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Irrotational flow is characterized by fluid motion where particles do not rotate around their axes, resulting in zero vorticity. For a flow to be irrotational, the curl of the velocity field must be zero. This imposes specific conditions on velocity gradients. For instance, to maintain zero rotation about the z-axis, the gradient condition:
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Surface Renewal: An Advanced Micrometeorological Method for Measuring and Processing Field-Scale Energy Flux Density Data
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Flows around Averaged Solar Active Regions.

D C Braun1

  • 1NorthWest Research Associates, 3380 Mitchell Lane, Boulder, CO 80301, USA.

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|May 7, 2021
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Summary
This summary is machine-generated.

Near-surface solar active regions exhibit converging flows and retrograde flows. These flows, measured using helioseismic holography, likely contribute to global-scale solar flows.

Keywords:
Sun: activitySun: helioseismologySun: magnetic fieldssunspots

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Area of Science:

  • Solar Physics
  • Helioseismology
  • Plasma Physics

Background:

  • Solar active regions are dynamic areas on the Sun's surface.
  • Understanding near-surface flows is crucial for solar dynamics.

Purpose of the Study:

  • To characterize near-surface flows around solar active regions.
  • To investigate the contribution of these flows to global solar circulation.

Main Methods:

  • Helioseismic holography applied to HMI Dopplergrams from the Solar Dynamics Observatory (SDO).
  • Ensemble averaging of flow measurements from 336 active regions (2010-2014).
  • Validation using MHD simulations of quiet-Sun convection and sunspots.

Main Results:

  • Prevalent converging flows (approx. 10 m/s) extending up to 10° from active region centers for flux > 10^21 Mx.
  • Retrograde flows (approx. 10 m/s) detected, primarily on the polar sides of active regions.
  • Active region flows plausibly contribute to time-varying global zonal and meridional flows.

Conclusions:

  • Near-surface flows in solar active regions possess distinct properties.
  • These flows are significant contributors to larger-scale solar circulation patterns.
  • Methodology validated, though potential artifacts in sunspot simulations noted.