Journal cover Journal topic
Annales Geophysicae An interactive open-access journal of the European Geosciences Union
Journal topic

Journal metrics

IF value: 1.490
IF 5-year value: 1.445
IF 5-year
CiteScore value: 2.9
SNIP value: 0.789
IPP value: 1.48
SJR value: 0.74
Scimago H <br class='widget-line-break'>index value: 88
Scimago H
h5-index value: 21
Volume 19, issue 7
Ann. Geophys., 19, 707–721, 2001
© Author(s) 2001. This work is distributed under
the Creative Commons Attribution 3.0 License.
Ann. Geophys., 19, 707–721, 2001
© Author(s) 2001. This work is distributed under
the Creative Commons Attribution 3.0 License.

  31 Jul 2001

31 Jul 2001

The dayside ultraviolet aurora and convection responses to a southward turning of the interplanetary magnetic field

K. A. McWilliams1, T. K. Yeoman1, J. B. Sigwarth2, L. A. Frank2, and M. Brittnacher3 K. A. McWilliams et al.
  • 1Department of Physics and Astronomy, Leicester University, University Road, Leicester LE1 7RH, UK
  • 2The University of Iowa, Department of Physics and Astronomy, Iowa City, Iowa 52242, USA
  • 3University of Washington, Geophysics Program, Box 351650, Seattle, Washington 98195, USA

Abstract. We examine the large-scale ultraviolet aurora and convection responses to a series of flux transfer events that immediately followed a sharp and isolated southward turning of the IMF. During the interval of interest, SuperDARN was monitoring the plasma convection in the dayside northern ionosphere, while the VIS Earth Camera and the Far Ul-traviolet Imager (UVI) were monitoring the northern hemisphere’s ultraviolet aurora. Reconnection signatures were seen in the SuperDARN HF radar data in the postnoon sector following a sharp southward turning of the IMF. The presence of flux transfer events is supported by measurements of a classic dispersed ion signature in the low-altitude cusp from the DMSP spacecraft. Subsequent to the onset of reconnection, the postnoon convection and ultraviolet aurora expanded in concert, reaching 18 MLT in half an hour. The auroral oval was found to move equatorward at the convection speed in the 16–18 MLT sector, implying that it was related directly to an adiaroic magnetospheric boundary. In the present study, we have estimated the field-aligned current response to magnetic reconnection in terms of the vorticity of the ionospheric plasma convection velocity. The convection velocities were obtained using two methods: (a) direct reconstruction of the full vector velocities from bistatic measurements of the convection by the SuperDARN HF radars in a relatively small region of the auroral zone, and (b) from global-scale spherical harmonic fits to the SuperDARN velocities deduced from the map potential model. Regions of high vorticity, which were predicted to be an estimate of a component of the total field-aligned current, agree extremely well with the images of the dayside UV aurora, indicating that, in this case, the plasma vorticity is an excellent estimator of the morphology of dayside field-aligned currents (FACs). The morphology of the aurora and ionospheric electric field in the postnoon sector supports the existence of a dayside current wedge induced in response to dayside reconnection.

Key words. Magnetospheric physics (auroral phenomena; magnetosphere-ionosphere interactions; solar wind magne-tosphere interactions)

Publications Copernicus