All solar and geomagnetic
indicators declined again last week. Compared to the previous seven days, from
March 31 through April 6 the average daily sunspot number slipped from 28.1 to
19.4. Average daily solar flux sank from 88.8 to 83.1, while average daily
planetary A index went from 11.9 to 9.4. Average daily mid-latitude A index went
to 7.6 from 8.6.
The latest prediction (from April 7)
has solar flux at 92 and 90 on April 8-9, 95 on April 10-15, 78 on April 16-17,
80 on April 18-22, 78 on April 23, 80 on April 24-28, 82 on April 29 to May 1,
78 on May 2-5, 82 on May 6-7, 80 on May 8-12 and 78 on May 13-14. Solar flux
then continues to dither between 78 and 80 over the remainder of the 45 day
forecast. You can find daily updates of this forecast at ftp://ftp.swpc.noaa.gov/pub/forecasts/45DF/ .
Predicted planetary A index is 15 and 8
on April 8-9, 5 on April 10-12, then 12, 20, and 8 on April 13-15, 5 on April
16-20, 8 on April 21-22, then 5 and 12 on April 23-24, 10 on April 25-26, 8 on
April 27, 5 on April 28-29, then 22, 8, 15 and 12 on April 30 through May 3,
then 8 on May 4-5 and 5 on May 6-7.
The big factor in bringing the week’s
average sunspot number down nearly 9 points was the fact that the daily sunspot
number was 11 on March 31 through April 2. 11 is the lowest sunspot number we
can possibly observe, unless there are zero sunspots, then the sunspot number is
zero. Each sunspot group is counted as 10 points, and these are added to the
total number of sunspots which count as one each, so a sunspot number of 11 is
what you get with just one sunspot visible.
Spaceweather.com reported early
Thursday that on April 7, Earth is expected to cross a fold in the Heliospheric
Current Sheet, which could trigger unsettled geomagnetic conditions.
The Heliospheric Current Sheet
separates regions of solar wind where the magnetic field points toward or away
from the sun. See http://bit.ly/25MG4lW for a continuous animation of
this effect from 2001 until 2009. See https://en.wikipedia.org/wiki/Heliospheric_current_sheet
for more information.
Sure enough, early on April 8 at 0007
UTC the Australia’s Space Weather Services issued a geomagnetic warning:
“The geomagnetic conditions are
currently at minor storm levels and are expected to remain at these levels for
the next 6-12 hours. This is a combined effect of sustained strongly southwards
IMF Bz (see http://bit.ly/1S6H68D ) starting from 07/1800 UTC
but with stable, weak solar wind speeds (380 km/s). However, the solar winds are
expected to gradually increase later today in response to a small recurrent
southern hemisphere coronal hole moving into a geo-effective location on the
solar disk. The aurora may be visible from as low as some parts of the state of
Victoria, Australia, on the local night of 8 April.
Increased geomagnetic activity expected
due to a coronal hole high speed wind stream from 08-09 April 2016.”
More here:
