QST de W1AW  
Propagation Forecast Bulletin 52  ARLP052
>From Tad Cook, K7RA
Seattle, WA  December 28, 2015
To all radio amateurs 

SB PROP ARL ARLP052
ARLP052 Propagation de K7RA

This bulletin was released on Christmas Day. The last time Christmas
fell on a Friday (our normal day for publishing this bulletin) was
back in 2009, and we released it the day before:

www.arrl.org/w1aw-bulletins-archive/ARLP053/2009

Note that the solar indices for that week were no better than for
this past week, six years later.

This is the last propagation bulletin for 2015, and the next
bulletin will be released next Friday on January 1, 2016.

Over the past week, average daily sunspot numbers rose just 1.6
points to 49.6 compared to the previous seven days, December 10-16.
Average daily solar flux rose from 102.2 to 122.3 for the December
17-23 reporting period.

A big geomagnetic storm on Sunday, December 20 drove our geomagnetic
averages way up this week. On that day the mid-latitude A index
(recorded in Virginia) reached 33, the planetary A index (recorded
at a number of northern hemisphere sites) was 66, and the college A
index (recorded near Fairbanks, Alaska) was 89.

The day before, at 2323 UTC on December 19, the Australian Space
Forecast Centre issued a geomagnetic warning:

'Geomagnetic disturbance in progress following a CME impact after
1500 UTC December 19. Expect Active geomagnetic conditions December
20.

Increased geomagnetic activity expected due to coronal mass ejection
from 20-21 December 2015.'

Then on December 23, Spaceweather.com sent out this bulletin:

'A new sunspot (AR2473) is growing rapidly in the Sun's southern
hemisphere, more than quadrupling in size in the past 24 hours.
Crackling with M-class solar flares, the sunspot has already caused
several minor shortwave radio blackouts, mainly south of our
planet's equator. More flares and radio blackouts are in the offing
as the growing sunspot turns toward Earth. Visit
spaceweather.com for more information.'

Over this reporting week (December 17-23) average planetary A index
rose from 9.9 to 21.7 and average mid-latitude A index rose from 6.6
to 12.6.

Predicted solar flux for the near term is 130 on December 25, 125 on
December 26-31, then 115, 110 and 105 on January 1-3, 110 on January
4-6, 115 on January 7-9, 120 on January 10-13, 118 on January 14-15,
115 on January 16, 120 on January 17-18, then 115, 105 and 100 on
January 19-21, 98 on January 22-23, 95 on January 24-25, 98 on
January 26-27, and 100 on January 28-29.

Predicted planetary A index is 12, 10, 8 and 6 on December 25-28, 5
on December 29-31, then 15, 20, 18 and 10 on January 1-4, then 8,
20, 18 and 12 on January 5-8, then 10, 20, 18, 10 and 8 on January
9-13, and 5 on January 14-16.

OK1MGW from the Czech Propagation Interest Group sends us his
geomagnetic prediction this week, and it says to expect the
geomagnetic field to be quiet to active December 25-28, quiet to
unsettled December 29, mostly quiet December 30-31, active to
disturbed January 1-2, quiet to active January 3, quiet to unsettled
January 4, quiet to active January 5, active to disturbed January 6,
quiet to active January 7, quiet to unsettled January 8-9, active to
disturbed January 10, quiet to active January 11, quiet to unsettled
January 12-14, mostly quiet January 15-17, quiet on January 18-19,
and quiet to unsettled January 20.

OK1MGW expects increased solar wind on December 25-28, January 1-3,
5-6, and 10-11.

The Winter Solstice was three days ago, on Tuesday, December 22,
2015.  Now the days will get longer for the next six months, until
the Summer Solstice in the Northern Hemisphere, June 20, 2016.
Spring begins at the Vernal Equinox, March 19-20, 2015.

As the days get longer, HF conditions will generally improve in the
Northern Hemisphere. We can test some paths with a simple free
program, W6ELprop.

Testing from Dallas, Texas to Germany, a path of 8,222 km (5,109
miles) on the shortest day of 2015 we can see that 15 meters has the
best possibility of propagation from 1500-1630 UTC with an A rating
(75-100% chance of communication) at 23 dB above .5 microvolt at the
receiving end) and a B rating (50-74% probability) 1430-1700 UTC.

At the end of January 2016, the opening runs from 1430-1730 UTC for
the B rating, (A rating 1500-1700 UTC), with signals about 2 dB
lower.

At the Vernal Equinox, on March 20, 2016 the 15 meter opening
stretches from 1400-2100 UTC. All of these tests were done with a
solar flux of 127, to look at seasonal variation only.

Over the same path on 17 meters on December 22, 2015 it is open from
1400-1730 UTC, on January 31 1400-1830 UTC and on March 20, 2016,
1300-2200 UTC.

But for lower frequencies, such as 75 meters, conditions are better
during long periods of darkness, such as late December. On December
22, over the same path 75 meters looks best 2330-0830 UTC, but on
January 31 the best conditions are from 0030-0730 UTC and on March
20 conditions look best at 0200-0530 UTC.

If you would like to make a comment or have a tip for our readers,
email the author at, [email protected].

For more information concerning radio propagation, see the ARRL
Technical Information Service web page at,
arrl.org/propagation-of-rf-signals. For an explanation of the
numbers used in this bulletin, see
arrl.org/the-sun-the-earth-the-ionosphere. An archive of past
propagation bulletins is at
arrl.org/w1aw-bulletins-archive-propagation. More good
information and tutorials on propagation are at k9la.us/.

My own archives of the NOAA/USAF daily 45 day forecast for solar
flux and planetary A index are in downloadable spreadsheet format at
bit.ly/1VOqf9B and bit.ly/1DcpaC5 .

Click on 'Download this file' to download the archive, and ignore
the security warning about file format. Pop-up blockers may suppress
the download.

Monthly propagation charts between four USA regions and twelve
overseas locations are at arrl.org/propagation.

Instructions for starting or ending email distribution of ARRL
bulletins are at arrl.org/bulletins.

Sunspot numbers for December 17 through 23 were 52, 49, 44, 33, 38,
68, and 63, with a mean of 49.6. 10.7 cm flux was 117.8, 117.1, 119,
116.6, 121.7, 130.1, and 133.9, with a mean of 122.3. Estimated
planetary A indices were 7, 5, 12, 66, 38, 13, and 11, with a mean
of 21.7. Estimated mid-latitude A indices were 6, 4, 8, 33, 22, 8,
and 7, with a mean of 12.6.