We assess the prevalence of ducted and non-ducted whistler propagation using burst mode data from the Van Allen Probes Electric Field and Waves instrument (EFW). We have identified burst periods containing lightning-generated whistlers (LGWs), resulting in a data set available for future use. The entire burst data set is filtered through an analysis of the search coil magnetometer (SCM) noise, identifying signals in frequency space that exceed an adaptive noise threshold. We implement DBSCAN (Density-Based Spatial Clustering of Applications with Noise) to identify individual whistlers and clusters of whistlers. With magnetic spectral analysis, we calculate the mean wave normal angle (WNA) for each LGW group. We use ray tracing to estimate the expected WNA distributions for non-ducted LGWs to compare to the data and determine methods for identifying potentially ducted LGWs. The ray-tracing results provide a clear threshold in WNA for ducted whistlers. Using this threshold, we estimate that at least 10.1% $10.1\%$ of LGWs in this data set are ducted. We find that the majority of potentially ducted whistlers are below L=2 $L=2$ and nearly half of LGWs below L=2 $L=2$ and within 9-18 MLT may be ducted. Lightning-generated whistlers (LGWs) are very-low-frequency waves produced when lightning-generated radio pulses known as sferics excite whistler mode waves through the ionosphere and into the magnetosphere. LGW wave power contributes to pitch angle scattering and precipitation of trapped energetic electrons, affecting atmospheric chemistry and helping maintain the slot region between the radiation belts. Field-aligned plasma density irregularities, or ducts, affect the propagation of LGWs. Ducting can determine where the wave energy travels, how long it persists, and which energetic particle populations are affected. We present distributions of LGW wave properties and explore methods of determining ducting of LGWs. We present a complete Van Allen Probes Electric Field & Waves whistler data set generated through density-based clustering Most whistlers in this data set have high wave normal angles consistent with non-ducted propagation Likely ducted whistlers are mainly below L=2 $L=2$; about half of whistlers between 9 and 18 MLT and below L=2 $L=2$ are likely ducted

Whistler mode waves have been proposed as a crucial mechanism in determining the velocity-space distribution of electrons on the dayside crustal magnetic fields of Mars. A superthermal electron transport model has been unable to reproduce the observed pitch angle distributions on a crustal field line. The two key differences are that the observed pitch angle distributions are much more isotropic and the observed high energy pitch angle distributions have a flux peak at perpendicular pitch angles. We solve the bounce-averaged quasi-linear diffusion equation to calculate the steady-state pitch angle distribution of electrons along a crustal field line when in resonance with whistler mode waves. We perform two simulations, changing the background ionosphere, which affects what energies are in resonance with the whistler mode wave. The wave parameters are chosen based on previous observations of whistlers at Mars. Our results reconcile both qualitative differences between the previous data-model comparisons. Plain Language Summary An understanding of how electrons move through space environments is important for a multitude of reasons. It tells us where electrons will transfer their energy to the neutral atmosphere and it can indirectly inform us of where the magnetic field lines are connected to (the planet or solar wind). If the physical processes that control electron transport are unknown, then incorrect assumptions may be made. At Mars, our satellite observations and numerical simulations have not agreed, indicating that we do not include all the relevant physics in our models. Whistler mode waves are extremely low frequency radio waves that interact with electrons and can change the direction they are moving and increase their velocity. In this study, we simulate the effect of whistler mode waves on electrons at Mars. We find that our simulation results agree quite well with the data and reconciles the two key qualitative differences between previous data-model comparisons.

Pitch angle distributions of high‐energy superthermal electrons (> 100 eV) observed at Mars show evidence of a ubiquitous energization process occurring on dayside crustal magnetic fields. Wave–particle interactions have been put forth as one explanation and in this study we investigate if the conditions are right at Mars for this process to occur regularly. The resonant energy of electrons is dependent on not only the whistler wave frequency and normal angle but also the characteristic energy of the plasma environment. The characteristic energy is determined by the magnetic field strength and thermal electron density, both measured quantities by the Mars Atmosphere and Volatile EvolutioN mission. Bounce‐averaged diffusion coefficients are calculated using a typical characteristic energy profile and observed wave parameters. Time constants are also calculated and it is shown that wave–particle interactions are more efficient than Coulomb collisions. Low‐energy electrons have fast wave–particle interaction time scales and electrons can be scattered across the source cone and energized. High‐energy electrons have slow wave–particle interactions time scales and electrons energized to these energies will become trapped and modify the pitch angle distribution. Modeling the evolution of the electron distribution function will provide more insight into the process.

The magnetospheric physics research community uses a broad array of quantitative data-model comparison methods (metrics) when conducting their research investigations. It is often the case, though, that any particular study will only use one or two metrics, with the two most common being Pearson correlation coefficient and root mean square error (RMSE). Because metrics are designed to test a specific aspect of the data-model relationship, limiting the comparison to only one or two metrics reduces the physical insights that can be gleaned from the analysis, restricting the possible findings from modeling studies. Additional physical insights can be obtained when many types of metrics are applied. We organize metrics into two primary groups: 1) fit performance metrics, often based on the data-model value difference; and 2) event detection metrics, which use a discrete event classification of data and model values determined by a specified threshold. In addition to these groups, there are several major categories of metrics based on the aspect of the data-model relationship that the metric assesses: 1) accuracy; 2) bias; 3) precision; 4) association; 5) and extremes. Another category is skill, which is a measure of any of these metrics against the performance of a reference model. These can be applied to a subset of either the data or the model values, known as reliability and discrimination assessments. In the context of magnetospheric physics examples, we discuss best practices for choosing metrics for particular studies.

Multiple studies have reported either isotropic or trapped pitch angle distributions of high‐energy (>100 eV) electrons on closed crustal field lines on the dayside of Mars. These pitch angle distributions are not to be expected from collisional scattering and conservation of adiabatic invariants alone. We use 2 years of data from the Mars Atmosphere and Volatile EvolutioN mission to analyze the pitch angle distributions of superthermal electrons on dayside‐closed crustal magnetic fields and compare to results from an electron transport model. Low‐energy electrons (10–60 eV) have pitch angle distributions in agreement with modeling results, while high‐energy electrons (100–500 eV) do not. High‐energy electrons have a flux peak at perpendicular pitch angles which suggests there is a ubiquitous energization process occurring on crustal fields. Wave‐particle interactions seem to be the most likely candidate. Trapping of high‐energy electrons may impact the nightside ionosphere dynamics.

We investigated 7 years worth of data from the electron reflectometer and magnetometer aboard Mars Global Surveyor to quantify the deposition of photoelectron and solar wind electron populations on the nightside of Mars, over the strong crustal field region located in the southern hemisphere. Just under 600,000 observations, each including energy and pitch angle distributions, were examined. For solar zenith angles (SZA) less than 110 degrees, photoelectrons have the highest occurrence rate; beyond that, plasma voids occur most often. In addition, for SZA > 110 degrees, energy deposition of electrons mainly occurs on vertical field lines with median pitch angle averaged energy flux values on the order of 10(7) - 10(8) eV cm(-2) s(-1). The fraction of downward flux that is deposited at a given location was typically low (16% or smaller), implying that the majority of precipitated electrons are magnetically reflected or scattered back out. The average energy of the deposited electrons is found to be 20-30 eV, comparable to typical energies of photoelectrons and unaccelerated solar wind electrons. Median electron flux values, from near-vertical magnetic field lines past solar zenith angle of 110 degrees, calculated in this study produced a total electron content of 4.2 x10(14) m(-2) and a corresponding peak density of 4.2x10(3) cm(-3).