Integrating the Sun-Earth System (ISES): The 2008-2009 Whole Heliosphere Intervals

We simulate the Sun-Earth system throughout the extended solar minimum epoch from 2008 to 2009 using coupled geospace, heliosphere and solar numerical models, systematically validating individual model components with databases of observed geospace composition and solar and heliospheric parameters. We isolate and quantify observed changes of 10% to 20% in global ionosphere electron density and thermospheric mass density at 250 km associated with fluctuating solar EUV radiation and geomagnetic activity during this nominally “quiet” period. Corresponding modeled changes are smaller than is observed, especially in response to solar EUV radiation. We identify, as well, semiannual and annual oscillations that produce geospace variability comparable to solar and geomagnetic influences, and cause distinct differences among the three individual Whole Heliosphere Intervals. Decreases of ~35% in total electron content and mass density at 250 from the first Whole Heliosphere Interval (March-April 2008) to the third Whole Heliosphere Interval (June-July 2009) are attributable to these oscillations, which originate primarily in the lower atmosphere and must be properly distinguished from solar and heliospheric effects or reliable attribution of the geospace base state during the 2008-2009 solar minimum epoch, and geospace comparisons among the Whole Heliosphere Intervals. This work was sponsored by the Office of Naval Research.