{
  "id": "1601.06348",
  "version": "v1",
  "published": "2016-01-24T06:15:15.000Z",
  "updated": "2016-01-24T06:15:15.000Z",
  "title": "A new simple dynamo model for stellar activity cycle",
  "authors": [
    "Nobumitsu Yokoi",
    "Dieter Schmitt",
    "Valery Pipin",
    "Fujihiro Hamba"
  ],
  "comment": "14 pages, 6 figures",
  "categories": [
    "astro-ph.SR",
    "physics.flu-dyn"
  ],
  "abstract": "A new simple dynamo model for stellar activity cycle is proposed. By considering an inhomogeneous mean flow effect on turbulence, it is shown that turbulent cross helicity (velocity--magnetic-field correlation) should enter the expression of turbulent electromotive force as the coupling coefficient for the mean absolute vorticity. The inclusion of the cross-helicity effect makes the present model different from the current $\\alpha$--$\\Omega$-type models mainly in two points. First, in addition to the usual $\\alpha$ (helicity effect) and $\\beta$ (turbulent magnetic diffusivity), we consider the $\\gamma$ coefficient (cross-helicity effect). Second, unlike the $\\alpha$ and $\\beta$ coefficients, which are often treated as an adjustable parameter in the current studies, the spatiotemporal evolution of $\\gamma$ coefficient should be solved simultaneously with the mean magnetic-field equations. The basic scenario for the stellar activity cycle in the present model is as follows: In the presence of turbulent cross helicity, the toroidal field is induced by the toroidal rotation in mediation by the turbulent cross helicity. Then, as usual models, the $\\alpha$ or helicity effect generates the poloidal field from the toroidal one. This poloidal field, induced by the $\\alpha$ effect, produces a turbulent cross helicity whose sign is opposite to the original one (negative production of cross helicity). The cross helicity with the opposite sign starts producing a reversed toroidal field. Eigenvalue analyses of the simplest possible present model give a butterfly diagram, which confirms the above scenario as well as the equator-ward migrations, the phase relationship between the cross helicity and magnetic fields, etc.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2016-01-24T06:15:15.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "stellar activity cycle",
      "simple dynamo model",
      "turbulent cross helicity",
      "poloidal field",
      "coefficient"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 14,
      "language": "en",
      "license": "arXiv",
      "status": "editable",
      "adsabs": "2016arXiv160106348Y"
    }
  }
}