Tuesday, April 30, 2013

Time-Lapse 171 Image Question

The "Three Years of SDO Images" shows two bands of bright coronal loops in the 171 time-lapse image. Several people have asked whether this is real. Yes, it is real and it is caused by how sunspots form on the Sun.

We have seen that sunspots tend to occur below 35º latitude in both hemispheres of the Sun, just as you noticed. This gives us the Butterfly Diagram shown here for for sunspots since 1965. Northern active regions (or sunspots) are shown in blue and southern in red. A few regions appear at higher latitudes, but most sunspots are seen at low latitudes. Sunspots also tend to occur closer to the equator as a sunspot cycle moves along. They don't usually form at the equator, but the tilt of the Sun can make that difficult to verify.

The coronal loops in the time-lapse image follow this pattern because they live above sunspots. Although few sunspots and coronal loops are seen in the polar regions, prominences and coronal holes are seen there. We do not have a perfect explanation, but it comes from how material moves in the convection zone and how that movement creates magnetic fields. This is called the solar dynamo problem. Perhaps the explanation will be similar to why we have the Horse Latitudes here on Earth.