Understanding Magnetic Cloud Structure From Shock/Discontinuity Analysis

We reexamine the magnetic cloud (MC) event during the period of 21–23 May 2007. In this event, the axis of the MC has a high inclination to the ecliptic plane and the heliospheric current sheet happens to be on the ecliptic plane. Therefore, we can use the feature of zero north-south component of interplanetary magnetic field to identify the MC boundaries. Inside the MC, there is an enhanced pressure/density region enclosed by two discontinuities. We verified these discontinuities through multiple spacecraft in situ observations. The front one is a forward fast shock, which is a quasi-perpendicular shock at STEREO B but a quasi-parallel shock at Wind location. The discontinuity at the rear part of the enhanced pressure region resembles a reverse slow shock. However, we verify it is a tangential discontinuity (TD) using multispacecraft observations. Furthermore, we analyze the successive TDs inside the MC based on the TD signature of no normal magnetic field component to estimate the magnetic field morphology along the spacecraft trajectories. A novel method to evaluate the uncertainties of those TDs in this study has been given. It is found that the errors of the TD normal are much smaller than that calculated by conventional methods.