12th September

Solar wind was at nominal levels during the first half of the period
with wind speed near 360 km/s and total field around 5 nT. At 11/2258
UTC an interplanetary shock was observed. IMF Bt jumped from 5
nT to 16 nT while solar wind speeds increased from approximately 370
km/s to a maximum of 528 km/s in conjunction with an increase in both
density and temperature as the 09 Sep CME impacted the geomagnetic
field. The Bz component went south initially to a maximum of -14 nT at
11/2355 UTC. By approximately 12/0400 UTC, the Bz component was mostly
north (positive) varying from +8 nT to -5 nT, while solar wind speeds
continued to decrease to near 430 km/s by the end of the period. Phi
angle was in a mostly positive (away) sector for the entirety of the

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