Complementary and Catalytic Roles of Man-Made VLF Waves and Natural Plasma Waves in the Loss of Radiation Belt Electrons

By simulating the energy and pitch angle diffusions of radiation belt electrons caused by ground-based VLF transmitter waves, plasmaspheric hiss and lightning-generated whistlers (LGWs), we quantitatively estimated the electron change rates caused by individual and multiple waves. We found that man-made VLF waves and naturally generated hiss or LGWs play complementary and catalytic roles in the loss of radiation belt electrons. Man-made VLF waves mainly reduce the hundreds of keV electrons in inner radiation belt (L < 2), but they alone cannot effectively remove the MeV electrons in slot region (L similar to 2-3) because of unefficient diffusions at small pitch angles (<60 degrees). On the contrary, natural hiss and LGWs do not affect the hundreds of keV electrons in the inner belt, but they are able to effectively reduce the hundreds of keV and MeV electrons at small pitch angles in the slot region. The loss of the small pitch electrons caused by hiss or LGWs offer a necessary phase space density gradient for the diffusion of large pitch angle MeV electrons (>60 degrees) driven by man-made VLF waves toward the loss cone. The combined diffusions by three types of the waves ultimately catalyze the loss of the large pitch angle MeV electrons in the slot region, and thus cause more electron losses in the wider energy and pitch angle ranges.