Ionospheric convection response to a northward turning of the Interplanetary Magnetic Field on March 23, 1995 studied employing SuperDARN HF radar data

Abstract. Analysis of the diurnal and seasonal variation of polar patches, as identified in two years of HF-radar data from Halley, Antarctica during a period near sunspot maximum, shows that there is a broad maximum in occurrence centred about magnetic noon, not local noon. There are minima in occurrence near midsummer and midwinter, with maxima in occurrence between equinox and winter. There are no significant correlations between the occurrence of polar patches and the corresponding hourly averages of the solar wind and IMF parameters, except that patches usually occur when the interplanetary magnetic field has a southward component. The results can be understood in terms of UT and seasonal differences in the plasma concentration being convected from the dayside ionosphere into the polar cap. In summer and winter the electron concentrations in the polar cap are high and low, respectively, but relatively unstructured. About equinox, a tongue of enhanced ionisation is convected into the polar cap; this tongue is then structured by the effects of the interplanetary magnetic field, but these Halley data cannot be used to separate the various competing mechanisms for patch formation. The observed diurnal and seasonal variation in the occurrence of polar patches are largely consistent with predictions of Sojka et al. (1994) when their results are translated into the southern hemisphere. However, the ionospheric effects of flux transfer events are still considered essential in their formation, a feature not yet included in the Sojka et al. model.

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Two-dimensional electric field measurements in the ionospheric footprint of a flux transfer event

Annales Geophysicae ◽

10.1007/s00585-001-1584-2 ◽

2000 ◽

Vol 18 (12) ◽

pp. 1584-1598 ◽

Cited By ~ 17

Author(s):

K. A. McWilliams ◽

T. K. Yeoman ◽

S. W. H. Cowley

Keyword(s):

Magnetic Field ◽

Interplanetary Magnetic Field ◽

Flux Tube ◽

Convection Velocity ◽

Hf Radar ◽

Two Dimensional ◽

Plasma Convection ◽

Transfer Event ◽

Ionospheric Convection ◽

Flux Transfer

Abstract. Line-of-sight Doppler velocities from the SuperDARN CUTLASS HF radar pair have been combined to produce the first two-dimensional vector measurements of the convection pattern throughout the ionospheric footprint of a flux transfer event (a pulsed ionospheric flow, or PIF). Very stable and moderate interplanetary magnetic field conditions, along with a preceding prolonged period of northward interplanetary magnetic field, allow a detailed study of the spatial and the temporal evolution of the ionospheric response to magnetic reconnection. The flux tube footprint is tracked for half an hour across six hours of local time in the auroral zone, from magnetic local noon to dusk. The motion of the footprint of the newly reconnected flux tube is compared with the ionospheric convection velocity. Two primary intervals in the PIF's evolution have been determined. For the first half of its lifetime in the radar field of view the phase speed of the PIF is highly variable and the mean speed is nearly twice the ionospheric convection speed. For the final half of its lifetime the phase velocity becomes much less variable and slows down to the ionospheric convection velocity. The evolution of the flux tube in the magnetosphere has been studied using magnetic field, magnetopause and magnetosheath models. The data are consistent with an interval of azimuthally propagating magnetopause reconnection, in a manner consonant with a peeling of magnetic flux from the magnetopause, followed by an interval of anti-sunward convection of reconnected flux tubes.Key words: Magnetospheric physics (magnetosphere · ionosphere interactions; plasma convection; solar wind · magnetosphere interactions)

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Interhemispheric contrasts in the ionospheric convection response to changes in the interplanetary magnetic field and substorm activity: a case-study

Annales Geophysicae ◽

10.1007/s00585-998-0764-8 ◽

1998 ◽

Vol 16 (7) ◽

pp. 764-774 ◽

Cited By ~ 1

Author(s):

B. A. Shand ◽

T. K. Yeoman ◽

R. V. Lewis ◽

R. A. Greenwald ◽

M. R. Hairston

Keyword(s):

Magnetic Field ◽

Interplanetary Magnetic Field ◽

Radar Data ◽

Conjugate Points ◽

Convection Flow ◽

Ionospheric Convection ◽

Substorm Activity ◽

Anglo American ◽

Auroral Phenomena ◽

The Imf

Abstract. Interhemispheric contrasts in the ionospheric convection response to variations of the interplanetary magnetic field (IMF) and substorm activity are examined, for an interval observed by the Polar Anglo-American Conjugate Experiment (PACE) radar system between ~1600 and ~2100 MLT on 4 March 1992. Representations of the ionospheric convection pattern associated with different orientations and magnitudes of the IMF and nightside driven enhancements of the auroral electrojet are employed to illustrate a possible explanation for the contrast in convection flow response observed in radar data at nominally conjugate points. Ion drift measurements from the Defence Meteorological Satellite Program (DMSP) confirm these ionospheric convection flows to be representative for the prevailing IMF orientation and magnitude. The location of the fields of view of the PACE radars with respect to these patterns suggest that the radar backscatter observed in each hemisphere is critically influenced by the position of the ionospheric convection reversal boundary (CRB) within the radar field of view and the influence it has on the generation of the irregularities required as scattering targets by high-frequency coherent radar systems. The position of the CRB in each hemisphere is strongly controlled by the relative magnitudes of the IMF Bz and By components, and hence so is the interhemispheric contrast in the radar observations.Key words. Magnetospheric physics · Auroral phenomena · Magnetosphere-ionosphere interactions · Storms and substorms

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