Kelly A. Cantwell

The Balloon Array for Radiation belt Relativistic Electron Losses (BARREL) mission was designed to study the loss of radiation belt electrons to the upper atmosphere. Previous analysis of data from balloon pairs showed that electron precipitation events manifest coherent quasi‐periodic variations (with periodicity on the order of 10–60 min) often lacking an obvious trigger internal to the magnetosphere. This suggested that the loss mechanism was related to solar wind driving involving quasi‐static magnetospheric field modulation and/or triggering of ultra low frequency waves by periodic density structures (PDSs). In this study, we performed a statistical investigation of the occurrence of quasi‐periodic X‐ray (QPX) variations in the ≈0.5–3.4 mHz (≈4.9–36.2 min) range from the seven BARREL campaigns and their relation to solar wind PDSs. QPX variations occur around 43%–73% of the campaign time of which 26%–30% involve PDSs. The frequency distribution of the QPX variations showed preferential occurrence at ≈0.6–1.0 mHz, ≈1.6–2.3 mHz, and tentatively ≈1.3 mHz. The QPX events map to different regions in the space depending on the frequency of the QPX variations and the type of solar wind driving. Simultaneous observations of the event by multiple balloons show QPX events extending up to 7.3 and 6.5. Finally, PDSs are more likely related to the X‐ray modulation during quiet to moderate geomagnetic conditions following substorm activity and possibly magnetospheric compressions.

Electron microbursts are among the most important loss mechanisms for energetic electrons in the Earth's radiation belts and are often driven by wave‐particle interactions with discrete chorus wave elements. Observations from the Balloon Array for Radiation‐belt Relativistic Electron Losses (BARREL) mission have revealed microburst events with simultaneous burst and smooth precipitation components. We conduct numerical experiments for the reported events and identify the driving mechanisms for these dual‐component structures. A realistic atmospheric backscattering module based on Monte Carlo simulations is incorporated into test particle simulations of wave‐particle interactions to more accurately model electron precipitation. Using parameters constrained by BARREL observations, our simulations reproduce the observed dual‐component microbursts with similar burst‐to‐smooth ratios. Comparative runs show that energy dispersion in precipitation, driven by intense and discrete chorus elements, can naturally produce a smooth component alongside bursty precipitation. This indicates that the smooth component is an intrinsic feature of intense microbursts and contributes significantly to the total electron loss. We show that electron loss rates from microbursts are likely underestimated due to the neglect of these smooth components in observations with insufficient energy resolution. Although the backscattering module does not strongly affect the formation of the smooth component, it does reduce the peak precipitation rate and extends the overall duration of precipitation. These findings highlight the importance of incorporating realistic atmospheric backscattering into wave‐driven precipitation models to improve the accuracy of estimating electron precipitation.

From 10 to 12 May 2024, a series of coronal mass ejections led to one of the strongest geomagnetic storms of the century, referred to as the Mother's Day or Gannon Storm. MMS's position on the dayside magnetosphere on 11 May provided observations of a strongly driven and compressed reconnecting magnetopause. Because of the driving conditions, the magnetopause became saturated with outflows that dominated the mass density of the plasma environment. In the reconnecting magnetopause, MMS observes signatures of parallel electron heating on the magnetopause's magnetosheath side, but anomalous and significant electron cooling, especially from the perpendicular electron temperature on the magnetosphere side, possibly driven by additional mechanisms besides reconnection. Even with the strong driving and outflows, we find an expected normalized reconnection rate for the primary exhaust, indicating insensitivity to these conditions. The unnormalized rate, however, is atypically large and scales with the driving conditions.

This meeting report summarizes outcomes from the AGU Chapman Conference on Particle Precipitation : Drivers , Properties , and Impacts on Atmosphere , Ionosphere , Magnetosphere (AIM) Coupling , held 14–21 February 2025, in Melbourne, Australia. This conference brought together scientists from around the world to identify pressing AIM open science questions and next steps for solidifying cross‐community collaborations. Efforts have resulted in the upcoming Town Hall session Building Bridges Between the Atmosphere , Ionosphere , Magnetosphere (AIM) Communities at the 2025 AGU meeting in New Orleans, USA. This Town Hall aims to establish a recurring meeting to address the scientific and societal challenges of AIM coupling.

From 10-12 May 2024, a series of coronal mass ejections led to one of the strongest geomagnetic storms of the century, referred to as the Mother’s Day or Gannon Storm. MMS’s position on the dayside magnetosphere on 11 May provided observations of a strongly driven and compressed (~7 Re) reconnecting magnetopause. Because of the driving conditions, the magnetopause became saturated with O+ outflows that dominated the mass density of the plasma environment. MMS observes signatures of an embedded secondary reconnection site that potentially impacted the magnetopause’s structure and heating. Additionally, MMS observes anomalous electron cooling on the magnetosphere side of the magnetopause, possibly driven by additional mechanisms besides reconnection. Even with the strong driving, secondary structures, and O+ outflows, we find an expected (0.20±0.05) normalized reconnection rate for the primary exhaust, indicating insensitivity to these conditions. The unnormalized rate, however, is atypically large and scales with the driving conditions.

The magnetopause represents the boundary layer between Earth's magnetic field and the solar wind and plays a crucial role in mediating the transport of the solar wind's energy into the Earth's magnetosphere through the process of magnetic reconnection. Magnetopause properties, magnetospheric plasma outflows, and mesoscale structures along the magnetopause surface all can dampen magnetic reconnection and limit this energy transfer. To resolve this process and the effects that these mesoscale phenomena have at the magnetopause, we propose the Compression and Reconnection Investigations of the Magnetopause (CRIMP) mission as a Helio MIDEX A/O targeted concept mission designed to study the interactions between the Earth's magnetosphere and the solar wind in the magnetopause boundary layer. CRIMP targets open goals from the Heliophysics Decadal Survey by uncovering how local mass density enhancements affect global magnetic reconnection, how mesoscale structures drive magnetopause dynamics, and if the magnetopause acts as a perfectly absorbing boundary for radiation belt electrons through innovative in situ, multi-point, contemporaneous measurements. CRIMP was designed by 18 early career researchers in collaboration with Team X at NASA JPL as a part of the NASA Heliophysics Mission Design School. Presented at the 2024 AGU Fall Meeting, Advancing Fundamental Space Weather Research: Flares, CMEs, Solar Wind, and Earth/Planetary Impacts II Poster Session

Microbursts are impulsive injections of energetic (few keV to >MeV) electrons into the atmosphere, primarily caused by nonlinear scattering driven by whistler mode chorus waves. While the relative importance of microburst precipitation as a loss process has not been fully quantified, many studies have shown microbursts may play a significant role in the loss of outer radiation belt electrons. We present a multi‐platform statistical analysis of chorus and energetic electron precipitation in an attempt to constrain the azimuthal spatial extent (MLT) of the microburst precipitation region and determine how this extent varies with geomagnetic activity. Statistical upper bounds of this azimuthal extent are determined with observations of general energetic electron precipitation that can include direct microburst detections, while statistical lower bounds determination requires direct microburst detections. The resulting distributions of both upper and lower bounds azimuthal extent suggest that microbursts may frequently constitute an important source of electron loss from the outer radiation belt. We find that 36% of upper bound events in the dawn sector span more than 5 hr in MLT. This azimuthal extent increases with geomagnetic activity, particularly in the dawn and noon MLT sectors.

Electron microburst precipitation has been shown to have significant potential for depletion of the outer radiation belt. We present observations from the Balloon Array for Radiation belt Relativistic Electron Losses (BARREL) of six (five unique and one dual‐balloon observation) microburst events, each containing minutes to hours of persistent microbursts. We find that each event included a slowly‐varying smooth precipitation component underlying the bursty component. The smooth component has not yet been fully characterized in the literature; we have written a program to identify microburst events and quantify the relative contributions of each component in the BARREL data. In all six events analyzed, the smooth component contributed more to the total X‐ray counts measured, indicating that the smooth component could contribute significantly to radiation belt loss.

We use microwave-induced dynamic nuclear polarization (DNP) of the substitutional nitrogen defects (P1 centers) in diamond to hyperpolarize bulk ¹³C nuclei in both single crystal and powder samples at room temperature at 3.34 T. The large (>100-fold) enhancements demonstrated correspond to a greater than 10 000-fold improvement in terms of signal averaging of the 1% abundant ¹³C spins. The DNP was performed using low-power solid state sources under static (nonspinning) conditions. The DNP spectrum (DNP enhancement as a function of microwave frequency) of diamond powder shows features that broadly correlate with the EPR spectrum. A well-defined negative Overhauser peak and two solid effect peaks are observed for the central (m _I = 0) manifold of the ¹⁴N spins. Previous low temperature measurements in diamond had measured a positive Overhauser enhancement in this manifold. Frequency-chirped millimeter-wave excitation of the electron spins is seen to significantly improve the enhancements for the two outer nuclear spin manifolds (m_I = ±1) and to blur some of the sharper features associated with the central manifold. The outer lines are best fit using a combination of the cross effect and the truncated cross effect, which is known to mimic features of an Overhauser effect. Similar features are also observed in experiments on single crystal samples. The observation of all of these mechanisms in a single material system under the same experimental conditions is likely due to the significant heterogeneity of the high pressure, high temperature (HPHT) type Ib diamond samples used. Large room temperature DNP enhancements at fields above a few tesla enable spectroscopic studies with better chemical shift resolution under ambient conditions.