arXiv subjects

Noé Lugaz

Publications and source records attributed to Noé Lugaz.

At least 19 recordsLinked to original sources

arXiv2026

Investigating potential benefits of future sub-L1 missions with STEREO-A

We present the first statistical study of geomagnetic storm forecasting using in situ data from the STEREO-A spacecraft as a sub-L1 monitor. Between November 2022 and June 2024, STEREO-A crossed the Sun-Earth line, covering longitudinal and radial separations of +/-15° from the Sun-Earth line and 0.01-0.06 au from Earth. This passage provides a unique opportunity to assess future sub-L1 mission concepts by ESA, such as HENON and SHIELD. We identify 32 coronal mass ejections (CMEs) observed by both STEREO-A and L1 spacecraft. Eight of these 32 CME events are first detected at L1, indicating that radial spacecraft separations of up to ~0.05 au do not always yield lead time advantages. Furthermore, we find greater (smaller) gains in lead time when STEREO-A is east (west) of the Sun-Earth line. We develop a baseline methodology for the use of future sub-L1 in situ data to enable time-shifting and real-time modeling of the geomagnetic SYM-H index. This is run continuously over the entire time period, therefore modeling the geomagnetic response of all solar wind structures. Our methodology is empirically motivated and should be considered a first approach in addressing the use of sub-L1 data. Following this methodology, 26 of 47 observed geomagnetic storms are correctly identified from STEREO-A data. Intense events (82%, SYM-H<-100 nT) are well detected, most of which are also associated with an identified CME event. Most SYM-H minima are predicted later (72%) and stronger (58%) than those observed due to biases introduced by our methodology.

physics.space-ph↗

arXiv2026

Evolution of Coronal Mass Ejection Properties through Superposed Epoch Analysis from 0.2 to 2.2 au

Coronal mass ejections (CMEs) are explosive and energetic events consisting of strong magnetic structures erupting from the solar corona. We use superposed epoch analysis to investigate the general properties of CMEs as measured {\it in situ} from 0.2 to 2.2 au based on over 1600 events obtained from the HELIO4CAST catalog. We examine the dependence of the CME global properties on solar cycle phase, and compare the CME parameters derived in the active phase (AP) with the quiet phase (QP). Our findings show that during the AP of the solar cycle, the occurring CMEs are faster and have stronger magnetic field strength than during the QP, which has denser but weaker magnetic strength. These differences in magnetic field strength and density remain even when controlling for the speed. This may indicate that the enhanced profiles observed during the AP are not only a consequence of the CME propagation speed but may also reflect intrinsic differences in the eruption mechanism during different solar cycle phases. We also study how the magnetic field strength and components of the CME magnetic ejecta (ME) structure evolve with heliocentric distance. We find that the toroidal and poloidal ME magnetic field components have a similar power law decrease with distance, indicating a comparable expansion behavior of CMEs in these dimensions. We further quantify the CME magnetic field asymmetry %(often associated with CME aging) using the front-to-rear ratio of the toroidal component across heliocentric distance and find evidence of an increase of this ratio with heliocentric distance.

physics.space-ph↗

arXiv2025

The evolution of CME sheath turbulence from L1 to Earth: Wind and MMS observations of the 2023-04-23 CME

An interplanetary shock driven by a coronal mass ejection (CME) containing an interval of sub-Alfvénic flow impacted Earth on April 23, 2024. In this article, we analyze the turbulence in the sheath region between the shock and CME to determine how it evolves from L1 (as observed by Wind) to Earth (as observed by MMS, upstream of the bow shock). Wind and MMS were separated by $55\,\mathrm{R_{E}}$ in the dawn-dusk direction, but the shock normals differ by only $2.8^{\circ}$ and the Pearson correlation coefficient between time-shifted magnetic field components is $ρ=0.93$. We observe a shift in the break point of the magnetic power spectral density between inertial and ion kinetic scales toward the ion inertial length and a steepening of the spectral slope, indicating more active energy cascade closer to Earth. The distribution of increments becomes more non-Gaussian near Earth, particularly at ion kinetic scales, indicating the turbulence becomes more intermittent. Finally, the correlation length at Earth is 25\% longer than at L1, indicating that the turbulence is smoothing out the magnetic field. The results present an example of substantial evolution of CME sheath turbulence from L1 to Earth.

physics.space-ph↗

arXiv2025

First observations of a geomagnetic superstorm with a sub-L1 monitor

Forecasting the geomagnetic effects of solar coronal mass ejections (CMEs) is currently an unsolved problem. CMEs, responsible for the largest values of the north-south component of the interplanetary magnetic field, are the key driver of intense and extreme geomagnetic activity. Observations of southward interplanetary magnetic fields are currently only accessible directly through in situ measurements by spacecraft in the solar wind. On 10-12 May 2024, the strongest geomagnetic storm since 2003 took place, caused by five interacting CMEs. We clarify the relationship between the CMEs, their solar source regions, and the resulting signatures at the Sun-Earth L1 point observed by the ACE spacecraft at 1.00 AU. The STEREO-A spacecraft was situated at 0.956 AU and 12.6° west of Earth during the event, serving as a fortuitous sub-L1 monitor providing interplanetary magnetic field measurements of the solar wind. We demonstrate an extension of the prediction lead time, as the shock was observed 2.57 hours earlier at STEREO-A than at L1, consistent with the measured shock speed at L1, 710 km/s, and the radial distance of 0.04 AU. By deriving the geomagnetic indices based on the STEREO-A beacon data, we show that the strength of the geomagnetic storm would have been decently forecasted, with the modeled minimum SYM-H=-478.5 nT, underestimating the observed minimum by only 8%. Our study sets an unprecedented benchmark for future mission design using upstream monitoring for space weather prediction.

physics.space-ph↗

arXiv2025

Influence of the Deformation of Coronal Mass Ejections on Their In-Situ Fitting with Circular-Cross-Section Flux Rope Models

Understanding the properties, especially the magnetohydrodynamic (MHD) invariants, of coronal mass ejections (CMEs) measured in-situ is key to bridging the CME properties from the Sun to interplanetary space. In order to investigate CMEs from the in-situ measurements that provide a one-dimensional (1-D) cut of the CME parameters over the spacecraft trajectory, various magnetic flux rope (MFR) models have been developed, among which the models with a circular cross-section are the most popular and widely used. CMEs are found to be deformed during their propagation in interplanetary space, in which the cross-section may be flattened in the direction of propagation, i.e., to develop an elliptical or even pancake-like shape. We use numerical MHD simulations in 2.5-D to investigate the influence of the CME deformation on the in-situ fitting using two linear force-free MFR models with a circular cross-section, and we focus on the axial and poloidal magnetic fluxes, which are conserved in the ideal MHD frame and simulations. We quantitatively compare the fitted axial and poloidal fluxes with those in simulations. We find that both models underestimate the axial flux compared to that in simulations, and such underestimation depends on the CME deformation. However, the fitting of the poloidal flux is independent of the deformation. We discuss the reasons for the axial flux underestimation and the implication of the CME deformation for the CME in-situ fitting.

physics.space-ph↗

arXiv2024

Can Alfvénic Fluctuations Affect the Correlation and Complexity of Magnetic Fields in Magnetic Ejecta? A Case Study Based on Multi-Spacecraft Measurements at 1~au

We investigate whether Alfvénic fluctuations (AFs) can affect the structure of magnetic ejecta (MEs) within interplanetary coronal mass ejections (ICMEs). We study an ICME observed on 2001 December 29 at 1 au by ACE and Wind, at a total angular separation of $\sim$0.8$^\circ$ ($\sim0.014$~au). We focus on the correlation and complexity of its magnetic structure measured between two spacecraft in association with large-amplitude AFs. The Alfvénicity of the ME is investigated in terms of the residual energy and cross helicity of fluctuations. We find that as for the event of interest, large-amplitude AFs occur in the rear region of the ME at both Wind and ACE with a duration of about six hours. We compare the correlation of the magnetic field strength and vector components measured between Wind and ACE, and investigate complexity in terms of the magnetic hodograms. The region showing AFs is found to be associated with a decreased correlation of the magnetic field components and an increased complexity of the ME magnetic configuration detected at ACE and Wind, which may be due to the fact that the two spacecraft crossing the same ME along different trajectories likely sampled AFs in different oscillation phases. Combining multi-point in-situ measurements and remote-sensing observations of the ICME source region, we further discuss different potential sources of the AFs.

physics.space-ph↗

arXiv2024

A Survey of Coronal Mass Ejections Measured In Situ by Parker Solar Probe During 2018-2022

We present a statistical investigation of the radial evolution of 28 interplanetary coronal mass ejections (ICMEs), measured in situ by the Parker Solar Probe (PSP) spacecraft from 2018 October to 2022 August. First, by analyzing the radial distribution of ICME classification based on magnetic hodograms, we find that coherent configurations are more likely to be observed close to the Sun. In contrast, more complex configurations are observed farther out. We also notice that the post-ICME magnetic field is more impacted following an ICME passage at larger heliocentric distances. Second, with a multi-linear robust regression, we derive a slower magnetic ejecta (ME) expansion rate within 1~au compared to previous statistical estimates. Then, investigating the magnetic field fluctuations within ICME sheaths, we see that these fluctuations are strongly coupled to the relative magnetic field strength gradient from the upstream solar wind to the ME. Third, we identify ME expansion as an important factor in forming sheaths. Finally, we determine the distortion parameter (DiP) which is a measure of magnetic field asymmetry in an ME. We discover lower overall asymmetries within MEs. We reveal that even for expanding MEs, the time duration over which an ME is sampled does not correlate with DiP values, indicating that the aging effect is not the sole contributor to the observed ME asymmetries.

physics.space-ph↗

arXiv2024

Acceleration and Release of Solar Energetic Particles Associated with a Coronal Shock on 2021 September 28 Observed by Four Spacecraft

Extreme ultraviolet (EUV) waves are thought to be the propagating footprint of the shock on the solar surface. One of the key questions in SEP research is the timing of the SEP release with respect to the time when the EUV wave magnetically connects with an observer. Taking advantage of close-to-the-Sun measurements by Parker Solar Probe (PSP) and Solar Orbiter (SolO), we investigate an SEP event that occurred on 2021 September 28 and was observed at different locations by SolO, PSP, STEREO-A, and near-Earth spacecraft. During this time, SolO, PSP and STEREO-A shared similar nominal magnetic footpoints relative to the SEP source region but were at different heliocentric distances. We find that the SEP release times estimated at these four locations were delayed compared to the times when the EUV wave intercepted the footpoints of the nominal magnetic fields connecting to each spacecraft by around 30 to 60 minutes. Combining observations in multiple wavelengths of radio, white-light, and EUV, with a geometrical shock model, we analyze the associated shock properties, and discuss the acceleration and delayed release processes of SEPs in this event as well as the accuracy and limitations of using EUV waves to determine the SEP acceleration and release times.

physics.space-ph↗

arXiv2023

The Width of Magnetic Ejecta Measured Near 1 au: Lessons from STEREO-A Measurements in 2021--2022

Coronal mass ejections (CMEs) are large-scale eruptions with a typical radial size at 1 au of 0.21 au but their angular width in interplanetary space is still mostly unknown, especially for the magnetic ejecta (ME) part of the CME. We take advantage of STEREO-A angular separation of 20$^\circ$-60$^\circ$ from the Sun-Earth line from October 2020 to August 2022, and perform a two-part study to constrain the angular width of MEs in the ecliptic plane: a) we study all CMEs that are observed remotely to propagate between the Sun-STEREO-A and the Sun-Earth lines and determine how many impact one or both spacecraft in situ, and b) we investigate all in situ measurements at STEREO-A or at L1 of CMEs during the same time period to quantify how many are measured by the two spacecraft. A key finding is that, out of 21 CMEs propagating within 30$^\circ$ of either spacecraft, only four impacted both spacecraft and none provided clean magnetic cloud-like signatures at both spacecraft. Combining the two approaches, we conclude that the typical angular width of a ME at 1 au is $\sim$ 20$^\circ$-30$^\circ$, or 2-3 times less than often assumed and consistent with a 2:1 elliptical cross-section of an ellipsoidal ME. We discuss the consequences of this finding for future multi-spacecraft mission designs and for the coherence of CMEs.

astro-ph.SR↗

arXiv2023

New Observations Needed to Advance Our Understanding of Coronal Mass Ejections

Coronal mass ejections (CMEs) are large eruptions from the Sun that propagate through the heliosphere after launch. Observational studies of these transient phenomena are usually based on 2D images of the Sun, corona, and heliosphere (remote-sensing data), as well as magnetic field, plasma, and particle samples along a 1D spacecraft trajectory (in-situ data). Given the large scales involved and the 3D nature of CMEs, such measurements are generally insufficient to build a comprehensive picture, especially in terms of local variations and overall geometry of the whole structure. This White Paper aims to address this issue by identifying the data sets and observational priorities that are needed to effectively advance our current understanding of the structure and evolution of CMEs, in both the remote-sensing and in-situ regimes. It also provides an outlook of possible missions and instruments that may yield significant improvements into the subject.

astro-ph.IM↗

arXiv2023

Work-Life Balance Starts with Proper Deadlines and Exemplary Agencies

Diversity, equity and inclusion (DEI) programs can only be implemented successfully if proper work-life balance is possible in Heliophysics (and in STEM field in general). One of the core issues stems from the culture of "work-above-life" associated with mission concepts, development, and implementation but also the expectations that seem to originate from numerous announcements from NASA (and other agencies). The benefits of work-life balance are well documented; however, the entire system surrounding research in Heliophysics hinders or discourages proper work-life balance. For example, there does not seem to be attention paid by NASA Headquarters (HQ) on the timing of their announcements regarding how it will be perceived by researchers, and how the timing may promote a culture where work trumps personal life. The same is true for remarks by NASA HQ program officers during panels or informal discussions, where seemingly innocuous comments may give a perception that work is expected after "normal" work hours. In addition, we are calling for work-life balance plans and implementation to be one of the criteria used for down-selection and confirmation of missions (Key Decision Points: KDP-B, KDP-C).

astro-ph.IM↗

arXiv2023

Evolution of the Radial Size and Expansion of Coronal Mass Ejections Investigated by Combining Remote and In-Situ Observations

A fundamental property of coronal mass ejections (CMEs) is their radial expansion, which determines the increase in the CME radial size and the decrease in the CME magnetic field strength as the CME propagates. CME radial expansion can be investigated either by using remote observations or by in-situ measurements based on multiple spacecraft in radial conjunction. However, there have been only few case studies combining both remote and in-situ observations. It is therefore unknown if the radial expansion estimated remotely in the corona is consistent with that estimated locally in the heliosphere. To address this question, we first select 22 CME events between the years 2010 and 2013, which were well observed by coronagraphs and by two or three spacecraft in radial conjunction. We use the graduated cylindrical shell model to estimate the radial size, radial expansion speed, and a measure of the dimensionless expansion parameter of CMEs in the corona. The same parameters and two additional measures of the radial-size increase and magnetic-field-strength decrease with heliocentric distance of CMEs based on in-situ measurements are also calculated. For most of the events, the CME radial size estimated by remote observations is inconsistent with the in-situ estimates. We further statistically analyze the correlations of these expansion parameters estimated using remote and in-situ observations, and discuss the potential reasons for the inconsistencies and their implications for the CME space weather forecasting.

astro-ph.SR↗

arXiv2022

Characteristic Scales of Complexity and Coherence within Interplanetary Coronal Mass Ejections: Insights from Spacecraft Swarms in Global Heliospheric Simulations

Many aspects of the three-dimensional (3-D) structure and evolution of interplanetary coronal mass ejections (ICMEs) remain unexplained. Here, we investigate two main topics: (1) the coherence scale of magnetic fields inside ICMEs, and (2) the dynamic nature of ICME magnetic complexity. We simulate ICMEs interacting with different solar winds using the linear force-free spheromak model incorporated into the EUHFORIA model. We place a swarm of ~20000 spacecraft in the 3-D simulation domain and characterize ICME magnetic complexity and coherence at each spacecraft based on simulated time series. Our simulations suggest that ICMEs retain a lower complexity and higher coherence along their magnetic axis, but that a characterization of their global complexity requires crossings along both the axial and perpendicular directions. For an ICME of initial half angular width of $45^\circ$ that does not interact with other large-scale solar wind structures, global complexity can be characterized by as little as 7-12 spacecraft separated by $25^\circ$, but the minimum number of spacecraft rises to 50-65 (separated by $10^\circ$) if interactions occur. Without interactions, ICME coherence extends for $45^\circ$, $20^\circ$-$30^\circ$, $15^\circ$-$30^\circ$, and $0^\circ$-$10^\circ$ for $B$, $B_ϕ$, $B_θ$, and $B_r$, respectively. Coherence is also lower in the ICME west flank compared to the east flank due to Parker spiral effects. Moreover, coherence is reduced by a factor of 3-6 by interactions with solar wind structures. Our findings help constrain some of the critical scales that control the evolution of ICMEs and aid in the planning of future dedicated multi-spacecraft missions.

astro-ph.SR↗

arXiv2022

3UCubed: The IMAP Student Collaboration CubeSat Project

The 3UCubed project is a 3U CubeSat being jointly developed by the University of New Hampshire, Sonoma State University, and Howard University as a part of the NASA Interstellar Mapping and Acceleration Probe, IMAP, student collaboration. This project comprises of a multidisciplinary team of undergraduate students from all three universities. The mission goal of the 3UCubed is to understand how Earths polar upper atmosphere the thermosphere in Earths auroral regions, responds to particle precipitation and solar wind forcing, and internal magnetospheric processes. 3UCubed includes two instruments with rocket heritage to achieve the science mission: an ultraviolet photomultiplier tube, UVPMT, and an electron retarding potential analyzer ERPA. The spacecraft bus consists of the following subsystems: Attitude Determination and Control, Command and Data Handling, Power, Communication, Structural, and Thermal. Currently, the project is in the post-PDR stage, starting to build and test engineering models to develop a FlatSat prior to critical design review in 2023. The goal is to launch at least one 3U CubeSat to collect science data close to the anticipated peak of Solar Cycle 25 around July 2025. Our mother mission, IMAP, is also projected to launch in 2025, which will let us jointly analyze the science data of the main mission, providing the solar wind measurements and inputs to the magnetosphere with that of 3UCubed, providing the response of Earths cusp to these inputs.

astro-ph.IM↗

arXiv2022

Acceleration and Expansion of a Coronal Mass Ejection in the High Corona: Role of Magnetic Reconnection

The important role played by magnetic reconnection in the early acceleration of coronal mass ejections (CMEs) has been widely discussed. However, as CMEs may have expansion speeds comparable to their propagation speeds in the corona, it is not clear whether and how reconnection contributes to the true acceleration and expansion separately. To address this question, we analyze the dynamics of a moderately fast CME on 2013 February 27, associated with a continuous acceleration of its front into the high corona, even though its speed had reached $\sim$700~km~s$^{-1}$ and larger than the solar wind speed. The apparent CME acceleration is found to be due to the CME expansion in the radial direction. The CME true acceleration, i.e., the acceleration of its center, is then estimated by taking into account the expected deceleration caused by the solar wind drag force acting on a fast CME. It is found that the true acceleration and the radial expansion have similar magnitudes. We find that magnetic reconnection occurs after the CME eruption and continues during the CME propagation in the high corona, which contributes to the CME dynamic evolution. Comparison between the apparent acceleration related to the expansion and the true acceleration that compensates the drag shows that, for this case, magnetic reconnection contributes almost equally to the CME expansion and to the CME acceleration. The consequences of these measurements for the evolution of CMEs as they transit from the corona to the heliosphere are discussed.

astro-ph.SR↗

arXiv2022

Multi-Spacecraft Observations of the Evolution of Interplanetary Coronal Mass Ejections Between 0.3 and 2.2 AU: Conjunctions with the Juno Spacecraft

We present a catalogue of 35 interplanetary coronal mass ejections (ICMEs) observed by the Juno spacecraft and at least one other spacecraft during its cruise phase to Jupiter. We identify events observed by MESSENGER, Venus Express, Wind, and STEREO with magnetic features that can be matched unambiguously with those observed by Juno. A multi-spacecraft study of ICME properties between 0.3 and 2.2 AU is conducted: we firstly investigate the global expansion by tracking the variation in magnetic field strength with increasing heliocentric distance of individual ICME events, finding significant variability in magnetic field relationships for individual events in comparison with statistical trends. With the availability of plasma data at 1 AU, the local expansion at 1 AU can be compared with global expansion rates between 1 AU and Juno. Despite following expected trends, the local and global expansion rates are only weakly correlated. Finally, for those events with clearly identifiable magnetic flux ropes, we investigate the orientation of the flux rope axis as they propagate; we find that 64% of events displayed a decrease in inclination with increasing heliocentric distance, and 40% of events undergo a significant change in orientation as they propagate towards Juno. The multi-spacecraft catalogue produced in this study provides a valuable link between ICME observations in the inner heliosphere and beyond 1 AU, thereby improving our understanding of ICME evolution.

physics.space-ph↗

arXiv2022

On the utility of flux rope models for CME magnetic structure below 30$R_{\odot}$

We present a comprehensive analysis of the three-dimensional magnetic flux rope structure generated during the Lynch et al. (2019) magnetohydrodynamic (MHD) simulation of a global-scale, 360 degree-wide streamer blowout coronal mass ejection (CME) eruption. We create both fixed and moving synthetic spacecraft to generate time series of the MHD variables through different regions of the flux rope CME. Our moving spacecraft trajectories are derived from the spatial coordinates of Parker Solar Probe's past encounters 7 and 9 and future encounter 23. Each synthetic time series through the simulation flux rope ejecta is fit with three different in-situ flux rope models commonly used to characterize the large-scale, coherent magnetic field rotations observed in a significant fraction of interplanetary CMEs (ICMEs). We present each of the in-situ flux rope model fits to the simulation data and discuss the similarities and differences between the model fits and the MHD simulation's flux rope spatial orientations, field strengths and rotations, expansion profiles, and magnetic flux content. We compare in-situ model properties to those calculated with the MHD data for both classic bipolar and unipolar ICME flux rope configurations as well as more problematic profiles such as those with a significant radial component to the flux rope axis orientation or profiles obtained with large impact parameters. We find general agreement among the in-situ flux rope fitting results for the classic profiles and much more variation among results for the problematic profiles. We also examine the force-free assumption for a subset of the flux rope models and quantify properties of the Lorentz force within MHD ejecta intervals. We conclude that the in-situ flux rope models are generally a decent approximation to the field structure, but all the caveats associated with in-situ flux rope models will still apply...

astro-ph.SR↗

arXiv2022

A Coronal Mass Ejection and Magnetic Ejecta Observed In Situ by STEREO-A and Wind at 55$^\circ$ Angular Separation

We present an analysis of {\it in situ} and remote-sensing measurements of a coronal mass ejection (CME) that erupted on 2021 February 20 and impacted both the Solar TErrestrial RElations Observatory (STEREO)-A and the {\it Wind} spacecraft, which were separated longitudinally by 55$^\circ$. Measurements on 2021 February 24 at both spacecraft are consistent with the passage of a magnetic ejecta (ME), making this one of the widest reported multi-spacecraft ME detections. The CME is associated with a low-inclined and wide filament eruption from the Sun's southern hemisphere, which propagates between STEREO-A and {\it Wind} around E34. At STEREO-A, the measurements indicate the passage of a moderately fast ($\sim 425$~km\,s$^{-1}$) shock-driving ME, occurring 2--3 days after the end of a high speed stream (HSS). At {\it Wind}, the measurements show a faster ($\sim 490$~km\,s$^{-1}$) and much shorter ME, not preceded by a shock nor a sheath, and occurring inside the back portion of the HSS. The ME orientation measured at both spacecraft is consistent with a passage close to the legs of a curved flux rope. The short duration of the ME observed at {\it Wind} and the difference in the suprathermal electron pitch-angle data between the two spacecraft are the only results that do not satisfy common expectations. We discuss the consequence of these measurements on our understanding of the CME shape and extent and the lack of clear signatures of the interaction between the CME and the HSS.

physics.space-ph↗