摘要:

The variation of the atomic oxygen density inferred from Ogo 6 green nightglow emission between 100 km and 120 km is too rapid to be consistent with the temperature gradients in standard model atmospheres and an eddy diffusion coefficient that reaches its maximum below 115 km. The oxygen distribution can be reconciled with a constant eddy diffusion coefficient above 100 km if the temperature gradient reaches a value between 10° and 20°K/km for low values of the eddy diffusion coefficient (K∼ 5 × 105cm² s−1) or between 30° and 50°K/km forK∼ 1.6 × 106cm² s−1, compared with a maximum gradient of about 10°K/km in the Jacchia 1971 model. Such gradients as are implied by the oxygen profiles are also observed in Pitot tube experiments flown on sounding rockets and in incoherent scatter measurements. The lowKprofiles are also consistent with Ar/N2ratios measured on sounding rockets and are large enough to conduct away thermally a large part of the solar energy deposited below 120 km, thereby alleviating a serious problem in disposin

ISSN:0148-0227    

DOI:10.1029/JA080i034p04565

年代:1975

数据来源: WILEY

摘要:

Neutral atmospheric composition measurements were obtained by the Esro 4 gas analyzer during a series of geomagnetic storms in late February 1973. Complemented by ground‐based ionosonde data, these measurements show a complex latitudinal and longitudinal structure of the storm‐associated disturbances in the upper atmosphere. Specifically, a strong depression of the O/N2ratio developed and persisted for several consecutive days above the Australian‐African area. It was distinguished by a fairly sharp eastward boundary near 180°E longitude. This mid‐latitude disturbance zone was distinctly separated from strongly disturbed regions at higher latitudes. It is suggested that the energy causing this mid‐latitude disturbance was deposited primarily at altitudes below 150 km. Because of the long diffusion time constants in the lower thermosphere this can account for the persistence of the phenomena observed atF2lay

ISSN:0148-0227    

DOI:10.1029/JA080i034p04571

年代:1975

数据来源: WILEY

摘要:

Data from the Atmosphere Explorer‐C satellite clearly exhibit wavelike variations in neutral composition, ion density, and electron temperature, variations which appear to be a general feature of the atmosphere. The neutral constituents do not exhibit uniform wave characteristics, since the density variations of argon are approximately twice those of molecular nitrogen, which range between 5 and 15%. Helium structure, on the other hand, has about one half the amplitude of the N2variation and is 180° out of phase with the two heavy gases most of the time. The waves evident in the ion density are nearly in phase with the heavy neutrals, while the electron temperature variations are predominantly out of phase with those in the ion density. Scale sizes for the structure range from a few tens of kilometers to several hundred kilometers. A simple model is suggested to explain the neutral composition results, wherein the enhancements in the major gas densities are in phase with the vertical component of the perturbation velocity of the gas. The vertical velocity modifies the composition by transporting parcels of air to higher or lower regions where the composition is different. The phase relationship between the density and velocity implies phase velocities (assuming that these are gravity waves) of the order of 500 m s

ISSN:0148-0227    

DOI:10.1029/JA080i034p04576

年代:1975

数据来源: WILEY

摘要:

A fluid dispersion relation for the drift and interchange (Rayleigh‐Taylor) modes in a collisional plasma forms the basis for a linear theory of equatorial spreadF. The collisional drift mode growth rate will exceed the growth rate of the Rayleigh‐Taylor mode at short perpendicular wavelengths and density gradient scale lengths, and the drift mode can grow on top side as well as on bottom side density gradients. However, below theFpeak, where spreadFpredominates, we conclude that both the drift and the Rayleigh‐Taylor modes contribute to the total spreadFspectrum, the Rayleigh‐Taylor mode dominating at long and the drift mode at short perpendicular wavelengths above the ion Larmor

ISSN:0148-0227    

DOI:10.1029/JA080i034p04581

年代:1975

数据来源: WILEY

摘要:

Observations from five separate experiments on the Isis 2 spacecraft have permitted a study of the atmosphere/ionosphere during the December 16–20, 1971, magnetic storm. The data are most complete in the mid‐latitude region, thus permitting a study of the SAR arc (subauroral red arc) which developed during the night of December 17–18. Ion composition and temperature, electron temperature, electron density height profiles from the spacecraft to theFregion, and the intensity of the 6300‐Å oxygen emission are all presented for the region of interest. It is found that the H+concentration has sharp gradients near the SAR arc and that the plasma temperature was significantly enhanced over typical nighttime values, reaching nearly 7000°K at 1400 km on the field line which intersected the arc. To facilitate interpretation of the data presented, we have also solved a system of time dependent equations for atmospheric/ionospheric composition and temperature by using boundary conditions which were selected such that the solutions were in agreement with the observations. From these solutions we are able to assess the influence of (1) the efflux of plasma from the ionosphere to the magnetosphere, (2) the decrease in [O]/[N2] at the turbopause, (3) the increase in the loss coefficient as a result of an increase in the vibrational temperature of N2, and (4) the conduction of thermal energy into the i

ISSN:0148-0227    

DOI:10.1029/JA080i034p04591

年代:1975

数据来源: WILEY

摘要:

The action of ion‐neutral charge exchange collisions and the largeE × Bdrifts that can exist in the auroral ionosphericFregion lead to an ion velocity distribution which is anisotropic and can be peaked at finite υ⊥. Such distributions are unstable to the Post‐Rosenbluth instability if the relative ion‐neutral drift velocity exceeds 1.8 times the neutral thermal velocity. Such a drift velocity requires a large electric field, of the order of 50 mV/m or more, but such fields do exist at times in the auroral zone. By balancing the ion collision term in Boltzmann's equation with turbulent diffusion caused by the instability a lower bound of a few percent for the fluctuation level is obtained. In situ observations of this instability should be possible. Furthermore, the instability operates at short wavelengths (∼10–20 cm), and so the irregularities should be detectable by a UHF radar directed normal or nearly normal to the magnetic field in theFregion. Such geometry is difficult to achieve, however, and as yet there appears to be no clear radar evidence of the i

ISSN:0148-0227    

DOI:10.1029/JA080i034p04599

年代:1975

数据来源: WILEY

摘要:

An analysis of ac electric field data obtained on board the OV1‐17 satellite and ac magnetic field data obtained on board the Ogo 6 satellite has been made during the northern hemisphere spring and summer of 1969 with the purpose of studying extreme low frequency (ELF) electromagnetic waves above the earth's ionosphere. The results are in basic agreement with a number of previous ground‐based and low‐altitude satellite experiments in that the peak signal was observed at high latitudes outside the statistical location of the plasmapause on the day side of the earth, that ELF chorus was very often observed in conjunction with the steady ELF hiss emissions, that the winter hemisphere signal was considerably smaller than that observed in summer or in equinoctial months, and that the emission strength and region of occurrence are asymmetric about magnetic noon. Observations of such strong hiss signals outside the plasmasphere are somewhat surprising in light of Ogo 3 and Ogo 5 measurements which show steady ELF hiss to be closely confined to the plasmasphere at high altitudes during normal circumstances. The present study supports the hypothesis that hiss leaks out of the plasmasphere and refracts downward into the lower ionosphere; such a model predicts the observed summer‐winter asymmetry and the poleward skewing of the ELF peak signal strength with decreasing altitude. The observation reported here that the high‐latitude boundary for ELF signals in the ionosphere is very near the low‐latitude boundary for long‐wavelength ionospheric irregularities and, at least in the morning hours, very near the horizontal density gradient due to precipitation of magnetosheath plasma in the cusp suggests that these variations in the medium act to reflect the waves and to increase the high‐latitude intensity further. The relationship between signal strength and magnetic activity shown by these data is in agreement with other in situ measurements but not with some ground‐based data. It is argued, however, that the anticorrelation observed at high‐latitude ground stations is due to an equatorward displacement of the peak wave intensity region with increasing magnetic activity; such an equatorward displacement is shown in our results. It is also shown that a significant component of wave electric field is parallel to the wave numberkand hence that Landau resonant effects may occur at low altitudes between outer zone radiation belt par

ISSN:0148-0227    

DOI:10.1029/JA080i034p04603

年代:1975

数据来源: WILEY

摘要:

An intense downward field‐aligned thermal ion flow and intense narrow band waves with frequencies just below the local ion gyrofrequency have been observed at the equatorward edge of an auroral arc. The magnitude and direction of the field‐aligned current required by the measured dc electric field pattern are consistent with the ion flow measurements and with a differential drift between ions and electrons of 10–20 km/s. Such a drift is sufficient to destabilize the electrostatic ion cyclotron wave which has a narrow frequency spectrum near and above the gyrofrequency in the plasma reference frame. The narrow bandwidth of the observed electric field oscillations is in agreement with this mode, as is the frequency range which is shown to be consistent with a Doppler shift due to the relative velocity between the plasma and rocket. A second explanation for the observed ion flow involving saturation of the ion cyclotron instability by extreme heating of the plasma ions in a region above the rocket has been examined and also found to be consistent with the measurements. In this model the observed ion flow was due to a thermal expansion of the hot spot. Such heating would energize O+ions sufficiently that they could escape the gravitational field and could hence act as a source for energetic oxygen observed in the inner magnetos

ISSN:0148-0227    

DOI:10.1029/JA080i034p04612

年代:1975

数据来源: WILEY

摘要:

A study of 13 wave events having 10‐ to 45‐s periods observed by the synchronous satellite ATS 1 in the morning sector reveals that these events, which have been called band‐limited pulsations and are thought to be related to Pi 1, appear actually to be Pc 3. Digital power spectral and coherency analysis was used to determine the characteristics of the wave activity. The average peak frequency of the events (∼0.04 Hz) and their generally narrow banded nature correspond closely to the characteristics of Pc 3. The local time distribution of the events (peaking at 0900 LT) and their less than complete association with substorms also correspond more closely to Pc 3 characteristics. The orientation of the major axis of the polarization ellipse for these events was predominantly azimuthal, which agrees more closely with the east‐west polarization of Pi 1 observed on the ground. However, some examples of radial orientation were observed in the satel

ISSN:0148-0227    

DOI:10.1029/JA080i034p04621

年代:1975

数据来源: WILEY

摘要:

Top side electron density data obtained during the hours of ∼2100–2400 LT from the ionosphere sounder on the Isis 2 satellite are used to give indications of possible latitude gradients in the magnetospheric plasma density distributions. Studies are made of the amplitude and polarization characteristics of magnetohydrodynamic waves that occur in the frequency range of ∼ 10–30 mHz atL∼ 3.2 toL∼ 4.4 during time intervals of Isis 2 passes. It is found that reversals in the sense of wave polarization occur in the vicinity of latitudes whereLshell gradients are observed in the electron density distributions. The results of this study give strong support for the importance of magnetosphere plasma density gradients and the plasmapause in coupling ULF driving energy sources to locally resonant magnetospheric

ISSN:0148-0227    

DOI:10.1029/JA080i034p04627

年代:1975

数据来源: WILEY