How Do the Current Solar Wind and CME Data Compare to the Previous Minimum?
David F. Webb [David.Webb@hanscom.af.mil] Institute for Scientific Research (ISR),
Boston College, Chestnut Hill, Massachusetts
We compare results from two campaign intervals that were meant to characterize this and
the last solar minima: the Whole Heliosphere Interval (WHI), an in-depth study of the SunEarth system for a solar rotation in March-April 2008 and the Whole Sun Month (WSM)
campaign in August-September 1996. We also discuss how WHI fits within the broader
context of the recent deep, long and complex solar minimum. The comparison of these two
intervals demonstrates that sunspot numbers, while providing a good measure of solar
activity, do not provide sufficient information to gauge solar and heliospheric magnetic
complexity and its effect at the Earth. The recent solar minimum was exceptionally quiet,
with sunspot numbers the lowest in 75 years, solar wind density and IMF strength at the
lowest values ever observed, and geomagnetic indices and solar EUV fluxes the lowest in
three solar cycles. Possibly because of this global weakness in the heliospheric magnetic
field, large near-equatorial coronal holes lingered even as the sunspots disappeared,
indicating significant open magnetic flux at low latitudes. Consequently, before, during and
after the WHI campaign and into 2009, recurring high-speed streams in the solar wind
intercepted the Earth in contrast to the weaker and more sporadic streams that occurred
during the WSM campaign. Since the speed, duration and southward magnetic field
component in wind streams determine the severity of space weather effects, the geospace
environment responded quite differently to the two solar minimum heliospheric
morphologies. We also discuss how the other main transient component of the solar wind,
coronal mass ejections, varied between these two minima.