摘要:

Langmuir wave packets with short scale lengths l ≲ 100λehave been observed in Jupiter's foreshock. We assess whether the observations are consistent with the relatively new nucleation mechanism for nonlinear collapse of Langmuir waves. Theoretical constraints on the electric fields and scale sizes of collapsing wave packets are summarized, extended and placed in a form suitable for easy comparison with Voyager and Ulysses data. The published data are reviewed and possible instrumental underestimation of fields discussed. New upper limits for the fields of the published wave packets are estimated. Our results are: (1) Wave packets formed at the nucleation scale from the observed large‐scale fields cannot collapse because they are disrupted before collapse occurs. (2) The published wave packets are quantitatively inconsistent with strong turbulence collapse. (3) Strict constraints exist for more intense wave packets to be able to collapse:E≳ 1 – 8 mV m−1for scales l ≲ 1000λe. Means for testing these conclusions using Voyager and Ulysses data

ISSN:0094-8276    

DOI:10.1029/92GL01171

年代:1992

数据来源: WILEY

摘要:

Electron conics can be generated by fluctuations at roughly one Hz in a parallel electric field accelerating auroral electrons at altitudes of several thousand kilometers. The results from our simulations including such time‐varying electric fields are in good agreement with observed electron distributions. The simulation parameters are consistent with the ion beams and broadband waves associated with electron conics. Our calculations are used to predict for example oscillations in the low altitude electron fluxes. These results can be used to compare different possible mechanisms for the generation of electron conic

ISSN:0094-8276    

DOI:10.1029/92GL01022

年代:1992

数据来源: WILEY

摘要:

Simulations and analytic calculations of the steady‐state structure of the dissipation region during collisionless reconnection are presented. Ions are treated as particles and electrons as a dissipative fluid. The mechanism for electron/ion momentum coupling during collisionless reconnection is elucidated. A limiting reconnection rate results as the ions “blowout” the magnetic field in the dissipation region. The implications for understanding substorm dynamics are disc

ISSN:0094-8276    

DOI:10.1029/92GL01034

年代:1992

数据来源: WILEY

摘要:

An examination of IMP 8 and ISEE 3 magnetotail data during the 1983 Geotail Mission yielded one plasmoid event which was observed by both satellites and two other possible cases. These are the first multi‐satellite observations of plasmoids. These observations provide a unique opportunity to examine how plasmoid characteristics change as plasmoids propagate downtail and they show that plasmoids are very stable structure

ISSN:0094-8276    

DOI:10.1029/92GL00779

年代:1992

数据来源: WILEY

摘要:

Experimental data and a simulation study of the CRRES G‐9 ionospheric barium release are presented. Comparison of optical images of the release at times t ≈ 0 and 21 sec indicate that the cloud ‘skidded’ ∼ 9 km. The simulation study is based upon a 2D electrostatic code which incorporates time‐dependent coupling to the background plasma. We find that the densest portion of the barium ion cloud ‘skids’ ∼ 15 km within the first 3 sec following the release, consistent with analyses of

ISSN:0094-8276    

DOI:10.1029/92GL01109

年代:1992

数据来源: WILEY

摘要:

The yearly intensity variation of the day‐to‐day variability of the equatorial ionization anomaly (EIA) has been investigated. It is revealed that this yearly intensity variation is weakly anticorrelated with the solar activity and geomagnetic aa indices but obviously modulated by the QBO (Quasi‐Biennial Oscillation): in the east phase of the QBO the day‐to‐day variability of the EIA increases; in the west phase of the QBO the day‐to‐day variability of the EIA decreases. These effects seem to imply that it is not the solar bursts and/or geomagnetic storms but other disturbances to which the day‐to‐day variability of the EIA is to be ascribed. A possible explanation for this pheno

ISSN:0094-8276    

DOI:10.1029/91GL01564

年代:1992

数据来源: WILEY

摘要:

Doppler line profile measurements of the OI λ557.7 nm “green line” emission, made by the Fabry‐Perot interferometer on Dynamics Explorer 2, have provided altitude profiles of the meridional component of the lower‐thermospheric neutral wind. The wind inversion technique of Nardi [1991] has been used to extract the neutral wind profiles from the line‐of‐sight measurements. Individual λ557.7 nm Doppler line profiles and inverted volume‐emission‐rate and neutral‐wind profiles are presented. Neutral wind measurements from the ∼120 km altitude level, obtained on multiple orbital passes over the summer hemisphere polar region, have been merged to produce a synthesized averaged “vector” wind field in geomagnetic coordinates. The wind pattern exhibits a region of anticyclonic vorticity in the daytime sector of the magnetic polar cap. Averaged winds of ∼300 m/sec in the equatorial direction are observed in the early morning sector. The satellite winds are in reasonable agreement with the predictions of the NCAR and UCL thermosphere general circulation models, with significant regional discrepancies evident in b

ISSN:0094-8276    

DOI:10.1029/92GL01023

年代:1992

数据来源: WILEY

摘要:

The summer polar mesosphere was observed with the Sondrestrom 1.29‐GHz radar with a new high‐resolution data acquisition mode. On one occasion, a spatially narrow enhancement in the backscattered power was seen near an altitude of 88 km. We discuss possible explanations and propose that this layer may be the first example of polar mesosphere summer echoes (PMSE) detected above 1 GHz. Specifically, we suggest that these echoes are enhanced Thomson scatter from a layer of charged aerosols, and we speculate upon the size and charge st

ISSN:0094-8276    

DOI:10.1029/92GL01155

年代:1992

数据来源: WILEY

摘要:

The wind and constituent measurements from the polar aircraft data are used to compute the flux spectra. Although there is variation from flight to flight, the flux spectra generally fit a −2 to −1.5 power law as expected theoretically. This result suggests that tracer fluxes from small scale features do not substantially contribute to the overall tracer budget relative to the fluxes from the larger sca

ISSN:0094-8276    

DOI:10.1029/92GL01039

年代:1992

数据来源: WILEY

摘要:

Forty‐three vertical profiles of ozone and temperature were measured at McMurdo Station, Antarctica, from 23 August to 1 November 1991. The data showed severe ozone depletion, during the springtime, for the third consecutive year. The lowest total column ozone, 146 DU on 10 October, was equal to the minimum measured in 1990, while the 18 ± 1 km ozone mixing ratio on this day was 0.1 ppmv, a factor of 2 below the previous minimum observed at this altitude. Most of the ozone depletion was once again confined to the 12–20 km layer, where an 83% reduction (105 DU to 18 DU) was observed, although there were also signs of depletion occurring in the 24–30 km region and below 12 km. Intrusions of ozone‐rich air above 20 km caused substantial increases in total ozone during two periods when McMurdo was near or within the polar vor

ISSN:0094-8276    

DOI:10.1029/92GL01017

年代:1992

数据来源: WILEY