摘要:

Analyses of relativistic galactic cosmic ray intensity variations have been conducted to determine the nature of the modulations that are related to the presence of corotating interaction regions (CIR) in interplanetary space. The corotating interaction regions have been identified from the plasma and field observations recorded by Pioneer 10 and 11 spacecrafts during the period 1972–1974. This investigation has established that the nucleonic intensity recorded at the polar stations Thule and McMurdo decreases as the streams associated with the CIR overtake the earth. However, this modulation occurs only for those CIR‐associated streams in which a neutral sheet is imbedded. In contrast, geomagnetic storms are related to CIR streams with or without neutral sheets. Taken together, these results suggest that the ostensible effect of CIR's on the intensity of high‐energy particles is primarily a consequence of drifts related to neutral sheets, although diffusion effects cannot be ruled out at this

ISSN:0148-0227    

DOI:10.1029/JA086iA09p07473

年代:1981

数据来源: WILEY

摘要:

Based on the assumption of the undamped propagation of Alfven waves between 2 and 5RS, the possible range of Alfven wave energy flux density at the base of a polar coronal hole has been deduced. It is concluded that extended heating above 2RSis needed to maintain the temperature maximum above 2RSand to supply energy for the formation of high‐speed wind streams. The energy contribution of extended heating to high‐speed wind streams might be greater than that of Alfven waves by direct momentum addit

ISSN:0148-0227    

DOI:10.1029/JA086iA09p07480

年代:1981

数据来源: WILEY

摘要:

We compute the electromagnetic dispersion relation for right‐ and left‐hand circularly polarized low frequency waves propagating parallel and antiparallel to the upstream interplanetary magnetic field in the presence of both reflected and diffuse suprathermal ions. The ion distribution function is modeled after three‐dimensional observations of reflected and diffuse ions made upstream of the quasiparallel bowshock crossing of December 8, 1977, while the electron distribution function is based on concurrent three‐dimensional observations of low energy electrons. It is found that the reflected ions destabilize the plasma most strongly at ω ∼0.1Ωiby way of a resonant ion beam instability for waves propagating upstream, and by way of a nonresonant firehose‐like instability for waves propagating downstream. The diffuse ion population also destabilizes the plasma most strongly at ω ∼ .1Ωiby way of resonant instability of both right‐ and left‐hand polarized waves propagating away from the bow shock. The growth times of the unstable waves are roughly 60 s and 150 s for those associated with the reflected and diffuse ions, respectively, during which time the waves would be carried several e

ISSN:0148-0227    

DOI:10.1029/JA086iA09p07487

年代:1981

数据来源: WILEY

摘要:

The strong alignment of the average directions of minimum magnetic variance and mean magnetic field in interplanetary Alfvénic fluctuations is inconsistent with the usual wave‐propagation models. We investigate the concept of minimum variance for nonplanar Alfvénic fluctuations in which the field direction varies stochastically. It is found that the tendency of the minimum variance and mean field directions to be aligned may be purely a consequence of the randomness of the field direction. In particular, a well‐defined direction of minimum variance does not imply that the fluctuations are necessarily planar. The fluctuation power spectrum is a power law for frequencies much higher than the inverse of the correlation time. The probability distribution of directions of a randomly fluctuating field of constant magnitude is calculated. A new approach for observational studies of interplanetary fluctuations is sugg

ISSN:0148-0227    

DOI:10.1029/JA086iA09p07498

年代:1981

数据来源: WILEY

摘要:

Geomagnetic energy densities, computed at hourly intervals in three frequency bands from magnetometer data at Pittsburg, New Hampshire, (L∼3.5) for 28 days during July and August 1975, are correlated with upstream solar wind parameters obtained from instruments on the Imp J spacecraft. The diurnal ground magnetic energy variations generally show higher power levels for the lower frequency fluctuations. Enhancements in the power levels may appear at different local times on individual days. Dayside and nightside ground hourly magnetic energies are generally found to correlate best with the solar wind kinetic energy flux densityfk=1/2npmpV³ from amongst the various upstream interplanetary quantities examined. The highest linear correlation coefficients found between power versusfkand power versusVSWare generally obtained during local afternoon hours, with a sharp reduction in correlation occurring at local noon. We conclude that different interplanetary source mechanisms contribute to the dayside ground power in different frequency bands. Improved correlations are expected for nightside power levels with geomagnetic tail quantities rather than with upstream solar wind quantiti

ISSN:0148-0227    

DOI:10.1029/JA086iA09p07507

年代:1981

数据来源: WILEY

摘要:

The ambient background plasma is shown to have an important stabilizing influence on the generation of electrostatic, purely growing, finite ion gyroradius, flute instabilities driven by ion loss cone distribution functions associated with shaped barium injection across the ambient magnetic field in the ionosphere. This stabilization implies that such short scale size instabilities and the striations they produce will only be present if the background plasma density is low enough. Consistent with the experimental observations of the striations, it is shown that for the parameters of the Buaro barium release experiment the background plasma density is insufficient to completely stabilize the finite ion gyroradius modes; however, background ion density does reduce the growth rate from the level predicted with a theory which does not include the background plasma dynamics.

ISSN:0148-0227    

DOI:10.1029/JA086iA09p07513

年代:1981

数据来源: WILEY

摘要:

The distinction between the magnetic anomaly model of the outer Jovian magnetosphere (Dessler and Vasyliunas, 1979; Vasyliunas and Dessler, 1981) and the magnetodisc model (as, for example, discussed most recently by Goertz (1981)) is reviewed, and a further observational comparison of the two models is pointed out. The comparison involves the latitudinal variation of the intensity of energetic charged particles confined near the magnetic equatorial plane. Because of this confinement, there should be a direct relationship between the maximum latitude excursion (relative to the magnetic equatorial plane) made by a spacecraft during one 10‐hour planetary rotation period and the ratio of the maximum intensity observed in the magnetic equatorial plane to the minimum intensity observed off the equator. Thus if the maximum latitude excursion is large, the minimum between two maxima should be quite deep. If the maximum latitude excursion is known, a scale height for the energetic particle confinement can be estimated from observed maximum‐to‐minimum ratios. The two magnetospheric models (magnetic anomaly and magnetodisc) in general predict different maximum latitude excursions. For the outbound passes of Voyagers 1 and 2, these predictions are combined with observations of energetic particle intensities (Krimigis et al., 1979a, b) to calculate the confinement scale heights for the energetic particles. For the magnetodisc model, the scale height is generally less than 2RJand is a weakly decreasing function ofr, in excellent quantitative agreement with the scale height derived from a combination of simple MHD theory and a magnetic field model based on Pioneer 10 outbound magnetic field measurements (Goertz, 1976). The magnetic anomaly model, on the other hand, yields a scale height which apparently increases to large values at large radial distances. Furthermore, when the calculation is reversed for the magnetodisc model, so that the observed max/min ratio is combined with the theoretically predicted scale height to yield a maximum latitude excursion for each of the current sheet encounters, it is found that the resultant current sheet latitude agrees very well with the current sheet latitude estimated on other grounds, namely, the timing of the intensity maxima. Moreover, as shown by Goertz (1981), excursions of this current sheet latitude away from the nominal value of 9.6° are reasonably well associated with periods of enhanced solar wind dynamic pr

ISSN:0148-0227    

DOI:10.1029/JA086iA09p07519

年代:1981

数据来源: WILEY

摘要:

We report ionospheric scintillation observations made at Natal, Brazil, during a period of 2½ years. The nighttime scintillations of satellite signals at 250 MHz commonly exceeded 20 dB peak‐to‐peak. Seasonally, it showed a typical behavior for the South American sector with a single peak centered around October–November months and the local evening hours of 2100–2300 LMT. This seasonal behavior was different from that of the African sector and very different from that of the Pacific sector. On a spacing of 278 m the eastward irregularity drift speed was measured by the method of similar fades. This, together with the determination of Fresnel frequency from the power spectrum analysis, was used to calculate the height of the irregularity patch. A value of 294 km was obtained. Multisatellite scintillation observations indicated that even though the initiation of an irregularity cloud commonly occurred earlier on signals transmitted by the eastern satellite, there were substantial cases when the reverse was observed. One case which was analyzed in detail suggested that the irregularity clouds formed independently along two radio paths separated b

ISSN:0148-0227    

DOI:10.1029/JA086iA09p07527

年代:1981

数据来源: WILEY

摘要:

Phase recordings at Atibaia, Brazil (23°S, 46°W), of 13.6 ‐kHz signal transmitted from Golfo Nuevo, Argentina (43°S, 65°W), a trajectory confined almost completely within the South Atlantic anomaly region, show significant perturbations, indicative of the lowering of the VLF reflection level, following the onset of magnetic disturbances. Simultaneous measurements of the Eslayer parameters ftEsand fbEsover Cachoeira Paulista (22°S, 45°W) also show enhancements, with some delay with respect to the magnetic disturbance onset, as was found in our earlier work (Batista and Abdu, 1977). These results show magnetic storm associated ionization enhancements taking place in a height region from approximately 110 km down to 70 km, which we interpret as having been produced by precipitation of high‐energy charged particles in the South Atlantic magnetic anomaly. The results also suggest some degree of day to day variability in the abundance of metallic species and/or in the dynamics of the E region over th

ISSN:0148-0227    

DOI:10.1029/JA086iA09p07533

年代:1981

数据来源: WILEY

摘要:

Medium‐energy ions (E>25 keV) measured by the ISEE 2 satellite are used to provide information on plasma sheet motions during expansions following substorms. We show that the upward speed of the plasma sheet edge measured locally is commonly ∼50 km/s, a value high in comparison with two‐satellite measurements. It is thought that waves in the form of field‐aligned corrugations of the sheet boundary may be responsible for the high speeds measured in some cases. The boundary between the lobe and plasma sheet intensity fluxes is about 2 Rgthick at the ion energies looked at, or 1000–3000 km. After the passage of the plasma sheet boundary, particle fluxes drifting downward toward the neutral sheet are often encountered. This is interpreted as anE×Bdrift, in which case the electric field is about 1 mV/m. This could imply high cross‐tail potentials. At the outer boundary of the plasma sheet, it is found that the streaming ion layer recently reported by Möbius et al. [1980] and Spjeldvik and Fritz [unpublished manuscript, 1980]shows a peaked spectrum that softens as the plasma sheet is approached. The observation of a rising plasma sheet boundary, downward‐drifting flux tubes, and the behavior of the streaming ion layer are consistent with the tailward motion of a source region together with a cross‐tail electric field. The data can be interpreted to show that the source region when the plasma sheet 20 REdowntail has expanded to about 6 REis

ISSN:0148-0227    

DOI:10.1029/JA086iA09p07543

年代:1981

数据来源: WILEY