Survey of the global distribution of the fast magnetosonic mode from Van Allen Probes EMFISIS plasma wave analysis

The 'fast magnetosonic mode' at frequencies between the proton and the lower hybrid frequency is believed to play an important role in the energization of radiation belt electrons. We have performed a global survey of this mode using the Waves experiment which is part of EMFISIS covering the first year of the Van Allen Probes mission. This survey consists of over 300,000 measurements in time and frequency during which this mode was detected. We will present various cross sections of the survey as function of frequency, power, radial distance, magnetic latitude, magnetic local time and its variation with geomagnetic conditions. Global estimates of this mode's wave distribution function (WDF) and its variation with geomagnetic conditions are necessary inputs for modeling the energization of the radiation belt electrons. The WDF gives the wave energy density as a function of frequency, wave normal angle (WNA) and azimuth angle. It has been shown that a variation of the WDF's angular half width in WNA between 1 and 5 degrees makes a difference in energization of radiation belt electrons. Using local analysis only, one will not get the required accuracy for the wave normal angle. Therefore one must use a more global approach. It has been demonstrated that the latitudinal extent of the waves heavily constrains its WNA. Our approach is to analyze the latitudinal variation of the wave power with frequency which when coupled with ray tracing can be used to estimate the WNA. Because the spacecraft are in an equatorial orbit we use a superimposed epoch analysis to determine the latitudinal variation of the power of this mode with frequency. Similar to findings from the polar orbiting Dynamics Explorer-1 spacecraft, our superimposed radiation patterns show a funnel shaped outline in frequency as a function of magnetic latitude, with the higher frequencies much more extended in magnetic latitude than the lower frequencies. We perform plasma wave ray tracing using an observationally based plasma density model to generate synthetic radiation patterns. We adjust the weighting of the individual ray traces in order to match spectral power density of the synthetic radiation patterns with that of the observed radiation patterns, from which a few preliminary WDFs are derived.