scholarly journals Observations of dipolarization at geosynchronous orbits and its response in the polar cap convection during extreme southward interplanetary magnetic field conditions

2007 ◽  
Vol 112 (A10) ◽  
pp. n/a-n/a
Author(s):  
P. T. Jayachandran ◽  
J. W. MacDougall ◽  
A. M. Hamza ◽  
M. G. Henderson
Keyword(s):  
Magnetic Field ◽  
Interplanetary Magnetic Field ◽  
Field Conditions ◽  
Polar Cap ◽  
Geosynchronous Orbits

scholarly journals Daily variation at Concordia station (Antarctica) and its dependence on IMF conditions

2007 ◽  
Vol 25 (9) ◽  
pp. 2045-2051 ◽  
Author(s):  
L. Cafarella ◽  
D. Di Mauro ◽  
S. Lepidi ◽  
A. Meloni ◽  
M. Pietrolungo ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Diurnal Variation ◽  
Interplanetary Magnetic Field ◽  
Daily Variation ◽  
Field Conditions ◽  
Time Shift ◽  
Polar Cap ◽  
Geomagnetic Pole ◽  
Short Test ◽  
Current Systems

Abstract. After some short test surveys, during the 2004–2005 summer expedition in Antarctica, a geomagnetic French-Italian observatory was installed on the plateau (geographic coordinates: 75.1° S, 123.4° E; corrected geomagnetic coordinates: 88.9° S, 54.3° E; UT=LT−8) very close to the geomagnetic pole. In this paper we present some peculiarities of the daily variation as observed at this polar cap observatory during the years 2005 and 2006, taking into account the different Loyd seasons and different interplanetary magnetic field conditions. Some interesting results emerge from the analysis, confirming the dependence of the daily variation (and of the associated polar current systems) on the IMF Bz and By components. In particular the analysis showed that different Bz conditions correspond to different contribution to daily variation of ionospheric and field aligned currents, while particular By conditions lead to a time shift of the diurnal variation, indicating an asymmetry with respect to the noon meridian.

scholarly journals Propagation of low frequency geomagnetic field fluctuations in Antarctica: comparison between two polar cap stations

2007 ◽  
Vol 25 (11) ◽  
pp. 2405-2412 ◽  
Author(s):  
L. Santarelli ◽  
S. Lepidi ◽  
L. Cafarella
Keyword(s):  
Magnetic Field ◽  
Interplanetary Magnetic Field ◽  
Phase Difference ◽  
Low Frequency ◽  
Propagation Direction ◽  
Field Conditions ◽  
Polar Cap ◽  
Night Time ◽  
Substorm Activity ◽  
A Minor

Abstract. We conduct a statistical analysis of the coherence and phase difference of low frequency geomagnetic fluctuations between two Antarctic stations, Mario Zucchelli Station (geographic coordinates: 74.7° S, 164.1° E; corrected geomagnetic coordinates: 80.0° S, 307.7° E) and Scott Base (geographic coordinates: 77.8° S 166.8° E; corrected geomagnetic coordinates: 80.0° S 326.5° E), both located in the polar cap. Due to the relative position of the stations, whose displacement is essentially along a geomagnetic parallel, the phase difference analysis allows to determine the direction of azimuthal propagation of geomagnetic fluctuations. The results show that coherent fluctuations are essentially detectable around local geomagnetic midnight and, in a minor extent, around noon; moreover, the phase difference reverses in the night time hours, indicating a propagation direction away from midnight, and also around local geomagnetic noon, indicating a propagation direction away from the subsolar point. The nigh time phase reversal is more clear for southward interplanetary magnetic field conditions, suggesting a relation with substorm activity. The introduction, in this analysis, of the Interplanetary Magnetic Field conditions, gave interesting results, indicating a relation with substorm activity during nighttime hours. We also conducted a study of three individual pulsation events in order to find a correspondence with the statistical behaviour. In particular, a peculiar event, characterized by quiet magnetospheric and northward interplanetary magnetic field conditions, shows a clear example of waves propagating away from the local geomagnetic noon; two more events, occurring during southward interplanetary magnetic field conditions, in one case even during a moderate storm, show waves propagating away from the local geomagnetic midnight.

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 The Earth's passage of the April 11, 1997 coronal ejecta: geomagnetic field fluctuations at high and low latitude during northward interplanetary magnetic field conditions

1999 ◽  
Vol 17 (10) ◽  
pp. 1245-1250 ◽  
Author(s):  
S. Lepidi ◽  
P. Francia ◽  
U. Villante ◽  
A. Meloni ◽  
A. J. Lazarus ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Interplanetary Magnetic Field ◽  
Geomagnetic Field ◽  
Field Conditions ◽  
Mhd Waves ◽  
Low Latitude ◽  
Terra Nova Bay ◽  
Field Fluctuations ◽  
Terra Nova

Abstract. An analysis of the low frequency geomagnetic field fluctuations at an Antarctic (Terra Nova Bay) and a low latitude (L'Aquila, Italy) station during the Earth's passage of a coronal ejecta on April 11, 1997 shows that major solar wind pressure variations were followed at both stations by a high fluctuation level. During northward interplanetary magnetic field conditions and when Terra Nova Bay is close to the local geomagnetic noon, coherent fluctuations, at the same frequency (3.6 mHz) and with polarization characteristics indicating an antisunward propagation, were observed simultaneously at the two stations. An analysis of simultaneous measurements from geosynchronous satellites shows evidence for pulsations at approximately the same frequencies also in the magnetospheric field. The observed waves might then be interpreted as oscillation modes, triggered by an external stimulation, extending to a major portion of the Earth's magnetosphere. Key words. Magnetospheric physics (MHD waves and instabilities; solar wind-magnetosphere interactions)

Sign in / Sign up

Export Citation Format

Share Document