Descriptions of the surface magnetic-to-electric field relationship, using magnetotelluric impedance tensors, have seen refinement in recent years. Correspondingly, models of geomagnetically induced currents flowing in power line conductors using input from more fundamental observables (e.g., the surface magnetic field or solar wind drivers) have become more sophisticated. Magnetometer data used for purposes of surface electric field modeling typically have cadences between 1 s and 1 min. Using 1-D and 3-D magnetotelluric impedance tensors, we quantify the effect of magnetometer cadence on modeled peak surface electric fields during the 22 geomagnetic storms. It is shown that 1-min magnetometer data sampling leads to median biases in the peak electric field of 10-20% magnitude attenuation and 2-17 ∘ in direction (depending on the storm) across the United States using the Fernberg 1-D conductivity models and 11-26% (0.9-8 ∘ ) using the 3-D impedance tensors derived from the USArray magnetotelluric survey. The largest 10% of attenuations almost entirely occur near low-resistivity subsurface structures in the western and eastern United States, reaching a 50% median attenuation during the 17 March 2015 event. It is concluded that cadence, local geology, and the spectral content of the geomagnetic field all play a significant role in the bias.Under the standard magnetotelluric assumptions (neglect of displacement and polarization currents, free-space permeability, and quasi-uniformity of the source field; Chave & Weidelt, 2012, and
We show the ionospheric signatures of the 28 October 2012 Haida Gwaii tsunami in both the total electron content (TEC) and the airglow layer. In addition, previously reported ionospheric signatures from the 11 March 2011 Tohoku and 27 February 2010 Chile tsunamis are reexplored in comparison to the newer Haida Gwaii detections. These events provide excellent test cases in the study of tsunami-ionospheric coupling efficiency, which is most notably affected by the observation geometry, tsunami propagation direction, and background ionospheric density. A simple calculation is developed that incorporates observation geometry to predict the relative coupling efficiency. The predictions are compared to the TEC observations and limitations are discussed.
Tsunamis generate internal gravity waves (IGWs) that propagate vertically into the atmosphere and can create detectable signatures in the ionosphere. These signatures have consistently been observed in the presence of a tsunami for over a decade in the total electron content and for over 5 years in the 630.0 nm airglow. Here we show perturbations appearing in filtered GPS‐derived total electron content (TEC) and 630.0 nm airglow above Hawaii during the passing of the tsunami induced by the 16 September 2015 earthquake in Illapel, Chile. We report measurements of IGW parameters from both observation methodologies using a combination of prior methods and a newly developed method that uses a Gabor filter bank. A previously developed geometric model that takes into account the assumed posture of tsunami‐induced IGWs in the geomagnetic field and the observation geometry is shown to predict fairly well the expected location of the observation in the sky. Results of the Gabor filtering technique are also compared to previously published results for the 11 March 2011 Tohoku event. An overall comparison between all of the tsunami‐induced signatures that have appeared in both the 630.0 nm airglow and TEC above Hawaii to date is provided.
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