October 14, 2015 – NASA’s Solar Dynamics Observatory captured this picture of the sun on October 10, 2015. The dark area across the top of the sun is a coronal hole, a region on the sun where the magnetic field opens up and sends material into the solar system in what is called a high-speed solar wind stream. High-speed solar winds travel at about 400-500 miles per second, roughly twice the speed of the normal solar wind.
As the current coronal hole in the Sun’s northern hemisphere continues to progress to the solar west (to the right), the solar wind speed will remain elevated. As a result, forecasters expect an increase in geomagnetic storming and a G1-Minor storm watch has been issued for the 14th through the 16th of October. Forecasters will monitor the solar wind environment and issue warnings and alerts as appropriate.
A coronal hole occurs when the sun’s magnetic field reaches out into space rather than looping back down onto the surface of the sun. The magnetic field lines can extend far out into the solar system and allow a continuous outflow of high-speed solar wind from the sun.
Each time a coronal hole rotates by Earth, scientists can measure the particles flowing out of the hole as a high-speed stream, another source of space weather. Its speed, density and the magnetic fields associated with that plasma affect Earth’s protective magnetic shield in space (the magnetosphere.) When the charged particles come in contact with the magnetosphere, some get trapped and travel toward the Earth’s magnetic poles, where some of the energy can be seen as an aurora.
Scientists carefully monitor these types of space weather events because modern society depends on a variety of technologies that are susceptible to extreme space weather. Strong electrical currents driven along the Earth’s surface during auroral events can disrupt electric power grids and contribute to the corrosion of oil and gas pipelines, as well as disrupting GPS and transportation systems.
Coronal holes were first spotted by NASA’s Skylab in the early 1970’s. Data and images from Skylab showed that the solar corona was far more dynamic than had previously been surmised. Skylab’s continuous observations of coronal holes, coupled with measurements of the solar wind at Earth, clearly established coronal holes as the long-sought source of recurrent solar wind disturbances that buffet the upper atmosphere of Earth; this enabled scientists to create models and measurements that more accurately predict the effects of the Sun on Earth.
Scientists now know that the size and number of coronal holes varies in concert with the sun’s solar cycle, which occurs over a period of 11 years. Coronal holes tend to be most numerous in the years following solar maximum.
Goddard Space Flight Center built, operates and manages the SDO spacecraft for NASA’s Science Mission Directorate in Washington, D.C. SDO is the first mission of NASA’s Living with a Star Program. Data from all three SDO instruments (AIA, HMI, and EVE) are used by the NOAA Space Weather Prediction Center in Boulder, Colorado to create space weather forecasts.
SDO includes an instrument built in partnership with the University of Colorado at Boulder’s Laboratory for Atmospheric and Space Physics (LASP) and another built by Lockheed Martin Solar & Astrophysics Laboratory in Palo Alto, California.