Historical records of the Great S. Tropical Disturbance (STropD) passing the Great Red Spot (GRS), 1902-1913.

In 2018, we have been watching a STropD passing the GRS, a phenomenon that has never before been observed at such high resolution.  This encounter was keenly awaited because of the remarkable behaviour of the great STropD over a century ago.  The great STropD appeared in 1901 [refs.1-3].  It always moved faster (eastward) than the GRS, so it caught up and overtook the GRS six times from 1902 to 1913.  Whenever it caught up with the GRS, the preceding (east) end of the STropD (p-STropD) was reported to stream rapidly round the south side of the GRS and to re-form p. the GRS within days or weeks [ref.1: Fig.1]. However in 2018, although dark material and intense turbulence from the STropD has been streaming round the S side of the GRS for 3.5 months, it has still not re-formed a p-STropD.

Therefore, I have reviewed the accounts of 1902-1913 in the original BAA Journals and Memoirs.  To summarise the conclusions: the observations (all visual) were often incomplete, and very few good drawings were published.  On the first passage of the p-STropD past the GRS, in 1902, it was reported to have re-formed rapidly but this does not seem to be well established.  (Original strip-maps by P.B. Molesworth in 1902 are published here for the first time.)  The second passage (1904) was not observable, but the next 4 passages (1906, 1908, 1910, 1913) all occurred in a more subtle and prolonged manner.  The p-STropD was not actually observed for some weeks after it arrived at the RSH, then it only formed indistinctly, via vague ill-defined shadings. Although it did eventually reappear in its classic curved dark form on each occasion, the idea that it had passed the GRS rapidly (taking only days or weeks) was only inferred by extrapolating its subsequent motion back to the RSH. 

Here is the full report:  STropD_historical review-JHR.pdf

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