A coronal mass ejection (CME) on May 13 at 1650 UTC emanated from a tremendous explosion near Sunspot 759.
A coronal mass ejection (CME) on May 13 at 1650 UTC emanated from a tremendous explosion near Sunspot 759. |
NEWINGTON, CT, May 16, 2005--The space weather appears to have calmed down a bit, but things got quite exciting over the May 14-15 weekend, and a watch remains in effect through May 16 for a geomagnetic A index of 30 or greater. An extended warning for a K index of 6 was in effect until 1500 UTC today. The activity prompted ARRL propagation guru Tad Cook, K7RA, to issue a special bulletin.
"On Friday the Thirteenth at 1650 UTC, a tremendous explosion near Sunspot 759 blasted toward Earth," he reported. "The impact on Earth's magnetic field was felt at 0230 UTC on May 15, producing an extreme geomagnetic storm." A geomagnetic storm is a disturbance of Earth's magnetic field.
According to Cook, the planetary K index reached 9 on Sunday, May 15. "This is huge!" he exclaimed. "The middle-latitude, high-latitude and planetary A indices for Sunday were 44, 77 and 105 respectively--all very high values." Cook says the solar flux was expected to stay around 100 through Wednesday, May 18.
The A and K indices indicate the severity of magnetic fluctuations and, as a result, the disturbance to the ionosphere. The K index describes the same level of magnetic disturbance, no matter whether the observatory is located. The A index, a daily average, is derived from incremental readings of the A index. During very severe geomagnetic storms it can reach values of up to 200 or greater. The A index can vary from one observatory to the next.
K indices of 2 or 4 indicate unsettled or even active magnetic conditions--likely to be reflected in a degradation of HF conditions. An index of 5 represents a minor storm, 6 a larger storm and 7 through 9 represent a major storm that would result in an HF blackout.
Cook says Michael Schaffer, KA3JAW, in Tampa, Florida, began scanning low VHF television channels on May 13 because of the possibility of aurora from a coronal mass ejection on May 11. "He e-mailed several photos he took of his television displaying KGAN, channel 2, in Cedar Rapids, Iowa," Cook reports. "He received both audio and video for about 30 minutes after 5 PM local time. The distance was about 1100 miles."
 Vic and Jen Winter near Warrensburg, Missouri, experienced this auroral display, which they called "one of the most amazing displays of aurora we have ever seen in Missouri." |
Randy Wing, N0LD, in Kansas, reports he was able to make two auroral contacts over the weekend on 6 meters--one with K0RI in Colorado (DM78) and the second with KC0PUN in Nebraska (EN11). "The aurora was visible from the horizon up to past the zenith!" he exclaimed. "It was the most amazing aurora I have ever seen in Kansas!"
Cook says that in the early stages of a new solar cycle, sunspot groups tend to form in the higher latitudes of the solar disk, while and toward the end of a cycle, they favor equatorial latitudes. "The greater emergence of sunspots toward the sun's equator later in the cycle heightens the probability that the energy from those spots will be Earth-directed," he explains.
For more information concerning radio propagation and an explanation of the numbers used in propagation bulletins and "The K7RA Solar Update," visit the ARRL Technical Information Service Propagation page. A table of space weather alerts is available on the NOAA Space Environmental Center Web site.
Sunspot numbers for May 5 through 11 were 50, 66, 55, 79, 106, 106 and 117
with a mean of 82.7. The 10.7 cm flux was 109.1, 110.4, 99.9, 101.3, 110,
119.2 and 125.3, with a mean of 110.7. Estimated planetary A indices were
6, 4, 10, 64, 11, 10 and 11 with a mean of 16.6. Estimated mid-latitude A
indices were 3, 3, 10, 38, 10, 6 and 7, with a mean of 11.
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