MIST reunited

Emma Woodfield, Andy Smith and colleagues outline the research presented and discussed at the Autumn MIST meeting in November 2022

Measuring Low Plasma Density in the Earth's Equatorial Magnetosphere From Magnetosonic Waves

The plasma density is one of the most fundamental quantities of any plasma yet measuring it in space is exceptionally difficult when the density is low. Measurements from particle detectors are contaminated by spacecraft photoelectrons and methods using plasma wave emissions are hampered by natural plasma instabilities which dominate the wave spectrum. Here we present a new method which calculates the density from magnetosonic waves near the lower hybrid resonance frequency. The method works most effectively when the ratio of the plasma to cyclotron frequency is fpe/fce < 3.5. The method provides a lower bound on the plasma density. Using the new method we show that wave acceleration of electrons to relativistic energies is increased by orders of magnitude. The method enables years of satellite data to be re-analyzed for the Earth and the effectiveness of wave acceleration at the Earth, Jupiter and Saturn to be re-assessed

A New Four‐Component L*‐Dependent Model for Radial Diffusion Based on Solar Wind and Magnetospheric Drivers of ULF Waves

The outer radiation belt is a region of space comprising highly energetic electrons. During periods of extreme space weather, the number and energy of these electrons can rapidly vary. During these periods as the electron energies and numbers become enhanced, they can pose a threat to satellite and space infrastructure. While we have an excellent understanding of the physical processes which drive radiation belt electron dynamics, we still have a limited ability to model and forecast radiation belt dynamics; this is a result of the complexity of Earth's radiation belt system. One of the key processes controlling radiation belt dynamics is Ultra Low Frequency (ULF) wave radial diffusion. In this work we detail the development a new model quantifying the strength of ULF wave radial diffusion in the outer radiation belt utilizing space base observations of the electric and magnetic fields in Earth's magnetosphere. Accurately quantifying ULF wave radial diffusion is fundamental to understanding radiation belt dynamics and any improvement or refinements in radial diffusion models can help to provide a better understanding of the complex radiation belt system and importantly improve hindcasts, nowcasts, and forecasts

A New Four‐Component <i>L</i>*‐Dependent Model for Radial Diffusion Based on Solar Wind and Magnetospheric Drivers of ULF Waves

Funder: NASA ISFMFunder: NSERCFunder: UK Royal SocietyFunder: CSAAbstractWaves which couple to energetic electrons are particularly important in space weather, as they drive rapid changes in the topology and intensity of Earth's outer radiation belt during geomagnetic storms. This includes Ultra Low Frequency (ULF) waves that interact with electrons via radial diffusion which can lead to electron dropouts via outward transport and rapid electron acceleration via inward transport. In radiation belt simulations, the strength of this interaction is specified by ULF wave radial diffusion coefficients. In this paper we detail the development of new models of electric and magnetic radial diffusion coefficients derived from in‐situ observations of the azimuthal electric field and compressional magnetic field. The new models use as it accounts for adiabatic changes due to the dynamic magnetic field coupled with an optimized set of four components of solar wind and geomagnetic activity, , , , and , as independent variables (inputs). These independent variables are known drivers of ULF waves and offer the ability to calculate diffusion coefficients at a higher cadence then existing models based on Kp. We investigate the performance of the new models by characterizing the model residuals as a function of each independent variable and by comparing to existing radial diffusion models during a quiet geomagnetic period and through a geomagnetic storm. We find that the models developed here perform well under varying levels of activity and have a larger slope or steeper gradient as a function of as compared to existing models (higher diffusion at higher values).</jats:p