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Using the Van Allen Probe-A observations, we obtained the global distribution of proton rings and calculated the linear wave growth rate of fast magnetosonic (MS) waves in the region L similar to 3-6. Our statistical and calculated results demonstrate that MS waves can be locally excited on the dayside outside the plasmapause, as well as in the dusk sector inside the plasmapause. The frequency range of unstable MS waves is strongly modulated by the ratio of the proton ring velocity (V-r) to the local Alfven speed (V-A). High harmonic MS waves (omega > 20 Omega(H+)) can be excited outside the plasmapause where V-r/V-A < 1, while low harmonic MS waves (omega < 10 Omega(H+)) with frequencies less than similar to 30 Hz are found to be excited both outside and inside the plasmapause where 1 < V-r/V-A < 2.

Plain Language Summary Since MS waves can propagate radially and azimuthally in the inner magnetosphere, it is difficult to attribute observed MS waves to propagation or local excitation. Because MS waves can be excited by proton ring distributions, it will be an effective method to research the characteristics of locally excited MS waves through global distribution of observed proton rings. With observations of Van Allen Probe-A spacecraft between October 2012 and August 2015, we obtain the global statistical distribution of the occurrences of proton rings both outside and inside the plasmapause. Proton rings, as a source of exciting fast magnetosonic (MS) waves, are distributed mainly on the dayside at L similar to 3-6. In order to find the characteristics of locally excited MS waves, through combining observed particle properties and a quantitative calculation of linear wave growth rate, we demonstrate that MS waves can be locally excited on the dayside outside the plasmapause, as well as in the dusk sector inside the plasmapause. The frequency range of unstable MS waves is strongly modulated by the ratio of the proton ring velocity to the local Alfven speed. This paper provides the global distribution of proton rings and locally excited MS waves.