Radio waves are naturally produced in the near-Earth space environment. Chorus waves are a type of such radio waves that interact with relativistic particles in the radiation belts. Understanding the interactions between these waves and particles is important for predicting the changing space environment and its societal impacts. In particular, this allows us to predict space weather and prepare for impacts to national commercial and defense satellites and communications - a priority set out in the National Space Weather Action Plan.
This project aims to explore the origin of banded chorus waves in Earth's radiation belt by analyzing data from the Van Allen Probes and performing particle-in-cell simulations to aid in interpretation. Naturally occurring chorus waves are believed to play a key role in accelerating relativistic electrons in the Earth's outer radiation belt, and in precipitating ~keV (and higher) electrons to the upper atmosphere, causing diffuse aurorae and pulsating aurorae. Chorus typically occurs in two distinct frequency bands separated by a gap at half of the electron gyro-frequency. The origin of this two-band structure has been a half-century-long open scientific question. This project, by systematically surveying the chorus waves and their properties right in the source region, will explore whether the spectral gap at half the electron gyro-frequency is generated at the magnetic equator, or is formed by damping as the waves propagate to higher latitudes. The electron distributions that accompany banded chorus waves will be statistically investigated and linear growth calculations made to investigate the direct energy source of banded chorus waves. Based on typical observations of waves and particle distribution, 1-Dimensional and 2-Dimensional particle-in-cell simulations will be performed to explore the multi-stage interaction processes that could account for the banded chorus waves.
This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
