High‐frequency Electrostatic Waves Modulated by Whistler Waves behind Dipolarization Front

Both the whistler waves and high-frequency electrostatic waves (HFEWs), playing significant roles in energy conversion, have been widely studied behind dipolarization fronts (DFs). Nevertheless, interactions between them have been so far elusive. Utilizing high-resolution MMS data, we present two cases that HFEWs were modulated by whistler waves behind a DF. The HFEWs with frequency at f(ce) similar to f(pe), propagating along the ambient magnetic field, were detected near delta E-// minimum (maximum) of parallel-propagating (antiparallel-propagating) whistler waves. The amplitudes of the HFEWs are comparable to that of the whistler waves, while their energy densities are two orders of magnitude lower than that of the whistler waves. The analysis indicates that the whistler waves were locally excited by anisotropic electron distributions and the HFEWs were excited by electron beams produced by the whistler waves via Landau resonance. Our study advances the understanding of wave-wave interactions and cross-scale processes in space plasmas.