altitude, although irregularities are found as high as 1000 km. The patch initially has a westward expansion following the solar terminator, then, maintaining its integrity, moves eastward. Evidence over a limited series of experiments suggests that premidnight patches are formed within 1½ hours after ionospheric sunset in the absence of special magnetic conditions. From Ascension Island (∼16°S dip latitude) the individual patches can be clearly distinguished. The decay of patches in the midnight time period was studied, pointing to a rapid decrease in scintillation intensity in this time

ISSN:0148-0227    

DOI:10.1029/JA085iA01p00139

年代:1980

数据来源: WILEY

摘要:

A three‐axis flux gate magnetometer was included in the Atmosphere Explorer C (AE‐C) payload for engineering functions. The instrument was activated during the last half of AE‐C's life, and its output appears to be useful only during approximately one‐half of the data gathering time when the vehicle was spinning. Still, the addition of even a partial magnetic field data set to the already broad spectrum of AE‐C measurements is an exciting prospect. The high telemetry rate (128 bits/s per axis) could produce a spatial resolution inBof ∼½ km, but the 8‐bit word size yields an amplitude resolution of only 562 nT. A large modulation (15,000 nT) of the output from the spin axis (Z) magnetometer occurs during sunlit orbit segments. Application of a spin‐averaging technique to the modulated output signal has enabled us to improve the amplitude resolution of the signal to ∼40 nT (rms), although a corresponding loss in spatial resolution from ∼½ to ∼15 km results from the averaging procedure. By taking the difference between the spin‐averaged signal and a model magnetic field in a manner similar to that used by McDiarmid et al. (1978) we deduce a resultant magnetic perturbation ΔBZ. Attributing ΔBZto field‐aligned current (FAC) sheets, we arrive at typical values of ∼1 µA/m² for sheet current densities. The amplitudes and distributions of these FAC’s are observed to be consistent with those measured by Triad (Iijima and Potemra, 1976a, b). Simultaneously measuredZcomponents of the plasma drift velocity (Vz) show correlations with magnetometer measurements indicating that the positions of FAC's correspond to the gradients in the component of the electric field along the satellite track (Xcomponent). By using the current continuity equation for the ionosphere (▽ ·I⊥=J∥), values of height‐integrated Pedersen conduct

ISSN:0148-0227    

DOI:10.1029/JA085iA01p00151

年代:1980

数据来源: WILEY

摘要:

Ps 6 magnetic variations are quasi‐periodic perturbations of the auroral zone magnetic field found in the morning sector during periods of strong magnetospheric activity. The disturbance affects mainly theDandZcomponents of the perturbation field and amplitudes can reach several hundred nanoteslas. In this report we show that Ps 6 activity has a peak in occurrence frequency around magnetic local dawn and that there are significantly more Ps 6 variations detectable in the months around summer solstice than during the months around winter solstice. Our results suggest that the electric field configuration is the most crucial factor in the control of the generation of Ps 6 magnetic disturbance

ISSN:0148-0227    

DOI:10.1029/JA085iA01p00161

年代:1980

数据来源: WILEY

摘要:

A general form of the integral equation of exospheric transport on moon‐like bodies is derived in a form that permits arbitrary specification of time varying physical processes affecting atom creation and annihilation, atom‐regolith collisions, adsorption and desorption, and nonplanetocentric acceleration. Because these processes usually defy analytic representation, the Monte Carlo method of solution of the transport equation, the only viable alternative, is described in detail, with separate discussions of the methods of specification of physical processes as probabalistic functions. Proof of the validity of the Monte Carlo exosphere simulation method is provided in the form of a comparison of analytic and Monte Carlo solutions to three classical, and analytically tractable, exosphere problems. One of the key phenomena in moonlike exosphere simulations, the distribution of velocities of the atoms leaving a regolith, depends mainly on the nature of collisions of free atoms with rocks. It is shown that on the moon and Mercury, elastic collisions of helium atoms with a Maxwellian distribution of vibrating, bound atoms produce a nearly Maxwellian distribution of helium velocities, despite the absence of speeds in excess of escape in the impinging helium velocity distribut

ISSN:0148-0227    

DOI:10.1029/JA085iA01p00164

年代:1980

数据来源: WILEY

摘要:

Simplified multicomponent diffusion calculations are made for the ionosphere of Venus. Large differences in temperature between electrons and ions and appreciable temperature gradients that are near those of recent measurements are used. Compositions for which binary thermal diffusion coefficients for ions are the same as multi‐ion ones are examined as well as those that are quite different. An attempt to combine binary coefficients to give multi‐ions ones has not been particularly success

ISSN:0148-0227    

DOI:10.1029/JA085iA01p00171

年代:1980

数据来源: WILEY

摘要:

This paper describes the results of meteor radar observations which have been carried out at Kyoto University since December 1977. The radar, a coherent pulse Doppler radar with transmitting frequency of 31.57 MHz and nominal peak power of 10 kW, measures wind fields at meteor heights of 80–110 km. The solar semidiurnal tide generally dominates the wind oscillations at these heights. The less regular diurnal tide has comparable magnitude. The variability of the tidal structure suggests the possibility of interaction between respective waves or winds, particularly the influence of disturbed conditions in the lower atmosphere. Other components of winds as mean flow or a quasi 2‐day planetary wave have also been observed. The combination of meteor wind radar and other observational techniques will further the understanding of the global dynamics of atmospheric wa

ISSN:0148-0227    

DOI:10.1029/JA085iA01p00177

年代:1980

数据来源: WILEY