Astronomy and Astrophysics – Astrophysics
Scientific paper
Dec 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufmsh11a1501g&link_type=abstract
American Geophysical Union, Fall Meeting 2009, abstract #SH11A-1501
Astronomy and Astrophysics
Astrophysics
[0310] Atmospheric Composition And Structure / Airglow And Aurora, [2784] Magnetospheric Physics / Solar Wind/Magnetosphere Interactions, [7536] Solar Physics, Astrophysics, And Astronomy / Solar Activity Cycle, [7984] Space Weather / Space Radiation Environment
Scientific paper
A system-oriented analysis of new observations from the recent international Whole Heliosphere Interval (WHI) campaign in comparison with the equivalent Whole Sun Month (WSM) campaign from last cycle’s minimum yields new insight into solar quiet intervals and the solar minimum Sun-Earth system. We use a side-by-side comparison of these two intervals to demonstrate 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 present solar minimum is 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. Despite, or perhaps 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, for the months surrounding the WHI campaign, strong, long, and recurring high-speed streams in the solar wind intercepted the Earth in contrast to the weaker and more sporadic streams that occurred around the time of 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 illustrate this point with the behavior of relativistic electrons in the Earth’s outer radiation belt, which were more than three times stronger during WHI than in WSM. The cause is clear: it is well-known that high-speed streams drive radiation belt population, and indeed, for the months surrounding WHI, geospace and upper atmospheric parameters were ringing with the periodicities of the solar wind in a manner that was absent last cycle minimum. Such behavior could not have been predicted using sunspot numbers alone, indicating the importance of considering variation within and between solar minima in analyzing and predicting space weather responses at the Earth during solar quiet intervals, as well as in interpreting the Sun’s past behavior as preserved in geological and historical records.
de Toma Giuliana
Emery Barbara A.
Gibson Sarah Elizabeth
Kozyra Janet U.
Onsager T. G.
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