Jupiter's Decametric Rotation Period I will comment upon the 1972 paper by Professor Carr :
In this work the author presented new accurate
values for the rotation period, based on 14 succesive years of
observation from UFRO, the University of Florida Radio Observatory.
Figure 4 summarizes the data : Notice the large variations in probability as the years go by.
WHY ??
There is a 11.9 year cycle in the activity of Source A (IoA nowadays).
Some investigators had proposed that it could be due to the solar
cycle, but Carr in 1962 and Douglas in 1964 had proposed the
alternative that the variation in the declination of the Earth, as seen
from Jupiter, was the real cause.
This figure shows IoA's probability versus Earth's declination DE and the Zurich Sunspot Number, with annotated years You can see that the correlation with DE between 1957 and 1971 is much better. Notice the more than 10 to 1 range in probabilities along the cycle.
The System III longitude of IoA (Source A) also shows a variation with a 11.9 year cycle, measured at 18 and 22.2 Mhz :
And the correlation between the Longitude and DE is very good :
The cause is the shape of the emission beam, as explained by Prof. Carr:
We know that this interpretation was detailed in the following years.
These are the very precise rotation periods determined from the UFRO observations between 1957 and 1971:
I had a wonderful time reading this classic paper.
