Evolution of Coronal Holes with the Solar Cycle: Implications for the Solar Wind at Earth

Details Evolution of Coronal Holes with the Solar Cycle: Implications for the Solar Wind at Earth Evolution of Coronal Holes with the Solar Cycle: Implications for the Solar Wind at Earth

Dec 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufmsm54b..01d&link_type=abstract

American Geophysical Union, Fall Meeting 2011, abstract #SM54B-01

Astronomy and Astrophysics

Astrophysics

[2169] Interplanetary Physics / Solar Wind Sources, [2788] Magnetospheric Physics / Magnetic Storms And Substorms, [7511] Solar Physics, Astrophysics, And Astronomy / Coronal Holes, [7536] Solar Physics, Astrophysics, And Astronomy / Solar Activity Cycle

Scientific paper

The two main sources of space weather are coronal mass ejections (CMEs) and high speed solar wind streams, both of which vary with the solar activity cycle. Fast CMEs with strong southward fields are responsible for the most intense geomagnetic storms. Because the CME rate and speed follows the solar cycle, i.e. CMEs are more frequent and on average faster near solar maximum, strong and short-duration geomagnetic storms are prevalent during times of high solar activity. High speed solar wind streams emanating from low-latitude coronal holes at the Sun can also drive weak to moderate but long-duration geomagnetic storms. This kind of storms are more common during the declining phase of the solar cycle, when coronal holes at low latitudes tend to be large in size and long-lived. In this paper, we will focus on high speed solar wind streams and their solar sources. We will show how the distribution of coronal holes at the Sun affects the solar wind speeds seen at Earth and will discuss the importance of the solar polar magnetic fields for coronal holes near solar minimum, and particularly during recent minima. The past solar minimum and early phase of solar cycle 24 were characterized by low magnetic activity and weak polar magnetic fields. This magnetic configuration gave rise to small polar coronal holes and allowed large, low- to mid-latitude coronal holes to survive during times of very low solar activity, resulting in solar wind properties markedly different from the previous minima during the Space Age.

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