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Memorial Weekend Light Show
Aurora over Alberta prairies, east of Edmonton, Canada. › View larger
"In the Alberta prairies east of Edmonton, Canada, it looked like it was raining auroras," reports photographer Zoltan Kenwell. Credit: NASA/Zoltan Kenwell

After a quiet couple of weeks our Sun is once again awakening with activity. Over the Memorial holiday weekend Earth experienced category G1 (Minor) and G2 (Moderate) geomagnetic storms on May 28-29 due to a coronal hole high-speed solar wind stream. Bright auroras at high latitudes were visible at both poles of the Earth, including Tasmania, New Zealand, Antarctica, Wisconsin and Minnesota.

In addition, R1 (Minor) radio blackouts also occurred due to solar flares on the Sun. NOAA is predicting a continuing possibility of category R1 radio blackouts through June 9, 2011.

A coronal hole, the darker area in the center of the northern hemisphere, is the source of high-speed solar wind stream flow. › View larger
A solar wind stream flowing from the indicated coronal hole could reach Earth on or about June 4th. Credit: SDO/AIA
What is a coronal hole?

The solar corona is the outer atmosphere of the sun, extending from the solar surface out into space. Coronal holes are large regions in the solar corona that appear darker and are less dense and cooler than surrounding areas. The open structure of their magnetic field allows a constant flow of high-density plasma to stream out of the holes. The high-speed solar wind is known to originate in coronal holes.

There is an increase in the intensity of the solar wind effects on Earth when a coronal hole faces us. During solar minimum, coronal holes are mainly found at the Sun's polar regions. They can be located anywhere on the sun during solar maximum, which is our sun's current cycle. Coronal holes are the sources of many of the disturbances to the ionosphere (and HF communications) and to the geomagnetic field of planet Earth.

For answers to other space weather questions, please visit the Spaceweather Frequently Asked Questions page.

Tony Phillips/Holly Zell
NASA's Goddard Space Flight Center