摘要:

A theory is presented that describes the formation of the discrete radio tones that could apply to the radio emission observed in the outer heliosphere by the Voyager spacecraft. Specifically, a broadband emission is assumed to be trapped within the heliospheric cavity. If the heliospheric outer boundary, the heliopause, has a large‐scale, monochromatic oscillation, the trapped emission will form intense, discrete tones at wave frequencies where the photon travel time is an integer ratio of the boundary oscillation period. A new set of nonlinear coupled difference equations are presented that describe the interaction of the trapped photon with the boundary, the set appearing similar to that used to model Fermi acceleration of particles via oscillatory boundaries. Results indicate that heliopause oscillation periods on the order of 1000s of seconds could generate tones at frequencies near those observed by Voyager. The tones can also drift in association with the changing cavity size or oscillation perio

ISSN:0094-8276    

DOI:10.1029/93GL01114

年代:1993

数据来源: WILEY

摘要:

Numerical simulations of the slow‐mode switch‐off shock with kinetic electrons give significantly different results from hybrid simulations with fluid electrons. With appropriate downstream boundary conditions there results a more coherent and more strongly damped trailing magnetic wave with fewer back‐streaming ions than with the hybrid model under the same conditions. Evidently, kinetic effects cause a more equal sharing of shock‐induced entropy increases between ions and electrons, which results in lower ion temperatures downstream and greater electron energy transport from downstream to u

ISSN:0094-8276    

DOI:10.1029/93GL02243

年代:1993

数据来源: WILEY

摘要:

Results from modeling ion distribution functions in a two‐dimensional reduction of the Tsyganenko [1989] magnetic field model have enabled us to calculate the full ion pressure tensor inside the model magnetotail. A thin current sheet is formed in the distant tail and the pressure tensor within this sheet has significant off‐diagonal terms. These terms resulting from quasiadiabatic ion trajectories create azimuthally asymmetric distribution functions which are capable of maintaining stress‐balance. Outside the current sheet the off‐diagonal terms disappear and moderate anisotropy builds up with P⟂/P∥∼ 0.8. Closer to the Earth rapid isotropization of the distri

ISSN:0094-8276    

DOI:10.1029/93GL01695

年代:1993

数据来源: WILEY

摘要:

We show how shift theorem yields a routine quantitative test to determine whether a structure seen by two or more spacecraft is a quasistatic convecting object, such as a boundary layer. The test indicates the frequency range over which the data is consistent with a structure which is coherent between spacecraft, planar, and time independent in its rest frame. A cluster of four non coplanar spacecraft is required to determine the velocity of the structure in the spacecraft frame. Whether or not the data is found to be consistent with quasistatic convecting object, this analysis of the data from four non coplanar spacecraft yields the convection velocity of the plasma given the dispersion relation or vice versa, as well as the wavevectors corresponding to given frequency components. The test for coherence, planarity and time independence is shown to be robust against detector and systematic inter‐spacecraft timing and positional uncertainties. Random errors will affect a finite frequency range, in principle this can be determined to restrict the frequency range over which the test can be applie

ISSN:0094-8276    

DOI:10.1029/93GL02053

年代:1993

数据来源: WILEY

摘要:

The effects of solar EUV line resonance scattering by a population of ions in gyration, bounce and drift motion in the magnetosphere are formulated and demonstrated numerically with the O+834 Å line as test example. It is shown that anisotropies of motion induced by the geomagnetic field and source perspective effects caused by 834 Å earthshine profoundly affect the morphology and magnitude of the EUV line images, thus enhancing the effects of Doppler shifts on narrow EUV lines. These effects have little impact, though, on relatively wide resonance scattering lines such as the He+304 Å li

ISSN:0094-8276    

DOI:10.1029/93GL01697

年代:1993

数据来源: WILEY

摘要:

We describe the very‐early‐time expansion processes (≈0 ‐ 3 s) of the CRRES G‐9 Ba+/Li+cloud release, as manifested by thermal‐ and photo‐ionization mechanisms, by coupling to the background ionosphere, and by differential acceleration of multi‐ion constituents. In our data analysis we present the very first “in situ” evidence of electrostatic snowplow effects in an expanding plasma cloud, with arguments that these effects are the result of ambipolar fields and that kinetic effects of ion‐neutral collisions have little influence in the G‐9 scenario. In addition to the electrostatic snowplow process, the results show mass‐dependent effects on the expansion of ion and neutral constituents in the cloud. These effects are manifested in the observation that the Li+ions “outpace” the heavier Ba+in the expansion process, and take on forerunner characteristic

ISSN:0094-8276    

DOI:10.1029/93GL01451

年代:1993

数据来源: WILEY

摘要:

Ground‐based observations of Doppler line profiles from the F‐Region O+(²P) state, made with the Fabry‐Perot interferometer (FPI) at Søndre Strømfjord, Greenland have been analyzed to provide measurements of the ion convection velocity and ion temperature. The FPI line‐of‐sight (LOS) ion drift and temperature measurements have been compared with simultaneous incoherent scatter radar (ISR) measurements; the results from the two techniques are in go

ISSN:0094-8276    

DOI:10.1029/93GL01966

年代:1993

数据来源: WILEY

摘要:

Results of a recent modeling study of gravity wave breaking in three dimensions byAndreassen et al.andFritts et al.showed wave saturation to occur via a three‐dimensional instability oriented normal to the direction of wave propagation. The instability was found to occur at horizontal scales comparable to the depth of unstable regions within the wave field and to lead to substantial vertical displacements and tilting of isentropic surfaces. Because of strong similarities between the wave and instability structures in the simulation and the structure observed in noctilucent cloud layers near the summer mesopause, we have used these model results to compute the advective effects on cloud visibility and structure for a range of viewing angles and cloud layer widths. Our results show the gravity wave breaking signature to provide a plausible explanation of the observed structures and suggest that noctilucent cloud structures may be used in turn to infer qualitative properties of gravity wave scales, energy and momentum transports, and turbulence scales near the summer mesopaus

ISSN:0094-8276    

DOI:10.1029/93GL01982

年代:1993

数据来源: WILEY

摘要:

Reaction of fast non‐thermal N(4S) atoms with O2molecules is shown to produce NO with large rotational and vibrational excitation. It is suggested that the process is responsible for the highly rotationally excited nitric oxide detected by the space shuttle experiment CIRRIS I

ISSN:0094-8276    

DOI:10.1029/93GL02486

年代:1993

数据来源: WILEY

摘要:

A one dimensional photochemical model has been used to evaluate the hypothesis that the oxidation ofH2andN2ObyO2(b¹Σg) could lead to significant production ofOHand odd‐nitrogen in the middle atmosphere. For the reaction withH2, even if all the quenchings lead to oxidation, the change in theOHcolumn is only 13%. This is still too small to resolve the discrepancy between the model and ground based measurements and furthermore could not account for the apparent change in the ground based column with time. For the reaction withN2O, it is possible to produce significant odd‐nitrogen in the lower stratosphere only if the oxidation yield is at least 5–10%. However, one then gets a surplus of odd‐nitrogen in the upper stratosphere unless one makes the additional assumption that the production ofO2(b¹Σg) fromO(¹D) quench

ISSN:0094-8276    

DOI:10.1029/93GL02471

年代:1993

数据来源: WILEY