ORCID Profile
0000-0001-7633-4750
Current Organisation
University of South Australia
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Publisher: Oxford University Press (OUP)
Date: 08-2014
Publisher: Copernicus GmbH
Date: 14-07-2020
DOI: 10.5194/ANGEO-38-845-2020
Abstract: Abstract. Electric fields are a ubiquitous feature of the ionosphere and are intimately linked with aurora through particle precipitation and field-aligned currents. They exhibit order-of-magnitude changes on temporal and spatial scales of seconds and kilometres respectively which are not easy to measure knowing their true magnitude and temporal variability is important for a theoretical understanding of auroral processes. We present a unique method to estimate ionospheric electric fields in the region close to (kilometre scale) a dynamic auroral arc by solving the continuity equation for the metastable O+(2P) ions, which emit as they move under the influence of electric fields during their 5 s lifetime. The main advantage of this optical method is the increase in temporal resolution over other methods such as ground-based radars. Simultaneous measurements of emission at 732.0 nm (from the O+(2P) ions) and prompt emissions at 673.0 nm (N2) and 777.4 nm (O), all at high spatial (100 m) and temporal (0.05 s) resolution, are used in the solution of the continuity equation, which gives the dynamic changes of the O+ ion population at all heights in a 3D volume close to the magnetic zenith. Perspective effects are taken into account by a new geometric method, which is based on an accurate estimate of the magnetic zenith position. The emissions resulting from the metastable ions are converted to brightness images by projecting them onto the plane of the ground, and the projected images are then compared with the measured images. The flow velocity of the ions is a free parameter in the solution of the continuity equation the value that minimises the difference between the modelled and observed images is the extracted flow velocity at each time step. We demonstrate the method with an ex le event during the passage of a brightening arc feature, lasting about 10 s, in which the inferred electric fields vary between 20 and 120 mV m−1. These inferred electric fields are compared with SuperDARN measurements, which have an average value of 30 mV m−1. An excellent agreement is found in the magnitude and direction of the background electric field an increase in magnitude during the brightening of the arc feature supports theories of small-scale auroral arc formation and electrodynamics.
Publisher: American Geophysical Union (AGU)
Date: 03-2014
DOI: 10.1002/2013JA019627
Publisher: Copernicus GmbH
Date: 20-07-2015
DOI: 10.5194/ANGEO-33-837-2015
Abstract: Abstract. Measurements of naturally enhanced ion acoustic line (NEIAL) echoes obtained with a five-antenna interferometric imaging radar system are presented. The observations were conducted with the European Incoherent SCATter (EISCAT) radar on Svalbard and the EISCAT Aperture Synthesis Imaging receivers (EASI) installed at the radar site. Four baselines of the interferometer are used in the analysis. Based on the coherence estimates derived from the measurements, we show that the enhanced backscattering region is of limited extent in the plane perpendicular to the geomagnetic field. Previously it has been argued that the enhanced backscatter region is limited in size however, here the first unambiguous observations are presented. The size of the enhanced backscatter region is determined to be less than 900 × 500 m, and at times less than 160 m in the direction of the longest antenna separation, assuming the scattering region to have a Gaussian scattering cross section in the plane perpendicular to the geomagnetic field. Using aperture synthesis imaging methods volumetric images of the NEIAL echo are obtained showing the enhanced backscattering region to be aligned with the geomagnetic field. Although optical auroral emissions are observed outside the radar look direction, our observations are consistent with the NEIAL echo occurring on field lines with particle precipitation.
No related grants have been discovered for Sam Tuttle.