Turbulent Power: A Discriminator Between Sheaths and CMEs

Abstract

Solar coronal mass ejections (CMEs) directed at the Earth often drive large geomagnetic storms. Here, we use velocity, magnetic field, and proton density data from 152 CMEs that were sampled in situ at 1 AU by the Wind spacecraft.We Fourier analyze fluctuations of these quantities in the quiescent pre-CME solar wind, sheath, and magnetic cloud. We quantify the extent by which the power in turbulent (magnetic field, velocity, and density) fluctu-ations in the sheath exceeds that in the solar wind background and in the magnetic cloud. For instance, the mean value of the power per unit volume in magnetic field fluctuations in the sheath is 76.7 times that in the solar wind background, while the mean value of the power er unit mass in velocity fluctuations in the sheath is 9 times that in the magnetic cloud. Our detailed results show that the turbulent fluctuation power is a useful discriminator between the ambient solar wind background, sheaths, and magnetic clouds and can serve as an input for space weather prediction