On the efficiency of the Cowling mechanism in the auroral electrojet

By using Chatanika radar measurements of the ionospheric electric field and conductivity, an attempt is made to estimate the extent to which the Cowling mechanism is taking place in the westward auroral electrojet. We assess the effectiveness of this mechanism in terms of the ratio α = IPS/IHN, where IHN and IPS are the northward Hall and the southward Pedersen currents, respectively. Estimates of α are made for regions in which the electric field had both westward and southward components in the midnight sector during high geomagnetic activity. It is found that α varies considerably with latitude within the westward electrojet and that α decreases with increasing IHN. Assuming east-west uniformity of the associated ionospheric quantities, these variations indicate that significant portions of the charges carried by the northward Hall current (due to the westward electric field) are removed from the "excess" charge region without generating an intense polarization field. This implies that the classical Cowling mechanism is taking place only incompletely.

[1]  C. Clauer,et al.  DP 1 and DP 2 current systems for the March 22, 1979 substorms , 1985 .

[2]  J. Kan,et al.  A mechanism for the westward traveling surge during substorms , 1984 .

[3]  Y. Kamide,et al.  Variability of the Harang discontinuity as observed by the Chatanika radar and the IMS Alaska magnetometer chain , 1983 .

[4]  Wolfgang Baumjohann,et al.  Rocket and ground-based study of an auroral breakup event , 1982 .

[5]  R. Hoffman,et al.  Auroral arc electrodynamic parameters measured by AE‐C and the Chatanika Radar , 1981 .

[6]  Wolfgang Baumjohann,et al.  JOINT TWO-DIMENSIONAL OBSERVATIONS OF GROUND MAGNETIC AND IONOSPHERIC ELECTRIC FIELDS ASSOCIATED WITH AURORAL ZONE CURRENTS: CURRENT SYSTEMS ASSOCIATED WITH LOCAL AURORAL BREAK-UPS , 1981 .

[7]  R. Vondrak,et al.  Radar observations of electric fields and currents associated with auroral arcs , 1977 .

[8]  P. Banks,et al.  Chatanika observations of the latitudinal structure of electric fields and particle precipitation on November 21, 1975 , 1977 .

[9]  C. Carlson,et al.  Observation and interpretation of particle and electric field measurements inside and adjacent to an active auroral arc , 1977 .

[10]  A. Brekke,et al.  Incoherent scatter measurements of E region conductivities and currents in the auroral zone , 1974 .

[11]  C. Kennel,et al.  Polarization of the auroral electrojet , 1972 .

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

[13]  Wolfgang Baumjohann,et al.  Ionospheric and field-aligned current systems in the auroral zone: a concise review , 1982 .

[14]  S. Matthews,et al.  The diurnal and latitudinal variation of auroral zone ionospheric conductivity , 1981 .