MIST
Magnetosphere, Ionosphere and Solar-Terrestrial
Statistical Scale Analyses of a Diurnal Periodicity in Auroral Kilometric Radiation, Observed by Wind/WAVES
By Alexandra Ruth Fogg (Dublin Institute for Advanced Studies)
The Earth is a natural radio emitter with Auroral Kilometric Radiation (AKR) its strongest frequency component. AKR is highly correlated with space weather activity, but can also be modulated by the rotation of the planet. Beyond the Earth, rotational periodicities in the intensity of planetary radio emissions can be used to estimate the rotation rate of planets without trackable surface features. While the rotational period of the Earth is well known, understanding periodicities in the intensity of AKR is still of scientific interest. Firstly, observations of terrestrial radio emissions can be used as a laboratory to assess periodicity detection methods, exploiting the large historical and contemporary observational archives. Secondly, to understand AKR as a barometer for space weather, a clear description of other affects on the signal (visibility, periodicities, etc) must be determined.
Using a decade-long archive of observations of AKR, Fogg et al (2026) test a variety of analyses to detect a 24-hour periodicity in AKR intensity. Lomb-Scargle and autocorrelation analyses determined a ~24-hour periodicity in long, unprocessed datasets, but on short (31-day) datasets, data had to be log-transformed to extract this result. Some evidence to support the lighthouse/rotating beam periodicity driver was found; this suggests that the AKR source, which is tied to a magnetic field line, rotates with the planet at a 24-hour periodicity since the field line itself is tied to the interior of the rotating planet.
Fogg, A. R., Wu, S., Jackman, C. M., Walker, S. J., Rutala, M. J., Louis, C. K., et al. (2026). Statistical scale analyses of a diurnal periodicity in auroral kilometric radiation, observed by wind/WAVES. Journal of Geophysical Research: Space Physics, 131, e2026JA035423. https://doi.org/10.1029/2026JA035423
See publication for more details:
Fogg, A. R., Wu, S., Jackman, C. M., Walker, S. J., Rutala, M. J., Louis, C. K., et al. (2026). Statistical scale analyses of a diurnal periodicity in auroral kilometric radiation, observed by wind/WAVES. Journal of Geophysical Research: Space Physics, 131, e2026JA035423. https://doi.org/10.1029/2026JA035423
Normalized Lomb‐Scargle periodogram for (a) synthetic oscillating signal (b) 10 years of data and (c) 142 days and 11 hours of data (a period of continuous nightside observation). Where two signals are plotted, integrated power across 100–400 kHz is in grey and 50–100 kHz in orange. Vertical black arrows indicate periods of 12 and 24 hr along the top x axis. False Alarm Level (FAL) is the 97.7th percentile of 100 bootstraps and is indicated for each signal with a horizontal arrow, with colour matching the trace.
Cometary ion dynamics at a weakly outgassing comet
By Victor Steinwand (Imperial College London)
The ESA/Rosetta mission escorted comet 67P/Churyumov─Gerasimenko for 2 yr, exploring its plasma environment across diverse outgassing conditions. Plasma density observations from the Rosetta Plasma Consortium (RPC) are broadly categorized into two regimes for the ion dynamics, linked to the presence of a diamagnetic cavity at Rosetta's location. With a diamagnetic cavity present, ions detected by Rosetta are accelerated with respect to the neutral coma. Without a diamagnetic cavity present, at lower outgassing, and nearer the nucleus, ions co-move with the neutrals. We examine the transition between regimes following Rosetta's last detection of the cavity in 2016 February. During this transition, global 3D plasma models of the cometary ionosphere underestimate plasma densities. To investigate this underestimation, we assess the sensitivity of cometary ion densities to different parameters using a 3D collisional ion test particle model, driven by electromagnetic fields from hybrid modelling. We show that considering cometary electron cooling is necessary to model cometary ion dynamics within 100 km of the surface. Electron temperatures derived from collisional electron modelling affect ion dynamics via the ambipolar electric field, increasing ion number densities. We further show that the cometary electron cooling exobase organizes Rosetta plasma density observations; different ion dynamics regimes are linked to the position of Rosetta relative to the exobase. These findings demonstrate that Rosetta was below this exobase for much of the post-perihelion period. They justify the absence of ion acceleration in plasma density assessments and the use of uniform electron-impact ionization frequencies between Rosetta and the surface during post-perihelion.
See publication for more details:
https://academic.oup.com/mnras/article/550/2/stag1256/8723309
Two-dimensional histograms of post-perihelion number density data from 2016 February 17 to 2016 September 30, for a total ion production rate 19.85 ≤ log10(νQ[s−2]) ≤ 20.15, showing the organization of the data in the parameter space r/rexo against u_i r/rexo = (ν/100σn_i)(1 − rc/r). The boxes and points are values of (ν/100σni)(1 − rc/r) binned in r/rexo. The local gradient in this parameter space gives the local ion velocity u_i. The straight line represents ions moving at the speed of the neutral background u_n. Below the exobase, the data are clustered around the ui = un line, showing the utility of the acceleration-free model inside the flattened region of the ambipolar potential well. They depart from the line above r ∼ rexo, indicating acceleration.
Autumn MIST 2026 (20th November)
Autumn MIST 2026
Friday 20th November 2026
Talks will be held at the Geological Society of London and posters will be on display at the neighbouring Royal Society of Chemistry. We hope you enjoy the meeting!
Registration
Registration is open until Friday 6th November. Please note that the Autumn MIST 2026 online registration is being hosted by the University of St Andrews online shop, so please do not be alarmed that the link takes you there. Please visit this link to register for Autumn MIST 2026 (coffee, tea, and biscuits are included). We cannot accept on-site payments on the day.
Venue Information
The Geological Society of London and the Royal Society of Chemistry are both situated in the historic Burlington House (Piccadilly, London, W1J 0BD). Google Maps link.
Burlington House is a 5-minute walk from Green Park or Piccadilly Circus tube stations.
If you are travelling by train, please see below for details on which tube line to take.
Euston Station - Victoria line to Green Park (~5 minutes)
King’s Cross Station - Piccadilly line to Piccadilly Circus (~8 minutes)
Paddington Station - Bakerloo line to Piccadilly Circus (~10 minutes)
Marylebone Station - Bakerloo line to Piccadilly Circus (~8 minutes)
Schedule
TBD