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Plasmaspheric hiss waves are commonly observed in the inner magnetosphere. These waves efficiently scatter electrons, facilitating their precipitation into the atmosphere. Predictive inner magnetosphere simulations often model hiss waves using parameterized empirical maps of observed hiss power. These maps nearly always include parameterization by magnetic L value. In this work, data from the Van Allen Probes are used to compare variation in hiss wave power with variation in both L value and cold plasma density. It is found that for L > 2.5, plasmaspheric hiss wave power increases with plasma density. For L > 3, this increase is stronger and occurs regardless of L value and for all local times. This result suggests that the current paradigm for parameterizing hiss wave power in many magnetospheric simulations may need to be revisited and that a new parameterization in terms of plasma density rather than L value should be explored.

Plain Language Summary The space near Earth is filled with waves. Some of these waves jostle particles that would be otherwise trapped in Earth's magnetic field, causing them to collide with the atmosphere and be lost from near-Earth space. One of the most common waves near Earth is called plasmaspheric hiss, because it exists mostly in the cold, dense plasma near Earth (the plasmasphere) and because it sounds like static hiss when recorded by antennas on Earth and played back in audio. Hiss is very effective at jostling particles, and so understanding its behavior is key to predicting the behavior of particles trapped in Earth's magnetic field, including the Van Allen radiation belts. In this study, we use new data to test a long-standing assumption about hiss waves, that their power is organized by their location in Earth's magnetic field. We find that the data do not support this assumption. Instead, hiss wave power is found to be organized by the density of cold particles in near-Earth space. This result is important because it suggests that current models of hiss waves used for predicting behavior of particles trapped in Earth's magnetic field may need to be significantly changed.