Speaker
Description
The Low Frequency Array (LOFAR) is one of the most advanced radio telescopes in the world. When radio waves from a distant astronomical source traverse the ionosphere, structures in this plasma affect the signal. The high temporal resolution available (~10 ms), the range of frequencies observed (10-90 MHz & 110-250 MHz) and the large number of receiving stations (currently 52 across Europe) mean that LOFAR can also observe the effects of the midlatitude and sub-auroral ionosphere at an unprecedented level of detail.
Case studies have shown substructure within a sporadic-E layer (Wood et al., 2024), substructure within a Medium Scale Travelling Ionospheric Disturbance (TID) (Dorrian et al., 2023), a Small Scale TID (Boyde et al., 2022) and symmetric quasi-periodic scintillations (Trigg et al., 2024). The small-scale size of many of these features (kilometres to tens of kilometres) implies a local source. A climatology of observations during daylit hours shows that ionospheric waves primarily propagate in the opposite direction to the prevailing wind, suggesting that the structures observed are the ionospheric manifestation of quasi-upward propagating Atmospheric Gravity Waves (AGWs; Boyde et al., 2025). A statistical study (manuscript in preparation) shows that there is a statistically significant link between ionospheric structures observed by LOFAR and lightning activity, with a lag of two hours.
The Dynamic Ionospheric Notifications for Operations and Scheduling project is using ionospheric results to attempt to mitigate the ionospheric effects on LOFAR observations. A database of 2,911 hours of observations is used to determine the quality of the radio astronomy observations on these occasions. The ionospheric conditions associated with these observations are established, using different approaches with different instruments. These approaches include using ionosondes, magnetometers and HF Continuous Doppler Sounding Systems. Different approaches provide information on different scales of plasma density variations. The suitability of these approaches to forecast when ionospheric conditions will be appropriate for low-frequency radio astronomy is determined. Such a forecast could reduce the number of observations which later need to be discarded due to the ionospheric conditions, optimizing the usage of telescope time, and making the operations more sustainable by reducing the computational and storage resources required. These methods could also predict when the ionosphere will be extremely depleted, enabling observations at lower frequencies than have been routinely possible to date.
References
Boyde, B. et al. (2025). Statistics of Travelling Ionospheric Disturbances Observed Using the LOFAR Radio Telescope. J. Space Weather Space Clim., 14, doi:10.1051/swsc/2025002
Boyde, B. et al. (2022). Lensing from small-scale travelling ionospheric disturbances observed using LOFAR, J. Space Weather Space Clim., 12, 34. doi:10.1051/swsc/2022030
Dorrian, G. D. et al. (2023). LOFAR observations of substructure within a traveling ionospheric disturbance at mid-latitude, Space Weather, 21, 2022SW003198. doi:10.1029/2022SW003198
Trigg, H. et al. (2024). Observations of high definition symmetric quasi-periodic scintillations in the mid-latitude ionosphere with LOFAR. J. Geophys. Res., 2023JA032336. doi:10.1029/2023JA032336
Wood, A. G. et al. (2024). Quasi-stationary substructure within a sporadic E layer observed by the Low Frequency Array (LOFAR), J. Space Weather Space Clim. 14, 27. doi:10.1051/swsc/2024024
