Survey of the Frequency Dependent Latitudinal Distribution of the Fast Magnetosonic Wave Mode from Van Allen Probes Electric and Magnetic Field Instrument and Integrated Science Waveform Receiver Plasma Wave Analysis

• Published in: Journal of geophysical research. Space physics 2016-04, Vol.121 (4), p.2902-2921
• Main Authors: Boardsen, Scott A., Hospodarsky, George B., Kletzing, Craig A., Engebretson, Mark J., Pfaff, Robert F., Wygant, John R., Kurth, William S., Averkamp, Terrance F., Bounds, Scott R., Green, Jim L., De Pascuale, Sebastian
• Format: Article
• Language: English
• Subjects: Cyclotron frequency; Cyclotrons; Electric fields; Ellipticity; Equator; Equatorial waves; Estimates; fast magnetosonic waves; Geophysics; Histograms; Latitude; latitudinal distribution; Magnetic equator; Magnetic fields; Noon; Plane waves; Plasma density; Plasma waves; Polarization; Polls & surveys; Probes; Ray tracing; Space Sciences (General); statistical study; Superposition (mathematics); Uncertainty; Wave analysis; wave normal angle; Waveforms
• ISSN: 2169-9380; 2169-9402
• DOI: 10.1002/2015ja021844

We present a statistical survey of the latitudinal structure of the fast magnetosonic wave mode detected by the Van Allen Probes spanning the time interval of 21 September 2012 to 1 August 2014. We show that statistically, the latitudinal occurrence of the wave frequency (f) normalized by the local proton cyclotron frequency (f(sub cP)) has a distinct funnel-shaped appearance in latitude about the magnetic equator similar to that found in case studies. By comparing the observed E/B ratios with the model E/B ratio, using the observed plasma density and background magnetic field magnitude as input to the model E/B ratio, we show that this mode is consistent with the extra-ordinary (whistler) mode at wave normal angles (theta(sub k)) near 90 deg. Performing polarization analysis on synthetic waveforms composed from a superposition of extra-ordinary mode plane waves with theta(sub k) randomly chosen between 87 and 90 deg, we show that the uncertainty in the derived wave normal is substantially broadened, with a tail extending down to theta(sub k) of 60 deg, suggesting that another approach is necessary to estimate the true distribution of theta(sub k). We find that the histograms of the synthetically derived ellipticities and theta(sub k) are consistent with the observations of ellipticities and theta(sub k) derived using polarization analysis.We make estimates of the median equatorial theta(sub k) by comparing observed and model ray tracing frequency-dependent probability occurrence with latitude and give preliminary frequency dependent estimates of the equatorial theta(sub k) distribution around noon and 4 R(sub E), with the median of approximately 4 to 7 deg from 90 deg at f/f(sub cP) = 2 and dropping to approximately 0.5 deg from 90 deg at f/f(sub cP) = 30. The occurrence of waves in this mode peaks around noon near the equator at all radial distances, and we find that the overall intensity of these waves increases with AE*, similar to findings of other studies.