摘要:

Tidman and Krall[1971] have studied extensively the behavior of nonlinear magnetic fields in MHD plasmas. We have closely followed their work but our emphasis is different. We demonstrate here that the nonlinear magnetic field equations can be cast in the form of Duffing's equation. A Duffing system includes chaotic behavior; hence our study provides a different perspective on magnetic field development not previously discussed.

ISSN:0094-8276    

DOI:10.1029/92GL00085

年代:1992

数据来源: WILEY

摘要:

We present in this paper numerical solutions of the nonlinear magnetic field equations that have been cast in the form of Duffing's equation. These results show features that resemble the behavior of magnetic fields observed in space. Our work suggests that some of the observed magnetic field structures could be chaotic in origin.

ISSN:0094-8276    

DOI:10.1029/92GL00635

年代:1992

数据来源: WILEY

摘要:

Recent spacecraft observations near Venus and Mars have shown that the position and shape of the planetary bow shock do not agree well with predictions of gas dynamic models in which the obstacle boundary is defined by ionopause/magnetopause pressure balance estimations. In order to simulate some aspects of this problem, we have considered plasma flow into a "heavy" ion cloud, whose maximum density is comparable to that of the inflowing protons. A simple bi‐ion fluid model is used which takes into account the electrostatic coupling between protons and (heavy) ions of exospheric origin; magnetic field effects are ignored. One‐dimensional studies show that for subsonic flows, representing the post‐shock solar wind, a critical cloud density exist at which the flow is accelerated up to the bi‐ion sound speed. Above this critical value no continuous solutions exist. The flow behaviour in three dimensions was studied in an axially‐symmetric model. For overcritical clouds the "critical density layer" appears as an "obstacle" forming an extended proton cavity. The planetopause at Mars may find an explanation within the pres

ISSN:0094-8276    

DOI:10.1029/92GL00124

年代:1992

数据来源: WILEY

摘要:

The Ulysses URAP experiment has detected Jovian radio emissions in the VLF range at distances from Jupiter in excess of 1.5 A.U. The URAP observations represent the first synoptic observations of Jupiter in the VLF band, 3 to 30 kHz. In this band lie the low‐frequency extent of the bKOM emission, the escaping continuum emission, and the Jovian type IIIs. Initial results indicate that the continuum varies in frequency with the solar wind ram pressure at Jupiter, whereas, the Jovian type IIIs appear to be controlled to some extent by the planetary rotation, often appearing when system III longitude 100° faces the spacecra

ISSN:0094-8276    

DOI:10.1029/92GL00387

年代:1992

数据来源: WILEY

摘要:

Quasi‐electrostatic ELF/VLF chorus emissions immediately above the equatiorial half‐gyrofrequency, observed to propagate with wave normal angle (Ψ) within 0.4–1.2° of the resonance cone (Ψr) [Muto et al., 1987], are shown to efficiently resonate with 0.1–10 keV electrons. These waves may thus be important in driving the relatively low energy (<10 keV) component of pulsating aurorae and the morning‐side diffuse auro

ISSN:0094-8276    

DOI:10.1029/92GL00402

年代:1992

数据来源: WILEY

摘要:

The Digisonde at Qanaq, Greenland (87°Λ) measures the ionospheric convection velocity in the central polar cap. The average local time variation of the velocity for Bznorthward under various Byconditions is presented. The nightside drifts for Bznorthward tend to be antisunward, and resemble those which occur for southward IMF, as pointed out by Heppner and Maynard (1987). However, it is difficult to reconcile the observed diurnal drift variation with the Heppner‐Maynard distorted two‐cell model. Modified forms of the Potemra et al. (1984) four cell model offer a more plausible framework in which to understand the Qanaq data. The polar cap cells are relatively small, and are displaced towards the da

ISSN:0094-8276    

DOI:10.1029/92GL00395

年代:1992

数据来源: WILEY

摘要:

Tristatic observations of photoelectron‐enhanced plasma‐lines with the EISCAT UHF incoherent scatter radar are presented. It is shown that electron temperatures can be derived from these measurements with a time resolution of the order of a minute and a statistical accuracy of 50–

ISSN:0094-8276    

DOI:10.1029/92GL00523

年代:1992

数据来源: WILEY

摘要:

Recent observations of rare cloud‐to‐stratospheric lightning discharges suggest the events are inherently “slow‐rising”, with the emitted energy reaching peak values in about 10 milliseconds. Applying a dipole radiation model, we demonstrate that the emitted radio wave energy from such slow‐rising events is strongest below about 50 Hz, and possesses a significant rolloff at higher frequencies. In the analysis, various current distributions are considered in order to determine the effect on the radio spectrum. Near 10 kHz, the emission from cloud‐to‐stratospheric lightning is significantly reduced as compared to the typical cloud‐to‐ground return stroke, with amplitudes as much as 50 dB lower. This result may explain the lack of detection of VLF signals from recently observed long‐las

ISSN:0094-8276    

DOI:10.1029/91GL02955

年代:1992

数据来源: WILEY

摘要:

The analysis of the Voyager 2 Ultraviolet Spectrometer (UVS) solar occultation data obtained at Triton is consistent with a spherically symmetric, isothermal thermosphere above 400 km atT∞. = 96 K. A detailed calculation of energy loss processes in a pure N2atmosphere, heating and cooling rates, and resultant thermal structure associated with solar UV irradiance and magnetospheric electron precipitation indicates that solar heating, with calculatedT∞= 70 K, is insufficient to account for the inferredT∞= 96 K. The magnetosphere must deposit twice as much power as the sun (λ<800 Å) to heat the thermosphere to 96 K and generate the observed N2tangential column densities above 450 km. The thermal escape of H and N atoms and the downward diffusion of N atoms to recombine below 130 km results in local ionospheric heating efficiency of 24%. An upper limit on the tropopause CO mixing ratio of 2 × 10−4is inferred in the absence of aerosol heating to balance its efficient cooling by LTE rotational lin

ISSN:0094-8276    

DOI:10.1029/92GL00651

年代:1992

数据来源: WILEY

摘要:

The inter‐annual variability of trace gases in the equatorial lower stratosphere is examined in order to explore the usefulness of comparisons between measurements from LIMS and the UARS satellite instruments. The quasi biennial oscillation (QBO) is simulated in a two dimensional model by relaxing the modelled equatorial winds towards observed values. It is shown that during the LIMS data period the QBO was in the opposite phase to that expected during the first winter of the UARS measurements. The model predicts that LIMS measurements of ozone, NO2, and HNO3may have been up to 30% less than the long‐term average in the equatorial lower stratosphere while the first few months of UARS measurements may observe abundances up to 30% more than the long‐term average. The importance of taking this variability into account and the desirability of several complete cycles of the QBO in the derivation of climatological values is

ISSN:0094-8276    

DOI:10.1029/92GL00650

年代:1992

数据来源: WILEY