摘要:

Long‐term averages of solar wind speed data obtained in the ecliptic plane from July 1964 through December 1975 have been examined for a regular variation in flow speed associated with the earth's yearly excursion to latitudes ±7¼° about the solar equator. Regular speed modulations of ∼70 km s−1peaking at the highest latitudes are discernible from mid‐1964 through 1966 and from early 1969 to early 1971. During the remainder of this 11½‐year interval the modulations in speed seem to be aperiodic. A superposed epoch analysis of all the data fails to reveal a general solar latitude gradient in the solar wind flow for these 11½ years. It is concluded that with near‐earth observations a latitude dependence of the flow speed is too small to be detected on a regular basis against a background ‘noise’ of solar wind streams, which vary in longitude

ISSN:0148-0227    

DOI:10.1029/JA082i001p00173

年代:1977

数据来源: WILEY

摘要:

Intense electron microbursts were detected by means of bremsstrahlung X ray measurements during a period of strong substorm activity on July 31, 1973. The time resolution of the X ray data was sufficient to examine in detail the temporal and spectral features of individual microbursts in differential energy windows of 25–50, 50–75, and 75–100 keV. The duration (full width at half maximum) of a typical microburst was ∼150 ms; periodic spacings in multiple microbursts were of the order of 0.5 s. Both of these characteristic times are at the low end of the range of corresponding times observed for microbursts at higher latitudes. With respect to the mean spacing in multiple microbursts, this result is consistent with precipitation models which predict anLdependence for this characteristic time. Power spectra of long segments of data showed that the microbursts tended to cluster in groups spaced from 3 to 7 s apart. Significant substructure of the order of 30–70 ms was evident in many microbursts. Double‐peaked bursts were frequently observed in the 75‐ to 100‐keV channel. Microbursts exhibiting substantially different rise times, of the order of 30 and 70 ms, could also be distinguished in the 75‐ t

ISSN:0148-0227    

DOI:10.1029/JA082i001p00177

年代:1977

数据来源: WILEY

摘要:

The theoretical prediction of the enhancement of the maximum growth rate of the electromagnetic ion cyclotron instability, occurring in thermally anisotropic plasmas, in the presence of a cold plasma component was investigated by a computer simulation experiment. The plasma parameters used are βp≡ 8πnp,wkT∥,p/B0² = 1 and kT∥,p= 25 keV. Three relevant cases were considered: case I, pure warm (np,c= 0) isotropic (Ap≡T⊥,p/T∥,p− 1 = 0) plasma; case II, pure warm (np,c= 0) anisotropic (Ap= 0.5) plasma; and case III, a mixed warm‐cold (np,c/np,w= 2) anisotropic (Ap= 0.5) plasma system. The results of the investigation confirm the linear theory of the enhancement of the instability. Moreover, they show the evolution of the unstable plasma systems through their quasi‐linear and nonlinear stages. These results are relevant for active magnetospheric experiments to be performe

ISSN:0148-0227    

DOI:10.1029/JA082i001p00181

年代:1977

数据来源: WILEY

摘要:

The plasma in the dayside magnetosheath exhibits a persistent pressure anisotropy in the sensep⊥>p∥. A likely source for this anisotropy is the effect of field compression and plasma depletion along field lines as magnetosheath plasma flows toward the magnetopause. The model of Zwan and Wolf describing this effect for the case of isotropic pressure is combined with the double‐adiabatic fluid equations to predict the behavior of the anisotropic pressure. For a fluid element following a streamline inward from the bow shock, we find theoretical pressure anisotropies of magnitude large enough to trigger the mirror instability over most of the dayside magnetosheath. These findings are supported by the observations of Kaufmann et al. of large‐amplitude hydromagnetic waves in the inner magnetosheath believed to be generated by the mirror inst

ISSN:0148-0227    

DOI:10.1029/JA082i001p00185

年代:1977

数据来源: WILEY

摘要:

We have investigated the direct effect of soft electron precipitation on the nitrogen vibrational distribution and on the rate coefficient for the ion‐atom interchange reaction between O+and N2using a spectrum of the precipitating electrons characteristic of the dayside cusp region. Substantial increases in the nitrogen vibrational temperature and in the rate of the O+destruction reaction do not occur unless the flux of incident electrons is as large as 1012cm−2s−1. For such large fluxes, departures of the vibrational distribution from a Boltzmann distribution have a significant effect on the rate coefficient. Incident fluxes less than 1011cm−2s−1, such as are usually observed, have little direct effect on nitrogen vibration, although the indirect effect resulting from enhanced electron temperatures might be

ISSN:0148-0227    

DOI:10.1029/JA082i001p00187

年代:1977

数据来源: WILEY

摘要:

We report the results of a study of the daytime ion chemistry of NO+using Atmosphere Explorer‐C measurements made at altitudes above 155 km. We determine that the rate coefficient for dissociative recombination of NO+as a function of electron temperatureTeduring the daytime is accurately represented by the expression 4.5 × 10−7(Te/300)−0.83, derived from laboratory measurements of Walls and Dunn. The total rate of recombination in the lower thermosphere is consistent with the rate of ionization produced by the AE‐C reference spectrum of Hin

ISSN:0148-0227    

DOI:10.1029/JA082i001p00191

年代:1977

数据来源: WILEY

摘要:

During several days in April–May 1976 the Chatanika, Alaska, incoherent scatter radar and a temporary Doppler auroral radar located at Aniak, Alaska, were directed toward ionospheric volumes along a common magnetic field line in order to compareEregion andFregion drifts and associated electric fields. The Chatanika radar measuredFregion plasma drifts via the incoherent scatter technique, while the Aniak radar measured the drifts ofEregion irregularities (i.e., the radar aurora). The radar geometry was arranged so that both radars measured approximately the same velocity component of a magnetically westward or eastward motion. Preliminary data show good agreement between the drift velocity components measured by the two techniques during most of the experimental period. This result indicates that relatively modest auroral radar systems may be used, with some qualifications, to determine auroral electric field

ISSN:0148-0227    

DOI:10.1029/JA082i001p00195

年代:1977

数据来源: WILEY

ISSN:0148-0227    

DOI:10.1029/JA082i001p00198

年代:1977

数据来源: WILEY

ISSN:0148-0227    

DOI:10.1029/JA082i001p00199

年代:1977

数据来源: WILEY