摘要:

The neutral atmosphere composition experiment on Atmosphere Explorer C measured N2, O, Ar, and He densities during a magnetic storm in February 1974 at altitudes down to about 160 km. At latitudes above 45°N, N2and Ar densities generally increase during the storm, while He and O densities decrease. Below 45°N all densities tend to increase during the storm. The density increases at perigee indicate that density or temperature profile changes are taking place below 160 km. The return to prestorm conditions is very slow, demonstrating the integrating effect of the atmospheric response. A recent theoretical model incorporating thermospheric circulation and diffusion effects reproduces the longitudinally averaged data including latitude trends and the asymmetry about the storm maximum. Comparison with the mass spectrometer and incoherent scatter empirical model shows qualitative agreement with latitude trends but not with storm asymmetry, while the earlier J71 model based on total mass density is not in agreement with observed latitudinal trends. No significant correlation is found with the short‐term variations of theapindex. At any fixed altitude and for latitudes above 45°N (perigee) the density variations are closely correlated with invariant (or magnetic) latitude, although invariant latitude alone is not adequate to order the data completely. A close correlation is found between in situ O/N2measurements and in situ and ground‐based ionosonde measurements of electron d

ISSN:0148-0227    

DOI:10.1029/JA082i022p03183

年代:1977

数据来源: WILEY

摘要:

We have determined the structure and nature of ‘discontinuities’ in the interplanetary magnetic field at 1 AU in the period March 18 to April 9, 1971, by using high‐resolution magnetic field measurements from Explorer 43. The discontinuities that were selected for this analysis occurred under a variety of interplanetary conditions at an average rate of 0.5/hour. This set does not include all discontinuities that were present, but the sample is large, and it is probably representative. Both tangential and rotational discontinuities were identified. Tangential discontinuities were observed every day, even among Alfvénic fluctuations. In particular, on one day during which Alfvénic fluctuations were intense and persistent in a high‐speed stream, tangential discontinuities (TD's) were seen throughout the day at an average rate of 0.5/hour; rotational discontinuities (RD's) were also observed during this day at a higher than usual rate, the ratio of TD's to RD's being approximately one. The structure of most of the current sheets was simple and ordered; i.e., the magnetic field usually changed smoothly and monotonically from one side of the current sheet to the other. The thickness distributions of the TD's and RD's with very smooth current sheets were similar. The average thickness of the RD's was 1200 km (13 proton Larmor radii), and the average thickness of the TD's was 1300 km (12 proton Larm

ISSN:0148-0227    

DOI:10.1029/JA082i022p03191

年代:1977

数据来源: WILEY

摘要:

The Helios search coil experiment provides accurate low background noise measurements of interplanetary magnetic fluctuation spectra from about 4 Hz to 2.2 kHz adjacent to the frequency band from 0 to 4 Hz of the Technical University of Braunschweig flux‐gate magnetometer. Apart from a slowly varying fluctuation component ranging up to 100 Hz near 1 AU and beyond 500 Hz near 0.3 AU the following superposed ‘events’ can be discerned in the fluctuation spectra which also have a distinct signature in the slowly varying magnetic field: (1) directional discontinuities acting as wave guide boundaries, (2) directional discontinuities producing whistler wave fields because of instability, (3) reversible magnetic field variations, mostly dips of about 1 min duration associated with whistler wave fields, (4) interplanetary shocks, where, for example, the oblique shock of January 8, 1975, has a thickness of about 1 proton gyroradius and produces an increase in whistler wave fields by more than 2 orders o′ magnitude in power spectral density leading to a power spectrum of 1 γ²/Hzf−3.64in the

ISSN:0148-0227    

DOI:10.1029/JA082i022p03201

年代:1977

数据来源: WILEY

摘要:

The two‐fluid solar wind equations have been solved by a method which is approximately 50 times faster than any previously developed, through the use of asymptotic expansions which are self‐consistently iterated upon to find a solution that passes through the critical point. The energy assumptions in two‐fluid solar wind models are reexamined, and the conclusions are as follows: (1) proton thermal conduction may not be neglected, (2) the Coulomb logarithm must be calculated as a function of radius, and (3) the electron and proton temperatures at the base need not be equal, even when the time scale for energy exchange between the species is an order of magnitude smaller than the expansion time at the base. It is possible to reproduce reasonable quiet time solar wind parameters at 1 AU, but only if the proton temperature is approximately twice the electron temperature at 1Rs. This may indicate that extended proton heating is important in the outer solar corona. Winds with velocities at 1 AU of 450 km/s are generated without nonthermal energy deposition but require high proton temperatures as well as very low densities at the base. Higher‐velocity solutions are not possible in a spherically symmetric geometry for reasonable particle fluxes at 1 AU, and it is suggested that these higher‐velocity states probably require additional heating, acceleration mechanisms, or nonra

ISSN:0148-0227    

DOI:10.1029/JA082i022p03213

年代:1977

数据来源: WILEY

摘要:

The winter nighttime ionosphere atL= 4 reveals frequent increases inFregion peak density (Nmax) accompanied by a constant or declining total electron content (TEC). This effect is examined statistically by using two winter periods of simultaneous TEC andNmaxdata and 24 years of DecemberfoF2observations. The month of December 1971 was chosen for a detailed analysis. Two nights, December 9 and 15, were used in simulation attempts to identify the conditions needed to account for the increasingNmax‐constant TEC effect. For each case study, Isis 2 topside sounderNe(h) interpolated data andNe(h) profiles from ground‐based ionosondes were combined with simultaneous TEC measurements to form a semiempirical computer model forNe(h) versus latitude fromh= 0 to geostationary satellite height. The results indicate that vertical distortions of theNe(h) profile over a wide latitude range are needed to reproduce the increasingNmax‐constant TEC effect. The mechanism causing these distortions is still poorly understood. It is suggested that substorm‐enhanced westward electric fields induce a lowering of theFlayer during which air drag effects may permit a buildup of plasma athmaxbefore enhanced loss processes ta

ISSN:0148-0227    

DOI:10.1029/JA082i022p03223

年代:1977

数据来源: WILEY

摘要:

Ionospheric currents calculated from incoherent scatter measurements at Arecibo are compared to ground magnetic variations at San Juan and to electric fields measured in theFregion for two slightly disturbed periods and one very disturbed period, comprising a total of 7 days of data. The measurements indicate that the currents primarily responsible for the ground magnetic variations were flowing in the ionosphere on the slightly disturbed days. On the very disturbed days the variation in the horizontal intensity appears to be primarily due to an asymmetric ring current of magnetospheric origin. The eastward wind had to be modeled above 130 km in the calculations. A semidiurnalS2,2wind model consistent with the measured southward winds drives southward currents that produce a totalDvariation of 20–40 γ with approximately the observed phase, indicating that theS2,2component should be included in theoreticalSqcalculations. A diurnal component also appears to be necessary if theDvariation is to be well reproduced. The electrostatic field was found to drive about as much net horizontal current as the neutral winds. The horizontal components of the electrostatic field tended to be perpendicular to the calculated ionospheric currents on all da

ISSN:0148-0227    

DOI:10.1029/JA082i022p03233

年代:1977

数据来源: WILEY

摘要:

Neutral wind observations over the 100‐ to 200‐km height region at Arecibo are presented for a summer, an equinox, and a winter period. Observations confirm that the wind below 110 km is predominately diurnal, with a vertical wavelength of about 20 km, and can be identified with theS1,1mode. This tide reaches amplitudes of 100 m/s near 100 km but exhibits large day to day and seasonal variation. The vertical energy flux associated with theS1,1mode is of the order of 0.25 erg/cm²/s at 100 km. A semidiurnal oscillation dominates the wind field from about 115 km to at least 170 km during the summer and equinox observations. A nighttime intermediate layer of enhanced electron density consistently descends through theF1valley in the postsunset hours along the convergent null inVzassociated with the semidiurnal winds. TheS2,2mode dominates the semidiurnal oscillation above 125 km during these periods, reaching a maximum amplitude of 90 m/s at 153 km. Higher‐order modes contribute to the semidiurnal oscillation principally below 125 km during spring and summer but appear to dominate at all heights in the winter observations, when theS2,2mode appears to be largely absent. The vertical energy flux associated with theS2,2mode is at least an order of magnitude less than that associated with theS1

ISSN:0148-0227    

DOI:10.1029/JA082i022p03243

年代:1977

数据来源: WILEY

摘要:

Ground‐based data on magnetospheric wave activity in the American longitude sector are studied for a 13‐day period that includes a major magnetic storm and some isolated substorm activity. The wave intensity in the 0.5‐ to 10‐ kHz range shows clear association with geomagnetic activity. A detailed examination of VLF spectra shows that the strongest waves emerging from the middle magnetosphere during the storm recovery period and during isolated substorm activity are often emissions stimulated by radiation from the electrical power distribution system. Several different types of power line radiation effects are illustrated by using broadband spectral data from stations in Antarctica and North America. It appears that man‐made VLF noise has a strong influence on the energetic particle population in the magn

ISSN:0148-0227    

DOI:10.1029/JA082i022p03251

年代:1977

数据来源: WILEY

摘要:

Pc 1 band micropulsations recorded at Siple, Antarctica, in 1973 are analyzed by Fourier and correlative techniques. Dynamic Fourier analysis shows that events lasting 5 hours or more and occurring near local dawn tend to consist of bands which rise in frequency prior to dawn and fall in frequency after dawn. Occasionally, more than one such band is present at a time. Events containing such signatures are frequently modulated in amplitude with periods of the order of an hour. The correlation of Pc 1 occurrences with Kp, at a lag thought to be characteristic of the plasmapause response to magnetic activity, is studied through a three‐dimensional histogram of Pc 1 occurrences versus local time and lagged Kp (similar to Roth and Orr (1975)). The distribution of Pc 1 occurrences in this plot is a well‐defined band about 3 Kp units wide which migrates across Kp with changes in local time, attaining its lowest Kp values near dawn (highest near dusk). These results of our spectrographic and correlative studies are well understood if the generation region for Pc 1 activity is located at the plasmapause. When the Siple data are interpreted as being of plasmapause origin, they appear to contain useful information concerning plasmapause structure and the propagation path for Pc 1 to Siple. Fluting of the plasmasphere surface is suggested by the periodic modulation of long pulsation trains, which appears to be a modulation of the generation process rather than a propagation effect. Analysis of the extent of the distribution of Pc 1 occurrences over Kp indicates that ionospheric ducting does not contribute strongly to Pc 1 reception at Si

ISSN:0148-0227    

DOI:10.1029/JA082i022p03261

年代:1977

数据来源: WILEY

摘要:

We present a study of the spectral properties of terrestrial kilometric radiation (TKR) derived from observations made by the Goddard radio astronomy experiments on board the Imp 6 and Radio Astronomy Explorer 2 spacecraft. As viewed from near the equatorial plane, TKR is most intense and most often observed in the 2100–2400 LT zone and is rarely seen in the 0900–1200 LT zone. The absolute flux levels in the 100 to 600‐kHz TKR band increase significantly with increasing substorm activity as inferred from the auroral electrojet index (AE). In the late evening sector the median power increases by about 3 orders of magnitude between quiet periods (AE200 γ). The peak flux density usually occurs near 250 kHz, although the frequency of the peak in the flux spectrum appears to vary inversely with AE from a maximum near 300 kHz during very quiet times to a minimum below 200 kHz during very disturbed times. The half‐power bandwidth is typically 100% of the peak frequency. The variation of TKR flux density with apparent source altitude indicates that source strength decreases more rapidly

ISSN:0148-0227    

DOI:10.1029/JA082i022p03273

年代:1977

数据来源: WILEY