Whistler mode wave is a crucial emission which can significantly affect the electron dynamics in the magnetosphere. The nonlinear three-wave interaction between whistler mode waves has been frequently observed, while the four-wave interaction between these waves is seldom reported. Here, we present two multiband whistler mode wave events by Van Allen Probes, in which the relatively weak wave bands occur exactly corresponding to the strong wave bands. We find that the frequencies of the weak and strong bands satisfy the frequency matching conditions of the four-wave interaction, and the wave no...
