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 Previous: Tampere Convention Eases International Emergency Telecommunications |  Next: FCC Chairman Michael K. Powell Announces his Resignation |
SEATTLE, WA, Jan 21, 2005--This has been a very active week for solar flares and geomagnetic storms. The average daily sunspot number rose more than 57 points this week to 89, and the average daily solar flux was up nearly 43 points to 132.7, as compared to the previous reporting week. The average daily planetary A index more than doubled--from 17.9 to 36.6.
Huge sunspot 720 provided lots of excitement over the past week. Clay Evans from Colorado wrote to say that on January 14 he was driving to work near Boulder, and through the heavily-filtered clouds he could see a large dark spot on the sun. This was probably sunspot 720.
Two large flares (coronal mass ejections or CMEs) erupted from this sunspot on Saturday, January 15. Over the next few days the geomagnetic numbers bumped up dramatically, with planetary A indices of 63, 72 and 62 for January 17-19. The high-latitude collage A indices for the same three days were 114, 136 and 106.
On Monday, January 17, another big flare blasted in our direction. It peaked around 0950 UTC. As sunspot 720 moves off the center of the visible solar disk, more flares erupted, including a huge X7-class event on Thursday, January 20. The energy could sweep past Earth today, January 21.
This flare was the largest of any during the past year, and it triggered the largest radiation storm in the current 11-year solar cycle. This radiation storm had not resulted in a geomagnetic storm here as of January 20, when this update was compiled.
The current prediction is for a planetary A index of 25, 20 and 20 for January 21-23, but these numbers could be higher depending on how direct the radiation hits Earth. With sunspot 720 moving beyond view, daily solar flux values are expected to dip below 100 around January 23-24.
For more information concerning propagation and an explanation of the numbers used in this bulletin see the ARRL Technical Information Service Propagation page .
Sunspot numbers for January 13 through 19 were 77, 65, 100, 99, 107, 109 and 66, with a mean of 89. The 10.7 cm flux was 115.6, 129.8, 144.9, 144.5, 137.5, 124.3 and 132.5, with a mean of 132.7. Estimated planetary A indices were 13, 12, 22, 12, 63, 72 and 62 with a mean of 36.6. Estimated mid-latitude A indices were 10, 11, 11, 10, 27, 35 and 31, with a mean of 19.3.
Amateur
solar observer Tad Cook, K7RA, Seattle, Washington, provides this weekly report
on solar conditions and propagation. This report also is available via W1AW every
Frida,y and an abbreviated version also appears in The ARRL Letter. Readers may contact
the author via e-mail.
| Previous: Tampere Convention Eases International Emergency Telecommunications | Next: FCC Chairman Michael K. Powell Announces his Resignation |
