Happy 5th Birthday to SDO Science Data!

Today is the 5th birthday of SDO Science Data. On May 1, 2010, SDO was commissioned as a NASA observatory and began sending science data to scientists and the public. We have watched Solar Cycle 24 rise to solar maximum, storing about 7 PBytes of data, releasing almost 200 million images, and having about 1900 scientific papers published describing new things we have learned.

I thought I would share two new images that show the solar magnetic field as only SDO can. The first is the average of the HMI magnetic field at each point on the Sun. White areas show where the magnetic field points out of the Sun and black regions are where the field points into the Sun. Grey regions have a magnetic field of zero. The Carrington longitude is used to give features on the Sun a position. We use the sine(latitude) rather than the latitude to avoid having the Sun look distorted like the Mercator maps of the Earth. The little circles are individual active regions. Even though this is an average over the last 5 years, we can see diagonal swaths of field in both the north and south hemispheres.

The other picture is how much each point on the Sun changed over those five years. The white points changed a lot while the black points changed very little. Now you see the diagonal lines a little better. Most of the changes in the solar magnetic field happen in the "active latitudes" where sunspots and flares are found. Very little happens at high latitudes. There is also very little happening along the Sun's equator.
You should compare these pictures with the averages of AIA 171 released two years ago.

SDO was launched to study the Sun's magnetic field. It is done a great job of recording the magnetic field, flares, filaments, and coronal holes during the rise of Solar Cycle 24. As Solar Cycle 24 fades SDO will continue to measure and report the magnetic field and what that magnetic field does in the solar atmosphere.

Thanks to the HMI for creating the maps of the magnetic field I used to create these pictures, and many thanks to the entire SDO team for the amazing mission they have run for the last 5 years.

SDO is GO!

SDO on the Astronomy Picture of the Day

An very nice animation of SDO images for the month of January 2014 is featured on the Astronomy Picture of the Day for March 12, 2014. The images show the brighter active latitudes on either side of the equator, a coronal hole in the northern hemisphere, and filaments covering the disk of the Sun. In the HMI visible light image in the six-image montage you can see the sunspots that make up the active regions. The image is too small to see the faculae that go along with sunspots, but the latest HMI flattened image shows them quite well.

January's 31 days are a little longer than one solar rotation of 27.27 days. That means you see a part of the Sun that is just off limb at the beginning of the month a second time as that part of the Sun rotates back into view. Active region 11944 is present throughout the month in the southern hemisphere and reappears as AR 11967 at the end of the movie. AR 11946 grows in the northern hemisphere and will reappear as AR 11968. AR 11944 will also return as AR 11990 in late February. On February 25 it will be the location of an X-4.9 flare as it rotates back into view.

Long-lived active regions are a sign that solar maximum is here and starting to fade.

Check it out!

Solar Max Geek Out

When I think about solar maximum it isn’t just sunspot number. I think about how bright the Sun has gotten in the wavelengths of light that cause space weather. Satellite drag and radio outages are two space weather effects that are caused by light at extreme ultraviolet (EUV) wavelengths, roughly 10-125 nm. This light is so completely absorbed by the atmosphere that it never reaches the surface of the Earth. In space we must be to see the EUV.

Here is a squiggly line chart of the Sun's EUV brightness in six wavelengths, averaged over each day. The data come from EVE on SDO. The squiggles start in May 2010 and continue until February 2014. I plotted the logarithm of the brightness to make all of the lines visible. As the Sun emits more light at one wavelength the squiggle goes higher on the chart. Each line has a different color and they are labeled to the right with the element and wavelength of the line. The other number is we will explain in a minute. He II 304 is the brightest, followed by C III 977 and H I 1026. The three iron wavelengths are next.

You can make similar plots of each wavelength with the EVE data browser on the SDO website.

Since SDO was launched each of these wavelengths has gotten brighter in its own way. The peak He II 304 irradiance was in February 2014 and a horizontal line is drawn at that value. The smallest He II 304 value was in June 2010 and another horizontal line is drawn at that value. The ratio of the brightest to the dimmest is 2.1. The same max and min lines are drawn for the H I 1026 irradiance, with a ratio of 1.7. The Fe XVI 335 wavelength is 12 times brighter, the biggest ratio of these wavelengths. We now see that the other number in the label is the ratio of the brightest to the dimmest the Sun has been in the EVE data.

The biggest monthly sunspot number so far in Solar Cycle 24 is 97 in November 2011. I drew a vertical line at that date. The sunspot number was 91 for January 2014, a little less than November 2011. The iron wavelengths are all about the same brightness now as they were then, but He II 304 is distinctly brighter now. H I 1026 is as bright now as it was in November 2011. These differences in brightness during solar maximum show how complicated the sunspot cycle is.

The different wavelengths look the same at other times. A “wave” appears during the second half of 2012 in all six wavelengths. Each wave is a turn of the Sun. During this time the Sun was brighter and dimmer in a pattern that turned with the Sun. We see the rotations most of the time but 2012 is a great episode of “As the Sun Turns.”

These data show why it so difficult to say when solar maximum happened. Each wavelength has a different timing of it’s peak brightness. Even as we use sunspot number to say when solar maximum was, we should keep in mind that solar maximum is not a point in time but extends over several years.