Dr Gareth Dorrian: Publications

Variability of Ionospheric Plasma: Results from the ESA Swarm Mission

Space Science Reviews Springer Science and Business Media LLC 218:6 (2022) 52

Authors:

Alan G Wood, Lucilla Alfonsi, Lasse BN Clausen, Yaqi Jin, Luca Spogli, Jaroslav Urbář, James T Rawlings, Ian C Whittaker, Gareth D Dorrian, Per Høeg, Daria Kotova, Claudio Cesaroni, Antonio Cicone, Jan Miedzik, Ewa Gierlach, Paula Kochańska, Pawel Wojtkiewicz, Golnaz Shahtahmassebi, Wojciech J Miloch

Abstract:

Abstract Swarm is the first European Space Agency (ESA) constellation mission for Earth Observation. Three identical Swarm satellites were launched into near-polar orbits on 22 November 2013. Each satellite hosts a range of instruments, including a Langmuir probe, GPS receivers, and magnetometers, from which the ionospheric plasma can be sampled and current systems inferred. In March 2018, the CASSIOPE/e-POP mission was formally integrated into the Swarm mission through ESA’s Earthnet Third Party Mission Programme. Collectively the instruments on the Swarm satellites enable detailed studies of ionospheric plasma, together with the variability of this plasma in space and in time. This allows the driving processes to be determined and understood. The purpose of this paper is to review ionospheric results from the first seven years of the Swarm mission and to discuss scientific challenges for future work in this field.

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LOFAR observations of refractive scattering from substructure within a traveling ionospheric disturbance at mid-latitude.

(2022)

Authors:

Gareth Dorrian, Richard Andrew Fallows, Alan George Wood, David R Themens, Ben Boyde, Andrzej Krankowski, Mario Mark Bisi, Bartosz Dabrowski, Christian Vocks

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Lensing from small-scale travelling ionospheric disturbances observed using LOFAR

Journal of Space Weather and Space Climate EDP Sciences 12 (2022) 34-34

Authors:

Ben Boyde, Alan Wood, Gareth Dorrian, Richard A Fallows, David Themens, Jens Mielich, Sean Elvidge, Maaijke Mevius, Pietro Zucca, Bartosz Dabrowski, Andrzej Krankowski, Christian Vocks, Mario Bisi

Abstract:

Observations made using the LOw-Frequency ARray (LOFAR) between 10:15 and 11:48 UT on the 15th of September 2018 over a bandwidth of approximately 25–65 MHz contain discrete pseudo-periodic features of ionospheric origin. These features occur within a period of approximately 10 min and collectively last roughly an hour. They are strongly frequency dependent, broadening significantly in time towards the lower frequencies, and show an overlaid pattern of diffraction fringes. By modelling the ionosphere as a thin phase screen containing a wave-like disturbance, we are able to replicate the observations, suggesting that they are associated with small-scale travelling ionospheric disturbances (TIDs). This modelling indicates that the features observed here require a compact radio source at a low elevation and that the TID or TIDs in question have a wavelength <~30 km. Several features suggest the presence of deviations from an idealised sinusoidal wave form. These results demonstrate LOFAR’s capability to identify and characterise small-scale ionospheric structures.

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Plasma density gradients at the edge of polar ionospheric holes: the absence of phase scintillation

Annales Geophysicae Copernicus GmbH 38:2 (2020) 575-590

Authors:

Luke A Jenner, Alan G Wood, Gareth D Dorrian, Kjellmar Oksavik, Timothy K Yeoman, Alexandra R Fogg, Anthea J Coster

Abstract:

Polar holes were observed in the high-latitude ionosphere during a series of multi-instrument case studies close to the Northern Hemisphere winter solstice in 2014 and 2015. These holes were observed during geomagnetically quiet conditions and under a range of solar activities using the European Incoherent Scatter (EISCAT) Svalbard Radar (ESR) and measurements from Global Navigation Satellite System (GNSS) receivers. Steep electron density gradients have been associated with phase scintillation in previous studies; however, no enhanced scintillation was detected within the electron density gradients at these boundaries. It is suggested that the lack of phase scintillation may be due to low plasma density levels and a lack of intense particle precipitation. It is concluded that both significant electron density gradients and plasma density levels above a certain threshold are required for scintillation to occur.

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An unusual observation of a plasma structure in the mid-latitude ionosphere

(2020)

Authors:

Alan Wood, Gareth Dorrian, Richard Fallows

Abstract:

The LOFAR (Low Frequency Array) is one of the world&#8217;s leading radio telescopes, operating across the frequency band 10-250 MHz. As radio waves from astronomical sources pass through the ionosphere, they can undergo refraction and/or diffraction. The variations in the intensity of the received signal are caused by irregularities with a spatial scale size ranging from the Fresnel dimension to an order of magnitude below this value. The received signal can therefore be used to infer information on plasma structures in the ionosphere. As the frequencies used are significantly lower than the 1.4 GHz typically associated with Global Navigation Satellite Systems (GNSS), the plasma structures that affect the signals received by LOFAR are significantly larger, typically of the order of kilometres.On 14th July 2018 the Dutch stations of LOFAR observed the strong natural radio sources Cassiopeia A and Cygnus A between 17:00 UT and 18:05 UT at a frequency range of 20-80 MHz. During the observation, the signal intensity received by many of the stations underwent a substantial reduction across all frequencies, lasting approximately 10 minutes. Immediately before and after this, periodic enhancements in the signal strength were observed. These enhancements showed a noticeable frequency dependence, with longer period oscillations at lower frequencies. The feature was not observed simultaneously by the stations and evolved during the observations. Such a feature is most likely to be the result of a large-scale density structure in the ionosphere, which appears to move west and north over the northern Netherlands.The deep fading of the received signal may be due to the presence of sporadic-E, which is a consequence of variations in the neutral wind speed with altitude in the presence of the geomagnetic field, resulting in plasma accumulating in a thin layer. This can cause incident radio waves to be strongly refracted, affecting the strength of the received signal. The wave-like structure immediately before and after the deep fade is a likely consequence of scattering of the observed signal.

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Dr Gareth Dorrian

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Variability of Ionospheric Plasma: Results from the ESA Swarm Mission

Authors:

Abstract:

LOFAR observations of refractive scattering from substructure within a traveling ionospheric disturbance at mid-latitude.

Authors:

Lensing from small-scale travelling ionospheric disturbances observed using LOFAR

Authors:

Abstract:

Plasma density gradients at the edge of polar ionospheric holes: the absence of phase scintillation

Authors:

Abstract:

An unusual observation of a plasma structure in the mid-latitude ionosphere

Authors:

Abstract:

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Dr Gareth Dorrian

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Variability of Ionospheric Plasma: Results from the ESA Swarm Mission

Authors:

Abstract:

LOFAR observations of refractive scattering from substructure within a traveling ionospheric disturbance at mid-latitude.

Authors:

Lensing from small-scale travelling ionospheric disturbances observed using LOFAR

Authors:

Abstract:

Plasma density gradients at the edge of polar ionospheric holes: the absence of phase scintillation

Authors:

Abstract:

An unusual observation of a plasma structure in the mid-latitude ionosphere

Authors:

Abstract: