Field-aligned particle currents near an auroral arc

A Nike-Tomahawk rocket equipped to measure electric and magnetic fields and charged particles from a few ev to several hundred kev energy was flown into an auroral band from Fort Churchill on April 11, 1970. The particle detectors were oriented so as to measure net field-aligned currents. Electrons from a few to several kev were responsible for the auroral luminosity and represented a positive current away from the atmosphere of the order of 5×10−7 amp m−2. Changes in the fluxes of these particles are observed to be the cause of luminosity variations. Enhancements in the transverse electric field magnitude are correlated with auroral motions and increases in the over-all luminosity. The E×B drift imposed on the primary beam can account for auroral motions observed. North of the auroral luminosity, an intense current sheet was measured by the particle detectors. The precipitating electrons responsible for the current sheet had an energy of the order of a few hundred ev and resulted in a field-aligned current about an order of magnitude greater than that produced by the more energetic electrons responsible for the luminosity. The current sheet separated the region of hard spectra magnetically tied to the aurora from that characterized by soft spectra north of the luminosity. The spectrum of particles north of the aurora was very soft, having a shape and intensity similar to that consistently seen in the tail of the magnetosphere by the Vela spacecraft. The implication of this is that perhaps the northern edge of the luminosity is a line of demarcation beyond which field lines commence to thread the plasma sheet. When intense field-aligned currents were observed, the direction of the electric field in the ionosphere pointed westward or southwestward. Outside of the region of luminosity and when the substorm was recovering, the electric field switched to an eastward direction as the magnitude of the field-aligned currents decreased. This correlation appears to be a spatial effect, although it could be interpreted temporally as a characteristic of magnetosphere tail fields during the substorm recovery. A correlation of particle fluxes measured by the rocket detectors and those seen simultaneously at 6.6 RE by the ATS 5 spacecraft is discussed.

[1]  N. Maynard.  Measurements of Ionospheric Currents. , 1966 .

[2]  On the Theory of Magnetic Storms and Aurorae , 1958 .

[3]  A. Dessler,et al.  Field‐aligned currents in the magnetosphere , 1967 .

[4]  R. E. Sweeney,et al.  Asymmetric ring current at twilight local time , 1971 .

[5]  J. A. V. Allen,et al.  Large diurnal variations of geomagnetically trapped and of precipitated electrons observed at low altitudes , 1964 .

[6]  L. J. Cahill,et al.  Magnetosphere inflation during four magnetic storms in 1965 , 1970 .

[7]  N. Ness,et al.  Configuration of the geomagnetic tail during substorms , 1970 .

[8]  C. Mcilwain.  Direct Measurement of Particles Producing Visible Auroras , 1960 .

[9]  H. B. Silsbee,et al.  Geomagnetic bays, their frequency and current‐systems , 1942 .

[10]  L. Frank.  Direct detection of asymmetric increases of extraterrestrial ‘ring current’ Proton intensities in the outer radiation zone , 1970 .

[11]  W. E. Potter.  INVESTIGATION OF AURORAL PHENOMENA BY SOUNDING ROCKET , 1969 .

[12]  J. Cain,et al.  OGO-2 magnetic field observations during the magnetic storm of March 13-15, 1966. , 1968 .

[13]  G. Rostoker,et al.  Magnetic field perturbations in the magnetotail associated with polar magnetic substorms , 1970 .

[14]  E. W. Hones,et al.  Energy spectra and angular distributions of particles in the plasma sheet and their comparison with rocket measurements over the auroral zone , 1971 .

[15]  C. Meng,et al.  A study of polar magnetic substorms: 2. Three‐dimensional current system , 1969 .

[16]  D. C. Rose,et al.  DIRECT MEASUREMENT OF CHARGED PARTICLES ASSOCIATED WITH AURORAL ZONE RADIO ABSORPTION , 1961 .

[17]  D. L. Carpenter.  Whistler evidence of the dynamic behavior of the duskside bulge in the plasmasphere , 1970 .

[18]  W. E. Potter.  Rocket measurements of auroral electric and magnetic fields , 1970 .

[19]  R. Hoffman.  Low‐energy electron precipitation at high latitudes , 1969 .

[20]  L. R. Davis,et al.  ROCKET AURORAL INVESTIGATIONS , 1961 .

[21]  The mutual effect of precipitated auroral electrons and the auroral electrojet , 1968 .

[22]  A. J. Zmuda,et al.  Field‐aligned current at 1100 km in the auroral region measured by satellite , 1970 .

[23]  M. Walt,et al.  Rocket‐borne measurements of particle fluxes and auroral light , 1966 .

[24]  R. Boström.  A model of the auroral electrojets , 1964 .

[25]  L. Frank,et al.  Observations of charged particle precipitation into the auroral zone , 1971 .

[26]  V. Vasyliūnas,et al.  A survey of low-energy electrons in the evening sector of the magnetosphere with OGO 1 and OGO 3. , 1968 .

[27]  P. Cloutier,et al.  Detection of geomagnetically aligned currents associated with an auroral arc , 1970 .

[28]  J. H. Martin,et al.  Dayside Magnetic Disturbances at 1100 Kilometers in the Auroral Oval , 1967 .

[29]  R. Albert.  ENERGY AND FLUX VARIATIONS OF NEARLY MONOENERGETIC AURORAL ELECTRONS. , 1967 .

[30]  D. Evans.  Rocket Observations of Low Energy Auroral Electrons , 1967 .

[31]  J. Burch.  Low‐energy electron fluxes at latitudes above the auroral zone , 1968 .

[32]  D. Evans.  The observations of a near monoenergetic flux of auroral electrons , 1968 .

[33]  U. Fahleson,et al.  Parallel and perpendicular electric fields in an aurora , 1970 .

[34]  L. J. Cahill,et al.  INFLATION OF THE INNER MAGNETOSPHERE DURING A MAGNETIC STORM , 1966 .

[35]  S.-I. Akasofu,et al.  On the asymmetric development of magnetic storm fields in low and middle latitudes , 1964 .

[36]  L. Westerlund.  The auroral electron energy spectrum extended to 45 ev. , 1969 .

[37]  W. Axford.  The Interaction Between the Solar Wind and the Magnetosphere , 1967 .

[38]  B. A. Whalen,et al.  ROCKET OBSERVATIONS OF ELECTRON PITCH-ANGLE DISTRIBUTIONS DURING AURORAL SUBSTORMS. , 1967 .

[39]  L. J. Cahill,et al.  Detection of an electrical current in the ionosphere above Greenland , 1959 .

[40]  N. Maynard.  Measurements of ionospheric currents off the coast of Peru , 1967 .