Authors

Citation

Na. Silant'Ev, The estimations of magnetic field fluctuations atmospheres in turbulent, ASTRON ASTR, 370(2), 2001, pp. 533-540

Citations number

19

Language

INGLESE

art.tipo

Article

Categorie Soggetti

Space Sciences

Journal title

ASTRONOMY AND ASTROPHYSICS

ISSN journal

0004-6361
→ ACNP

Volume

370

Issue

2

Year of publication

2001

Pages

533 - 540

Database

ISI

SICI code

0004-6361(200105)370:2<533:TEOMFF>2.0.ZU;2-M

Abstract

We qualitatively analyze the equations of the magnetohydrodynamics for vari
ous quadratic fluctuations of the magnetic field and the vector potential.
For the stationary inhomogeneous state, rye have established the exact inte
gral relations between the magnetic field fluctuations b(r, t) and the mean
magnetic field B-0(r, t). We estimate alpha approximate to (eta + beta )B-
0 (del x B-0)/B-0(2) where eta and beta are the ohmic (molecular) and turbu
lent diffusivities, respectively. The alpha - coefficient describes the enh
ancement of the mean magnetic field. We found that the exact Seehafer formu
la B-0.<u x b > = -eta <b.(del x b)> is also valid for the locally stationa
ry and homogeneous evolution of magnetic fluctuations (u is the Euler turbu
lent velocity). It is shown that tile usual a-coefficient; more correctly t
he term alphaB(0).(del x B-0), presents with opposite signs in equations fo
r B-0(2) and <b(2)>, i.e. the rate of increase of the total magnetic energy
does not depend directly on this coefficient. T We show that at the moment
tb of the maximum of magnetic fluctuations, <b(2)> approximate to B-0(2).
The same also holds for the locally homogeneous and stationary regime if th
e spectrum of tile turbulence has a slow decrease in the inertial region of
wave numbers. The detailed analysis of two-dimensional turbulence has show
n that the Zeldovich estimate <b(2)> approximate to beta/etaB(0)(2) is vali
d only at the maximum of the vector potential fluctuations. This estimate i
s corrected such that at tb it also gives <b(2)> approximate to B-0(2). We
also give the approximate expression for tile alpha -coefficient which take
s into account the back reaction of the mean magnetic field onto the turbul
ence itself.