Friday, October 31, 2014

Monday, October 27, 2014

What an Active Region!

What an active region 12192 has been! Six X-class flares in 9 days. Here is an HMI image of AR 12192 at 1615 UTC on 23-Oct-2014. You can see a couple light bridges going across the sunspots. There are some partial bridges in the left hand sunspot. But no matter how hard I squint I can't see a jack-o-lantern. It will soon be lost to view as it rotates over the limb of the Sun. Large flares often (but not always) come from large active regions. How did AR 12192 rank in size among active regions?

I downloaded the active region dataset produced by David Hathaway at Marshall SFC and looked at the largest active regions since 1874. This area data comes from the photographs taken at the Royal Greenwich Observatory until 1976 and various sources after that. I checked the list against the tables in Sunspot and Geomagnetic-Storm Data by Sir H. Spencer Jones just to make sure. I also added two regions from 2014 (AR 12192, of course, and AR 11967). Areas of active regions are measured in micro-hems (millionths of a solar hemisphere, where 1 micro-hem is about 1.54 million sq km.)

Here is the plot of maximum area of active regions in time. There are 32908 active regions in this plot. The color and symbol size changes as the area increases. AR 12192 is drawn as a black dot all the way at the right side of the plot. There is a dashed line drawn at 2750 micro-hems to help you compare this area with the others. From this we see that AR 12192 ranks 33rd in a list of active region sizes, not the biggest but in the top 0.1%. It is bracketed by AR 4497 on 08-Jan-1897 (2743 micro-hems) and AR 19109 on 08-Jan-1959 (2805 micro-hems). The area of the Earth is 83 micro-hems, meaning AR 12192 has an area of about 33 Earths.

The yearly Sunspot Number is drawn as a red line. This allows you compare how the maximum area of active regions changes with the number of active regions. It was surprising that the largest active regions are not in Solar Cycle 19, which has the largest amplitude in Sunspot Number, but in Solar Cycle 18. The top 5 active regions appeared between 1946 and 1951. Solar Cycle 19 started in 1954. The next set of large active regions have areas of 3000-4000 micro-hems and are spread across many sunspot cycles.

How big was the active region that was the site of the Carrington Flare? It was 2300 micro-hems, not even in the top 50! You can look it up on p. 102 of the table by Jones. The flare on 1-Sep-1859 has been estimated at X35, showing that large flares can come from medium-sized active regions.

So long for now to AR 12192 but perhaps we will see you next rotation!

Wednesday, October 22, 2014

It's Flare Season!

Active Region 12192 has grown to 2410 millionths of a solar hemisphere (0.2410 % of one side of the Sun), making it one of the larger active regions in Solar Cycle 24. It unleashed an X1.6 solar flare at 1400 UTC (10:00 am ET) today. Here is an HMI continuum, image with the visible active regions labeled. It had already been the site of several M flares and a half dozen C flares. This pattern of large active regions (and large flares) is common for Solar Cycles. Some of the largest flares ever recorded were in the later stages of Solar Cycle 23, and were also in the southern hemisphere of the Sun. I have been told AR 12192 is visible to a well-protected eye without a telescope. The rain in the Mid-Atlantic will prevent me from testing that, but others can check that out. (Always use appropriate eye protection when looking at the Sun! Eclipse glasses or other tested and approved filters should be used.)

This active region has caused a "Major Flare Watch" to be declared, so the two calibration maneuvers SDO had scheduled for today will be done in two weeks. Here is a summary of our projected activities for the rest of 2014.

  • 10/20/2014: Null Bias Application
  • 10/29/2014: EVE Cruciform (@1800ut)
  • 10/30/2014: Null Bias Removal
  • 11/05/2014: EVE FOV (1315-1537 UTC) and HMI/AIA Flatfield (1630-1907 UTC) Calibration Maneuvers
  • 11/12/2014: Null Bias Application
  • 11/22/2014: Lunar Transit (2229-2304 UTC)
  • 12/01/2014: Null Bias Removal