Characteristics of the Taylor microscale in the solar wind/foreshock: magnetic field and electron velocity measurements

摘要

The Taylor microscale is one of the fundamental turbulence scales.Not easily estimated in the interplanetary medium employing singlespacecraft data, it has generally been studied through two point correlations.In this paper we present an alternative, albeit mathematically equivalent,method for estimating the Taylor microscale (λ).We make two independent determinations employing multi-spacecraftdata sets from the Cluster mission, one using magnetic field dataand a second using electron velocity data. Our results using the magneticfield data set yields a scale length of 1538 ± 550 km,slightly less than, but within the same range as, values found in previousmagnetic-field-based studies. During time periods where both magneticfield and electron velocity data can be used, the two values can becompared. Relative comparisons show λ computedfrom the velocity is often significantly smaller than that from themagnetic field data. Due to a lack of events where both measurementsare available, the absolute λ based on the electronfluid velocity is not able to be determined.