Monster minimum or short solar cycle?
Guest essay by David Archibald
This recent post was on the fact that the Sun’s EUV emissions had fallen to solar minimum-like levels well ahead of solar minimum. The implication was that the Solar Cycle 24/25 minimum was either going to be very deep and prolonged, or that Solar Cycle 24 would be very short, which in turn would be strange for a weak cycle.
The indicator of the EUV flux is the Lyman alpha index. To recap, this chart shows the index over the last three cycles, starting from solar minimum:
Figure 1: Lyman alpha index Solar Cycles 22,23,24
Figure 1 shows that Solar Cycle 24 has reached solar minimum-like levels three years ahead of minimum, if Solar Cycle was going to be 12 years long. What happens at solar minimum is that the proportion of EUV as part of Total Solar Irradiance…
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