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Journal articleWaters CL, Eastwood JP, Fargette N, et al., 2025,
Bridging in situ satellite measurements and simulations of magnetic reconnection using recurrent neural networks
, Journal of Geophysical Research: Space Physics, Vol: 130, ISSN: 2169-9380Magnetic reconnection is inherently structured, with distinct spatial regions such as inflows, outflows, and separatrices playing key roles in energy conversion and particle transport. While in situ spacecraft measurements provide detailed local information, determining where a spacecraft lies within the global reconnection geometry remains a major challenge. Proxy-based methods are often ambiguous, while full reconstructions require strong assumptions and are difficult to apply systematically across events. Here, we present a method that bridges these approaches by using machine learning to infer global structural context from local measurements. We first apply k-means clustering to a 2.5-D particle-in-cell simulation to identify six characteristic symmetric reconnection regions. A recurrent neural network (RNN) is then trained on spacecraft-like trajectories through the simulation to classify time series data into these regions. When applied to Magnetospheric Multiscale (MMS) observations of magnetotail reconnection, this method successfully identifies regional transitions, including inflow, outflow, and separatrix crossings, in agreement with previous reconstructions where available. The approach provides a practical, scalable, and automated framework for determining spatial context in reconnection events without requiring full geometric reconstruction, enabling large-scale and efficient statistical studies of reconnection dynamics across multiple events.
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Journal articleArcher M, Evans V, Eastwood J, et al., 2025,
First detection of field-aligned currents using engineering magnetometers from the OneWeb mega-constellation
, Space Weather, Vol: 23, ISSN: 1539-4956Field-aligned currents (FACs) are the main physical mechanism behind magnetosphere–ionosphere coupling, with these currents communicating environmental changes between the two regions of geospace. Field-aligned currents are thus a key factor in monitoring space weather, both from an operational and scientific perspective. While the AMPERE project has demonstrated that engineering fluxgate magnetometers on commercial satellite constellations can be assimilated to estimate the FACs across the entire polar cap, a limiting factor in the spatio-temporal resolution of this assimilation is the coverage of measurement points. However, in recent years much larger satellite mega-constellations have been launched into low Earth orbit (LEO) which might offer unprecedented opportunities. Here we leverage engineering anisotropic magnetoresistive magnetometer data from the OneWeb constellation for the first time. A case study during the 12 May 2021 geomagnetic storm is presented. We show conclusive evidence that OneWeb engineering magnetometers were able to detect FAC signatures present during this event by validating against AMPERE magnetic field and current maps from the same time. However, this result was despite significant challenges due to the OneWeb spacecraft instrumentation, data availability, and magnetic cleanliness, which we discuss in detail. Finally, we provide an outlook on the next steps required for OneWeb magnetic field data to provide valuable contributions to space weather science and operations.
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Journal articleDesai RT, Perrin J, Meredith NP, et al., 2025,
Multi-MeV Electron Occurrence and Lifetimes in the Outer Radiation Belt and Slot Region During the Maximum of Solar Cycle 22
, SPACE WEATHER-THE INTERNATIONAL JOURNAL OF RESEARCH AND APPLICATIONS, Vol: 23 -
Journal articleDing M, Lim SZJ, Yu X, et al., 2025,
A neural network approach for line detection in complex atomic emission spectra measured by high-resolution Fourier transform spectroscopy
, MACHINE LEARNING-SCIENCE AND TECHNOLOGY, Vol: 6 -
Journal articleTrotta D, Horbury TS, Giacalone J, 2025,
Variability in energetic particle observations at strong interplanetary shocks: Multi-spacecraft observations
, ASTRONOMY & ASTROPHYSICS, Vol: 702, ISSN: 0004-6361 -
Journal articleAuestad H, Shibu A, Ceppi P, et al., 2025,
The latent heating feedback on the mid-latitude circulation
, Geophysical Research Letters, Vol: 52, ISSN: 0094-8276Midlatitude storms transport warm and moist air poleward and upward, releasing latent heat. Latent heating is thus organized by the circulation but then modifies temperature gradients and winds, constituting a nonlinear feedback. We define the latent heating feedback as the effects that arise from latent heating being coupled with the circulation. Because of its nonlinearity, the climatic effects of this feedback are difficult to isolate and remain poorly understood. By decoupling latent heating from the circulation in an atmospheric general circulation model, we show that the latent heating feedback enhances storm track eddy diffusivity, modifying eddy heat fluxes beyond changes in mean baroclinicity. Simultaneously, tracked storms occur at lower latitudes, intensify more, and propagate further poleward, while the subtropical jet strengthens as coupled latent heating preserves lower latitude baroclinicity. The feedback response supports the idea that diabatic effects cause the “too zonal, too equatorward” storm track biases in climate models.
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Conference paperLin J, Gryspeerdt E, Clark R, 2025,
Cloud4D: Estimating cloud properties at a high spatial and temporal resolution
, 9th Conference on Neural Information Processing Systems (NeurIPS 2025)There has been great progress in improving numerical weather prediction and climate models using machine learning. However, most global models act at akilometer-scale, making it challenging to model individual clouds and factors such as extreme precipitation, wind gusts, turbulence, and surface irradiance. Therefore, there is a need to move towards higher-resolution models, which in turn require high-resolution real-world observations that current instruments struggle to obtain. We present Cloud4D, the first learning-based framework that reconstructs a physically consistent, four–dimensional cloud state using only synchronized ground-based cameras. Leveraging a homography-guided 2D-to-3D transformer, Cloud4D infers the full 3D distribution of liquid water content at 25 m spatial and 5 s temporal resolution. By tracking the 3D liquid water content retrievals over time, Cloud4D additionally estimates horizontal wind vectors. Across a two-month deployment comprising six skyward cameras, our system delivers an order-of-magnitude improvement in space-time resolution relative to state-of-the-art satellite measurements, while retaining single-digit relative error (< 10%) against collocated radar measurements. Code and data are available on our projectpage https://cloud4d.jacob-lin.com/.
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Journal articleKawaguchi K, Ceppi P, 2025,
Responses to lower-tropospheric stability dominate intermodel differences in the historical pattern effect
, Geophysical Research Letters, Vol: 52, ISSN: 0094-8276The sea surface temperature (SST) pattern modulates the Earth's radiative feedbacks at decadal timescales. However, decadal feedback variations over the historical period depend on the choice of climate model, even when forced with the same SST data set. We investigate these differences through analyzing amip-piForcing output, focusing on low cloud feedback. Time-variation in low cloud feedback results primarily from the SST pattern, mediated by changes in near-global lower tropospheric stability (LTS). We investigate the meteorological factors contributing to low cloud feedback variation through the cloud controlling factor analysis method, diagnosing cloud radiative sensitivities from 16 CMIP5 and CMIP6 models, and an observational constraint from MODIS. We find the radiative sensitivity of models to LTS in the stratocumulus regions dominates the magnitude of cloud feedback time variation due to the pattern effect. Additionally, models underestimate low cloud radiative sensitivity to changes in LTS and SST and thus the time-variation in feedback.
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Journal articleHuang Z, Velli M, Chandran BDG, et al., 2025,
Two Types of 1/<i>f</i> Range in Solar Wind Turbulence
, ASTROPHYSICAL JOURNAL LETTERS, Vol: 990, ISSN: 2041-8205 -
Journal articleRivera YJ, Klein KG, Wang JH, et al., 2025,
Observational constraints on the radial evolution of O⁶+ temperature and differential flow in the inner heliosphere
, Astrophysical Journal Letters, Vol: 990, ISSN: 2041-8205Over decades of solar wind observations, heavy ions have been observed to have a higher temperature and flow faster than protons in the solar corona and heliosphere. Remote observations have largely been limited to the low corona (<4 R⊙), while in situ observations for heavy ions (Z > 2) have only been sampled at 1 au and beyond. As a result, theories that address heavy ion heating and acceleration remain largely unconstrained. With the launch of Solar Orbiter, heavy ion kinetics can be probed closer to the Sun, as close as the orbit of Mercury (65 R⊙), to examine their radial behavior. Through a statistical analysis of O6+, this work provides a comprehensive analysis of the velocity and temperature of O6+ from 0.3 to 1 au. The study finds that the O6+ relative drift, normalized to the local Alfvén speed, and its temperature compared to protons both decrease with distance from the Sun and show some speed dependence. The O6+ temperature is well fit by a single temperature adiabatic profile across all wind speeds, suggesting that there is no significant heating at these heliocentric distances, which is in contrast to what is observed for protons and He2+. Alfvénic fluctuations, some with full 180∘ field rotation, create momentary negative differential streaming where the speed of O6+ trails the protons. The amount of negative differential streaming gradually increases at larger distances. These results provide critical constraints on the proposed mechanisms seeking to describe ion heating and acceleration in the solar wind.
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Journal articleKrasnoselskikh V, Jebaraj IC, Cooper TRF, et al., 2025,
Plasma Instability in Front of Ejected Energetic Electrons and Type III Solar Radio Bursts
, ASTROPHYSICAL JOURNAL, Vol: 990, ISSN: 0004-637X -
Journal articleRovithakis A, Burke E, Burton C, et al., 2025,
Estimating future wildfire burnt area over Greece using the JULES-INFERNO model
, Natural Hazards and Earth System Sciences, Vol: 25, Pages: 3185-3200, ISSN: 1561-8633Our previous studies have shown that fire weather conditions in the Mediterranean and specifically over Greece are expected to become more severe with climate change, impling potential increases in burnt area. Here, we employ the Joint UK Land Environment Simulator (JULES) coupled with the INFERNO fire model driven by future climate projections from the UKESM1 model to investigate the repercussions of climate change and future vegetation changes on burnt area over Greece. We validate modelled burnt area against the satellite-derived GFED5 dataset, and find the model's performance to be good, especially for the more fire-prone parts of the country in the south Greece. For future simulations, we use future climate data following three Shared Socioeconomic Pathways (SSPs), consisting of an optimistic climate change scenario where fossil fuel emissions peak and decline beyond 2020 (SSP126), a middle-of-the-road scenario (SSP370), and a pessimistic scenario where emissions continue to rise throughout the century (SSP8.5). Our results show increased burnt area in the future compared to the present-day period in response to overall hotter and drier climatological conditions. We use an additional JULES-INFERNO simulation in which dynamic vegetation was activated, and find that it features smaller future burned area increases compared to our simulation with static present-day vegetation. For this dynamically changing vegetation simulation the greatest burnt area increases are found for southern Greece, due to higher future availability of flammable and heat-resistant needleleaf trees and the smallest decreases in agricultural areas of northern Greece due to a reduction in the aforementioned tree category.
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Journal articleSakellaris IA, Bartzis JG, Grillakis E, et al., 2025,
Simulation of Air Pollution Produced by Forest Fires Using the WRF-SFIRE-CHEM Model in Greece: Study Cases
, FIRE TECHNOLOGY, ISSN: 0015-2684 -
Journal articleElsden T, Southwood DJ, Allanson O, et al., 2025,
Theory and modeling of large scale plasmapause surface waves
, Journal of Geophysical Research: Space Physics, Vol: 130, ISSN: 2169-9380The plasmapause in Earth's magnetosphere represents the boundary between the plasma which co-rotates with the Earth (plasmasphere), and the more tenuous plasmatrough outside. The density change across the plasmapause can be large, changing by approximately 1–2 orders of magnitude depending on the prevailing conditions. This would suggest it to be a location where magnetohydrodynamic (MHD) surface waves can form, and indeed, this has been proposed in previous works to explain ultra-low frequency (ULF) wave observations around the plasmapause location. The main question is how such a large scale surface wave on the plasmapause would be excited. In this paper, we propose a model whereby surface waves at the plasmapause are driven by energy input from the magnetopause through solar wind driving. We derive an analytical form for the amplitude of these surface waves with this new driven boundary condition at the magnetopause. The excitation of these waves is then tested in several MHD simulations, where the model geometry, wavenumbers and temporal dependence of the magnetopause driver are varied. We establish that surface waves on the plasmapause can be excited by driving from the magnetopause, and that this still occurs with impulsive and continuous broadband driving. The azimuthal scale of the wave is a critical factor for this excitation, with longer azimuthal scales more favorable for driving larger amplitude surface waves. This mechanism provides new insight for how large scale and large amplitude ULF waves can access the inner magnetosphere, with potential implications for their interaction with radiation belt particles.
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Journal articlePanditharatne S, Cox C, Song R, et al., 2025,
Exploiting airborne far-infrared measurements to optimise an ice cloud retrieval
, Atmospheric Chemistry and Physics, Vol: 25, Pages: 9981-9998, ISSN: 1680-7316Studies have indicated that far-infrared radiances hold significant information about the microphysics of ice clouds, particularly the ice crystal habit. In support of the European Space Agency's Far-Infrared Outgoing Radiation Understanding and Monitoring mission, we perform the first retrieval on an observation of coincident upwelling far- and mid-infrared radiances taken from an aircraft above a cirrus cloud layer. Four retrievals are performed: including and neglecting the far-infrared portion of the spectrum and assuming two different habit mixes. Results are compared to in situ measurements of the cloud optical thickness, cloud top height, cloud effective radius, and habit distributions. We find that despite the known limitations of ice cloud optical property models, all the retrievals show agreement within the in situ measurements of the cloud optical thickness, cloud top height, and cloud effective radius. However, the inclusion of the far-infrared enables a distinction between two different habits that is not possible using only mid-infrared channels. Furthermore, in this case study, the uncertainty in the retrieval of cloud top height and cloud optical thickness halves with the inclusion of the far-infrared. As with other studies, we also see an additional degree of freedom for the temperature and water vapour retrievals. Our study highlights the need for the improvement of current ice cloud optical models, with the radiance residuals from the converged retrievals still exceeding the instrument uncertainty within the far-infrared. However, it provides observational support for the theoretical improvement that far-infrared observations could bring to retrievals of ice cloud properties.
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Journal articleKoike M, Takigawa M, Morimoto S, et al., 2025,
Studies of atmospheric climate forcers in the Arctic during the ArCS II project
, POLAR SCIENCE, Vol: 45, ISSN: 1873-9652- Cite
- Citations: 2
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Journal articleFrankignoul C, Hall R, Kwon Y-O, et al., 2025,
On the Atmospheric Response to Oyashio Extension Front Disturbance and Mesoscale SST Variations
, JOURNAL OF CLIMATE, Vol: 38, Pages: 5055-5066, ISSN: 0894-8755 -
Journal articlePathak N, Ergun RE, Vo T, et al., 2025,
Observations of Large-Amplitude Parallel Electric Fields in the Turbulent Magnetotail
, JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 130, ISSN: 2169-9380 -
Journal articleToumi R, Sparks N, 2025,
The Hurricane Damage Index (HurDI)
, Journal of Catastrophe Risk and Resilience, Vol: 03, ISSN: 3049-7604Statistical hurricane risk assessments make long-term multi-decadal stationary climate assumptions, but there is large hurricane variability in the risk. It would be useful to also better estimate the “current” risk. The hurricane damage index (HurDI), is proposed as a measure of the underlying non-stationary risk. The HurDI is defined as the normalised annual average damage calculated with a stochastic wind only model, a single damage function, and uniform exposure across the continental U.S. The stochastic model is climate conditioned by weighting the historical basin hurricane counts, potential intensity, and tracks. The weights are chosen to give the best persistence forecast for each parameter for the next five years. There has been a substantial increase of the hurricane risk as measured by the HurDI. In 2024, the index was at a record high of 188, with a reference value of 100 in 1989. The HurDI is a dynamic view of risk based on the hurricane variability only and can be compared to U.S. property catastrophe reinsurance rates. There are periods of varying difference between the rates and the HurDI reflecting the volatile market cycles.
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Journal articleBowen TA, Mallet A, Dunn CI, et al., 2025,
Formation of magnetic switchbacks via expanding Alfvén waves
, ASTRONOMY & ASTROPHYSICS, Vol: 700, ISSN: 0004-6361 -
Journal articleNorgren C, Chen L-J, Graham DB, et al., 2025,
Electron and ion dynamics in reconnection diffusion regions
, Space Science Reviews, Vol: 221, ISSN: 0038-6308Magnetic reconnection is a fundamental plasma process responsible for the sometimes explosive release of magnetic energy in space and laboratory plasmas. Inside the diffusion regions of magnetic reconnection, the plasma becomes demagnetized and decouples from the magnetic field, enabling the change in magnetic topology necessary to power the energy release over larger scales. Since it was launched in 2015, the Magnetospheric MultiScale (MMS) mission has significantly advanced the understanding of the particle dynamics key to magnetic reconnection by providing high-resolution, in-situ measurements able to resolve ion and electron kinetic scales, i.e. a fraction of a gyroradius, that have confirmed theoretical predictions, revealed new phenomena, and refined existing models. These breakthroughs are critical for understanding not only space plasmas but also laboratory and astrophysical plasmas where magnetic reconnection occurs. In this work, we review the ion and electron dynamics occurring within the diffusion regions, in the inflow, along the separatrices, and downstream of the diffusion regions, in different reconnection configurations: symmetric, asymmetric, antiparallel, and guide field reconnection.
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Journal articleLewis ZM, Stephenson P, Beth A, et al., 2025,
Cometary ion dynamics at 67P: a collisional test-particle approach with Rosetta data comparison
, Monthly Notices of the Royal Astronomical Society, Vol: 541, Pages: 3590-3605, ISSN: 0035-8711The Rosetta spacecraft escorted comet 67P/Churyumov–Gerasimenko for two years, gathering a rich and variable data set.Amongst the data from the Rosetta Plasma Consortium (RPC) suite of instruments are measurements of the total electron densityfrom the Mutual Impedance Probe (MIP) and Langmuir Probe (LAP). At low outgassing, the plasma density measurements canbe explained by a simple balance between the production through ionization and loss through transport. Ions are assumed totravel radially at the outflow speed of the neutral gas. Near perihelion, the assumptions of this field-free chemistry-free modelare no longer valid, and plasma density is overestimated. This can be explained by enhanced ion transport by an ambipolarelectric field inside the diamagnetic cavity, where the interplanetary magnetic field does not reach. In this study, we explore thetransition between these two regimes, at intermediate outgassing (5.4 × 1026 s−1), when the interaction between the cometaryand solar wind plasma influences the transport of the ions. We use a 3D collisional test-particle model, adapted from Stephensonet al. to model the cometary ions with input electric and magnetic fields from a hybrid simulation for 2.5–3 au. The total plasmadensity from this model is then compared to data from MIP/LAP and to the field-free chemistry-free model. In doing so, wehighlight the limitations of the hybrid approach and demonstrate the importance of modelling collisional cooling of the electronsto understand the ion dynamics close to the nucleus.
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Journal articlePage B, Lecacheux A, Pulupa M, et al., 2025,
Calibration of Electrically Short Antennas Using the <i>l</i>=2 Spherical Harmonic Expansion Coefficients of the Radio Brightness Distribution on the Sky Between 0.5 and 6.8 MHz
, RADIO SCIENCE, Vol: 60, ISSN: 0048-6604 -
Journal articleVan de Koot EK, Byrne MP, Woollings T, 2025,
Tropical Cloud Feedbacks Estimated from Observed Multidecadal Trends
, Journal of Climate, Vol: 38, Pages: 3185-3199, ISSN: 0894-8755<jats:title>Abstract</jats:title><jats:p>Tropical cloud feedbacks are an important source of uncertainty in estimates of climate sensitivity. The extent to which changes in atmospheric circulation contribute to these feedbacks remains an open question. Here, all-sky radiative flux observations and an atmospheric reanalysis are used to estimate tropical cloud feedbacks from multidecadal trends (1985–2020) in cloud radiative effect and surface temperature. We decompose the observed feedbacks into dynamic and nondynamic components to quantify the impact of circulation trends. Narrowing and strengthening of tropical ascent lead to substantial dynamic feedbacks on regional scales that are similar in magnitude to the nondynamic feedbacks. However, as previously shown for high- and low-resolution climate models, large dynamic feedbacks in different circulation regimes are connected by the atmospheric mass budget and approximately cancel when averaged across the tropics due to the quasi-linear relationship between cloud radiative effect and vertical velocity. This results in small dynamic contributions to the tropical-mean net, longwave, and shortwave feedbacks. We suggest that this result will hold in future and thus that isolating the nondynamic components associated with individual cloud types can provide important insights into the processes controlling the tropical-mean cloud feedback and its uncertainty. Additionally, we show that feedbacks estimated from multidecadal trends differ from those estimated from interannual variability. We demonstrate that, for dynamic feedbacks, this is because changes are controlled by different mechanisms and this leads to a differing spatial distribution of temperature sensitivity. Finally, we provide new estimates of the uncertain combined tropical anvil area and albedo feedback using both multidecadal trends and interannual variability.</jats:p>
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Journal articleKretzschmar M, Brochot J-Y, Horbury TS, et al., 2025,
The Solar Orbiter merged magnetic field
, ASTRONOMY & ASTROPHYSICS, Vol: 699, ISSN: 0004-6361 -
Journal articlePulupa M, Bale SD, Jebaraj IC, et al., 2025,
Highly Polarized Type III Storm Observed with Parker Solar Probe
, ASTROPHYSICAL JOURNAL LETTERS, Vol: 987, ISSN: 2041-8205- Cite
- Citations: 2
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Journal articleNiwa Y, Tohjima Y, Terao Y, et al., 2025,
Multi-observational estimation of regional and sectoral emission contributions to the persistent high growth rate of atmospheric CH4 for 2020-2022
, Atmospheric Chemistry and Physics, Vol: 25, Pages: 6757-6785, ISSN: 1680-7316Atmospheric methane (CH4) growth rates reached unprecedented values in the years 2020-2022. To identify the main drivers of this increase, an inverse modeling study estimated regional and sectoral emission changes for 2016-2022. Three inverse estimates based on different sets of atmospheric CH4 observations (surface observations only, surface and aircraft observations, and GOSAT observations) consistently suggest notable emission increases from 2016-2019 to 2020-2022 in the tropics (15° S-10° N) (10-18 Tg CH4 yr-1) and in northern low latitudes (10-35° N) (ca. 20 Tg CH4 yr-1), the latter of which likely contributed to the growth rate surge from 2020. The emission increase in the northern low latitudes is attributed to emissions in South Asia and northern Southeast Asia, which abruptly increased from 2019 to 2020, and elevated emissions continued until 2022. Meanwhile, the tropical emission increase is dominated by Tropical South America and Central Africa, but emissions were continuously increasing before 2019. Agreement was found in the sectoral estimates of the three inversions in the tropics and northern low latitudes, suggesting the largest contribution of biogenic emissions. Uncertainty reductions demonstrate that the flux estimates in Asia are well constrained by surface and aircraft observations. Furthermore, a sensitivity test with the probable reduction of OH radicals showed smaller emissions by up to 2-3 Tg CH4 yr-1 in each Asian region for 2020, still suggesting notable emission contributions. These results highlight the importance of biogenic emissions in Asian regions for the persistent high growth rate observed during 2020-2022.
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Journal articleWilson III LB, Mitchell JG, Szabo A, et al., 2025,
Large-amplitude Whistler Precursors and >MeV Particles Observed at a Weak Interplanetary Shock by Parker Solar Probe
, ASTROPHYSICAL JOURNAL, Vol: 987, ISSN: 0004-637X- Cite
- Citations: 1
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Journal articleRen T, Yang P, Brindley HE, et al., 2025,
Temperature-dependent optical properties of ice crystals in the far-infrared regime
, Geophysical Research Letters, Vol: 52, ISSN: 0094-8276A database of temperature-dependent hexagonal ice aggregate optical properties in the far-infrared (FIR) spectrum is developed to support FIR missions, particularly the current Polar Radiant Energy in the Far InfraRed Experiment and the upcoming Far-infrared-Outgoing-Radiation Understanding and Monitoring. Based on this data set, simulations of the brightness temperatures (BTs) in the 100–667 cm−1 FIR region are conducted for an anvil-like ice cloud in a tropical atmosphere. The results show nonnegligible impact of ice cloud temperature on simulated BTs, which can be as large as 3 K due to the difference between fixed 160 or 270 K cloud temperature and the benchmark counterpart, varying in accordance with the ambient temperature profile for a cloud residing between 249.6 and 199.6 K. To enhance the accuracy of FIR radiative transfer modeling, it is recommended to incorporate temperature-dependent optical properties of ice clouds.
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Journal articleTurc L, Archer MO, Zhou H, et al., 2025,
Interplay between a foreshock bubble and a hot flow anomaly forming along the same rotational discontinuity
, Geophysical Research Letters, Vol: 52, ISSN: 0094-8276Solar wind directional discontinuities can generate transient mesoscale structures such as foreshock bubbles and hot flow anomalies (HFAs) upstream of Earth's bow shock. These structures can have a global impact on near-Earth space, so understanding their formation conditions is essential. We investigate foreshock transient generation at a rotational discontinuity using a global 2D hybrid-Vlasov simulation. As expected, a foreshock bubble forms on the sunward side of the discontinuity. Later, when the discontinuity reaches the shock, new structures identified as HFAs develop, despite the initial discontinuity not being favorable to HFA formation. We demonstrate that the foreshock bubble provides the necessary conditions for their generation. We then investigate the evolution of the transient structures and the large-scale bow shock deformation they induce. Our results provide new insights on the formation and evolution of foreshock transients and their impact on the shock.
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