Home » Zhang et al. 2017

Properties, propagation, and excitation of EMIC waves observed by MMS: A case study

Zhang J., S. A. Boardsen, V. N. Coffey, M. O. Chandler, A. Saikin, E. M. Mello, C. T. Russell, R. B. Torbert, S. A. Fuselier, B. L. Giles, D. J. Gershman, (2017), Properties, propagation, and excitation of EMIC waves observed by MMS: A case study, AGU 2017 Fall Meeting

Abstract

Electromagnetic ion cyclotron (EMIC) waves (0.1-5 Hz) play an important role in particle dynamics in the Earth's magnetosphere. EMIC waves are preferentially excited in regions where hot anisotropic ions and cold dense plasma populations spatially overlap. While the generation region of EMIC waves is usually on or near the magnetic equatorial plane in the inner magnetosphere, EMIC waves have both equatorial and off-equator source regions on the dayside in the compressed outer magnetosphere. Using field and plasma measurements from the Magnetospheric Multiscale (MMS) mission, we perform a case study of EMIC waves and associated local plasma conditions observed on 19 October 2015. From 0315 to 0810 UT, before crossing the magnetopause into the magnetosheath, all four MMS spacecraft detected long-lasting He+-band EMIC wave emissions around local noon (MLT = 12.7 - 14.0) at high L-shells (L = 8.8 - 15.2) and low magnetic latitudes (MLAT = -21.8º - -30.3º). Energetic (> 1 keV) and anisotropic ions were present throughout this event that was in the recovery phase of a weak geomagnetic storm (min. Dst = -48 nT at 1000 UT on 18 October 2015). The testing of linear theory suggests that the EMIC waves were excited locally. Although the wave event is dominated by small normal angles, its polarization is mixed with right- and left-handedness and its propagation is bi-directional with regard to the background magnetic field. The short inter-spacecraft distances (as low as 15 km) of the MMS mission make it possible to accurately determine the k vector of the waves using the phase difference technique. Preliminary analysis finds that the k vector magnitude, phase speed, and wavelength of the 0.3-Hz wave packet at 0453:55 UT are 0.005 km-1, 372.9 km/s, and 1242.9 km, respectively. We will discuss the characteristics of the wave and particle measurements and their significance in this locale.

Authors (sorted by name)

Russell Saikin Torbert Zhang

Journal / Conference

AGU 2017 Fall Meeting

Bibtex

@ARTICLE{2017AGUFMSM13D2397Z,
   author = {{Zhang}, J. and {Boardsen}, S.~A. and {Coffey}, V.~N. and {Chandler}, M.~O. and 
	{Saikin}, A. and {Mello}, E.~M. and {Russell}, C.~T. and {Torbert}, R.~B. and 
	{Fuselier}, S.~A. and {Giles}, B.~L. and {Gershman}, D.~J.},
    title = "{Properties, propagation, and excitation of EMIC waves observed by MMS: A case study}",
  journal = {AGU Fall Meeting Abstracts},
 keywords = {2723 Magnetic reconnection, MAGNETOSPHERIC PHYSICS, 2724 Magnetopause and boundary layers, MAGNETOSPHERIC PHYSICS, 2744 Magnetotail, MAGNETOSPHERIC PHYSICS, 2784 Solar wind/magnetosphere interactions, MAGNETOSPHERIC PHYSICS},
abstract = {Electromagnetic ion cyclotron (EMIC) waves (0.1-5 Hz) play an important role in particle dynamics in the Earth's magnetosphere. EMIC waves are preferentially excited in regions where hot anisotropic ions and cold dense plasma populations spatially overlap. While the generation region of EMIC waves is usually on or near the magnetic equatorial plane in the inner magnetosphere, EMIC waves have both equatorial and off-equator source regions on the dayside in the compressed outer magnetosphere. Using field and plasma measurements from the Magnetospheric Multiscale (MMS) mission, we perform a case study of EMIC waves and associated local plasma conditions observed on 19 October 2015. From 0315 to 0810 UT, before crossing the magnetopause into the magnetosheath, all four MMS spacecraft detected long-lasting He+-band EMIC wave emissions around local noon (MLT = 12.7 - 14.0) at high L-shells (L = 8.8 - 15.2) and low magnetic latitudes (MLAT = -21.8º - -30.3º). Energetic (> 1 keV) and anisotropic ions were present throughout this event that was in the recovery phase of a weak geomagnetic storm (min. Dst = -48 nT at 1000 UT on 18 October 2015). The testing of linear theory suggests that the EMIC waves were excited locally. Although the wave event is dominated by small normal angles, its polarization is mixed with right- and left-handedness and its propagation is bi-directional with regard to the background magnetic field. The short inter-spacecraft distances (as low as 15 km) of the MMS mission make it possible to accurately determine the k vector of the waves using the phase difference technique. Preliminary analysis finds that the k vector magnitude, phase speed, and wavelength of the 0.3-Hz wave packet at 0453:55 UT are 0.005 km-1, 372.9 km/s, and 1242.9 km, respectively. We will discuss the characteristics of the wave and particle measurements and their significance in this locale.},
     year = 2017,
    month = dec,
doi = {2017AGUFMSM13D2397Z},
   adsurl = {http://adsabs.harvard.edu/abs/2017AGUFMSM13D2397Z},
  adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}