Transient evolution regimes in a multiscale dynamo model: Timescales of the reversal mechanism | INSTITUT DE PHYSIQUE DU GLOBE DE PARIS

Twitter

Aller au compte twitter

  Transient evolution regimes in a multiscale dynamo model: Timescales of the reversal mechanism

Type de publication:

Journal Article

Source:

Journal of Geophysical Research-Solid Earth, Volume 110, Ticket B1 (2005)

ISBN:

0148-0227

URL:

http://www.agu.org/journals/jb/

Mots-clés:

INTENSITY; MANTLE

Résumé:

<p>In order to better understand the origin and nature of reversals of the Earth's magnetic field, we examine the reversal mechanism of a multiscale dynamo model. This model can be described as a cellular automaton with long-range interaction. Different states correspond to different types of helical motions, and a hierarchical structure of length scales is used to mimic helicity transfers in fully developed turbulence. These multiscale helical motions and a differential rotation are the ingredients of a schematic alphaomega dynamo. The model exhibits rich behavior, including long periods of stable magnetic polarity (i.e., chrons), sudden reversals, excursions, and secular variation. Three transient regimes of evolution emerge: (1) Chrons are initiated by an amplification mechanism, which involves spontaneous reorientation of large length scale circulation and an alpha-quenching mechanism reinforcing the asymmetry of flow during runaway growth in magnetic field intensity. (2) During the chrons the injection of turbulence at small length scale slowly restores the symmetry of the system and leads to reversal. (3) During reversals the magnetic field does not remember its previous polarity, its intensity collapses, and spontaneous reorientation of large length scale circulation is more likely to occur (see regime 1). Reversal duration therefore corresponds to an upper value of the time constants for underlying turbulence in the absence of a magnetic field. We observe a constant excursion rate during chrons and a power law relationship between the reversal rate and the magnitude of helical forcing until a limit for dynamo action is reached. Extrapolated to the Earth's dipole field, this model predicts the duration of both chrons and reversals and sheds light on physical processes that may be responsible for their systematic occurrence.</p>

Notes:

J. Geophys. Res.-Solid EarthISI Document Delivery No.: 891KVTimes Cited: 0Cited Reference Count: 49Cited References:ANDLER D, 2002, PHILOS SCIBAK P, 1997, HOW NATURE WORKSBLANTER EM, 1999, PHYS REV E A, V59, P5112BLANTER EM, 2002, PHYS REV E 1, V65BLOXHAM J, 1989, PHILOS T R SOC A, V329, P415BRAGINSKY SI, 1987, GEOPHYS ASTRO FLUID, V38, P327BRITO D, 1995, PHYS EARTH PLANET IN, V91, P77BULLARD EC, 1955, P CAMBRIDGE PHIL SOC, V51, P744CANDE SC, 1995, J GEOPHYS RES, V100, P6093COURTILLOT V, 1978, CR ACAD SCI D NAT, V287, P1095DORMY E, 2000, GEOCHEM GEOPHYS GEOS, V1FRISCH U, 1975, J FLUID MECH, V68, P769GAILITIS A, 2000, PHYS REV LETT, V84, P4365GIRE C, 1990, PHYS EARTH PLANET IN, V59, P259GLATZMAIER GA, 1995, NATURE, V377, P203GLATZMAIER GA, 1995, PHYS EARTH PLANET IN, V91, P63GUYODO Y, 1999, NATURE, V399, P249HIDE R, 1995, GEOPHYS RES LETT, V22, P1057HOLLERBACH R, 1992, GEOPHYS ASTROPHYS FL, V67, P1HOYNG P, 2001, GEOPHYS ASTRO FLUID, V94, P263HOYNG P, 2002, PHYS EARTH PLANET IN, V130, P143HULOT G, 2002, NATURE, V416, P620JAULT D, 1995, GEOPHYS ASTRO FLUID, V79, P99JONKERS ART, 2003, PHYS EARTH PLANET IN, V135, P253KADANOFF LP, 2001, PHYS TODAY, V54, P34KAGEYAMA A, 1997, PHYS REV E, V55, P4617KRAUSE F, 1980, MEAN FIELD MAGNETOHYKUANG WL, 1997, NATURE, V389, P371LABROSSE S, 1997, PHYS EARTH PLANET IN, V99, P1LABROSSE S, 2002, EARTH PLANET SC LETT, V199, P147LEHUY M, 2000, EARTH PLANETS SPACE, V52, P163LEMOUEL JL, 1997, P NATL ACAD SCI USA, V94, P5510MACMILLAN S, 1996, EARTH PLANET SC LETT, V137, P189MERRILL RT, 1996, INT GEOPHYS SER, V63MOFFATT HK, 1978, MAGNETIC FIELD GENERMOFFATT HK, 1994, GEOPHYS J INT, V117, P394NARTEAU C, 2000, PHYS EARTH PLANET IN, V120, P271NIEMELA JJ, 2000, NATURE, V404, P837OLSON P, 1999, J GEOPHYS RES-SOL EA, V104, P10383POUQUET A, 1978, J FLUID MECH, V85, P305QUIDELLEUR X, 2003, EARTH PLANET SC LETT, V208, P149RIKITAKE T, 1958, P CAMBRIDGE PHIL SOC, V54, P89ROBERTS PH, 1965, J GEOMAGN GEOLECTR, V17, P137SREENIVASAN KR, 2002, PHYS REV E 2, V65TILGNER A, 2000, PHYS EARTH PLANET IN, V117, P171VALET JP, 1993, NATURE, V366, P234VALET JP, 2003, REV GEOPHYS, V41WOLFRAM S, 1986, THEORY APPL CELLULARZHANG KK, 2000, ANNU REV FLUID MECH, V32, P409B01104