Harry spies a Solar Dragon

February 18, 2017









2016 December, “Here be Dragons!”: Back in 2007 most Heliophysicists predicted that solar cycle 24 (SC24), the current cycle, would be a strong one: “the strongest for a century”, asserted one well known agency!  Only a few ‘lesser-known’s’ correctly predicted the current state of affairs. Why?

Basically, because the modelling of solar activity is still in its infancy and many were misled by the strong activity cycles of the second half of the 20C. Flaring, for instance, showed a steady rise in peak flare power (GOES Xray flux) over cycles SC21, 22 and 23. This trend, if extrapolated to SC24, suggests many flares with fluxes > X20. In reality, thus far, only one flare in SC24 has reached GOES X5 – just 25% of that trend level. All other measures of solar activity, and there are many, tell the same story: it’s the weakest cycle in a century!

Yet the Sun remains an exciting place for ‘explorers’ with narrowband ‘scopes. Here we consider some events in early December – and ponder what they tell us about current activity.

“Dragon”. Dec 8 at 21:15 UT(9th local date, Eastern Australian time) showed a spectacular prominence on the Sun’s NW limb. Though faint in parts, it looked like the ‘classical’ Chinese Dragon. Timings showed the ‘beast’ stretched around the limb for some 20deg of solar latitude, or 220Mm (220,000km), with detached ‘bits’ covering >300Mm, and the dragon’s ‘head’ towered 82Mm above the limb, with most of the ‘body’ ~40Mm high. Earth is shown to scale. A detailed sketch was made (Fig 2). Pity it wasn’t the ‘Year of the Dragon’!

Fig 1 maps the feature (schematic) at the solar limb – and also shows a disc filament logged on the 3rd (UT), five days earlier.  A single timing at the filament’s following (f) end sited it at +35°lat. and 163°long. (+35,163). The preceding (p) end is interpolated to lie at about +17,185.  When this ‘snaky’ filament rotated to the limb 5d later – it became the fearsome ‘Dragon’!

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