摘要:

The green line (557.7 nm) of atomic oxygen and the Herzberg bands of molecular oxygen (measured between 250 and 280 nm) as observed from the Ogo 4 airglow photometer from August 1967 through January 1968 are discussed in terms of their spatial and temporal distributions and their relation to the atomic oxygen content in the lower thermosphere. Daily maps of the distribution of emissions show considerable structure (cells, patches, and bands) with appreciable changes from day to day. When data are averaged over periods of several days in length, the resulting patterns have only occasional tendencies to follow geomagnetic parallels. The seasonal variation is characterized by maxima in both the northern and the southern hemispheres in October, the northern hemisphere having substantially higher emission rates. These maxima tend to move toward the poles, leaving very low values of emission at low latitudes in December and January. Noting the similarity of the atomic oxygen profiles in the lower thermosphere to the profile of a Chapman distribution, formulae are derived relating the vertical column emission rates of the green line and the Herzberg bands to the atomic oxygen peak density. Global averages for the time period for these data (August 1967 to January 1968), when expressed in terms of maximum atomic oxygen densities near 100 km, have a range of 2.0 × 1011cm−3to 2.7 × 1011cm−3. Their variation closely follows the phase of the semiannual variation in total density observed at higher altitudes from the analysis of satellite drag

ISSN:0148-0227    

DOI:10.1029/JA080i022p03053

年代:1975

数据来源: WILEY

摘要:

Airglow measurements of the disk of Venus, made by the ultraviolet photometer on Mariner 5 on October 19, 1967, are analyzed to determine the sources of the observed emission. Rayleigh‐scattering models for a semi‐infinite atmosphere are used to determine the scale height and single‐scattering albedo of the scatterer and to determine the 1304‐Å emission rate. It is found that (1) the scale height of the Rayleigh‐scattered radiation is 4.5 ± 0.5 km, (2) the single‐scattering albedo near 2000 Å is 0.8 ± 0.1, and (3) 500 R of 1304‐Å radiation is detected at solar zenith angles b

ISSN:0148-0227    

DOI:10.1029/JA080i022p03063

年代:1975

数据来源: WILEY

摘要:

A model for the aeronomy of odd nitrogen in the thermosphere is constructed that satisfactorily describes published measurements of odd nitrogen species. On the basis of theoretical considerations of the molecular processes associated with N2++ O → NO++ N and N2dissociation by electron impact and EUV radiation between 800 and 1000 Å, we argue that essentially every reaction of N2++ O leads to the formation of N(²D) and that the latter processes proceed through the same intermediate states which predissociate to form one N(²D) and one N(4S) atom. The model predicts NO δ (0, 0) band emission, in good agreement with the measurements by Feldman and Takacs (

ISSN:0148-0227    

DOI:10.1029/JA080i022p03068

年代:1975

数据来源: WILEY

摘要:

The largest source of error in the deduction of atmospheric densities from orbital data stems from uncertainty in our knowledge of the interaction of atmospheric molecules with satellite surfaces. A method of determining two of the important parameters, the accommodation and drag coefficients, is developed in detail. As an example, the method is applied to observational data from the paddle wheel satellite Ariel 2. Because of the importance of spherical satellites the drag coefficient for a sphere under the conditions of Ariel 2 (a moderately eccentric orbit with perigee near 300 km) is also obtained. The importance of well‐designed orbital experiments to improve our knowledge of surface‐particle interactions at a variety of altitudes is stres

ISSN:0148-0227    

DOI:10.1029/JA080i022p03077

年代:1975

数据来源: WILEY

摘要:

We hypothesize that type 1 VHF radar echoes can only be observed when the electrojet plasma is linearly unstable at half the radar wavelength and that further, for reasons not yet understood, the phase velocity of the unstable waves always corresponds to the threshold conditions for instability, even when the destabilizing forces (electron drift and plasma density gradient) exceed the threshold. This phase velocity, which produces the Doppler shift of the radar echoes, is usually close to the ion acoustic velocity of the medium but can differ from it to some extent because of the effect of the density gradient. This difference can be positive or negative, is proportional to λ², and can be substantial at night, when the vertical density gradients in the equatorialEregion are large and variable. Nighttime equatorial radar observations do seem to indicate considerable variability in the type 1 velocity. These effects may also be important in explaining auroral radar observation

ISSN:0148-0227    

DOI:10.1029/JA080i022p03087

年代:1975

数据来源: WILEY

摘要:

By using the data of total electron content (TEC) obtained from the Faraday rotation of signals from geostationary satellites recorded at several locations, the day‐to‐day variability of the daily range and hour of maximum of TEC is studied. Fluctuations sometimes as large as ±50% in the magnitude of TEC and ±4 hours in the time of the maximum are observed, even on quiet days. Changes in TEC andNmaxeven at the same location are not always completely parallel. Also TEC changes at locations separated by more than about 3000 km in latitude or longitude show poor correlations. No relation with changes in solar EUV is indicated. It is suggested that erratic neutral winds blow away from the polar regions toward the equator even during quiet times and create convection cells which may result in ionospheric irregularities of scale lengths of about 3000 km which wander about the globe slowly and give the observed day‐to‐day variability of TEC and the equivalent slab th

ISSN:0148-0227    

DOI:10.1029/JA080i022p03091

年代:1975

数据来源: WILEY

摘要:

The generation of ULF waves by ground‐based magnetic and electric dipoles is studied with a simplified model consisting of three adjoining homogeneous regions representing the ground, the vacuum (free space) region, and the ionosphere. The system is assumed to be immersed in a homogeneous magnetic field with an arbitrary tilt angle. By the use of Fourier techniques and the method of stationary phase, analytic expressions are obtained for the field strength of the compressional Alfvén waves in the ionosphere. Expressions are also obtained for the strength of the torsional Alfvén wave in the ionosphere and the ULF magnetic field at ground level. Numerical results are obtained for the compressional Alfvén wave field strength in the ionosphere with a nonvertical geomagnetic field and for the ULF magnetic field at ground level for a vertical geomagnetic f

ISSN:0148-0227    

DOI:10.1029/JA080i022p03100

年代:1975

数据来源: WILEY

摘要:

Linearized stability analysis of a one‐dimensional plasma cloud coupled to a background ionosphere shows that if the ionosphere is relatively incompressible (i.e., is at sufficiently high altitudes relative to the cloud), then ionospheric short‐circuiting of the cloud leads to short‐wavelength stabilization of theE × Binstability responsible for striation development. Short‐circuiting reduces the polarization potential of the striations, slowing their ion cross‐field negative diffusion and allowing ordinary ion cross‐field diffusion to dominate and to suppress the instability at short wavelengths. A maximum in the growth rate is thereby induced at a wavelength which may be identified as the preferred scale size for striations. In contrast, if the ionosphere is relatively compressible (i.e., is at low altitudes relative to the cloud), then the ionosphere causes destabilization of the cloud, increasing the growth rate for striations of all wavelengths. In practice, these conclusions imply that plasma clouds released at twilight in the mid‐latitudeF1region will be stabilized at short wavelengths by coupling with the relatively incompressibleF2region, whose conductivity (integrated alongB) dominates that of the compressible (and therefore destabilizing)Eregion. Such clouds therefore exhibit well‐defined striations with a consistent and predictable scale size. The quantitative predictions of the theory compare favorably with observations of striation development in an actual mid‐latitude twilight barium release. On the other hand, at equatorial latitudes or during the day the integrated conductivity may be dominated by theEregion. Under these circumstances theEregion compressibility may lead to destabilization for all wavelengths, and the consistent formation of well‐defined striations with a predictable scale size is not to be expected. The destabilizing influence of theEregion is not caused by Hall currents but is simply a consequence of the compressibili

ISSN:0148-0227    

DOI:10.1029/JA080i022p03111

年代:1975

数据来源: WILEY

摘要:

We have obtained solutions of the coupled continuity, momentum, and energy equations for NO+, O2+, and O+ions for conditions appropriate to the daytime high‐latitudeEandFregions. Owing to the rapid increase of the reaction O++ N2→ NO++ N with ion energy, high‐latitude electric fields and consequentE⊥× Bdrifts deplete O+in favor of NO+. For electric field strengths less than about 10 mV m−1the depletion of O+is small, and the altitude profiles of ion density are similar to those found at mid‐latitudes. However, for moderate electric field strengths (∼50 mV m−1), NO+is substantially increased in relation to O+and becomes an important ion throughout theFregion. For these conditions the electron density has a tendency to become nearly constant with altitude in the range 160–360 km. For large electric fields (∼200 mV m−1), NO+completely dominates the ion composition to at least 600 km, decreasing at high altitudes with a diffusive equilibrium scale height. Since the overallFregion electron density decreases markedly with increasing electric field strength, it appears that high‐latitude, daytime electron density troughs are directly related to the presence of ionospheric electric fields. In addition, since increases in the N2density or the N2vibrational temperature also affect ion composition and electron densities in a manner similar to that of electric fields, the observed daytime troughs may arise from both process

ISSN:0148-0227    

DOI:10.1029/JA080i022p03121

年代:1975

数据来源: WILEY

摘要:

Observational evidence from a latitudinal array of four ground‐based magnetometer stations nearL= 4 suggests that magnetic disturbances at latitudesL≳ 4.4 can excite damped sinusoidal oscillations at plasma density gradients at or inside the plasmasphere. The observations, together with the theoretical interpretations of Chen and Hasegawa (1974a), suggest that the oscillations can be attributed to a magnetohydrodynamic surface eigenmode excited at the density gradients. The wave frequency, damping rate, and latitudinal dependence of the amplitude for each event can be used to infer the steepness of the plasma density gradient as well as the plasma density inside the gradient reg

ISSN:0148-0227    

DOI:10.1029/JA080i022p03131

年代:1975

数据来源: WILEY