ARRL

ARRL Propagation Bulletin ARLP005 (2002)

SB PROP @ ARL $ARLP005
ARLP005 Propagation de K7VVV

ZCZC AP05
QST de W1AW  
Propagation Forecast Bulletin 5  ARLP005
From Tad Cook, K7VVV
Seattle, WA  February 1, 2002
To all radio amateurs 

SB PROP ARL ARLP005
ARLP005 Propagation de K7VVV

Average solar flux was up nearly 30 points this week, and average
sunspot numbers rose by nearly 15. Solar flux peaked on Tuesday at
261, and is probably headed down for a while. Predicted solar flux
for Friday through Monday is 250, 245, 240 and 235.

There was an M-1 solar flare at 2005z on Saturday and the flare may
have enhanced the daily solar flux reading for that day, which was
256.5. This reading is at noon local time (2000z) in Penticton,
British Columbia, but there are also a morning reading and a third
one in the afternoon. The morning reading for that day was 244.1 and
the afternoon flux was 248.8.

Sometimes a flare will throw so much energy at earth that the 10.7
cm receiver used for recording solar flux will be completely
overwhelmed. An extreme example was on December 28, 2001 when
Penticton reported an 1800z reading of 263.3, at 2000z it was 655.6,
and at 2200z it was 331.8. The official number reported for that day
and reported in this bulletin was adjusted down to 263, which was
the morning reading rounded off.

There are three classes of solar flares, and from small to large
they are C, M and X. The X-class flares trigger radio blackouts all
over the earth if they are aimed our direction. M-class flares may
cause brief radio blackouts and high absorption over polar paths.
C-class flares are small, with few effects.

Each flare class has nine ratings, so there are 27 in all. The M-1
flare was the smallest in the medium sized class.

Saturday's flare didn't cause any noticeable geomagnetic
disturbance. Friday had a brief period when the planetary K index
was 4 and the high-latitude Alaska College K index was 5, but the
rest of the periods were so quiet that for all week, the A index was
in the single-digits.

Sunspot region 9800 is near the center of the visible solar disk,
which means that its energy is aimed at earth. Currently it has a
twisted complex magnetic field, which could unleash energy for a
major earth-directed X-class flare. If it doesn't explode, we should
have good HF radio conditions.

K1TEO wrote to report that good 6-meter conditions continue. On
Wednesday, January 23 many stations in the Eastern United States
worked stations in the Ukraine with S9 signals. The next day he
worked ES/YL/OH/SM stations with good signals, and on Friday he
mainly worked Western Europe. There were also openings to the West
Coast and Western Canada. Jeff says that the openings are not as
strong or widespread as in November and December, ''but still plenty
of action.''

Sunspot numbers for January 24 through 30 were 173, 196, 194, 189,
207, 214 and 210 with a mean of 197.6. 10.7 cm flux was 230.8,
234.8, 256.5, 248, 259.8, 261 and 256.3, with a mean of 249.6, and
estimated planetary A indices were 4, 8, 7, 7, 6, 4 and 3 with a
mean of 5.6.
NNNN
/EX