The dark area across the top of the sun in this image of NASA's Solar Dynamics Observatory is a coronal hole, a region on the sun where the magnetic field is open to interplanetary space, sending coronal material speeding out in what is called a "high-speed solar wind stream." (NASA)
High-speed solar-wind streams emanate from solar coronal holes; the fast wind interacts with upstream slow streams producing regions of enhanced magnetic field strength and particle density that are known as co-rotating interaction regions. Due to the recurring nature of coronal holes near solar minimum, this results in periodic driving of the magnetosphere that can last for several days and input as much energy as a storm driven by a coronal mass ejection.
When we talk about space weather we can often conjure images of large coronal mass ejections (CMEs) or dramatic solar flares that drive spectacular effects in the Earth's near-space environment, such as the northern and southern lights.
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