摘要:

Whistler precursors are discrete emissions which are occasionally seen just before two‐hop whistlers. Most theories of precursors assume they are triggered emissions and focus on creating a triggering signal with the proper time delay from the causative sferic. Whistler precursors have now been seen on a signal from the Siple VLF transmitter. Phase analysis shows that these precursors are caused by a rapid increase in growth activity, and not by a triggering signa

ISSN:0148-0227    

DOI:10.1029/JA095iA01p00225

年代:1990

数据来源: WILEY

摘要:

Discrete VLF wave emissions in association with auroral light intensity fluctuations have been recorded at L=4 during simultaneous operation of a broadband VLF receiver and a low light level TV system. The correlated wave‐particle interaction events are interpreted as being typical examples of the electron cyclotron resonance process responsible for the precipitation of energetic electrons in the vicinity of the plasmapause. A range of delay times between the correlated VLF wave and the optical signals, coupled with the frequency versus time characteristics of the VLF wave emissions, is consistent with the electron cyclotron source region being randomly located within 8000 km of the equatorial plane. The events are shown to be triggered by ducted whistler mode waves that originate from the opposite hemisphere to that of the station at which the observations are made. Events characterized by VLF waves of rising tone are presumed to occur in a region of enhanced plasma density commonly observed within the plasma trough. It is proposed that this region is responsible for ducting the VLF waves from the source to groun

ISSN:0148-0227    

DOI:10.1029/JA095iA01p00233

年代:1990

数据来源: WILEY

摘要:

Characteristics of eastward drifting forms, previously described in the literature as black aurorae, have been identified in low‐light level TV camera data. The TV field of view was within the field of view of STARE and that of an all‐sky camera. On the basis of these observations we propose that these euroral forms are a manifestation of folds or waves on the borders of auroral bands propagating along the dark regions between neighboring auroral bands. Conditions under which the folds or waves occur are compatible with their formation by the Kelvin‐Helmholtz electrostatic instab

ISSN:0148-0227    

DOI:10.1029/JA095iA01p00241

年代:1990

数据来源: WILEY

摘要:

Total columnal electron content in the ionosphere over the magnetic equator during the postsunset hours is found to be greatly reduced on the nights with strong equatorial spread F conditions, as compared to that on nonspread F nights. The association of spread F and reduction of electron content over the magnetic equator is suggested to be due to the additional fountain generated on the nights when electric field continues eastward for a couple of hours even after sunset.

ISSN:0148-0227    

DOI:10.1029/JA095iA01p00247

年代:1990

数据来源: WILEY

摘要:

We develop the theory describing electric currents in magnetized plasma for the case of static equilibrium with isotropic pressure. The current density is determined by pressure balance and charge conservation. We show that the current density can be expressed as the sum of the current density determined by plasma pressure gradients,Jp=c▽F× ▽P, and the force‐free current density,Jf=gB, where F = ∫ds/Bis the flux tube volume per unit flux measured from a surface at which the normal component ofJpvanishes,Pis the scalar pressure, andgis a field line constant. The expression explicitly satisfies charge conservation, and its perpendicular component is the usual perpendicular current density. In the absence of force‐free currents,Jis a curl; in this case it is possible to introduce a magnetic scalar potential, ψ, that satisfies the equation ▽²ψ = −4π▽ ·P▽F; the magnetic field can then be deter

ISSN:0148-0227    

DOI:10.1029/JA095iA01p00251

年代:1990

数据来源: WILEY

ISSN:0148-0227    

DOI:10.1029/JA095iA01p00259

年代:1990

数据来源: WILEY

ISSN:0148-0227    

DOI:10.1029/JA095iA01p00261

年代:1990

数据来源: WILEY