Understanding Solar Cycle Ultraviolet Variations from SME, UARS, TIMED, and SORCE
Satellite Measurements
Thomas N. Woods [tom.woods@lasp.colorado.edu] and Gary J. Rottman; LASP, University of
Colorado, Boulder
The Solar Mesosphere Explorer (SME) measured the solar ultraviolet (UV) irradiance from
1981 to 1989, and those observations are the foundation for a series of solar UV measurements
continued through today by LASP. The solar UV radiation between 115 nm and 300 nm is a
critical energy input for studying Earth’s atmosphere, such as for ozone photochemistry, thus
understanding the solar UV variations was an important part of the SME mission and continues
to be important for Earth science studies today. After SME, there were additional solar UV
irradiance measurements from the Upper Atmosphere Research Satellite (UARS), the
Thermosphere, Ionosphere, Mesosphere, Energetics, and Dynamics (TIMED) spacecraft, and the
Solar Radiation and Climate Experiment (SORCE). These four sets of observations that span
1981 to the present day enable the evaluation of the solar UV variations over multiple solar
cycles. For comparison to these measurements, there are the series of NOAA Solar Backscatter
Ultraviolet Instrument (SBUV), Shuttle Atmospheric Laboratory of Applications and Science
(ATLAS), and rocket measurements that started as early as 1972. While solar rotation 27-day
variability is very similar from the different instruments, there are some differences in the solar
cycle 11-year variations, partly due to observations made during different solar cycles and
perhaps also due to uncorrected instrumental effects. These observations across a solar cycle
minimum offer one way to check for these uncorrected instrumental trends, and this technique is
applied for these four instrument data sets. The composite time series of these UV irradiance
measurements provide an important climate record of the solar UV irradiance, for understanding
solar cycle variations, and for studying solar forcing in Earth’s atmosphere.