Long Lifetime Hiss Rays in the Disturbed Plasmasphere

Plasmaspheric hiss waves are important to shape the Earth's electron radiation belt. These waves are commonly envisioned to have a long lifetime which allows them to permeate the global plasmasphere from a spatially restricted source. However, this hypothesis has not been experimentally confirmed yet, because of the challenging observational requirements in terms of location and timing. With wave and particle measurements from five magnetospheric satellites and detailed modeling, we present the first report of long lifetime (similar to 42 s) hiss rays in the substorm-disturbed plasmasphere. The low-frequency hiss waves are found to originate from the middle piece of the plasmaspheric plume, bounce between two hemispheres, and eventually drift into the plasmaspheric core. These hiss rays can travel through similar to 3 hr magnetic local time and similar to 4 magnetic shell. Such a long-time and large-scale permeation of hiss rays could benefit from the ducting process by plasmaspheric field-aligned density irregularities. Earth's plasmasphere is populated by a type of whistler-mode wave named plasmaspheric hiss which is able to shape the electron radiation belt. Hiss waves were commonly envisioned to have a long lifetime which allows them to permeate the global plasmasphere from a spatially restricted source. Although there have been numerous studies on the source of plasmaspheric hiss waves, the hypothesis regarding their long lifetime remains not experimentally confirmed yet because of the challenging observational requirements in terms of location and timing. On the basis of wave and particle measurements from five magnetospheric satellites covering the entire plasmasphere and detailed modeling, we show that the hiss rays can survive at least 42 s in the plasmasphere disturbed by substorms. Within the survival period, these hiss rays migrated from the middle piece of the plasmaspheric plume to the plasmaspheric core, whose path lengths reached 25 Earth radii. Such a long-time and large-scale permeation of hiss rays from the plasmaspheric plume to the plasmaspheric core could benefit from the ducting process by plasmaspheric field-aligned density irregularities. Low-frequency hiss waves were excited by energetic electrons inside the dayside plasmaspheric plume following substorms Low-frequency hiss rays survived at least 42 s, allowing themselves to migrate from the plasmaspheric plume to the plasmaspheric core Plasmaspheric density ducts facilitated the permeation of hiss rays from the plasmaspheric plume to the plasmaspheric core