scholarly journals Seasonal and interplanetary magnetic field-dependent polar cap contraction during substorm expansion phase

2010 ◽  
Vol 115 (A11) ◽  
pp. n/a-n/a ◽  
Author(s):  
K. M. Laundal ◽  
N. Østgaard ◽  
H. U. Frey ◽  
J. M. Weygand
Keyword(s):  
Magnetic Field ◽  
Interplanetary Magnetic Field ◽  
Polar Cap ◽  
Expansion Phase ◽  
Field Dependent

scholarly journals Central polar cap convection response to short duration southward Interplanetary Magnetic Field

2000 ◽  
Vol 18 (8) ◽  
pp. 887-896 ◽  
Author(s):  
P. T. Jayachandran ◽  
J. W. MacDougall
Keyword(s):  
Magnetic Field ◽  
Interplanetary Magnetic Field ◽  
Short Duration ◽  
Initial Response ◽  
Plasma Convection ◽  
Polar Cap ◽  
Ionosphere Plasma ◽  
Rapid Transition ◽  
Convection Speed ◽  
A Chain

Abstract. Central polar cap convection changes associated with southward turnings of the Interplanetary Magnetic Field (IMF) are studied using a chain of Canadian Advanced Digital Ionosondes (CADI) in the northern polar cap. A study of 32 short duration (~1 h) southward IMF transition events found a three stage response: (1) initial response to a southward transition is near simultaneous for the entire polar cap; (2) the peak of the convection speed (attributed to the maximum merging electric field) propagates poleward from the ionospheric footprint of the merging region; and (3) if the change in IMF is rapid enough, then a step in convection appears to start at the cusp and then propagates antisunward over the polar cap with the velocity of the maximum convection. On the nightside, a substorm onset is observed at about the time when the step increase in convection (associated with the rapid transition of IMF) arrives at the polar cap boundary.Key words: Ionosphere (plasma convection; polar ionosphere) - Magnetospheric physics (solar wind - magnetosphere interaction)

scholarly journals A new formulation for the ionospheric cross polar cap potential including saturation effects

2005 ◽  
Vol 23 (11) ◽  
pp. 3533-3547 ◽  
Author(s):  
A. J. Ridley
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Mach Number ◽  
Interplanetary Magnetic Field ◽  
Polar Cap ◽  
Pressure Balance ◽  
Simple Modification ◽  
Post Shock ◽  
Cross Polar Cap Potential ◽  
New Formulation

Abstract. It is known that the ionospheric cross polar cap potential (CPCP) saturates when the interplanetary magnetic field (IMF) Bz becomes very large. Few studies have offered physical explanations as to why the polar cap potential saturates. We present 13 events in which the reconnection electric field (REF) goes above 12mV/m at some time. When these events are examined as typically done in previous studies, all of them show some signs of saturation (i.e., over-prediction of the CPCP based on a linear relationship between the IMF and the CPCP). We show that by taking into account the size of the magnetosphere and the fact that the post-shock magnetic field strength is strongly dependent upon the solar wind Mach number, we can better specify the ionospheric CPCP. The CPCP (Φ) can be expressed as Φ=(10-4v2+11.7B(1-e-Ma/3)sin3(θ/2)) {rms/9 (where v is the solar wind velocity, B is the combined Y and Z components of the interplanetary magnetic field, Ma is the solar wind Mach number, θ=acos(Bz/B), and rms is the stand-off distance to the magnetopause, assuming pressure-balance between the solar wind and the magnetosphere). This is a simple modification of the original Boyle et al. (1997) formulation.

Digisonde measurements of polar cap convection for northward interplanetary magnetic field

1992 ◽  
Vol 97 (A11) ◽  
pp. 16877 ◽  
Author(s):  
Paul S. Cannon ◽  
Geoffrey Crowley ◽  
Bodo W. Reinisch ◽  
Jurgen Buchau
Keyword(s):  
Magnetic Field ◽  
Interplanetary Magnetic Field ◽  
Polar Cap

scholarly journals Diurnal and seasonal occurrence of polar patches

1996 ◽  
Vol 14 (5) ◽  
pp. 533-537 ◽  
Author(s):  
A. S. Rodger ◽  
A. C. Graham
Keyword(s):  
Magnetic Field ◽  
Seasonal Variation ◽  
Interplanetary Magnetic Field ◽  
Radar Data ◽  
Hf Radar ◽  
Polar Cap ◽  
Sunspot Maximum ◽  
Ionospheric Effects ◽  
Flux Transfer Events ◽  
Local Noon

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.

Response of the polar cap F region convection direction to changes in the interplanetary magnetic field: Digisonde measurements in northern Greenland

1991 ◽  
Vol 96 (A2) ◽  
pp. 1239-1250 ◽  
Author(s):  
Paul S. Cannon ◽  
Bodo W. Reinisch ◽  
Jurgen Buchau ◽  
Terence W. Bullett
Keyword(s):  
Magnetic Field ◽  
Interplanetary Magnetic Field ◽  
Polar Cap ◽  
F Region

scholarly journals Dayside ionospheric response to changes in IMF polarity: optical and plasma-flow observations

2000 ◽  
Vol 18 (7) ◽  
pp. 782-788 ◽  
Author(s):  
S. E. Pryse ◽  
A. M. Smith ◽  
L. Kersley
Keyword(s):  
Magnetic Field ◽  
Interplanetary Magnetic Field ◽  
Plasma Flow ◽  
Line Emission ◽  
Line Of Sight ◽  
Magnetospheric Physics ◽  
Polar Cap ◽  
Ionospheric Response ◽  
Present Case Study

Abstract. The response of the dayside ionosphere to changes in polarity of the interplanetary magnetic field was observed by two independent techniques. The signatures were seen in the 630.0 nm red-line emission, measured by a meridian scanning photometer at Ny-Ålesund on Svalbard, and also in the line-of-sight plasma velocities monitored by the Finland CUTLASS SuperDARN radar. A time difference of some 6 to 8 min occurred between the responses of the two techniques, with the flows being first to respond. In the present case study, the longer delay in the optics suggests that ion precipitation controls the auroral emission.Key words: Ionosphere (ionosphere-magnetosphere interactions) · Magnetospheric physics (magnetosphere-ionosphere interactions; polar cap phenomena)

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