Plasma Wave Excitation Regions in the Earth’s Global Magnetosphere Jichun Zhang, Ph.D. Space Science Center & Department of Physics University of New Hampshire, Durham, NH SWMF Users Meeting, Ann Arbor, MI Oct. 13, 2014

First, a few things about me at UNH Title: Research Assistant Professor Affiliation: Space Science Center (SSC), Institute for the Study of Earth Oceans and Space (EOS) Department of Physics, College of Engineering and Physical Sciences (CEPS) Research – Magnetospheric Physics: Electromagnetic ion cyclotron (EMIC) waves Ion injection into the inner magnetosphere Missions Involved: Van Allen Probes Cluster

Outline Background Summary and Future Work with SWMF/GM-IM-IE Magnetospheric Plasma Waves EMIC Waves: Excitation and effects Occurrence spatial distribution Summary and Future Work with SWMF/GM-IM-IE

Magnetospheric Waves [Thorne, 2010] (see Slide 9)

Magnetospheric Waves [Thorne, 2010]

What are EMIC waves? Electromagnetic ion cyclotron (EMIC) waves are induced by anisotropic distributions of energetic H+ (10-100 keV, i.e., typical ion energies in the ring current and plasma sheet), which are often unstable to the EMIC instability [Kennel and Petschek, 1966; Anderson et al., 1996]. EMIC waves occur in a region where total plasma density is large and magnetic field magnitude is minimized, i.e., low characteristic energy for cyclotron interactions (=B2/2μ0N) [Kennel and Petschek, 1966]. EMIC waves perpendicularly energize ions, especially heavy ions such as He+ and O+, through resonant wave-particle interactions [e.g., Young et al., 1981; Zhang et al., 2010 & 2011].

Why are EMIC waves important? EMIC waves are an important type of magnetospheric waves, which affect particle dynamics in the magnetosphere. A better understanding of EMIC waves in the magnetosphere is critical for understanding and predicting changes in the near-Earth environment, e.g., the scattering loss of relativistic electrons in the radiation belts as well as energetic ions in the ring current.

Electromagnetic Ion Cyclotron (EMIC) Waves in ONE Cartoon EMIC waves play an important role in the cross-energy population interactions in the magnetosphere.

Occurrence Spatial Distribution: MLAT Dependence Inner Magnetosphere Dayside Outer Magnetosphere Magnetic field is approximately a dipole. Minimum B is on the equatorial plane. Statistical study using CRRES found EMIC wave source region to be within 11 degrees of magnetic equator [Loto’aniu et al., 2005]. Limitations: Did not observe 0800 – 1400 MLT Did not observe |MLAT| > 30° Only observed L = 3.5-8.0 Magnetic field is compressed. Local minimum B regions form off-equator, resulting in the so-called Shabansky orbits of the bulk plasma population [Shabansky, 1971]. Study using Ogo 5 found chorus waves off-equator [Tsurutani et al., 1997]. [Loto’aniu et al., 2005] [Tsurutani et al., 1997]

Off-equator Anisotropy: Theoretical Study Simulations using a compressed magnetosphere have shown that the anisotropies required for EMIC wave generation can be developed in the Shabansky orbits [McCollough et al., 2012]. The figure on the right shows the distorted field with blue +’s on the local magnetic minima. The figure on the bottom shows the resulting anisotropy. [McCollough et al., 2012]

Observed EMIC Wave Events boring surprising puzzling [Allen et al., 2013] Bidirectional Unidirectional Multiple Bidirectional Three EMIC wave events were observed in the realistic magnetosphere. The wave generation regions are not easily identified and predicted.

Complex Min. B Regions in the Realistic Magnetosphere Due to dipole tilt and magnetospheric dayside compressions, local minimum B regions in the 3-D magnetosphere are complex, e.g., Is the magnetic equatorial plane actually a “planar surface ”? How responsive are the off-equator local min. B regions to variations in the solar wind? Courtesy of Darren De Zeeuw

Summary and Future Work Plasma waves play a critical role in particle heating, cooling, and loss, and energy transfer between hot and cold plasma populations in the the Earth’s magnetosphere. Plasma waves inside the magnetosphere occur in a region where total plasma density is large and magnetic field magnitude is minimized, i.e., on the magnetic equatorial plane in the inner magnetosphere; off and on the magnetic equatorial plane in the outer magnetosphere. Simulations of the global magnetosphere with the SWMF can address important questions, e.g., How do different solar wind conditions affect the spatial distribution and temporal evolution of newly injected plasma and local min. magnetic field strength (B) regions in the 3-D magnetosphere? How well does SWMF, a state-of-the-art coupled model, reproduce the wave excitation-associated plasma and magnetic field in the global magnetosphere?