Maxime Grandin

This study compares the capabilities of different sized micro‐pore optic (MPO) based soft X‐ray telescopes and their ability to observe features and phenomena of the magnetosheath at Earth. The basic science is the starting point and different instrument properties are applied to test which would be capable of studying features of the near‐Earth space, such as the magnetopause and bow shock location, as well as transients such as flux transfer events and mirror‐mode waves. Nine model optics are evaluated with optic radius of curvature ranging from 75 to 800 cm, and their effective area and production factor calculated. Soft X‐ray emission data from the day‐side magnetosphere is extracted from Vlasiator numerical simulation results (Grandin et al., 2024, https://doi.org/10.26464/epp2023052 ) and converted into counts detected by the nine different MPO telescopes with each unique production factor. A cosmic X‐ray background and Poisson noise are added to make realistic model instrument images. A natural tradeoff is presented between instrument size and science performance. Detection accuracy of the magnetopause location, a primary science goal for many magnetosphere observing MPO telescopes, is shown to range from 0.396 with a signal to noise (SNR) of 0.918 (75 cm at 10 s observation duration) to 0.014 and SNR of 7.491 (800 cm at 300 s observation duration). Flux transfer events can be observed in model telescope images at 10 and 30 s observation durations. The analysis shows that larger optic size improves instrument grasp, and permits shorter observation durations to image magnetospheric transients.

Identifying the coupling mechanisms that operate in the two directions, upward and downward, between Earth's lower atmosphere and geospace (ionosphere, magnetosphere, and beyond) is currently one of the greatest scientific challenges to be addressed by the atmosphere and space science communities. To meet this challenge, an ISSI Forum on “Physical Links between Weather in Space and Weather in the Lower Atmosphere” was organized in Bern in November 2022. This paper presents a synthesis of the scientific discussions, conclusions and recommendations of this Forum, aimed primarily at the space- and atmospheric-science communities while also identifying implications for operational services, space agencies and other stakeholders. The Forum discussed how the lower atmosphere influences the upper layers through gravity waves, atmospheric tides and planetary waves, thunderstorms, chemical transport and seismic activity, and conversely how solar and space phenomena may affect chemistry, dynamics and climate in the lower atmosphere. It also considered the redistribution of chemical species, momentum and energy within the thermosphere–ionosphere, where forcing from above and below interact. Based on this analysis, the Forum identified observational gaps and needs for new observations, particularly in the lower thermosphere (~ 90 to 200 km), as well as modeling needs. Rather than implying that whole-atmosphere models lack all upper-atmosphere electrodynamics, we identify the need to strengthen quantitative coupling between neutral dynamics, ionospheric electrodynamics and magnetospheric forcing, together with systematic model validation and data assimilation. In order to implement its recommendations, the Forum highlighted the need for co-ordinated international efforts to understand the whole atmosphere as a coupled system. It emphasized the importance of developing at the international level a “Great Ionosphere–Thermosphere–Mesosphere (ITM) Observatory”, understood as an interoperable framework linking distributed space- and ground-based assets and models rather than as a single physical observatory. Finally, the Forum emphasized the need for closer collaboration between space scientists, meteorologists and climate scientists, and the importance of upper atmospheric processes for appropriately addressing space sustainability and for understanding possible links between space weather and lower atmospheric climate. The conclusions and recommendations of the Forum motivated the organization of the ISSI Workshop on “Physical Links Between Weather and Climate in Space and the Lower Atmosphere”, held in Bern in January 2024.

We present NORVIS (NORdlys Versatile Imaging Spectrograph), a portable broadband imaging spectrograph developed for ground-based auroral observations. Based on the Star'Ex optical concept, NORVIS is optimized for auroral emissions and covers approximately 380–860 nm in a single acquisition at a moderate spectral resolution of 1.2 nm FWHM. The instrument combines auroral spectroscopy, wide-field context imaging, field operation, automated spectral reduction, and centralized data archiving within a researcher-citizen science framework. First observations were obtained during a campaign at Skibotn Observatory, Norway, in February 2026, during which approximately 1200 spectra were acquired and reduced over three observing nights, with typical exposure times of 30 s. These observations demonstrate the simultaneous detection of key auroral emissions, including the N2+ 1NG bands at 391.4 and 427.8 nm and the [O I] emissions at 557.7 and 630.0/636.4 nm, while also providing access to the Hα region and to O I emissions at 777.4 and 844.6 nm. Representative observations illustrate the potential of NORVIS for emission-ratio diagnostics and geometry-aware interpretation of auroral structures. NORVIS is intended to form the basis of a distributed observing network, with coordinated deployments planned in Kiruna, Skibotn, Svalbard, and northern Finland, followed by permanent installations at Kiruna, Skibotn, the Kjell Henriksen Observatory in Svalbard, and Nyrölä.

Fragmented aurora-like emissions (fragments) are small-scale green E-region structures that have previously been reported mainly from high-latitude locations near the poleward auroral oval boundary. Here we present a global citizen-science dataset of 26 fragment observations from 2017 to 2025, collected through an international citizen-science campaign via the Skywarden platform. The observations span magnetic latitudes from approximately 53 to 76°, a wide range of magnetic local times and activity levels, both hemispheres, and diverse auroral conditions. The dataset substantially extends the observational record of fragments beyond previously reported high-latitude regions. Both isolated fragments (type I) and the quasi-periodic wave-like fragments (type II) are represented in this broader geographical context. To assess fragment locations relative to the auroral oval, three case studies combining satellite observations with ground-based auroral images were analysed in detail. These demonstrate that fragments occur poleward of the oval in Antarctica, equatorward of the oval in Manitoba, and within the oval near the diffuse-discrete boundary in Iceland. Together, the global dataset and case studies show that fragments occur across a much broader range of auroral and geomagnetic conditions and oval positions than previously documented. The results demonstrate the scientific value of citizen-science observations for studying short-lived and localised auroral phenomena.

Fragmented aurora-like emissions (fragments) are small-scale green E-region structures that have previously been reported mainly from high-latitude locations near the poleward auroral oval boundary. Here we present a global citizen-science dataset of 26 fragment observations from 2017 to 2025, collected through an international citizen-science campaign via the Skywarden platform. The observations span magnetic latitudes from approximately 53 to 76°, a wide range of magnetic local times and activity levels, both hemispheres, and diverse auroral conditions. The dataset substantially extends the observational record of fragments beyond previously reported high-latitude regions. Both isolated fragments (type I) and the quasi-periodic wave-like fragments (type II) are represented in this broader geographical context. To assess fragment locations relative to the auroral oval, three case studies combining satellite observations with ground-based auroral images were analysed in detail. These demonstrate that fragments occur poleward of the oval in Antarctica, equatorward of the oval in Manitoba, and within the oval near the diffuse-discrete boundary in Iceland. Together, the global dataset and case studies show that fragments occur across a much broader range of auroral and geomagnetic conditions and oval positions than previously documented. The results demonstrate the scientific value of citizen-science observations for studying short-lived and localised auroral phenomena.

This paper presents a quantitative measure for the intensities of auroras, as well as a new magnetic index which can indicate the probability of auroras locally. Auroras are an important factor in the business of nature tourism in polar areas. Nowcasts and short-term forecasts of auroral activity can be based on near-real-time all-sky camera (ASC) and magnetometer data. The parameter I , introduced in this paper, can indicate quantitatively the brightness of auroras as measured using ASC images at the three brightest aurora wavelengths (428, 558 and 630 nm). Furthermore, the ℛ-index indicates the variations of magnetic field measured by a magnetometer, which is proposed as a proxy for the aurora. Statistical results of both I and ℛ are presented. It is found that both parameters have similar statistical variations with time of day, season and solar cycle phase, which are also similar to those previously reported for auroral activity. Empirical relations between I and ℛ for each of the three aurora wavelengths are also established. With this relation, combined with previously published formulae for Rayleigh-to-candela conversion, we can build a link between magnetic field measurements and auroras visible for the naked human eye. Based on our data sets, average probabilities of human eye detectable auroras in rural night sky conditions vary in the range of 2–30% at geomagnetic latitudes 55°–65°.

Solar Cycle 25 (SC25) produced several major geomagnetic storms with distinctly different combinations of energetic electron precipitation (EEP) and solar proton event (SPE) forcing, providing a unique opportunity to investigate short-term ozone responses in the mesosphere-thermosphere system. We analyse four major storms occurring in May 2024, October 2024, November 2025, and January 2026 using Microwave Limb Sounder (MLS) observations and specified-dynamics WACCM-D simulations. Significant mesospheric ozone depletion was observed during all four events, with maximum ozone losses ranging from approximately 30 % to 80 %. Model-observation comparisons show that the dominant particle forcing varied substantially among the storms. The May 2024 superstorm was predominantly EEP-driven, whereas the October 2024 event was largely SPE-driven. The November 2025 and January 2026 storms represent mixed SPE-EEP cases, with a stronger proton contribution during January 2026. Negative ozone anomalies were consistently observed in the lower thermosphere during all four events. Although not reproduced by WACCM-D, their repeated occurrence suggests a lower-thermospheric response to major geomagnetic storms. Model simulations further reveal the indirect energetic particle precipitation (EPP) effect in the stratosphere, characterised by descending ozone depletion features dominated by EEP. The four SC25 storms demonstrate the value of combining satellite observations with chemistry-climate models to separate the contributions of SPEs, EEP, and atmospheric dynamics, while also revealing several areas where current representations of particle forcing and upper-atmospheric coupling can be further improved. Maintaining long-term observations of both EPP and atmospheric composition remains crucial for improving our understanding of atmosphere-space coupling during geomagnetic storms.

Fragmented aurora-like emissions (fragments) are small-scale green E-region structures that have previously been reported mainly from high-latitude locations near the poleward auroral oval boundary. Here we present a global citizen-science dataset of 26 fragment observations from 2017 to 2025, collected through an international citizen-science campaign via the Skywarden platform. The observations span magnetic latitudes from approximately 53 to 76°, a wide range of magnetic local times and activity levels, both hemispheres, and diverse auroral conditions. The dataset substantially extends the observational record of fragments beyond previously reported high-latitude regions. Both isolated fragments (type I) and the quasi-periodic wave-like fragments (type II) are represented in this broader geographical context. To assess fragment locations relative to the auroral oval, three case studies combining satellite observations with ground-based auroral images were analysed in detail. These demonstrate that fragments occur poleward of the oval in Antarctica, equatorward of the oval in Manitoba, and within the oval near the diffuse-discrete boundary in Iceland. Together, the global dataset and case studies show that fragments occur across a much broader range of auroral and geomagnetic conditions and oval positions than previously documented. The results demonstrate the scientific value of citizen-science observations for studying short-lived and localised auroral phenomena.

Auroral forms can provide information not only on the state of near-Earth space but also on conditions in the lower-thermosphere–ionosphere. The so-called dune aurora, consisting of brighter stripes forming a wave-like pattern in the dim, diffuse green aurora, has been hypothesised as being an optical signature revealing the presence of large-scale atmospheric waves above or near the mesopause. However, only a few dune aurora events have been studied to date, leaving many open questions regarding the nature of this phenomenon. We carry out the first systematic survey of dune aurora events by collecting citizen science observations of the dunes since 2000 using the Skywarden (https://taivaanvahti.fi, last access: 25 August 2026) database of observations. From a total of 308 dune aurora observations made during 61 different events by citizen scientists from Northern Europe, North America, Australia, and New Zealand, we investigate the distribution of dune events as a function of location, month, magnetic local time (MLT), solar wind and interplanetary magnetic field (IMF) conditions, and geomagnetic activity. We compare those distributions to that of all the aurora observations reported in Skywarden since 2000. We find that the vast majority (92 %) of the dune reports were made by observers below 61° geomagnetic latitude (to be compared to 74 % for all aurora observations), suggesting that they frequently occur in the equatorward part of the auroral oval. The dune observations are mostly (89 %) made in the pre-midnight sector, with a peak between 21:00 and 22:00 MLT (between 23:00 and 00:00 MLT for all aurora observations). The months with the highest number of reports of dune observations are October and March, which could be the result of a combination of geomagnetic, atmospheric, darkness, and cloudiness conditions needed for them to be observed. Regarding the solar wind and IMF driving parameters, no statistically significant differences are found between dune and all-aurora observations, but the differences are significant for geomagnetic indices, with dune observations being made during more active conditions than for all types of aurora considered together. Finally, we investigate a possible relationship between dune aurora and equivalent current patterns derived from ground-based magnetometer measurements. We find that, for all the reported events, the dunes are observed in association with strong (in most cases eastward but occasionally westward) auroral electrojet signatures and in the vicinity of the Harang discontinuity. These results suggest that the dune aurora formation mechanism might involve an interplay between proton precipitation, atmospheric dynamics, and nightside transition region processes.

Fragmented aurora-like emissions (fragments) are small-scale green E-region structures that have previously been reported mainly from high-latitude locations near the poleward auroral oval boundary. Here we present a global citizen-science dataset of 26 fragment observations from 2017 to 2025, collected through an international citizen-science campaign via the Skywarden platform. The observations span magnetic latitudes from approximately 53 to 76°, a wide range of magnetic local times and activity levels, both hemispheres, and diverse auroral conditions. The dataset substantially extends the observational record of fragments beyond previously reported high-latitude regions. Both isolated fragments (type I) and the quasi-periodic wave-like fragments (type II) are represented in this broader geographical context. To assess fragment locations relative to the auroral oval, three case studies combining satellite observations with ground-based auroral images were analysed in detail. These demonstrate that fragments occur poleward of the oval in Antarctica, equatorward of the oval in Manitoba, and within the oval near the diffuse-discrete boundary in Iceland. Together, the global dataset and case studies show that fragments occur across a much broader range of auroral and geomagnetic conditions and oval positions than previously documented. The results demonstrate the scientific value of citizen-science observations for studying short-lived and localised auroral phenomena.