Latitude Quenching Nonlinearity in the Solar Dynamo

TL;DR

This study compares two nonlinear mechanisms regulating the solar cycle, finding strong evidence for latitude quenching over tilt quenching, and suggests the Sun's dynamo operates within a narrow latitude range of less than 10 degrees.

Contribution

It provides empirical evidence favoring latitude quenching as the primary nonlinear regulation in the solar dynamo, supported by historical observations and flux transport modeling.

Findings

Strong evidence for latitude quenching in solar cycle regulation

Weak evidence for tilt quenching from historical data

Dynamo effectivity range is less than 10 degrees

Abstract

We compare two candidate nonlinearities for regulating the solar cycle within the Babcock-Leighton paradigm: tilt quenching (whereby the tilt of active regions is reduced in stronger cycles) and latitude quenching (whereby flux emerges at higher latitudes in stronger solar cycles). Digitized historical observations are used to build a database of individual magnetic plage regions from 1923 to 1985. The regions are selected by thresholding in Ca II K synoptic maps, with polarities constrained using Mount Wilson Observatory sunspot measurements. The resulting data show weak evidence for tilt quenching, but much stronger evidence for latitude-quenching. Further, we use proxy observations of the polar field from faculae to construct a best-fit surface flux transport model driven by our database of emerging regions. A better fit is obtained when the sunspot measurements are used, compared to a reference model where all polarities are filled using Hale's Law. The optimization suggests clearly that the "dynamo effectivity range" of the Sun during this period should be less than 10 degrees; this is also consistent with latitude quenching being dominant over tilt quenching.