摘要:

Measurements of N2, O, He, and Ar densities from neutral gas mass spectrometers on four satellites (Ogo 6, Aeros A, AE‐C, and AE‐D) and inferred O2and H densities from an ion mass spectrometer on AE‐C have been combined to produce a model of longitude/universal time (UT) variations in thermospheric neutral temperature and composition. The longitude/UT model is an extension of the mass spectrometer‐incoherent scatter thermospheric model and uses spherical harmonic terms dependent on geographic latitude, longitude, and universal time. The terms which depend only on longitude indicate a temperature enhancement of about 30°K somewhat equatorward of the magnetic poles. The temperature varies also in universal time, the greatest enhancement being about 30°K near 2130 UT in the northern hemisphere and about 70°K near 0930 UT in the southern hemisphere. The extrapolated 120‐km variations are generally in phase for Ar and O2and out of phase for He, O, and H. Changes during magnetic storms are relatively small. The combined longitude and UT variations reflect the influence of the earth's magnetic field but indicate that the variations may not be simply represented in magnetic coordinates. The longitude/UT model helps reduce differences in the local time variation between the incoherent scat

ISSN:0148-0227    

DOI:10.1029/JA084iA01p00001

年代:1979

数据来源: WILEY

摘要:

Simultaneous measurements of ambient [O2], [N2], and temperature were made near winter solstice, 1975, by the open source neutral mass spectrometer (OSS) on Atmosphere Explorer‐D. The data, taken at midmorning and all latitudes, are analyzed by using scatter plots and correlation coefficients. At 200 km the [O2] density exhibits a positive correlation with the magnetic indices. Owing to the latitude dependence, this description of the response of [O2] during or following periods of magnetic activity, while it is useful, is only qualitative. The increase in [O2] with increasing ambient temperature is much better defined over a wide range of latitudes. In addition to temperature, global scale wind systems may play a role in controlling the distribution of [O2]. To study this role further, measurements of [N2] are used to help distinguish between temperature and wind effects in [O2]. A survey of the latitudinal variations in [O2]/[N2] with temperature indicates a positive response in high‐latitude regions and a negative response near the equator. This is further substantiated with the calculation of correlation coefficients. Such an effect can be explained by inferring the existence of upward vertical winds at high latitudes, meridional flow toward lower latitudes, and subsidence near the equator. Such wind systems are in agreement with those predicted by models and measured in the high‐latitude regions. It is concluded that [O2], being a minor constituent, is controlled both by temperature variations and by wind induced diff

ISSN:0148-0227    

DOI:10.1029/JA084iA01p00010

年代:1979

数据来源: WILEY

摘要:

Four different two‐dimensional (perpendicular to the ambient magnetic field) plasma fluid‐type numerical simulations following the nonlinear evolution of the collisional Rayleigh‐Taylor instability in the nighttime equatorialFregion ionosphere have been performed. Realistic altitude dependent ion‐neutral collision frequencies, recombination rates, and ambient electron density profiles were used. In three cases (ESF 0, 1, 3) the electron density profile was kept constant, with a minimum bottomside background electron density gradient scale lengthL∼ 10 km, but the altitude of theFpeak was changed, withFpeak altitudes at 340, 350, and 430 km. All cases resulted in bottomside growth of the instability (spreadF) with dramatically different time scales for development. Plasma density depletions were produced on the bottomside with rise velocities, produced by nonlinear polarizationE × Bforces, of 2.5, 12, and 160 m/s and percentage depletions of 16, 40, and 85, respectively. In one case, ESF 0, the bubble did not rise to the topside, but in ESF 1 and 3, topside irregularities were produced by the bubbles (where linear theory predicts no irregularities). In these three cases, spreadFcould be described from weak to strong. In the fourth case (ESF 2) the altitude of theFpeak was 350 km, but the minimumLon the bottomside was changed to 5 km. This resulted in a bubble rise velocity of ∼23 m/s and a 60% depletion with strong bottomside and moderate topside spreadFand a time scale for development between ESF 1 and 3. Two other cases, ESF 0′ and 0″ with peaks at 330 and 300 km, respectively, and bottomsideL∼ 10 km, were investigated via linear theory. These cases resulted in extremely weak bottomside spreadFand no spreadF(entire bottomside linearly stable), respectively. These simulations show that under appropriate conditions, the collisional Rayleigh‐Taylor instability causes linear growth on the bottomside of theFregion. This causes the formation of plasma density depletions (bubbles) which rise to the topside (under appropriate conditions)Fregion by polarizationE × Bmotion. High altitude of theFpeak, small bottomside electron density gradient scale lengths, and large percentage depletions yield large vertical bubble rise velocities, with the first two conditions favoring bottomside linear growth of the instability. The numerical simulation results are in good agreement with rocket and satellite in situ measurements and radar backscatter measurements, including some of the recent results from the August 1977 coordinated ground‐based measurement campaign conducted by Defense Nucl

ISSN:0148-0227    

DOI:10.1029/JA084iA01p00017

年代:1979

数据来源: WILEY

摘要:

Total mass density data from the miniature electrostatic accelerometer (Mesa) experiment on AE‐E are analyzed to determine diurnal and semidiurnal tidal variations in the lower thermosphere (150–245 km) at low latitudes (<20°). The local time density structure changes from predominantly semidiurnal below 180±5 km to predominantly diurnal above this transition height, with no strong dependence on season. However diurnal phases in summer occur 6 hours (at low heights) to 1½ hours (at higher heights) earlier than winter, whereas semidiurnal phases during summer occur from 1 hour (at low heights) to 6 hours (at higher heights) later than winter. Analyses of data from all seasons to determine an annual mean semidiurnal amplitude can therefore lead to unrealistically small semidiurnal amplitudes due to phase cancellation effects. These results are compared with analyses of AE‐E data by other investigators, and with recent empirical and theoretical models of thermospheric composition and density. Variations between equatorial and middle latitudes as predicted by theory are estimated to be of the order of 20–50% in amplitude and 3–6 hours in phase for the semidiurnal component, 0–20% in amplitude and 0–6 hours in phase for the diurnal component, and 15 km with respect to the transition height from semidiurnal to diurnal predominance. Therefore tidal variations in total mass density as derived from AE‐E measurements cannot be extrapolated to middle latitudes without incurring errors o

ISSN:0148-0227    

DOI:10.1029/JA084iA01p00031

年代:1979

数据来源: WILEY

摘要:

A Fabry‐Perot interferometer has been used to determine midlatitude thermospheric wind velocities and temperatures during the large geomagnetic storm of March 26, 1976. These quantities were determined from the doppler shifts and broadening of the twilight and nightglow 630.0‐nm emission line observed from the Laurel Ridge Airglow Observatory (40°8′N, 790°10′W). Following the onset of the storm at ∼0300 hours UT, the wind vector increased from a twilight, quiet period value of ∼100 m/s (eastward) to a maximum of ∼600 m/s, directed generally southward. Large velocities (>200 m/s) persisted from ∼0400 hours UT to the end of the observing period (∼1100 hours UT) and were generally larger by a factor of ≥2 to the north of the observatory than to the south. A temperature rise of ≥500 K during the course of the storm was noted in all directions, with pronounced, relatively rapid fluctuations (of up

ISSN:0148-0227    

DOI:10.1029/JA084iA01p00037

年代:1979

数据来源: WILEY

摘要:

Assuming time stationarity of the one‐particle distribution functionfon the scale of the bounce motion of particles in a magnetic fieldB, we expand the Vlasov equation throughO(ϵ) in the adiabatic parameter ϵ, which is the ratio of particle gyroradius to scale length of the magnetic field. Sincefis directly proportional to particle fluxdΦ/dWdΩ differential in kinetic energyWand solid angle Ω,fis in principle measurable in space experiments, and our analysis is tailored to be explicitly applicable to space problems. ToO(1),fis gyrotropic; its first velocity moment is (if nonvanishing) parallel toB, and hence macroscopic parallel flow is included in this term. TheO(ϵ) contribution is nongyrotropic, and macroscopic flow perpendicular toBplus additional parallel flow results from these terms. The degree of nongyrotropy and hence the amount of cross‐field macroscopic flow depend on the perpendicular component of the electric fieldE, on curvature and shear in the magnetic field, and on the spatial gradient ▽f0, pitch angle derivative ∂f0/∂δ, and speed derivative ∂f0/∂υ of the lowest‐order distribution functionf0. We also show that the usual expression for the electric fieldE, which produces plasma corotation in an axisymmetric system such as a dipole, also holds for any nonaxisymmetric but rigidly rotating magnetic field pattern, provided the observed magnetic field is used in pl

ISSN:0148-0227    

DOI:10.1029/JA084iA01p00041

年代:1979

数据来源: WILEY

摘要:

One‐hour‐averaged fluxes of 1.8‐to 2.15‐MeV protons observed by the LET2detector on Pioneer 10 on the inbound trajectory showed anisotropies attributable to corotation of Jupiter’s magnetodisc only when Pioneer was near the dipole equator. Most of the time the anisotropy greatly exceeded the value expected from corotation. Gradients in the distribution function can be used to account for this excess anisotropy, but the amount of gradient required is unacceptably large by 1–2 orders of magnitude. If they were taken as real, these gradients would predict almost complete disappearance of these protons from Jupiter's magnetosphere in a matter of hours. The remedy is to introduce into the model of the distribution function proton flow along field lines away from the equator into both the southern and the northern hemisphere. The parallel flux at the southernmost latitudes reached by Pioneer can reach 25% of the product of proton density and velocity, i.e., 25% of the maxim

ISSN:0148-0227    

DOI:10.1029/JA084iA01p00047

年代:1979

数据来源: WILEY

摘要:

Fluxes of energetic electrons and protons in Jupiter's outer magnetosphere were observed to be modulated with the 10‐hour rotation period of the planet. This modulation is due to the concentration of particles at the magnetic equator: the nonalignment of Jupiter's spin and rotation axes causes Pioneer 10 to oscillate between +2° and −19° magnetic latitude and hence between regions of stronger and weaker fluxes. In this paper we investigate the relationship between electron and proton fluxes observed off the magnetic equator with those measured at the equatorial crossing radii of the same flux tubes. Liouville's theorem is applied with the assumption that particles move conserving their magnetic moments. A magnetic model which matches the intensity and direction of the magnetic field along the Pioneer 10 trajectory is used for determining the positions of the equatorial crossings. Energetic electrons (1.3 MeV) compared in this way appear to be consistently described. Protons, on the other hand, show much weaker fluxes at the off‐equatorial points than would be predicted by this simple application of Liouville's theorem. Violation of the first adiabatic invariant is one explanation; other potential explanations depend on slow magnetic field fluctuations which are not included in the magnetic model and which conserve the first invariant or on a large asymmetry in equatorial proton flux as a function of system III lo

ISSN:0148-0227    

DOI:10.1029/JA084iA01p00056

年代:1979

数据来源: WILEY

摘要:

Observational evidence suggests that magnetospheric substorms may be associated with the formation of a pair of neutral points or lines in the geomagnetic plasma sheet, containing an X‐type point (or line) and an O‐type one. While magnetic merging theory has concentrated almost entirely on X‐type neutral configurations (points, lines, or sheets), here the role of O‐type configurations is examined, with special attention to three points: (1) How does the X‐O configuration extend in three dimensions? To this end, an analytical model of the configuration was derived, useful for visualizing the geometry and for numerical treatment of plasma flows in it. (2) What modifications are needed in the MHD conditionE = v × Bnear the O‐type line, where it tends to make v grow without limit? By analyzing equations of motion for charged particles near an O‐type neutral line and their solutions in limiting cases, it was found that at a certain distance from the neutral line the mean particle motion became decoupled from that of magnetic field lines (which obeys the MHD condition). The decoupling distance depended on initial conditions in momentum space, suggesting that the MHD approximation which averages out such conditions may not suffice for describing plasma dynamics near the neutral line. Similar problems arise with merging flows near X‐type neutral lines, and although the treatment there is more difficult and requires more approximations, it appears that the same qualitative conclusions apply there as well. (3) What is the role of O‐type neutral lines in particle acceleration? It was found that after inflowing particles are decoupled from the field line motion, they go over to a mode of runaway acceleration along the neutral line. This process is much more efficient along an O‐type line than along an X‐type line, and it is concluded that if merging occurs at an X‐O pair, two particle populations may be expected: low‐energy particles accelerated adiabatically by earthward convection past the X‐type line, dependent mainly on the total amount of flux which has been merged, and high‐energy particles converted toward the O‐type line and undergoing there runaway acceleration. The second acceleration process depends critically on the rapidity of merging and is therefore expected to vary considerably from event to event. All this agrees with observations, and similar processes may also be important in solar flares, where a ‘Y‐type neutral point’ has been proposed, which actually represents the

ISSN:0148-0227    

DOI:10.1029/JA084iA01p00063

年代:1979

数据来源: WILEY

摘要:

Recent analysis has confirmed and expanded the characterization of the lobe plasma, the extension of the ‘boundary layer’ and ‘plasma mantle’ to lunar distances. Careful statistical analysis has verified that the observation of the ‘lobe plasma’ is strongly correlated with theycomponent of the Interplanetary Magnetic Field (IMF). When the moon is in the dawnside of the northern lobe or duskside of the southern lobe, the probability for observation of the lobe plasma is greatly increased when, in the hour preceding, the IMF has had a positiveycomponent. Conversely, when the moon is in the duskside of the northern lobe or dawnside of the southern lobe, the probability for observation is much increased when the IMF has a negativeycomponent. Analysis of lobe plasma data in conjunction with high time resolution IMF data has shown the probability of observation also is greater with a southward pointing IMF. The observed correlations with theyandzcomponents the IMF reflect the fact that the asymmetry and changes in magnitude of the polar cap electric field induced by the IMF extends to lunar distances and determines the depth into the tail to which the ions can drift. Generally, the lobe plasma is observed sporadically for a full day after the moon has entered the tail and a full day before the last magnetopause crossing as it exits the tail. An average extent of ∼8–10REinward from the magnetopause is inferred; however, the lobe plasma has been seen all

ISSN:0148-0227    

DOI:10.1029/JA084iA01p00072

年代:1979

数据来源: WILEY