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Doug L. Hoffman: The Sun's Hidden Power
Wednesday, September 21st 2011, 5:59 PM EDT
Co2sceptic (Site Admin)
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No phenomenon in astronomy has been studied more closely than solar flares, gigantic eruptions on the Sun that can affect Earth's climate and even disrupt power grids. Scientists have been watching the Sun with ground based instruments and orbiting satellites for years, so it might be thought that we know a lot about such eruptions. Well think again. A new report from NASA has revealed that, like earthquakes, solar flares often have aftershocks. Moreover, the aftershocks can emit bursts of ultraviolet (UV) radiation more powerful than the original eruption. Combine this new finding with the recently uncovered linkage between fluctuating UV levels and El Niño, and the Sun-Climate connection looks stronger than ever.

In a report, published in The Astrophysical Journal, NASA scientists are reporting that solar flares generate considerably more energy than previously suspected. About 1 flare in 7 experiences an “aftershock” around ninety minutes after the flare dies down. “We call it the ‘late phase flare,’” says Thomas N. Woods, a physicists at the University of Colorado and lead author. “The energy in the late phase can exceed the energy of the primary flare by as much as a factor of four.” The major findings are detailed in the article's abstract below:

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New solar extreme-ultraviolet (EUV) irradiance observations from the NASA Solar Dynamics Observatory (SDO) EUV Variability Experiment provide full coverage in the EUV range from 0.1 to 106 nm and continuously at a cadence of 10 s for spectra at 0.1 nm resolution and even faster, 0.25 s, for six EUV bands. These observations can be decomposed into four distinct characteristics during flares. First, the emissions that dominate during the flare's impulsive phase are the transition region emissions, such as the He II 30.4 nm. Second, the hot coronal emissions above 5 MK dominate during the gradual phase and are highly correlated with the GOES X-ray. A third flare characteristic in the EUV is coronal dimming, seen best in the cool corona, such as the Fe IX 17.1 nm. As the post-flare loops reconnect and cool, many of the EUV coronal emissions peak a few minutes after the GOES X-ray peak. One interesting variation of the post-eruptive loop reconnection is that warm coronal emissions (e.g., Fe XVI 33.5 nm) sometimes exhibit a second large peak separated from the primary flare event by many minutes to hours, with EUV emission originating not from the original flare site and its immediate vicinity, but rather from a volume of higher loops. We refer to this second peak as the EUV late phase. The characterization of many flares during the SDO mission is provided, including quantification of the spectral irradiance from the EUV late phase that cannot be inferred from GOES X-ray diagnostics.

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