Dr Gareth Dorrian

Abstract:

The Earth’s ionosphere can be driven by the Sun, the solar wind, the magnetosphere, as well as the neutral atmosphere. These drivers influence the ionosphere on a variety of spatial and temporal scales. The ionosphere is highly dependent on the driving processes and is highly dynamic. Modelling this plasma and capturing its full dynamic range is challenging.Swarm is the European Space Agency’s (ESA) first constellation mission for Earth Observation (EO), comprising multiple satellites in Low Earth Orbit (LEO). Numerous data products are available, including measures of the ionosphere at a range of spatial scales. During the Swarm-VIP-Dynamic project, which ended in February 2026, the technique of Generalised Linear Modelling was used to create a suite of statistical models. These models predict the electron density and the variability in the ionospheric plasma at spatial scales between 100 km and 7.5 km. The models were based upon proxies for the heliogeophysical processes, as well as measurements of the thermosphere and ionospheric current systems. In addition to the Swarm data, datasets from other satellites and ground-based instruments were used for model evaluation and validation activities.The performance of the models of the electron density approached the theoretical best values for some of the goodness-of-fit statistics that were to evaluate these models. This suggests that the modelling method is appropriate for the task undertaken. The models of ionospheric variability at larger spatial scales (~100 km) also performed well, however the model performance decreased at smaller spatial scales. This suggested that there is a physical process missing from the models. Possible candidates are instability processes or driving of the ionosphere by wave activity from below, neither of which are captured by the models at present. It is possible to test whether atmospheric waves originating in the lower atmosphere are driving the variability at European midlatitudes using different proxies for wave activity, and the ways in which this could be tested are discussed.

Abstract:

<jats:p>The May 2024 Mother’s Day superstorm, the strongest since November 2003, triggered significant ionospheric disturbances. Indeed, during the superstorm, the ionosphere above Europe was transformed into a severely depleted, super-high-altitude plasma structure extending beyond 1500 km above Earth’s surface. We highlight the unique contributions of the LOw Frequency ARray (LOFAR) to ionospheric weather research on this extreme event. Originally designed for radio astronomy, LOFAR’s extensive European network of 52 stations and wide-band capabilities enable high-resolution ionospheric monitoring at both local and regional scales. Leveraging LOFAR measurements, we characterise a plethora of ionospheric effects that occurred during the main and early recovery phases of the storm. We did this by observing significant signal fading associated with the equatorward expansion of the auroral oval during the main phase and by capturing high-speed moving ionospheric irregularities (up to ~800 m/s), and quantifying extreme ionospheric uplift (up to 1500 km) under conditions where conventional HF instruments were not usable due to the occurrence of D-layer absorption, ionospheric G-conditions and uplift above ionosonde altitude range. In this investigation, we harness the unique capabilities of LOFAR to direct view into the structure and dynamics of the ionosphere under the most extreme space weather conditions. Our results confirm LOFAR as an insightful instrument for ionospheric research, offering critical capabilities for advancing storm impact assessment, forecasting, and mitigation strategies.</jats:p>

Abstract:

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 &amp; 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., under review).The recent development of a light version of the LOFAR data means that, for the first time, it is possible to undertake a large statistical study spanning all seasons and local times. Approximately 3,000 hours of observations were used to create this first climatology. It is shown that the ionospheric structures occur most frequently on summer evenings, are not primarily driven by geomagnetic activity and that there are striking similarities to a climatology of lighting strikes. This adds to the body of evidence which suggests that these features are the ionospheric manifestation of AGWs. Such waves substantially affect the global atmospheric circulation and the potential use of LOFAR to better determine the effect of AGWs on the global circulation is discussed.This work is supported by the Leverhulme Trust under Research Project Grant RPG-2020-140.ReferencesBoyde, 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/2022030Dorrian, G. D. et al. (2023). LOFAR observations of substructure within a traveling ionospheric disturbance at mid-latitude, Space Weather, 21, 2022SW003198. doi:10.1029/2022SW003198Trigg, H. et al. (2024). Observations of high definition symmetric quasi-periodic scintillations in the mid-latitude ionosphere with LOFAR. J. Geophys. Res., 2023JA032336. doi:10.1029/2023JA032336Wood, 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

Abstract:

The 2022 Hunga Tonga Volcano Eruption (HTVE) had unprecedented impacts on atmospheric space weather. It provided a clear example of how space weather may be impacted by influences both &#8220;from above&#8221; (e.g. the solar wind, geo-magnetic storms) and &#8220;from below&#8221; (e.g. powerful volcanoes, hurricanes, earthquakes). Manifestations of unprecedented geophysical effects from HTVE were an acoustic wave that circled the Earth several times, the formation of strong ionospheric plasma bubbles and plasma depletion. An important method for diagnosing ionospheric space weather is ionospheric radio scintillation (IS). The purpose of this work is data analysis, modelling and interpretation of radio scintillation data of ionospheric effects from HTVE using the Low-Frequency Array (LOFAR), supported by observations from the European Space Agency&#8217;s Swarm mission and other geophysical instruments. Specifically, LOFAR observed TIDs in the ionospheric plasma over the Europe, which, based on typical velocities and pulse widths (on the order of 10 s), are interpreted as the effect of&#160; waves generated as a result of the HTVE. The physical modelling carried out corresponds to a picture corresponding to the penetration of Lamb waves into ionospheric altitudes, with their source being a pressure pulse associated with HTVE. Moreover, the corresponding physical explanation, based on the modelling carried out, is given from two points of view: (1) acoustic mode and (2) acoustic impulse representations. (1) Modes with periods of about 12 min were studied. It turned out that such frequencies correspond to a number of eigenmodes of Lamb waves which, accounting for attenuation, travelled thousands of km from the source to the observation site and having a finite/non-zero excitation efficiency (velocity value) near the Earth&#8217;s surface. At the same time, the acoustic field of such waves is concentrated at the heights of the altitude region of the E region of the ionosphere. (2) It has been shown that a pressure pulse with a duration of about 10 s in the lower atmosphere effectively penetrates to the heights of the E region of the ionosphere, its acoustic field is concentrated in the E region and it tends to propagate in the horizontal direction, exciting the E region. An analytical algorithm is proposed to determine the response of the ionosphere to the corresponding acoustic pulse, and a method of complex geometric optics is presented, which makes it possible to simulate the scattering of high-frequency (HF) electromagnetic waves (EMW) in the LOFAR (MHz) range. In general, the observations, estimates and numerical simulations confirm the effect of pulsed impact on the ionosphere of acoustic waves penetrating to ionospheric heights at distances of many thousands of kilometres from the source associated with HTVE and causing the scattering of HF EMW detected by the LOFAR radio telescope.&#160; The above-mentioned model is under development now. Its appropriate application will allow us to study and interpret other effects of acoustic waves from a source associated with HTVE and develop further the methods for radio diagnostics of ionospheric space weather.

Abstract:

The Low Frequency Array (LOFAR) is one of the most advanced radio telescopes in the world. When radio waves from a distant astronomical source pass through the Earth&#8217;s upper atmosphere, plasma structures act as lenses. The refraction of these radio waves, and their subsequent interference, significantly affects the received signal. Activities have been developed for secondary school students aged between 16-18 based on these observations.Students are given research data from LOFAR and work in groups to interpret these observations, drawing on material from both geometric optics and astronomy. They are also introduced to key research skills, such as how to create a numerical definition of a phenomena which is clear, rigorous and well-documented. These activities were developed with reference to the Oxford, Cambridge and RSA Exam Board A-level Physics Specification in the UK. They have been trialed and refined in a secondary school, are now made available to the wider community.