摘要:

An analysis is presented of a few of the sector boundary crossings measured by the Pioneer 8 magnetometer. By using a variance matrix technique, evidence is obtained of some amount of magnetic line reconnection through the sector boundaries. The thicknesses of such structures are around 0.1–2 × 104km and are therefore larger than typical ion Larmor radii, in contrast with the magnetic structures characteristic of the geomagnetic tail. A theoretical discussion is given of the possible physical causes of the observed reconnection process. In particular, the possible role of tearing instabilities is analyzed with reference to the results of the observatio

ISSN:0148-0227    

DOI:10.1029/JA081i001p00001

年代:1976

数据来源: WILEY

摘要:

The Atmosphere Explorer‐C satellite carries a large number of experiments including an open source neutral mass spectrometer. Among the measurements obtained with this instrument were ones of particle densities of N2, O, and He at northern latitudes in early February and late June 1974. The orbital geometry of the satellite was such that comparisons could be made for the winter/summer season at the same altitudes and latitudes and at similar local solar times. The helium density shows in midmorning a winter/summer enhancement of a factor of 29 at 400 km. The enhancement at other altitudes, both higher and lower, is less. At 250 km the winter/summer oxygen ratio is 1.7, whereas the winter/summer nitrogen ratio is 0.6. Both ratios decrease with increasing altitudes. The analysis identifies an oxygen enhancement at low altitudes in winter and at high altitudes in summe

ISSN:0148-0227    

DOI:10.1029/JA081i001p00007

年代:1976

数据来源: WILEY

摘要:

The rate coefficient for the quenching of N(²D) by O(³P) has been measured by using an afterglow source and resonance absorption detection for N(²D). Quenching by known concentrations of O atoms, generated by NO titration of a nitrogen discharge, was compared with the quenching by O2, N2O, and CO2, for which the rate coefficients are well known. The rate constant for N(²D) quenching by O(³P) derived in this manner is (1.8 ± 0.6) × 10−12cm³ molecule−1s−1at 315°K. A small increase with temperature in this rate constant relative to that for O2was found, consistent with an activation energy of 1 ± 0.5 kcal/mol fo

ISSN:0148-0227    

DOI:10.1029/JA081i001p00012

年代:1976

数据来源: WILEY

摘要:

The Atmosphere Explorer‐C satellite carries a neutral mass spectrometer having a quasi‐open ion source which can be operated either in a normal mode or in one which utilizes the velocity of the vehicle (∼8.5 km/s near perigee) to distinguish between incoming ambient particles and ambient particles which have struck instrument surfaces and become accommodated. In the normal mode it performs essentially like a closed source instrument. The combined use of the two modes makes possible the determination of ambient densities of chemically active constituents, such as atomic oxygen, as well as inactive species. An analysis of over 80 orbits between early February and late June, 1974, when the spacecraft's perigee was in the northern hemisphere, gave average particle densities at 200 km and mid‐latitudes as follows:n(N2), 3.0 × 109cm−3;n(O2), 2.4 × 108cm−3;n(O), 2.5 × 109cm−3. Comparisons are made with other experiments. Then(N2) andn(O2) values agree well with those obtained from rocket‐borne mass spectrometers. Then(O) concentration is approximately one half of the value given in the Jacchia (1971) model, There is no evidence for an increase in averagen(O2) from early February to late June; this result disagrees with reports of large s

ISSN:0148-0227    

DOI:10.1029/JA081i001p00017

年代:1976

数据来源: WILEY

摘要:

Ion velocity and temperature measurements at Arecibo for two winter days were analyzed to determine the large‐scale dynamical structure of theEregion. Southward neutral winds were derived directly from the ion velocity, while the southward electric field was obtained with a reasonable extrapolation of the measured ion‐neutral collision frequency. Eastward winds were estimated after assuming a model eastward electric field taken from previousFregion measurements at Arecibo. The main results are as follows: (1) Large oscillations in the ion drifts, neutral winds, and temperatures were present on the days of observation. The oscillations possessed a characteristic downward phase progression and dominant periods that were near semidiurnal. (2) Wind and temperature amplitudes were 40–100 m/s and 30°–60°K, respectively. Vertical wavelengths for a semidiurnal period were about 50 km. The calculated southward electric fields are typical of daytimeFregion values at Arecibo, −1 to −2 mV/m. (3) The observed semidiurnal amplitudes, phases, and vertical wavelengths of the wind and temperature oscillations do not closely match the predictions of classical tidal theory or the theory of Lindzen and Hong which includes dissipation and bac

ISSN:0148-0227    

DOI:10.1029/JA081i001p00025

年代:1976

数据来源: WILEY

摘要:

Number densities of N2, O, Ar, and He at a height of 280 km, derived from measurements made with the gas analyzer aboard the polar‐orbiting satellite Esro 4, were subjected to a preliminary analysis to establish a global pattern for variations that accompany geomagnetically induced disturbances. At middle and high latitudes, during periods of sustained geomagnetic activity, the number densities of N2and Ar display regular 24‐hour variations in phase with the variations of geomagnetic latitude caused by the earth's rotation under the satellite orbit; O and He display the same 24‐hour variations with an opposite phase. These variations can be quantitatively explained by assuming that the temperature increases with geomagnetic latitude and that a change in the temperatureTis accompanied by a change in the height of the homopause,zH. During such periods of sustained activity,dzH/dTis of the order of 50–60 m/°K, and the maximum temperature is reached near the magnetic pole. During transient magnetic storms, at higher latitudes, the 24‐hour variations with geomagnetic latitude are swamped by those roughly in phase (N2and Ar) or in antiphase (He) withKp; during the storm, O densities vary but little, almost erratically. Here, too, the observations are well represented by the previous assumption about the homopause, except that we need a smaller value ofdzH/dT, about 30 m/°K. From this and other evidence it appears that the homopause reacts slowly to geomagnetic activity, reaching a steady state height level only after 2 or 3 days. There is good indication that the maximum temperature during transient storms is shifted toward the auroral zones. An entirely different regime prevails in the equatorial region during magnetic storms. There all four atmospheric constituents vary in phase and with similar amplitudes, following the variations ofKpwith a lag of about 8 hours. Since the lag is much smaller at higher latitudes, this finding suggests a density wave proceeding from highe

ISSN:0148-0227    

DOI:10.1029/JA081i001p00036

年代:1976

数据来源: WILEY

摘要:

From late on October 29 until November 3, 1972, our experiment on the European Space Research Organization satellite Heos 2 recorded the arrival of an enhanced interplanetary particle intensity. A dramatic ‘slot’ in count rate and other sudden anisotropy and flux changes (measured in and perpendicular to the ecliptic plane) were found to coincide with changes in the θ (north‐south) ecliptic direction of the interplanetary magnetic field. However, reorientation of strongly field‐aligned particle distributions relative to the detectors was insufficient to explain the intensity changes recorded, and the conclusion had to be drawn that the spacecraft was repeatedly crossing a boundary between one regime and a neighboring one with a different particle population. Since the switching from one regime to the other continued for several days, it would seem reasonable to suggest that the boundary between regimes was roughly parallel to the ecliptic plane. This idea was reinforced by the discovery that each time that the particle regime changed, not only didBθchange, but the solar wind flow direction changed, the dip angle reversing sign. It would thus appear that when the solar wind blows three‐dimensional snakelike tubes in interplanetary space, MeV particles obediently follow the field line bundles within such tubes and experience considerable difficulty in crossing from one tube to a neighboring tube which encloses a different regime. Because of the absence of cross‐field particle movement, measurements made at higher solar latitudes, where most solar active regions occur, could reveal a somewhat different picture of the development of solar pa

ISSN:0148-0227    

DOI:10.1029/JA081i001p00043

年代:1976

数据来源: WILEY

摘要:

The process of adiabatic acceleration of relativistic cosmic rays between two converging shocks, through the first‐order Fermi mechanism, to which the unusual ground level event (GLE) of August 4, 1972, was attributed earlier is examined quantitatively, the nature of interplanetary shock waves and their propagation being taken into account. In the formal computational model the net evolution of the particle flux is determined by the balance between the acceleration of particles reflected from the moving shock waves and the loss of those particles which pass through the shocks. Comparison of the results of the theoretical calculations with the measurements has revealed that the observed abnormalities are a natural consequence of the proposed process. In particular, the computed times of maximum and the ratio of the enhancement at the mountain altitude South Pole station to that at the sea level polar neutron monitors are in good agreement, as is the rapid decay of the particle flux after the maximum. The initial growth of the nucleonic intensity appears to be delayed with respect to the prediction, but this discrepancy can be ascribed to the complexities in attempting to uniquely disentangle the GLE from the behavior of the total cosmic ray flux and to the late development of the particle reflection coefficient of the interplanetary shock fronts. An intensive search has revealed that the requisite conditions for observing GLE representing acceleration between converging shocks has occurred only twice over a period of two solar cycles, and on both occasions an abnormal GLE was in fact observe

ISSN:0148-0227    

DOI:10.1029/JA081i001p00051

年代:1976

数据来源: WILEY

摘要:

The flare‐associated interplanetary (IP) shock of February 15–16, 1967, observed by Explorer 33 and Pioneer 7 is analyzed to yield an estimation of the ecliptic plane geometry of the shock surface near 1 AU. These spacecraft were separated by 23° in heliocentric longitude, and Pioneer 7 was at a distance of 1.12 AU from the sun. There was an 18.9‐hour delay between the two observations. The estimated shock normal, obtained by using a least squares shock parameter fitting procedure for the Explorer 33 data, is found to be θSE= −53° and ϕSE= 198°, which agrees within the error cone with the estimate of Hirshberg et al. (1970), obtained by using the magnetic coplanarity theorem and the Ames Research Center magnetometer data from Explorer 33. The error cone angle for the shock normal of the Explorer 33 observation was approximately 7°. This severely inclined shock normal is not typical of IP shocks. The shock normal at the Pioneer 7 position is found to be θn= −14° and ϕn= 161°, referred to the spacecraft‐sun line, by using the magnetic coplanarity theorem and Goddard Space Flight Center magnetic field data. However, the uncertainty is large (≈25° for a 1σ cone angle). Although a data gap occurred at the apparent time of passage of the disturbance at Pioneer 6, which was 85° in heliocentric longitude from Pioneer 7 and 0.83 AU from the sun, the recovered data did suggest such a passage. A consistent picture of the shock propagation is given to explain the difference in arrival times at Pioneer 6 and 7 and at Explorer 33 and the difference of the shock normals observed by Pioneer 7 and Explorer 33. The average shock speed from the sun to each spacecraft and the local speed at Explorer 33 and their relations to the position of the initiating solar flare are obtained and discussed. In the region of space between the earth and Pioneer 7 the shock surface radius of curvature in the ecliptic plane appears t

ISSN:0148-0227    

DOI:10.1029/JA081i001p00060

年代:1976

数据来源: WILEY

摘要:

The bursts of relativistic electrons detected on Pioneer 10 upstream from Jupiter and within 400rJof the planet have been found to be correlated with the interplanetary magnetic field. In the three examples upon which this study is based, during the month prior to the Pioneer 10 encounter, electrons with energies between 3 and 6 MeV escaping from Jupiter's magnetosphere were observed only when the interplanetary magnetic field was along the Jupiter‐spacecraft line. In addition, large‐amplitude interplanetary waves with characteristic periods of 10 min were observed and found to be well correlated with intervals during which the field was along the Jupiter‐spacecraft line. Abrupt changes in the field away from the preferred direction caused equally abrupt terminations of the waves with an accompanying reduction in the electron flux. These results are consistent with propagation of the electrons from Jupiter to Pioneer along, rather than across, the magnetic field lines. The direction of the interplanetary magnetic field is apparently not affected by the electron bursts or by other particles from Jupiter. A histogram of 1‐min averages of the interplanetary magnetic field longitude during the period of the study clearly shows the average Parker spiral direction with no enhancement in the Jupiter‐spacecraft direction. Two alternative possibilities are considered for the origin of the waves. If they were generated near Jupiter, they would have to propagate to the spacecraft in the whistler mode. The expected attenuation of these waves over distances of several hundredrJand their long travel times make this explanation unattractive. Alternatively, hydromagnetic wave generation by Jovian charged particles, presumably the relativistic electrons themselves, as they travel upstream, appears to be an attractive explanation. At the observed frequency, hydromagnetic waves are Doppler‐shifted to the gyrofrequency of the relativistic electrons. A plasma instability that appears capable of explaining the observations is a cyclotron overstability originally discovered in thermonuclear research that occurs when the velocity of runaway electrons exceeds the velocity of hydromag

ISSN:0148-0227    

DOI:10.1029/JA081i001p00065

年代:1976

数据来源: WILEY