Future sunspots may behave like the Cheshire Cat: “the smile is there (magnetic fields) but the body is missing (no dark markings)“. Dr Bill Livingston and Dr Matt Penn of the National Solar Observatory have been recording the average magnetic field strength of sunspots for the past 13 years. What they have found is a decline of about 50 gauss per year during Cycle 23 and continuing in Cycle 24. See their chart below:
Typical sunspot magnetic field strength registers about “2500 to 3500 gauss” based upon their research. But Cycle 24 spots are running about 2000 gauss and Livingston and Penn are estimating that if the sunspot field strength drops to 1500 gauss: “the spots will largely disappear as the magnetic field is no longer strong enough to overcome forces on the solar surface.” That could occur in the next ten years, coinciding with Cycle 25.
Traditionally the measurements of sunspots seem to have focused on visible light and magnetic flux. Livingston and Penn emphasized the sunspot IR and magnetic field strength and that has brought a new perspective which seems to correlate with the other recent discoveries that were announced on 14 June 2011 at the AAS meeting in Las Cruces NM.
Dr Leif Svalgaard used Livingston and Penn data to illustrate the interrelationship of the magnetic field strength and visibility.
The pink line is visibility where 1 means invisibility. This “visibility/invisibility” is somewhat perverse. The spot (black) will no longer be seen because its temperature at the Sun’s surface is essentially the same as the surrounding gases. The black line is magnetic field strength.
Sunspots appear dark because they are cooler than the rest of the solar surface. From posting by Space.com: “The dark, heart of a sunspot, called the umbra, is surrounded by a brighter edge know as the penumbra, which is made of numerous dark and light filaments more than 1,200 miles long. They are relatively thin at approximately 90miles in width, making it difficult to resolve the detail of how they arise.
A photo of a sunspot taken in May 2010, with Earth shown to scale. The image has been colorized for aesthetic reasons. This image with 0.1 arcsecond resolution from the Swedish 1-m Solar Telescope represents the limit of what is currently possible in terms of spatial resolution.
Now scientists have discovered these columns are rapid downflows and upflows of gas, matching recent theoretical models and computer simulations suggesting these filaments are generated by the movement of hot and cold gases known as convective flow.
The researchers used the Swedish 1-meter Solar Telescope to focus on a sunspot on May 23, 2010. They found dark downflows of more than 2,200 miles per hour (3,600 kph) and bright upflows of more than 6,600 miles per hour (10,800 kph). The models suggest that columns of hot gas rise up from the interior of the sunspot, widen, cool and then sink downward while rapidly flowing outward.