Cooperative Institute for Research in Environmental Sciences

Abstracts: 2

Solar-Terrestrial Modeling and Data for Space Weather Forecasting

Tim Fuller-Rowell, Nick Arge, Mihail Codrescu, Dusan Odstricil, Dave Anderson, Leslie Mayer, Eduardo Araujo, Rob Markel, Adela Anghel, and Vic Pizzo
CIRES, University of Colorado and NOAA Space Environment Center

The title of NASA's "Living with a Star" initiative captures the essence of the societal consequences of our Sun being a variable star. CIRES scientists at NOAA Space Environment Center (SEC) are investigating ways to mitigate the impact of day-to-day changes in solar output on technological systems either by improving forecasts or by better characterizing Earth's response. Short-term changes in solar output are manifest in both solar radiation (photons) and in the solar wind (the plasma output of the sun). At shorter wavelengths, variability in solar radiation increases dramatically. For instance, during flares, solar X-rays (0.1-0.8nm) can increase by many orders of magnitude and the extreme ultraviolet (1-102nm) by 50%, for an hour or more, in stark contrast to the so-called solar constant which changes by only one part in a thousand over the 11 year solar cycle. Flare response at Earth is almost immediate (8 minute delay), whereas the solar plasma output is delayed by more than a day due to the variable propagation time for an event to transit from Sun to Earth. Coronal mass ejections or corotating streams are just two of the solar events that can eject plasma that can collide with Earth, disrupting communication, navigation, power systems, or other space-based or ground-based technological systems. CIRES scientists are improving forecasts of the arrival and impact of these events by modeling the transit of the plasma from Sun to Earth, and drawing on all available techniques from relatively simple empirical models to complex 3D magneto-hydrodynamic numerical simulations. Plasma striking Earth produces geomagnetic storms, which affect the magnetosphere and upper atmosphere. During these events, the ionosphere is disrupted, affecting satellite and ground-based communications, and neutral atmosphere density increases, causing drag and reduced lifetimes of low-Earth-orbiting satellites. CIRES scientists are working to improve our understanding of how the Earth system responds to these solar events, and are constructing an assimilative system paralleling the developments in meteorological weather forecasting.