Solar wind summary (Last 24 hours)

19 February


ACE data indicated nominal background conditions for the first half of
the period. At 19/0309 UTC, solar wind speed suddenly increased from 382
km/s to 504 km/s, IMF total field jumped from a steady 8 nT to 15 nT,
eventually increasing to 19 nT, and the Bz component of the IMF dropped
from -7 nT to -15 nT. While not as sharp, temperature and density both
saw increases as well. The sudden increase in activity is attributed to
what had originally been expected to be a glancing blow from a CME from
14 Feb.

18 February


Solar wind parameters, as measured at the Advanced Composition Explorer
(ACE) spacecraft, indicated nominal conditions. Wind speed began the
period near 420 km/s, then became sporadic with speeds as high as 441
km/s to as low as 345 km/s. Shortly before the end of the UT day, speeds
stabilized near the 360 km/s mark until around 18/0500 UTC, when speeds
increased to as high as 441 km/s through the end of the period. IMF Bt
(total field intensity) was consistently in the 4 to 7 nT range. The Bz
component of the IMF was variable in the 5 to -3 nT range until
approximately 18/0610 UTC when Bz had a maximum deflection of nearly -6
nT. Bz remained variable between -4 nT and +7 nT through the end of the
period. IMF phi remained primarily in a negative-polarity (toward)
solar-sector orientation during most of the period, with occasional dips
into positive (away) territory.

17 February


Solar wind speeds, measured at the ACE spacecraft, varied from a low of
near 335 km/s at 16/2300 UTC to a high of 429 km/s at 17/0238 UTC. IMF
total field was elevated near 15 nT at the start of the period and
gradually decreased to end-of-period readings of 4 nT. Bz was highly
variable through about 16/2000 UTC ranging from +14 to -10 nT. From
16/2000 UTC through the end of the period, the Bz component did not vary
much beyond +5 to -3 nT. Phi angle was predominantly positive (away)
through 16/2022 UTC when a shift to a more negative (towards)
orientation was observed through 16/2246 UTC. This was followed by a
brief shift back to a positive orientation through 17/0132 UTC when the
phi angle rotated back to negative for the remainder of the period.

16 February


Solar wind speed, measured at the ACE spacecraft, began the period at
about 375 km/s with Bt steady at 6 nT and Bz weakly northward at 1 nT.
At 15/1234 UTC an interplanetary shock was observed, indicating the
arrival of the 11-12 Feb CMEs. Solar wind speeds increased from
approximately 375 km/s to a peak of 487 km/s before settling to near 445
km/s. Solar wind temperature and density also rose in association with
the shock passage. Bt rose sharply to 16 nT and then varied between 1 nT
to 17 nT for the remainder of the period. Bz initially went south to -7
nT but then turned northward at 15/1330 UTC and remained mostly north
through 15/2054 UTC. After 15/2054 UTC, the Bz component began deviating
southward to -14 nT through about 16/0000 UTC where it again turned
north to a maximum of 17 nT through 16/0800 UTC. Through the remainder
of the period, Bz varied between +7 to -4 nT. After 15/2000 UTC, wind
speeds slowly declined to end-of-period values near 375 km/s. Phi angle
was predominantly positive (away) through 16/0424 UTC when a shift to a
more negative (towards) orientation was observed.

15 February


Solar wind speed, as measured at the ACE spacecraft, reflected nominal
conditions varying between approximately 330 km/s to 370 km/s. IMF total
field was steady between 5 nT and 7 nT for the majority of the period
with only a short dip to 2-3 nT from 14/1300-1400 UTC. Bz was
predominately north throughout the period with some southward incursions
to -3 nT between 15/0005-0217 UTC. The Phi angle began the period in a
negative (towards) orientation through 15/1335 UTC when a switch to
positive (away) was observed for the remainder of the period. Low energy
particles indicated a slow rise through about 15/0900 UTC when a sharper
increase in values was observed.

14 February


Solar wind parameters, as observed at the ACE spacecraft, reflected
nominal background conditions. Solar wind speeds steadily dropped
from beginning speeds near 375 km/s to end the period near 325 km/s. IMF
Bt was steady varying between 4 to 7 nT while the Bz component remained
predominately positive at 0 to 6 nT. Phi angle was in a negative
(towards) orientation through 14/0453 UTC where a transition to a
positive (away) orientation occurred.

13 February


Solar wind parameters, as observed at the ACE spacecraft, reflected
a return to nominal background conditions. Early in the period, there
were indications that Earth was riding near a solar sector boundary, but
parameters have since leveled off. Solar wind speeds steadily dropped
from beginning speeds near 450 km/s to end the period near 370 km/s. IMF
Bt was steady near 6 nT for most of the period. A slight increase in
speed back up to 400 km/s and an isolated bump in Bt to 9 nT was
observed just before 13/0900 UTC, likely the result of a near miss
transient. Bz began the period with brief deflections as low as -3 nT,
but remained mostly positive from 12/1600 UTC through the end of the
period. Phi angle remained in a negative (towards) orientation for the
entire period.

12 February


Solar wind parameters, as observed at the ACE spacecraft, reflected what
appears to be the recovery from a coronal hole high speed stream (CH
HSS) transitioning to the influence of weak transient. The beginning of
the period saw solar wind speeds steadily dropping from approximately
443 km/s to a minimum of 396 km/s. At the same time, IMF total filed
strength was fairly steady between 4 nT and 6 nT, IMF Bz was positive,
and Phi angle was in a negative (towards) sector. Around 11/1800 UTC, a
solar sector boundary change (SSBC) was observed, transitioning Phi
angle to a positive (away) orientation, dropping Bz to approximately -5
nT, and a slight increase in solar wind speed, back to approximately 440
km/s. Right around 11/2300 UTC, Phi angle again switched back to a
negative (towards) orientation, IMF Bt increased to approximately 6 nT,
Bz switched back to positive, and wind speeds began a steady climb. By
12/0330 UTC, wind speeds were back above 460 km/s, Bt was a steady 5 nT,
Bz dropped back southward to -3 nT, and Phi was firmly back into a
negative (towards) orientation. This is believed to be the influence of
a weak transient passing close enough to affect the Earth’s
magnetosphere.

11 February


Solar wind parameters, as observed at the ACE spacecraft, reflected the
continued influence of a negative polarity coronal hole high speed
stream (CH HSS). Solar wind speeds began the period near 450 km/s and
increased gradually to near 570 km/s just before the end of the UT day.
The peak speed observed was 617 km/s at 10/2205 UTC, but speeds then
began to taper off just after the new UT day, ending the period near
where they started at 450 km/s. Total field ranged between 2 and 7 nT,
with field strength holding steady near 5 nT for the majority of the
period. The Bz component ranged from -6 nT to +4 nT through most of the
first half of the period, becoming steady near -2 nT from approximately
10/2125 UTC to 11/0222 UTC. Following another period of sporadic
variations from +/- 4 nT, Bz remained positive after 11/0700 UTC through
the end of the period. Phi angle was in a predominately negative
(toward) orientation throughout the period.

10 February


Solar wind parameters were indicative of the onset of a negative
polarity coronal hole high speed stream (CH HSS). Solar wind speeds
began the period at near 420 km/s. At about 10/1630 UTC, wind speeds
gradually increased to an average of approximately 475 km/s and remained
so through the balance of the period. Total field ranged from about 5 to
10 nT with the Bz component mostly southward ranging from -9 nT to +7
nT. Phi angle was in a predominately negative (towards) orientation
throughout the period.