Title: Solar Extreme Ultraviolet Measurements from the NASA TIMED Satellite
Author: Tom Woods
Affil: LASP / Univ. of Colorado
Email: tom.woods@lasp.colorado.edu
Authors: Scott Bailey, Guiliana de Toma, Frank Eparvier, Judith Lean, Ray Roble, Gary Rottman, Stan Solomon, Kent Tobiska, and Dick White
Affils: Hampton Univ., HAO/NCAR, LASP/CU, NRL, JPL/SpaceWx
Abstract: The Solar EUV Experiment (SEE) on the NASA Thermosphere, Ionosphere, and Mesosphere Energetics and Dynamics (TIMED) mission will measure the solar vacuum ultraviolet (VUV) spectral irradiance from 0.1 to 195 nm. This solar radiation is the dominant global energy source for the heating of the thermosphere, creating the ionosphere, and driving the diurnal cycles of wind and chemistry in the upper atmosphere. The variability of the solar VUV irradiance over the 11-year solar cycle ranges from 10% to over a factor of 10, with more variability at the shorter wavelengths.
To cover the wide spectral range of 0.1 to 195 nm, two different types of instruments are used: a grating spectrograph for spectra above 25 nm and a set of silicon soft x-ray photodiodes with thin film filters for below 35 nm. Redundant channels of the spectrograph and soft x-ray photodiodes provide in-flight calibration checks on the time scale of a week, and annual rocket underflight measurements provide absolute calibration checks traceable to NIST photometric standards. Both types of instruments have been developed and flight proven as part of a NASA solar VUV irradiance rocket experiment. These solar rocket measurements in 1997 and 1998 will be presented.
The TIMED spacecraft is being developed for a shared launch on a Delta vehicle by the Applied Physics Laboratory (APL) at the Johns Hopkins University (JHU). The TIMED mission is being planned as a two year mission with a circular orbit altitude of 600 km and an orbit inclination of 74°. There are three other TIMED instruments which measure the composition, temperature, infrared cooling, and winds in the upper atmosphere. The TIMED launch is currently scheduled for August 10, 2001.