Numerical analysis for all of the 23 solar cycles appears to show presence of a short-term 400 day sub-cycle, Most of the normal cycles contain 3-4 (some even 5) sub-cycles, mainly evident during time of the more intense part of the normal cycle.

SC17 is the most prominent example.

SC17 compared to the most resent SC23 (SSNmax about 150) clearly shows that the sub-cycle intensity is not function of the SSNmax

If during a strong sub-cycle the Earth's magnetosphere is caught in the solar feedback loop this should be detectable in the secular changes of the Earth's magnetic field. Comparing Geomagnetic secular variability in the Epochs 1940 (SC17) and 2000 (SC23) appears to confirm the above assumption.

When the Earth's magnetosphere is well within the feedback loop, the sub-cycle is regular and the Earth's magnetic field shows greater secular variability.

More details here: Graphs and Formulae

© m.a. vukcevic