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Title: Observations of discrete magnetosonic waves off the magnetic equator

Fast mode magnetosonic waves are typically confined close to the magnetic equator and exhibit harmonic structures at multiples of the local, equatorial proton cyclotron frequency. Here, we report observations of magnetosonic waves well off the equator at geomagnetic latitudes from -16.5°to -17.9° and L shell ~2.7–4.6. The observed waves exhibit discrete spectral structures with multiple frequency spacings. The predominant frequency spacings are ~6 and 9 Hz, neither of which is equal to the local proton cyclotron frequency. Backward ray tracing simulations show that the feature of multiple frequency spacings is caused by propagation from two spatially narrow equatorial source regions located at L ≈ 4.2 and 3.7. The equatorial proton cyclotron frequencies at those two locations match the two observed frequency spacings. Finally, our analysis provides the first observations of the harmonic nature of magnetosonic waves well away from the equatorial region and suggests that the propagation from multiple equatorial sources contributes to these off-equatorial magnetosonic emissions with varying frequency spacings.
Authors:
 [1] ;  [2] ;  [3] ;  [3] ;  [4] ; ORCiD logo [5]
  1. China Earthquake Administration, Beijing (China). Inst. of Earthquake Science; Univ. of Texas at Dallas, Richardson, TX (United States)
  2. Univ. of Texas at Dallas, Richardson, TX (United States)
  3. Beihang Univ., Beijing (China). Space Science Inst., School of Astronautics
  4. British Antarctic Survey, Cambridge (United Kingdom)
  5. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Publication Date:
Report Number(s):
LA-UR-15-28228
Journal ID: ISSN 0094-8276; TRN: US1702874
Grant/Contract Number:
AC52-06NA25396; 2014DFR21280; 41204136; 41274166; 2011CB811404; 2014IES010203; AGS 1405041; 606716 SPACESTORM
Type:
Accepted Manuscript
Journal Name:
Geophysical Research Letters
Additional Journal Information:
Journal Volume: 42; Journal Issue: 22; Journal ID: ISSN 0094-8276
Publisher:
American Geophysical Union
Research Org:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org:
National Aeronautic and Space Administration (NASA); National Science Foundation (NSF); National Natural Science Foundation of China (NNSFC); European Union (EU); USDOE
Country of Publication:
United States
Language:
English
Subject:
79 ASTRONOMY AND ASTROPHYSICS; Heliospheric and Magnetospheric Physics; magnetsonic wave; off-equatorial region; discrete structure
OSTI Identifier:
1402596