Measuring solar active region inflows with local correlation tracking of granulation

Löptien, Björn; Birch, A. C.; Duvall, T. L.; Gizon, Laurent; Proxauf, Bastian; Schou, J.

doi:10.1051/0004-6361/201731064

Cited by 32 publications

(85 citation statements)

References 31 publications

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“…However, the predominance of 10 m s −1 retrograde flows towards the polar side of ARs is plausibly consistent with the net cyclonic circulation of ∼ 5 m s −1 found by Hindman et al (2009) around AR peripheries. On the other hand, the retrograde flows do not readily appear in the ensemble averaged flow map shown in Figure 8 of Löptien et al (2017). This discrepancy is not understood, but may result from differences in the background trend removal or other details in the analyses.…”

Section: Discussionmentioning

confidence: 97%

Flows around Averaged Solar Active Regions

Braun

2019

ApJ

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We explore the general properties of near-surface flows around solar active regions. Helioseismic holography is applied to HMI Dopplergrams yielding nearly 5000 flow measurements of 336 unique active regions observed by the Solar Dynamics Observatory between 2010 and 2014. Ensemble averages of the flows, over subsets of regions sorted on the basis of magnetic flux, are performed. These averages show that converging flows, with speeds about 10 m s −1 and extending up to 10 • from the active region centers, are prevalent and have similar properties for all regions with magnetic flux above 10 21 Mx. Retrograde flows are also detected, with amplitudes around 10 m s −1 , which predominantly, but not exclusively, flank the polar side of the active regions. We estimate the expected contribution of these active-region flows to longitudinal averages of zonal and meridional flows and demonstrate the plausibility that they are responsible for at least some component of the time-varying global-scale flows. The reliability of our flow determination is tested using publicly available MHD simulations of both quiet-Sun convection and of a sunspot. While validating the overall methodology in general, the sunspot simulation demonstrates the presence of artifacts which may compromise quantitative flow inferences from some helioseismic measurements.

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Section: Discussionmentioning

confidence: 97%

Flows around Averaged Solar Active Regions

Braun

2019

ApJ

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“…On the other hand, the activity-related meridional flow pattern may partly originate from the superposition of more localized circular inflows towards individual active regions (Haber et al 2004;Š vanda et al 2008;Löptien et al 2017). It is unclear whether such concentric flows can exert a torque on the flux loops that may reduce their tilt; however this may not even be necessary: simulations by Martin-Belda and suggested that the hindering effect on the inflows on the separation of leading and trailing polarity fluxes is sufficient to significantly reduce the amplitude of the dipolar seed field being built up for the next cycle.…”

Section: Alternatives To Tilt Quenching: Inflows and Latitude Quenchingmentioning

confidence: 99%

Solar cycle prediction

Petrovay

2020

Living Rev Sol Phys

200

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A review of solar cycle prediction methods and their performance is given, including early forecasts for Cycle 25. The review focuses on those aspects of the solar cycle prediction problem that have a bearing on dynamo theory. The scope of the review is further restricted to the issue of predicting the amplitude (and optionally the epoch) of an upcoming solar maximum no later than right after the start of the given cycle. Prediction methods form three main groups. Precursor methods rely on the value of some measure of solar activity or magnetism at a specified time to predict the amplitude of the following solar maximum. The choice of a good precursor often implies considerable physical insight: indeed, it has become increasingly clear that the transition from purely empirical precursors to model-based methods is continuous. Model-based approaches can be further divided into two groups: predictions based on surface flux transport models and on consistent dynamo models. The implicit assumption of precursor methods is that each numbered solar cycle is a consistent unit in itself, while solar activity seems to consist of a series of much less tightly intercorrelated individual cycles. Extrapolation methods, in contrast, are based on the premise that the physical process giving rise to the sunspot number record is statistically homogeneous, i.e., the mathematical regularities underlying its variations are the same at any point of time, and therefore it lends itself to analysis and forecasting by time series methods. In their overall performance during the course of the last few solar cycles, precursor methods have clearly been superior to extrapolation methods. One method that has This article is a revised version of

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“…We used an updated version of the flow maps generated by Löptien et al (2017), who described their processing procedure in detail. We summarize the important aspects below.…”

Section: Flows Inferred From Local Correlation Trackingmentioning

confidence: 99%

“…This work showed that the amplitude of the flows increases with magnetic flux, and reported a retrograde flow component mainly at the poleward side and, less distinct, the equatorward side of the AR. Löptien et al (2017) used local correlation tracking (LCT, November & Simon 1988) of the convective granulation pattern on the solar surface to measure inflows around an average highflux AR. The regions in their sample have fluxes higher than 5.9×10 21 Mx.…”

Section: Introductionmentioning

confidence: 99%

Evolution of solar surface inflows around emerging active regions

Gottschling

Schunker

Birch

et al. 2021

A&A

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Context. Solar active regions are associated with Evershed outflows in sunspot penumbrae, moat outflows surrounding sunspots, and extended inflows surrounding active regions. Extended inflows have been identified around established active regions with various methods. The evolution of these inflows and their dependence on active region properties as well as their effect on the global magnetic field are not yet understood. Aims. We aim to understand the evolution of the average inflows around emerging active regions and to derive an empirical model for these inflows. We expect that this can be used to better understand how the inflows act on the diffusion of the magnetic field in active regions. Methods. We analyzed horizontal flows at the surface of the Sun using local correlation tracking of solar granules observed in continuum images of the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory. We measured average flows of a sample of 182 isolated active regions up to seven days before and after their emergence onto the solar surface with a cadence of 12 h. About half of the active regions in the sample developed sunspots with moat flows in addition to the surrounding inflows. We investigated the average inflow properties with respect to active region characteristics of total flux and latitude. We fit a model to these observed inflows for a quantitative analysis. Results. We find that converging flows of about 20–30 m s−1 are first visible one day prior to emergence, in agreement with recent results. These converging flows are present regardless of the active region properties of latitude or flux. We confirm a recently found prograde flow of about 40 m s−1 at the leading polarity during emergence. We find that the time after emergence when the latitudinal inflows increase in amplitude depends on the flux of the active region, ranging from one to four days after emergence and increasing with flux. The largest extent of the inflows is up to about 7 ± 1° away from the center of the active region within the first six days after emergence. The inflow velocities have amplitudes of about 50 m s−1.

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Measuring solar active region inflows with local correlation tracking of granulation

Cited by 32 publications

References 31 publications

Flows around Averaged Solar Active Regions

Flows around Averaged Solar Active Regions

Solar cycle prediction

Evolution of solar surface inflows around emerging active regions

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