{
  "id": "1701.02723",
  "version": "v1",
  "published": "2017-01-10T18:39:04.000Z",
  "updated": "2017-01-10T18:39:04.000Z",
  "title": "Measurements of Solar Differential Rotation and Meridional Circulation from Tracking of Photospheric Magnetic Features",
  "authors": [
    "Derek A. Lamb"
  ],
  "comment": "Accepted by ApJ. 24 pages, 9 figures",
  "categories": [
    "astro-ph.SR"
  ],
  "abstract": "Long-lived rotational and meridional flows are important ingredients of the solar cycle. Magnetic field images have typically been used to measure these flows on the solar surface by cross-correlating thin longitudinal strips or square patches across sufficiently long time gaps. Here, I use one month of SDO/HMI line-of-sight magnetic field observations, combined with the SWAMIS magnetic feature tracking algorithm to measure the motion of individual features in these magnetograms. By controlling for perturbations due to short-lived flows and due to false motions from feature interactions, I effectively isolate the long-lived flows traced by the magnetic features. This allows me to produce high-fidelity differential rotation measurements with well-characterized variances and covariances of the fit parameters.I find a sidereal rotational profile of $(14.296\\pm0.006)+(-1.847\\pm0.056)\\sin^{2}b+(-2.615\\pm0.093)\\sin^{4}b$, with units of $\\textrm{ deg d}^{-1}$, and a large covariance $\\sigma_{BC}^{2}=-4.87\\times10^{-3}(\\textrm{ deg d}^{-1})^{2}$. I also produce medium-fidelity measurements of the much weaker meridional flow that is broadly consistent with previous results. This measurement shows a peak flow of $16.7\\pm0.6\\text{ m s}^{-1}$ at latitude $b=45^\\circ$ but is insufficiently characterized at higher latitudes to ascertain whether the chosen functional form $2\\cos b\\sin b$ is appropriate. This work shows that measuring the motions of individual features in photospheric magnetograms can produce high precision results in relatively short time spans, and suggests that high resolution non-longitudinally averaged photospheric velocity residual measurements could be produced to compare with coronal results, and to provide other diagnostics of the solar dynamo.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2017-01-10T18:39:04.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "solar differential rotation",
      "photospheric magnetic features",
      "high-fidelity differential rotation measurements",
      "meridional circulation",
      "line-of-sight magnetic field observations"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 24,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}