Magnetosphere‐Ionosphere Coupling via Prescribed Field‐Aligned Current Simulated by the TIEGCM

Abstract

The magnetosphere‐ionosphere (MI) coupling is crucial in modeling the thermosphere‐ionosphere (TI) response to geomagnetic activity. In general circulation models (GCMs) the MI coupling is typically realized by specifying the ion convection and auroral particle precipitation patterns from for example, empirical or assimilative models. Assimilative models, such as the Assimilative Mapping of Ionospheric Electrodynamics, have the advantage that the ion convection and auroral particle precipitation patterns are mutually consistent and based on available observations. However, assimilating a large set of diverse data requires expert knowledge and is time consuming. Empirical models, on the other hand, are convenient to use, but do not capture all the observed spatial and temporal variations. With the availability of Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) data, there is an opportunity for employing field‐aligned currents (FAC) in GCMs to represent the MI coupling. In this study, we will introduce a new method which enables us to use observed FAC in GCMs and solve for the interhemispherically asymmetric electric potential distribution. We compare Thermosphere‐Ionosphere‐Electrodynamics General Circulation Model (TIEGCM) simulations of a geomagnetic storm period using the new approach and two other often‐used methods for specifying MI coupling based on empirical and assimilative high latitude electric potentials. The comparison shows general similarities of the TI storm time response and improved temporal variability of the new method compared to using empirical models, but results also illustrate substantial differences due to our uncertain knowledge about the MI coupling process.Plain Language SummaryOur society is increasingly dependent on space assets for communication and navigation and ground infrastructures such as power grids and gas pipelines. The space environment is highly variable. Especially during geomagnetic storm large amount of energy enter Earth’s upper atmosphere along field‐lines from the magnetosphere and can drastically change the upper atmosphere, which can become hazardous for satellites and ground infrastructures. Numerical models are employed to simulate Earth’s upper atmosphere during geomagnetic storms and describing accurately the coupling to the magnetosphere is crucial. In numerical models the coupling is typically realized by specifying the high latitude ion drift and auroral particle precipitation patterns from for example, empirical or assimilative models. Assimilative models realistically describe the energy input since they ingest available observations but they require expert knowledge to run. Empirical models are convenient to use and describe average conditions and do not necessarily capture all the observed variations. With the availability of observed field‐aligned currents (FAC) there is the opportunity to represent the coupling via FAC. We introduce a new method using observed FAC in numerical models and compare results of a geomagnetic storm period using the new approach to using empirical and assimilative models for specifying coupling.Key PointsPresent new approach to prescribe observed field‐aligned current in the Thermosphere‐Ionosphere‐Electrodynamics General Circulation ModelPresent technique to solve for interhemispherically asymmetric electric potentialThe new approach increases the temporal thermosphere‐ionosphere‐variation compared to empirical models