Taylor Scale and Effective Magnetic Reynolds Number Determination from Plasma Sheet and Solar Wind Magnetic Field Fluctuations

WEYGAND J.M.; MATTHAEUS W.H.; DASSO S.; KIVELSON M.G.; WALKER R.J.

JOURNAL OF GEOPHYSICAL RESEARCH

Año: 2007 vol. 112 p. 1 - 12

0148-0227

Cluster data from many different intervals in the magnetospheric plasmas sheetand the solar wind are employed to determine the magnetic Taylor microscalefrom simultaneous multiple point measurements. For this study we define theTaylor scale as the square root of the ratio of the mean square magnetic field(or velocity) fluctuations to the mean square spatial derivatives of theirfluctuations. The Taylor scale may be used, in the assumption of a classicalOhmic dissipation function, to estimate effective magnetic Reynolds numbers,as well as other properties of the small scale turbulence. Using solar windmagnetic field data, we have determined a Taylor scale value of 2400 ± 100km, which is used to obtain an effective magnetic Reynolds number of about260,000 ± 20,000, and in the plasma sheet we calculated a Taylor scale of1900 ± 100 km, which allowed us to obtain effective magnetic Reynolds numbersin the range of about 7 to 110. The present determination makes use of a novelextrapolation technique to derive a statistically stable estimate from a rangeof small scale measurements. These results may be useful inmagnetohydrodynamic modeling of the solar wind and the magnetosphere and mayprovide constraints on kinetic theories of dissipation in space plasmas.