MIST

The Non-Linear Dependence of Daily Maximum Ionospheric Total Electron Content on F10.7

By Martin Cafolla (University of Warwick)

Solar Extreme Ultraviolet (EUV) radiation drives ionisation in the upper atmosphere to create the ionosphere. The variability of the intensity of this radiation results in regions of high electron number density across the ionosphere, characterised by the Total Electron Content (TEC). The daily solar flux at 10.7cm, the F10.7 index, is commonly used as a proxy to EUV in ionospheric models. Typically studies have shown how either the global averages or geographically local values of TEC vary with daily F10.7, F10.7A (the 81-day average) and F10.7p (a combination of daily F10.7 and F10.7A). We study how the daily maximum TEC correlates with daily F10.7 using 15-minute Global Ionospheric Maps (GIMs) from the Jet Propulsion Laboratory (JPL) between 2003-2024.

We find that for F10.7 ≳ 78 − 85 SFU, the daily maximum TEC saturates to a seasonally dependent value between 83−128 TECU. We asses the distribution of the residuals from linear and non-linear least squares fitting as a function of F10.7, as demonstrated in the figure below, and find that a tanh function out-performs a linear function for F10.7 ≥ 150 SFU. Our results are sensitive to different hemispheres, as a result of the construction of JPL-GIMs. Finally, we find that the daily F10.7 clearly resolves the saturation of daily maximum TEC, while F10.7 based on the average does not. Quantifying the value at which the daily maximum TEC saturates with F10.7, and its seasonal dependence, specifies the requirements of systems that are sensitive to extremes in TEC, important in planning of Low Earth Orbit satellite operations.

See publication for more details:

Cafolla, M. A., Chapman, S. C., Watkins, N. W., & Verkhoglyadova, O. P. (2026). The non-linear dependence of daily maximum ionospheric total electron content on F10.7. Space Weather, 24, e2025SW004745. https://doi.org/10.1029/2025SW004745

JWST Discovers the Vertical Structure of Uranus' Ionosphere

By Paola I. Tiranti (Northumbria University, School of Engineering, Physics and Mathematics, Newcastle, UK.)

Uranus’s upper atmosphere is one of the least understood in our Solar System, despite being critical for understanding how giant planets interact with their space environment. Using the James Webb Space Telescope, we observed Uranus for a full rotation and measured the vertical structure of its ionosphere - the charged layer of the atmosphere where aurorae form. Our results show that temperatures peak around 3,000 - 4,000 km above the planet, while ion densities peak near 1,000 km, and are significantly weaker than predicted by models. We also find two bright bands of auroral emission close to Uranus’ magnetic poles, as well as a surprising region where both emission and density are depleted, likely linked to the unusual geometry of Uranus’ tilted and offset magnetic field. These discoveries not only confirm that Uranus’ upper atmosphere has been cooling for decades, but also reveal new structures shaped by its magnetic environment. Together, they provide critical benchmarks for future missions and improve our understanding of how giant planets (both in our Solar System and beyond) balance energy in their upper atmospheres.

See publication for more details:

Tiranti, P. I., Melin, H., Moore, L., Thomas, E. M., Knowles, K. L., Stallard, T. S., K. Roberts & O’Donoghue, J. (2026). JWST discovers the vertical structure of Uranus' ionosphere. Geophysical Research Letters, 53(4), e2025GL119304. https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2025GL119304

Fig 1: Vertical profiles in different regions as observed by JWST on 2025-01-19. a) and b) H3+ temperature and number density, respectively, for auroral region 1 (A1, 0° - 112°W, dark grey), auroral region 2 (A2, 200° - 251°W, dark green), non auroral region 1 (NA1, 113° - 199°W, orange), non auroral region 2 (NA2, 252° - 360°W, brown), emission dip region (ED, 190° - 240°W, light grey). c) Limb data points projected on disk used for the different regional profiles, as described above, with L-shells contours from the Q3 model (Connerney et al, 1987).

Sun-to-Mud observations of the May and October storms of 2024: impacts on Ireland’s Space Weather

By Alexandra Ruth Fogg (Dublin Institute for Advanced Studies)

Around the peak of Solar Cycle 25 in 2024, Earth experienced two dramatic geomagnetic storms in May and October. In this study, we track both storms from the Sun, through interplanetary space, to the Earth and finally to the ground over the island of Ireland. We compare and contrasts the storms in terms of both their solar drivers, and their ground impacts. We term the events: the “May” storm which peaks around 11th May 2024 and the “October” storm which peaks around 11th October 2024.

Key comparisons:

• Multiple Coronal Mass Ejections (CMEs) were ejected from the Sun in May, resulting in CME-CME interaction as they propagated through the solar system. In October, a single CME propagated cleanly through the solar system to impact the Earth.
• The May solar active region had a more complex McIntosh classification in May than that observed in October, although their Hale classifications were the same.
• At the Earth, the period preceding the May storm was more quiescent in auroral and equatorial indices, whereas in October strong-moderate precursor activity was observed.
• Locally in Ireland, magnetometer stations observed sudden storm commencements with both storms, but in October this was again preceded by distinct precursor activity.
• Irish magnetometer stations indicate the auroral electrojets are poleward of observations.
• Both storms generate high geoelectric fields over Ireland. South-west Ireland is most susceptible due to particularly resistive geology.
• Moderately high GICs are modelled during both storms.
• Aurorae were visible across Ireland during both storms, including observations in urban regions.

We conclude that while the May storm was driven by a much more complex solar driving event, the Earth is primed by precursor activity in October, enhancing the strength of its response.

See publication for more details:

Fogg, A. R., Lucas, A. R., Hayes, L. A., Ivanov, S. M., Walker, S. J., Malone-Leigh, J., Murray, S. A., Leahy, S. R., Jackman, C. M., Gallagher, P. T. (2026). Sun-to-Mud observations of the May and October storms of 2024: impacts on Ireland’s Space Weather. Journal of Space Weather and Space Climate (Topical Issue - Severe space weather events of May 2024 and their impacts) 16, 2. https://doi.org/10.1051/swsc/2025044

Collection of images of the Aurora taken during both storms in Ireland. All photos were taken near Kells, Co. Meath, approximately indicated by the purple star on the map of Ireland in panel (d). The approximate locations of the MagIE magnetometers at Dunsink (north east) and Valentia (south west) are indicated with yellow crosses in panel (d). (a,b,f,g) show photos taken with an iPhone 13 by S. R. Leahy. (c,e) show timeseries of SMR for the May and October storms respectively, with purple vertical lines on inset panels indicating the timings of each photo.

Fraction of energy carried by coherent structures in the turbulent cascade in the solar wind

By Alina Bendt (SERENE, School of Engineering, University of Birmingham)

Turbulence is a highly disordered state of flow. It is ubiquitous in astrophysical plasma flows. Turbulence is a proposed mechanism to heat the solar wind, though to what extent turbulence can heat and drive the solar wind is yet an open question. Coherent structures are known to be sites of enhanced dissipation. We use the method proposed by Bendt & Chapman (2025) to distinguish between wave-packets and coherent structures in magnetic field observations by Solar Orbiter and to determine the power that is carried by coherent structures across the inertial (MHD, intermediate scales) and kinetic (small scales) ranges.

We find that coherent structures carry up to a maximum of 50% of the total power in magnetic field fluctuations. In the inertial range, from large to small scales, the percentage of power carried in coherent structures increases roughly linearly at distances less than 0.4 au from the Sun. At larger distances, there are two subranges in the inertial range. In the kinetic range, the percentage of power in coherent structures decreases approximately linearly towards smaller scales.

Our result of a significant percentage of the total power being carried in coherent structures supports the idea that coherent structures are important for turbulent heating of the solar wind. We also provide first insight into the recently discovered behaviour of two subranges in the inertial range.

Reference: Bendt & Chapman 2026 ApJL doi: https://doi.org/10.3847/2041-8213/ae3820

Bendt & Chapman 2025 PhysRevRes doi: https://doi.org/10.1103/PhysRevResearch.7.023176

See publication for details:

A. Bendt and S. C. Chapman 2026 Fraction of Energy Carried by Coherent Structures in the Turbulent Cascade in the Solar Wind ApJL https://iopscience.iop.org/article/10.3847/2041-8213/ae3820

Power in coherent structures as a function of frequency. Results are plotted for the magnetic field component B⟂(BxVsw). Left to right, the panels group the intervals by heliocentric distance: panels (a), (d) R <  0.4 au; panels (b), (e) 0.4 ≤ R < 0.8 au; and panels (c), (f) R ≥ 0.8 au. Upper panels plot the percentage of power in coherent structures LIM-P(fn) and lower panels overplot the power spectral density of coherent structures (purple ×, grey shading) on the total power (purple ⋆) for one of these intervals. On all panels, black vertical lines denote the 1 hr, 1 minute, and 1 s timescales. On upper panels, the vertical grey shading indicates the range of frequencies of the ion-gyro radius of all intervals. The of the single interval shown in the lower panels is indicated by a black vertical line. For the different intervals in the upper panels, the colours denote plasma beta, β < 0.5 (blue), 0.5 ≤ β < 2 (red), and β≥2 (black). Field-alignment angle value (range 0°–90° obtained by folding in angles ≥90°): θ < 20° (+), 20°–60° (∘), and θ ≥ 60° (△).