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Solar Flares Cause Radio Blackouts on Earth
Friday, November 24, 2000
Image right: Image of flare region - from SOHO Extreme ultraviolet Imaging Telescope (EIT) full-field Fe IX, X 171 Å images from NASA Goddard Space Flight Center [2000/11/24 19:00:14]
Two rather powerful solar flares occurred today which have caused radio blackouts on the side of Earth facing the sun. According to a NOAA Space Environment Center alert yesterday "A category R3 (strong) radio blackout occurred on November 23 at 10:02 p.m. MST (2000 November 24 0502 UT) due to a major solar flare. Category R3 radio blackouts usually result in the following system effects on the sunlit side of Earth: wide area blackout of high-frequency radio communication with loss of radio contact for about an hour and low-frequency navigation signals degraded for about an hour."
Today, in another alert, NOAA reported that "Another category R3 (strong) radio blackout occurred on November 24 at 08:13 a.m. MST (2000 November 24 1513 UTC) due to a major solar flare from a large active sunspot group near center disk on the sun (current location North 21 West 04). This region has produced two strong events in the past ten hours. The region is expected to be visible from Earth for the next seven days and is likely to produce additional major events. Category R3 radio blackouts usually result in the following system effects on the sunlit side of the Earth: wide area blackout of high-frequency radio communication with loss of radio contact for about an hour and low-frequency navigation signals degraded for about an hour."
In its daily "Report of Solar-Geophysical Activity" NOAA said " Solar activity is now at high levels. Magnetograms revealed developing complexity late last period in Region 9236 (N22W07) and a series of significant events followed. The first was an M1/1n at 23/2328Z with associated Type II sweep (1025km/s) and CME. At 24/0502Z, an X2/3b flare erupted with strong centimetric radio bursts including a Tenflare of 2200sfu. This event was also accompanied by a Type II sweep (1000km/s), a proton event, and a halo CME. The third significant event from this region was an X2/2b that occurred at 24/1513Z. This flare was also accompanied by large centimetric radio bursts, a Type II sweep (1200km/s), proton event, and a halo CME. This region, at over 500 millionths of sunspot areal coverage, is magnetically complex and still developing. Region 9231 (S24W74) was mostly stable this period, producing only an isolated low C-class flare. New region 9242 (N22E68) was numbered today."
These solar flares were accompanied by Coronal Mass Ejections (CMEs) which follow on the heels of two other CMEs already heading toward Earth. The CMEs are expected to cause increased auroral activity when they strike Earth's magnetosphere this weekend. According to NOAA: "The first of a series of CME 's are expected to impact the [Earth's geomagnetic] field early on day two. As many as four individual CME's occurring over the past forty hours appeared earthbound."
According to todays alert: "Geomagnetic storms reaching G3 (strong) levels are expected to start late on the UTC day Saturday, November 25, as a consequence of these events. Category G3 geomagnetic storms usually result in the following system effects: power system voltage corrections may be required, false alarms triggered on some protection devices, surface charging may occur on satellite components, drag may increase on low-Earth-orbit satellites, and corrections may be needed for orientation problems, intermittent satellite navigation and low-frequency radio navigation problems may occur, HF radio may be intermittent, and aurora has been seen as low as Illinois and Oregon (typically 50 degrees geomagnetic latitude)."
-- Uncle Bob (firstname.lastname@example.org), November 25, 2000