I

—r>----._

22:32 22:34 22:36 22:38 22:40 22:42 22:44 Time (UT)

FIG. 7.7 Impulsive and gradual phases of a flare The time profile of a solar flare observed at hard X-ray energies, above 30 keV (bottom), is characterized by an impulsive feature that lasts for about one minute. This impulsive phase coincides with the acceleration of high-speed electrons that emit non-thermal bremsstrahlung at hard X-ray wavelengths and non-thermal synchrotron radiation at centimeter radio wavelengths. The less-energetic emission, below 30 keV (top), can be composed of two components, an impulsive component followed by a gradual one. The latter component builds up slowly and becomes most intense during the gradual decay phase of solar flares when thermal radiation dominates. At even lower soft X-ray energies (about 10 keV), the gradual phase dominates the flare emission. This data was taken on 15 November 1991 with the Hard X-ray Telescope (HXT) aboard Yohkoh. (Courtesy of NASA, ISAS, the Lockheed-Martin Solar and Astrophysics Laboratory, the National Astronomical Observatory of Japan, and the University of Tokyo.)

FIG. 7.8 Flare loops Radiation from an arcade of magnetic loops was produced shortly after a solar flare erupted on 7 July 2002. This image was taken at a wavelength of 17.11 nanometers, emitted by eight and nine times ionized iron, denoted Fe IX and Fe X, at a temperature of about 1.0 million kelvin, using the Transition Region And Coronal Explorer, abbreviated TRACE. (Courtesy of the TRACE consortium and NASA; TRACE is a mission of the Stanford-Lockheed Institute for Space Research, ajoint program of the Lockheed-Martin Solar and Astrophysics Laboratory, or LMSAL for short, and Stanford's Solar Observatories Group.)

FIG. 7.8 Flare loops Radiation from an arcade of magnetic loops was produced shortly after a solar flare erupted on 7 July 2002. This image was taken at a wavelength of 17.11 nanometers, emitted by eight and nine times ionized iron, denoted Fe IX and Fe X, at a temperature of about 1.0 million kelvin, using the Transition Region And Coronal Explorer, abbreviated TRACE. (Courtesy of the TRACE consortium and NASA; TRACE is a mission of the Stanford-Lockheed Institute for Space Research, ajoint program of the Lockheed-Martin Solar and Astrophysics Laboratory, or LMSAL for short, and Stanford's Solar Observatories Group.)

When replenished and full, the post-impulsive flare loops contain plasma heated to temperatures of tens of millions of degrees, even hotter than the center of the Sun at 15.6 million kelvin. ttey appear to migrate upwards and outwards as successive field lines are reconnected at higher altitudes, tte post-flare loops bridge the magnetic neutral line between opposite polarity regions in the photosphere, stitching together and healing the wound inflicted by the solar flare and related events.

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