Total Solar Irradiance Measurements: Results and Future Requirements

Author: Judit M. Pap
Goddard Earth Sciences and Technology Center, University of Maryland, Baltimore County

Total irradiance has been monitored from space more than two decades. These measurements established conclusively that total irradiance varies from minutes to the 11-year solar cycle. Although considerable information exists about irradiance variations, their physical origin is not yet understood. It is still an open question whether the governing mechanism of irradiance changes is the surface manifestations of solar activity or more global events routed inside the Sun. An additional, debated, question is whether there is a secular trend superimposed on the 11-year cycle which can be climatologically more significant than the 0.1% cycle variability. In this paper we discuss the results of current measurement and future measurement/science requirements.