A Remarkable Recent Transition in the Solar Dynamo

We summarize the major aspects of the remarkable, fairly long lasting period(∼ 2005 to ∼ 2010) of low solar activity, that we will call the Transition. It is the transitionalstage between the Grand Maximum of the 20th century and a forthcoming (most probablyRegular) episode of solar activity. The various kinds of activity in the functioning of theequatorial components of the solar dynamo before and during the Transition are summarized.While the behavior of unipolar magnetic regions and their rest-latitudes already gavevery early indications – mid 20th century – of the forthcoming Transition, more such indicationsbecame available around 1995 and the main part of it occurred between 2005 and 2010.Some of the inferences are discussed.We submit the hypothesis that the solar tachocline undergoespulsations and we present some helioseismic evidences. In that scenario we findthat its equatorial part has moved downward over a fairly small semi-amplitude (∼ 0.03solar radii) during the time of the Transition. There are several indications, apart from this‘pulsation’, that the tachocline may even be pulsating with still smaller amplitudes in moremodes. We speculate about the physical mechanism(s)