Watts Up With That?

This arrived in my email tonight from Bill Livingston. It is hot off the press, date June 11th. I believe WUWT readers will be some of the first to see this. – Anthony

Guest Essay by:
W. Livingston, National Solar Observatory, 950 N. Cherry Ave, Tucson AZ 85718;
M. Penn, National Solar Observatory, Tucson AZ

Physical conditions in the infrared at 1.5 microns, including maximum magnetic field strength and temperature, have been observed spectroscopically in 1391 sunspots 1990 to 2009 (1). We emphasize the quantitative difference between our IR sunspot measurements and the visible light results from most solar magnetographs employed world-wide. The latter are compromised by scattered light and measure flux, not field strength. A lower limit of ~1800 Gauss is required to form spot umbra. The umbral maximum field strength has declined over the above interval, perhaps because spots have on average diminished in size. The present condition of solar activity minimum has more spotless days than since the 1910s (2). The Cheshire Cat behavior is related to magnetic surface fields often appearing without accompanying dark spots.

Sunspots recently are behaving like a Cheshire Cat: the smile is there (magnetic fields) but the body is missing (no dark markings). We are unsure about past cycles but at present sunspots, with their usual umbrae and penumbrae, are failing to materialize. For hundreds of years the Sun has shown an approximately periodic 11-year alteration in its activity where the number of sunspots increases and then decreases. Sunspots are dark regions on the solar disk with magnetic field strengths greater than 1500-1800 Gauss. The last sunspot maximum occurred in 2001. Magnetically active sunspots at that time (Figure 1A) produced powerful flares, caused large geomagnetic disturbances, and disrupted some space-based technology.

Figure 1a. An image of a sunspot from near the maximum of the last solar cycle, cycle 23, taken at the McMath-Pierce telescope on 24 October 2003. The sunspots clearly show a dark central umbra surrounded by a brighter, filamentary penumbra. The magnetic fields seen here range from 1797 to 3422 Gauss.

At present, presumably leaving a deep solar minimum, nothing more than tiny spots, or “pores”, have been seen for some time (again
Figure 1B).

Figure 1b. An image of a pore – a tiny sunspot with no penumbral structure – taken from the MDI instrument on the SOHO spacecraft, 11 January 2009; this is an example of what we observe today at solar minimum. The larger pore had a magnetic field of 1969 Gauss. Presently, the solar surface is mostly devoid of spots. Both images have the same spatial scale, and are roughly 360 Mm horizontally.

In the current solar minimum the number of spotless days has not been equaled since 1914 (2), see Figure 2. Some look at this figure and feel reassured; this has
happened before. Others sense abnormality. Read the rest of this entry »