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1.
Amano T 《The Astrophysical journal》2000,531(2):L161-L164
The lowest rotational transitions of CH in the ground electronic state (X2Pi), J=3&solm0;2, N=1<--J=1&solm0;2, N=1, have been observed in the laboratory in the 532.8 and 536.8 GHz regions. All six possible hyperfine components are identified, and the precise transition frequencies are determined. 相似文献
2.
Pi 2 magnetic pulsations are a frequent occurrence at the earth's surface and have been shown to be clearly correlated with substorm expansion onset. These pulsations are also observed in space at synchronous orbit at the same time as they are seen on the ground at the satellite conjugate point. In this brief report we describe three days in 1969 on which Pi 2 magnetic pulsations were simultaneously observed at the synchronous satellite ATS 1 and at Tungsten, N.W.T., Canada, near the foot of the ATS 1 magnetic field line. These Pi 2 bursts all exhibit the characteristic waveform and frequency, as well as an ～0.3 Hz enhancement, at both locations. This high frequency enhancement appears to be an integral part of Pi 2 bursts both on the surface and at synchronous orbit and should be considered in the development of models of generation mechanisms. 相似文献
3.
Ground observations of Pi 2 geomagnetic pulsations are correlated with satellite measurements of plasma density for three time intervals. The pulsations were recorded using the IGS network of magnetometer stations and the plasma density measurements were made on board GEOS-1 and ISEE-1. Using the technique of complex demodulation, the amplitude, phase and polarisation characteristics of the Pi 2 pulsations are observed along two meridional profiles; one from Eidar, Iceland (L = 6.7) to Cambridge, U.K. (L = 2.5) and the other from Tromso, Norway (tL = 6.2) to Nurmijarvi, Finland (L = 3.3). The observed characteristics of the Pi 2 pulsations are then compared with the plasma density measurements. Close relationships between the plasmapause position and the position of an ellipticity reversal and a variation in H component phase are observed. A small, secondary amplitude maximum is observed on the U.K./Iceland meridian well inside the position of the projection of the equatorial plasmapause. The primary maxima on the two meridians, in general occur close to the estimated position of the equatorward edge of a westward electrojet. Using the plasma density measurements, the periods of surface waves at the plasmapause for two intervals are estimated and found to be in good agreement with the dominant spectral peaks observed at the ground stations near the plasmapause latitude and within the plasmasphere. The polarisation reversal, together with phase characteristics, spectral evidence and the agreement between the theoretical and observed periods leads to the suggestion that on occasions a surface wave is excited on the plasmapause as an intermediate stage in the propagation of Pi 2 pulsations from the auroral zone to lower latitudes. 相似文献
4.
5.
The identification of substorm onset is quite important in studying the mechanism of excitation of substorm disturbances. At present, one of the most practical methods to identify accurately the onset of substorms is to use low-latitude Pi2, which is sensitively related to the plasma instability in the magnetosphere, that triggers the substorm disturbances. This method is applied to examine the onset times of three substorm events which were already defined by various methods other than the low-latitude Pi2 method. Preceding the onset times, other evident substorm onsets are clearly determined with Pi2 onsets for all the three events by examining only the H-component of rapid-run magnetogram from a single low-latitude station in the dark hemisphere. Cooperative monitoring of Pi2 at three low-latitude stations on three well-separated meridians, therefore, is really effective in detecting most substorms. 相似文献
6.
Evidence is presented from spectral analysis of Pi2 pulsations detected during a substorm by the University of Alberta meridian chain of magnetometers to support the conclusion that at auroral latitudes there is no apparent correlation between the principal spectral components of Pi2 pulsations and the latitude of the observations. From these data we infer that the Pi2 magnetic variations observed at the Earth's surface are not generated by simple MHD eigenoscillations of magnetospheric field. As well, the data show clear contributions to the Pi2 pulsation spectrum by ionospheric currents. These observations lead to the suggestion that Pi2 pulsation spectra are produced by the sudden changes in magnetospheric and ionospheric current systems which take place at the beginning of a substorm. 相似文献
7.
We have examined the polarizations of local night impulsive (Pi2-type) hydromagnetic waves measured on the ground during a field campaign using three magnetometer stations spaced in latitude near L ～ 1.9. We find, contrary to our results at these latitudes for more continuous waves on the dayside, that the sense of rotation and phases of the waves do not change over the array for a given event. We also find, statistically, that the ellipse orientations in the horizontal plane change from the first quadrant (Northeast/Southwest direction) for pre-local midnight events, to the second quadrant (Northwest/Southeast direction) for post-local midnight events. The wave ellipticities are found to be left-handed, independent of local time. These latter two results cannot be reconciled quantitatively in terms of hydromagnetic wave resonance theory for low latitude Pi2 events, where the plasmapause acts like a resonance region for one of the high latitude Pi2 source frequencies. The results are qualitatively in agreement with expectations from the substorm electrojet current wedge concept. 相似文献
8.
We report the results of a case study of two Pi 2 pulsations observed near the eastward electrojet by the Scandinavian Magnetometer Array. The power of the two Pi 2 pulsations, calculated using a standard Fast Fourier Transform method, peaks near the centre of the eastward electrojet. For both events there is a strong latitudinal gradient in the power poleward of the equatorward border of the electrojet. The sense of polarisation is predominantly clockwise at the northern stations and anticlockwise at the southern stations although the reversal from clockwise to anticlockwise does not occur at a constant latitude. For the first event the polarisation reversal occurs at higher latitudes in the western half of the array; for the second the polarisation reversal occurs at higher latitudes at the edges of the array. The polarisation reversal does not appear to be related to the location of the eastward electrojet. Equivalent current vectors of the Pi 2 pulsations, obtained by rotating the band pass filtered data through 90°, exhibit clear vortex structures in both events. The vortices change sense of direction at half the period of the Pi 2 pulsation. A simple model for the ionospheric electric field in accord with the field line resonance theory reconstructs the basic features of the observed Pi 2 equivalent current system. We thus conclude that Pi 2 signatures in the region of the eastward electrojet and far away from the auroral break-up region are governed by the field line resonance mechanism. 相似文献
9.
This paper expands the earlier results of Rostoker and Samson (1981), who noted that there are two latitudinal areas of Pi 2 localization near the high latitude, substorm enhanced electrojets. The detailed study presented here outlines the morphology of the polarizations of the Pi 2's in and near the westward travelling surge. There are two latitudinal areas of Pi 2 localization. A poleward Pi 2 predominates within the surge and to the East, whereas an equatorward Pi 2 predominates equatorward and West of the surge. These Pi 2 localizations appear to correlate with the substorm enhanced westward and eastward electrojets respectively. However, the maximum in the Pi 2 power does not always coincide with the center of the electrojet. The poleward Pi 2 has largest amplitudes to the East of the head of the westward travelling surge. This Pi 2 shows a latitudinal polarization reversal from clockwise on the equatorside (viewed down on H-D plane) to counterclockwise on the poleside of a latitudinal demarcation line, which occurs just poleward of the initial breakup. This demarcation line is usually equatorward of the most poleward expansion of the surge. To the West of the surge front, where the equatorward Pi 2 predominates, there is again a latitudinal polarization reversal but in this case the polarization is counterclockwise equatorward and clockwise poleward of the demarcation line. This demarcation is equatorward of that for the poleward Pi 2, and appears to lie at the latitude of the initial breakup. Consequently, the westward travelling surge appears to mark the longitudinal transition from equatorward to poleward Pi 2. The elliptical polarization of the Pi 2's is most likely caused by azimuthai (longitudinal) expansion of the field-aligned currents in the surge, in association with reflection of the field-aligned current pulses from northern and southern high latitude ionospheres. 相似文献
10.
K. I. Hopcraft 《Planetary and Space Science》1986,34(12):1259-1261
Pulsation Irregular Type 2 (Pi2) oscillations are transients in the Earth's geomagnetic field of typically 100s, duration and precursors of geomagnetic substorms. Though the periods of the oscillations are consistent with magnetic field line resonance in the Earth's dipole field, the polarization characteristics are not. A new theory for Pi2 oscillations based upon the resonant interaction of waves originating from the two principle magnetic field structures of the Earth's magnetosphere, that is, a resonance between standing waves in the Earth's dipole field and normal mode oscillations of the geomagnetic tail is forwarded. The effect of this interaction yields a variation of polarization in longitude consistent with that observed. 相似文献
11.
Using magnetic data from the North American IMS network at high latitudes, Pi 3 pulsations are analysed for a period of continuously-disturbed days. The data were obtained from 13 stations in the Alaska and Fort Churchill meridional chains and in the east-west chain along the auroral zone. In the past, Pi 3 pulsations associated with substorms have been classified into two sub-categories, Pi p and Ps 6. However, we find that Pi 3's which have longer periods than Pi p and which are different from Ps 6 are more commonly observed than these two special types. Power spectra, coherence and phase differences are compared among the stations. Results show that noticeable differences for latitudinal dependence of period and amplitude exist among midnight, morning and late-evening Pi 3 pulsations. Results for Pi 3 occurring near midnight indicate that the periods at which the power spectral density is a maximum are longest, and the amplitude largest, near the center of the westward auroral electrojet. On the other hand, for Pi 3 pulsations occurring in the morning, the periods at which the power spectral density is a maximum are longest, and the amplitude largest, near the poleward edge of the westward electrojet. Furthermore, for Pi 3 pulsations occurring in the late evening, their periods are longer and their amplitudes larger near both the Harang discontinuity and the poleward edge of the westward electrojet than near its center. Correlations between pairs of adjoining stations are better in the polar cap than at auroral latitudes. It is also found from hodograms that the sense of polarization often varies from one station to another for the same event, and that the time duration in which the same rotational sense is maintained is shorter near midnight than in the morning and late evening. It is suggested that the source regions of the morning and late-evening Pi 3's lie on the electrojet boundaries; that is at the Harang discontinuity (in the evening) and at the poleward edge of the westward electrojet (in the morning and evening). The generation of midnight Pi 3 pulsations, centered at a location within the westward auroral electrojet appears to be associated directly with the generation of that electrojet. 相似文献
12.
《Planetary and Space Science》1999,47(10-11):1371-1376
Implantation of reactive ions into targets of planetary interest is a relevant subject to be studied in the laboratory. It could in fact produce new molecular species that are not native to those surfaces. Presented here are new laboratory results obtained by nitrogen implantation (15–30 keV N+) on frozen mixtures of H2O:CH4 (2:1). These species have been chosen in view of their possible presence on the surface of Jovian and Saturnian satellites and rings. In fact these surfaces are exposed to intense irradiation by magnetospheric and/or solar energetic particles. The laboratory investigation utilizes IR spectroscopy. The main objectives of the present study are to identify newly produced species and to verify if these (or at least if the profile of their IR bands) are different from those produced by unreactive ions impinging on targets in which nitrogen is already present, occurring in the form of frozen NH3 (Strazzulla and Palumbo, 1998) or N2 (Palumbo et al., 1999). I find that CN-bearing group is in fact formed and its IR feature has a profile (peak position and band profile) that differs from that obtained after irradiation or frozen gases containing nitrogen. The relevance the results might have to elucidate the origin of some species observed on Jovian icy moons or predicted to be observed on Saturnian satellites are outlined. 相似文献
13.
P. R. Sutcliffe 《Planetary and Space Science》1975,23(12):1581-1587
The power spectra of Pi2 geomagnetic pulsations are obtained by applying the maximum entropy method (MEM) of spectrum analysis. The results indicate that Pi2's can be divided into 3 categories according to spectral characteristics: (i) those in which all the peaks belong to a harmonic series, (ii) those in which some peaks belong to a harmonic series while the remainder are harmonically unrelated, and (iii) those which exhibit no evidence of harmonic structure. The fundamental periods of the harmonic series lie in the range 50–150 sec and decrease with increasing Kp index. The findings on spectral structure enable us to resolve some of the existing differences of opinion on the spectral structure of Pi2's. It is suggested that the harmonically related peaks in Pi2 spectra originate as surface waves on the plasmapause. 相似文献
14.
Thaddeus P Gottlieb CA Hjalmarson A Johansson LE Irvine WM Friberg P Linke RA 《The Astrophysical journal》1985,294(1):L49-L53
The C3H radical, a linear carbon chain with a 2 pi electronic ground state, has been identified in the millimeter-wave spectra of two astronomical sources, IRC +10216 and TMC-1, and conclusively confirmed (accompanying Letter) in a laboratory glow discharge. In IRC +10216 four rotational transitions have been observed, three in the lower fine-structure ladder (2 pi 1/2) and one in the upper (2 pi 3/2), each a resolved or partially resolved lambda-doublet. In TMC-1, both lambda components of the lowest lying 3/2 --> 1/2 transition of the 2 pi 1/2 ladder have been observed, each with well-resolved hfs. In IRC +10216 the excitation of C3H is similar to that of SiCC: the rotational temperature Trot within the 2 pi 1/2 ladder is low (8.5 K), owing to rapid radiative decay, while Trot across the ladders is high (approximately 52 K) because interconnecting far-IR radiative transitions are only weakly permitted. The column density of C3H in IRC +10216 averaged over the estimated source diameter of 84" is 2.8 x 10(13) cm-2, an order of magnitude less than that of C2H and C4H. A determination of the spectroscopic constraints of C3H that permitted the entire radio spectrum of this molecule to be calculated to high accuracy has been derived from analysis of the combined astronomical and laboratory data presented in the accompanying Letter. 相似文献
15.
Several substorms were observed at Explorer 45 in November and December 1971, and January and February 1972, while the satellite was in the evening quadrant near L = 5. These same substorms were identified in ground level magnetograms from auroral zone and low latitude stations. The satellite vector magnetic field records and rapid run ground magnetograms were examined for evidence of simultaneous occurrence of Pi2 magnetic pulsations. Pulsations which began abruptly were observed at the satellite during 7 of the 13 substorms studied and the pulsations occurred near the estimated time of substorm onset. These 7 pulsation events were also observed on the ground and 6 were identified in station comments as Pi2. All of the events observed were principally compressional waves, that is, pulsations in field magnitude. There were also transverse components elliptically polarized counter-clockwise looking along the field line. Periods observed ranged from 40 to 200 sec with 80 sec often the dominant period. 相似文献
16.
P.R. Sutcliffe 《Planetary and Space Science》1974,22(11):1461-1470
Controversy exists over the spectral character of the class of magnetic pulsations designated Pi2. A novel method of spectral analysis, known as the maximum entropy method, is used to obtain power spectra of Pi2 pulsations with substantially improved resolution. Of the various theories presented for generating Pi2's, only that of Doobov and Mainstone (1973b) is in accord with our results. 相似文献
17.
Measurements of the properties of Pi 2 pulsations along a magnetic meridian at high latitudes during a number of substorms have been analyzed for their relationship to the auroral electrojet. It is found that the maximum Pi 2 pulsation amplitudes are closely associated with the instantaneous position of the electrojet. That is, the average pulsation amplitude in the Pi 2 band as well as the amplitudes of pulsations at specific frequencies in the band have maximum amplitudes at latitudes close to the instantaneous electrojet location. Stations equatorward of the electrojet tend to observe a classical Pi 2 waveform concurrent with the onset of the substorm electrojet. Stations near the electrojet observe a broad spectrum of pulsations indicating a multiplicity of sources. Stations poleward of the initial electrojet position see little pulsation activity until the electrojet moves overhead. The appearance of large amplitude Pi 2 pulsations at a station which was poleward of the electrojet at the onset of a substorm appears to be coincident with the arrival of the poleward border of the electrojet. 相似文献
18.
Magnetic pulsation Pi2 and substorm onset 总被引：1，自引：0，他引：1
Coincidence between the onset of sudden brightening of the auroral arc in the auroral oval and the onset of Pi2 magnetic pulsation in low latitudes is examined based on the auroral data obtained at a chain of stations in Alaska and the Pi2 data obtained at the low-latitude station Onagawa. The result shows that the low-latitude Pi2 occurs almost simultaneously with the sudden brightening of the auroral arc, i.e. the onset of an auroral substorm (T = 0). It is concluded that the onset of substorms can be identified quite well with the onset of the low-latitude Pi2. 相似文献
19.
20.
J. C. Samson 《Planetary and Space Science》1982,30(12):1239-1247
A review of recent experimental results from studies of high latitude Pi 2 pulsations indicates that these pulsations are fundamentally related to the initiation of the auroral breakup and substorm. At high latitudes, the Pi 2's show their peak intensities in the region where the breakup begins and appear to remain in this region after the breakup has spread poleward. In addition, the Pi 2's occur simultaneously with, or before all other ionospheric phenomena associated with the breakup. The field aligned and ionospheric currents associated with the Pi 2 resemble those of a typical substorm, but the ionospheric currents are phase shifted compared to the field aligned current. The periodic oscillations of the Pi 2's are probably caused by a reflection of the initial field aligned current pulse from the auroral ionosphere. This pulse is trapped on dipolar field lines leading to multiple reflections from North and South auroral ionospheres. 相似文献