February 16, 2018, 1:00 pm - 2:00 pm

February 16, 2018, 1:00 pm - 2:00 pm, Heliophysics Director's Seminar, Hosted by the Heliospheric Physics Laboratory (672)

STEREO Observations of Interplanetary CMEs in 2007-2016

Dr. Lan Jian

We have conducted a survey of 341 interplanetary coronal mass ejections (ICMEs) using STEREO A/B data, analyzing their properties while extending a Level 3 product of the mission through 2016. Among the 192 ICMEs with distinguishable sheath region and magnetic obstacle, the magnetic field maxima in the two regions are comparable, and the dynamic pressure peaks mostly in the sheath. The magnetic field north/south direction does not present any clear relationship between the sheath region and the magnetic obstacle. About 71% of ICMEs are expanding at 1 AU, and their expansion speed varies roughly linearly with their maximum speed except for ICMEs faster than 700 km s-1. The hourly average iron charge state reaches above 12+ ~31% of the time for MCs, ~16% of the time for non-MC ICMEs, and ~1% of the time for non-ICME solar wind. In comparison with the similar phases of solar cycle 23, the STEREO ICMEs in this cycle occur less often and are generally weaker and slower, although their field and pressure compressions weaken less than the background solar wind.

The Heliospheric Evolution of ICMEs

Dr. Teresa Nieves-Chinchilla

The heliospheric counterparts of coronal mass ejections (CMEs), usually studied with heliospheric imagers and in situ instrumentation, are referred as Interplanetary CMEs (ICMEs). The study of the evolution of ICMEs is of special interest since they are the primary cause of geoeffective space weather events. Knowledge of the magnetic structure of ICMEs is crucial to connect the solar origin of CMEs to their effects on the magnetosphere. Currently we are usually able to track the global morphology and kinematic parameters of CMEs using heliospheric white light imagers. And we are able to reconstruct the magnetic topology of such structures using in situ observations.

Detailed studies demonstrated that a simple radially propagating, self similarly expanding magnetic flux rope topology for CMEs is not sufficiently accurate. In fact, ICMEs can change significantly because of their internal evolution and interaction with the ambient solar wind. Thus, the magnetic topology, structure, and geometry of the CMEs are not yet fully and consistently described by current models/techniques. In this presentation, we will review case-studies to evaluate the amount and significance of distortion, rotation and deflection of CMEs.

Chasing Solar Storms with Radio

Dr. Vratislav Krupar (NPP)

Coronal mass ejections (CMEs) are large-scale eruptions of magnetized plasma that may cause severe geomagnetic storms if Earth directed. Type II radio bursts are generated by electron beams accelerated at shock waves ahead of CMEs. Here, we analyze radio emissions associated with the backside CME that occurred on July 23, 2012. This CME belongs among historical extreme solar events due to associated solar energetic particle fluxes and the CME-driven shock speed above 2000 km/s. We demonstrate the complementarity between space-based radio measurements and white-light reconstruction techniques for space weather applications.