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Topband: interesting low band conditions may be ahead

Subject: Topband: interesting low band conditions may be ahead
From: N7DF <>
Date: Tue, 29 Sep 2009 14:38:29 -0700 (PDT)
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This may explain greyline conditions and short term opening like we had a few 
days ago when european signals wer 20 over 9 on 160 here in NM . Sucj openings 
should become more erratic and extreme as the magnetic fields react
Read This from the Journal of Geophysical Research
Simultaneous measurements from the Polar satellite and by ground-based optical 
sensors suggest that brief variations of the poleward auroral boundary on the 
nightside correlate with changes in the interplanetary magnetic field (IMF) 
about an hour after a structure has propagated in the solar wind past the 
Earth. Short-lived Sun-aligned arcs may emerge along the open–closed magnetic 
field line boundary (OCB) and then disappear after ∼10 min. The arcs are fueled 
by energetic particles whose spectral characteristics are similar to those of 
the of boundary plasma sheet (BPS). Polar measurements confirm that these 
auroral protrusions into the polar cap occur on nearly isolated closed magnetic 
flux. Optical emissions from these arcs appear strongest at their intersection 
with the poleward boundary of the auroral oval. Detailed magnetohydrodynamic 
(MHD) simulations of dayside interactions, when the dominant IMF component BY 
changes sign, indicate that near
 the polarity reversal merging can occur between interplanetary field line 
segments within the magnetosheath [ Maynard et al., 2001b ]. Newly formed loops 
of interplanetary flux sweep past the Earth without interacting with the 
magnetosphere. Here, we consider some consequences within the distant 
magnetotail as the loops of disconnected flux propagate to XGSM ≈ −200 RE. The 
MHD simulations indicate that about an hour after intra-IMF merging events 
fingers of closed field lines protrude from the OCB into the polar cap. Like 
the observed Sun-aligned arc, these simulated auroral features grow and decay 
on scales of ∼10 min and have ionospheric footprints that are nearly surrounded 
by open magnetic flux. The simulated auroral fingers are conjugate to 
high-pressure channels in the distant plasma sheet. We suggest that the 
short-lived Sun-aligned arcs are created via an interchange process similar to 
that proposed by Kan and Burke [1985] to explain one
 class of theta auroral forms. The continuity of magnetotail currents across a 
high-pressure channel requires the development of field-aligned currents 
carried by obliquely propagating Alfvén waves. Plasma drifts associated with 
the dusk-to-dawn electric fields of the Alfvén waves are away from the Earth in 
the magnetotail and poleward in the nightside ionosphere. The correlation of 
phenomena at the nightside OCB with variations in the IMF indicate that 
processes other than substorms can influence boundary dynamics. Effects of 
self-interactions of the IMF within the dayside magnetosheath may be felt along 
the OCB as much as 1 hour later.

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