The above image of the sun shows the very Active Region 1504, which has been so since rotating into view June 10th. Image Credit: SDO/HMI
Since it came around the left limb of the sun on June 10, Active Region 1504 (AR 1504) has been just that. An now it has produced two M-class solar flares and two coronal mass ejections (CMEs). But before we proceed, lets make sure everyone is comfortable with some terminology.
Solar Flare Primer
To review, a solar flare is an explosion on the sun that occurs when the energy stored in twisted magnetic fields (usually above sunspots) is suddenly released. Flares produce a burst of radiation across the electromagnetic spectrum, from radio waves to X-rays and gamma-rays.
Solar flares are classified, from lowest to highest, as A, B, C, M and X according to the peak flux (in watts per square meter, W/m^2) of 100 to 800 picometer X-rays near Earth, as measured on the GOES spacecraft. The five categories break down as follows.
A-class: Peak flux of less than 10^-7 Watts/square meter. A-class flares produce no noticeable consequences on Earth.
B-class: Peak flux ranges from 10^-7 to 10^-6 Watts/square meter. B-class flares produce no noticeable consequences on Earth.
C-class: Peak flux ranges from 10^-6 to 10^-5 Watts/square meter. C-class flares produce few noticeable consequences
M-class: Peak flux ranges from 10^-5 to 10^-4 Watts/square meter. M-class flares can cause brief radio blackouts that affect Earth's polar regions. Minor radiation storms sometimes follow an M-class flare.
X-class: Peak flux is greater than 10^-4 Watts/square meter. X-class flare are major events that can trigger planet-wide radio blackouts and long-lasting radiation storms.
Within each category are nine subdivisions of strength. For example, C1 to C9, M1 to M9, and so on. On July 14, 2000, the sun produced a X6 flare which triggered a major radiation storm around Earth and was nicknamed the Bastille Day event.
Coronal Mass Ejection Primer
A coronal mass ejection (CME) is a massive burst of solar wind, plasma, and magnetic fields rising above the solar corona or being released into space.
CMEs are often associated with other forms of solar activity, most notably solar flares, but a causal relationship between the two has not been established. Most CMEs originate from active regions on Sun's surface, such as groupings of sunspots associated with frequent flares. Near a solar maximum — the period of greatest activity in a solar cycle — the sun produces about three CMEs every day, whereas near a solar minimum — the period of least activity in a solar cycle — there is about one CME every five days.
Now, Where Were We?...
Oh, yes. The region AR 1504 fired off two M-class flares and two CMEs on June 13th and June 14th. The first flare lasted for a relatively long three hours, peaking on June 13th at 9:17 AM EDT. The associated CME traveled at approximately 375 miles per second and is directed toward Earth, though due to its slow speed, the effect on Earth is expected to be minimal.
The second M-class flare was also a long-duration flare, and it peaked on June 14th at 10:08 AM EDT. The CME associated with this flare is traveling much faster – preliminary analysis at Goddard's Space Weather Center indicates it is traveling at speeds of approximately 800 miles per second. It is traveling toward Earth, and could also impact Mars and the Spitzer spacecraft.
Current models estimate that both CMEs will arrive on June 16th. Please stay tuned for more details as we learn them.
To learn more about the sun and to stay current on solar activity, visit the mission home page of Solar Dynamics Observatory (SDO), sdo.gsfc.nasa.gov/ .