Physics – Plasma Physics
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufmsm13b2060d&link_type=abstract
American Geophysical Union, Fall Meeting 2011, abstract #SM13B-2060
Physics
Plasma Physics
[6929] Radio Science / Ionospheric Physics, [7868] Space Plasma Physics / Wave/Wave Interactions, [7894] Space Plasma Physics / Instruments And Techniques, [7959] Space Weather / Models
Scientific paper
Bursty Langmuir waves have been interpreted as the result of the superposition of multiple Langmuir normal-mode waves, with the resultant modulation being the beat pattern between waves with e.g. 10 kHz frequency differences. The normal-mode waves could be generated either through wave-wave interactions or through independent linear processes. Previous observations have been one-dimensional, making it impossible to discern angular information about the participating modes. The Twin Rockets to Investigate Cusp Electrodynamics (TRICE) were launched 10 Dec 2007 at 0900 and 0902 UT from the Andoya Rocket Range, Norway, reaching apogees of 1145 km and 750 km. Each rocket's payload included an ensemble of high-frequency instruments. The NASA GSFC Tri-Axial Electric Field Wave Detector or TAEFWD consisted of three orthogonal double probes of 48 cm length, with 2.5 cm-diameter spherical sensors at their tips with embedded high-impedance pre-amps. Dartmouth College supplied a spin-axis aligned double probe, with 30 cm separation using 6 cm sensor spheres. The potential differences between all sensor pairs were digitized at 8 MHz in 2048-sample snapshots by a GSFC receiver with a low duty cycle, while the difference between the axial pair was also continuously digitized at 10 MHz through the Dartmouth HFE receiver. The TRICE high-flyer encountered several regions of strong Langmuir wave activity throughout the flight, including ~1,000 discrete Langmuir wave bursts [LaBelle et al., 2010]. In particular, the interval 690 to 780s from launch saw numerous waves in the 300 to 700 KHz frequency range. The waveforms in this range were individually examined, and 90 snapshots with strong activity in all three TAEFWD channels were selected. For this study, the set was further refined to 25 cases which showed strongly monochromatic Langmuir-wave activity. Of these 'best' 25, nine cases were found exhibiting a phase shift in the Langmuir burst modulation nulls between the X, Y, and/or Z channels. If we assume pure, linearly polarized Langmuir waves, the resultant beat modulation phase should be isotropic. We therefore theorize that the observed phase shifts arise due to the inclusion of waves with some degree of elliptical polarization: most likely whistler-mode waves. We test this hypothesis by characterizing the observed waves in detail, determining the theoretical polarization of possible participating wave modes using dispersion surfaces generated by the Waves in Homogeneous Anisotropic Magnetized Plasma (WHAMP) program, and then simulating the mixing of these wave modes in an attempt to roughly recreate the observed beat patterns and phase offsets. Reference LaBelle, J., I. H. Cairns, and C. A. Kletzing (2010), Electric field statistics and modulation characteristics of bursty Langmuir waves observed in the cusp, J. Geophys. Res., 115, A10317, doi:10.1029/2010JA015277.
Dombrowski M. P.
Kletzing C.
Labelle James W.
Pfaff Robert F.
Rowland Douglas E.
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