Dual sunspots and solar weather observation
Friday, October 17th, 2008For the first time in many months, Sol presently features more than one sunspot. As the Sun (belatedly) pulls out of an extended lapse in sunspot activity, it becomes increasingly unlikely that we’re in for anything like the Maunder Minimum, a 17th century dip in sunspot numbers correlated (which proves nothing about causation!) with the Little Ice Age. It was always a matter of piling long-shot atop long-shot to suppose that such a change in solar behavior was a) under way, and b) likely to affect climate dramatically. However, with man-made climate change pointed the other way, a small reduction in solar irradiance would have been a welcome development.
It now looks like the solar cycle is back on track, but that doesn’t mean nothing interesting is happening. The spacecraft Ulysses–18 years old and on the verge of failure even as it transmits important data–reports solar wind levels are the lowest ever recorded. Meanwhile, I’ve heard an unconfirmed report that Earth’s magnetic field, slowly declining for years, has jumped significantly during the current solar minimum. As far as I know, nobody has even proposed an explanation for either of these developments.
We know very little about the Sun or the energy transfer dynamics of the Solar System. Thanks to the increasing political importance of climate-change research, that is finally slated to change. Ulysses was a great spacecraft, but it is ready to be replaced by a new generation of solar observation satellites. Among these is SORCE, the SOlar Radiation and Climate Experiment, launched in 2003. If you’re interested in modern satellite design and instrumentation, I strongly encourage you to check out that link. This is a well conceived and designed set of sensors, with a website far more detailed and informative than we are usually treated to. I eagerly await reliable information about long-term trends in total solar irradiance and spectroscopy.
UPDATE: One important measurement that cannot be made by satellites in low Earth orbit is solar wind velocity. We can’t reliably measure this from near Earth, because of interference from the Earth’s magnetic field. The logical successor of Ulysses in making observations that require some distance from Earth is SOHO, which has something of a storied history, located about 1.5 gigameters toward the Sun. SOHO has one instrument, SWAN, which should be able to estimate the mass flux of the solar wind. It operates by detecting the surface of intersection between the solar wind and electrically neutral particles from interstellar space. Given the availability of SWAN, I’m a little perplexed as to why NASA and others are referring to Ulysses’ solar wind observations rather than SOHO’s. Is something wrong, either technically or theoretically, with SWAN? If so, with the imminent death of Ulysses, we may lose the ability to monitor solar wind even as variations are being observed that may not repeat themselves for years or centuries. At least, off the top of my head, I don’t know of another current mission that can observe the solar wind.