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.