Solar EUV Experiment (SEE): Mission overview and first results

The Solar EUV Experiment (SEE) is one of four scientific instruments on the NASA Thermo-sphere Ionosphere Mesosphere Energetics Dynamics (TIMED) spacecraft, which has been simul-taneously observing the Sun and Earth's upper atmosphere since January 2002. The SEE instru-ment measures the irradiance of the highly variable, solar extreme ultraviolet (EUV) radiation, one of the major energy sources for the upper atmosphere. The primary SEE data product is the solar spectral irradiances from 0.1 to 194 nm in 1 nm intervals that are fundamental for the TIMED mission's investigation of the energetics in the tenuous, but highly variable, layers of the Earth’s atmosphere above 60 km. The TIMED mission began normal operations on January 22, 2002, a time when the Sun displayed maximum levels of activity for solar cycle 23, and has pro-vided daily measurements as solar activity has declined to moderate levels. Solar irradiance vari-ability observed by SEE during the two years of the TIMED prime mission includes a variety of moderate and large flares over periods of seconds to hours, and dozens of solar rotational cycles over a typical period of 27 days. The SEE flare measurements provide important, new results be-cause of the simultaneous spectral coverage from 0.1 to 194 nm, albeit limited temporal coverage due to its 3 % duty cycle. In addition, the SEE measurements reveal important, new results con