Decorrelation time scale for turbulent structures in the solar wind

DASSO, S.; MATTHAEUS, W.H.; WEYGAND, J. M.; KIVELSON M.G.; MILANO, L.J.

Saint-Malo, France

Conferencia; Solar Wind 12; 2009

American Physical Society

The solar wind (SW) contains a very important level of fluctuations,which at 1 AU can be studied in the framework of the magnetohydrodynamic(MHD) turbulence for spatial scales in the range of $\sim 10^2-10^6$ km.These fluctuations in the SW are usually anisotropic, and frequently presentdifferent anisotropic properties in regions of the SW with different global magneticconnectivities (e.g., magnetic clouds) or different bulk plasma parameters.Previous studies analyzed turbulent properties of the SW, e.g. the magneticselfcorrelation function, using two times -- single point measurements,which assumes the analogues to the Taylor 'frozen-in-flow' hypothesis in hydrodynamics.However, the intrinsic mixing between spatial structures and their time evolutionproduced during the time of observation, can affect the interpretation of detailedobservations (e.g., anisotropy). Thus, it makes feasible the question:'How exact can be considered this hypothesis for SW turbulence studies ?';The answer can be determined by examining data from multiple spacecrafts,taking simultaneous measurements separated in space.In the present study we compare the magnetic autocorrelation functionfor the inertial range in the SW obtained from two times -- single pointobservations (single spacecraft) with the same quantity obtainedfrom single time -- two points measurements (two spacecraft).From this comparison we give estimations for the decorrelation time scalefor turbulent structures in the solar wind at 1AU combining {\it in situ} observationsfrom ACE and Wind spacecraft.