JOule heating effects on Ionosphere-thermosphere coupling and Neutral density (JOIN)

Understanding the detailed spatial and temporal dynamics of the space environment is a key task in solar-terrestrial research. This is also a fundamental requisite for providing successful space weather forecasts, such as predicting changes in atmospheric drag experienced by satellites at low-Earth orbits (LEO). The high-latitude auroral ionosphere is connected by magnetic field lines to a large part of the magnetospheric volume, making it a “focus area” of magnetospheric dynamics. Consequently, space weather disturbances are also most strongly manifested at high latitudes. The ionospheric and magnetospheric current systems are coupled (MI-coupling) by field-aligned currents (FAC) flowing along the geomagnetic field. The energy needed to sustain the current systems comes from the continuous interaction of the solar wind with the Earth’s magnetic field. Large part of that energy is dissipated in the auroral ionosphere as Joule heating, which among other things leads to changes in the thermospheric wind patterns and increased satellite drag via thermal expansion of the gas.

In the project, the team proposes to make a detailed investigation of the auroral Joule heating and its consequences on the ionosphere-thermosphere (IT) system at high latitudes. The main objectives or Science Cases are to:

1. Determine the global statistical distribution and variability of the high-latitude Joule heating during geomagnetic storms.
2. Correlate the storm-time Joule heating with observed large-scale atmospheric density variations.
3. Study and characterize the atmospheric scale height by directly comparing simultaneous and co-planar density measurements from two different altitudes during different solar and geomagnetic conditions.
4. Perform event studies of meso-scale density variations at auroral regions by utilizing Swarm – EISCAT conjunctions.

Together, these Science Cases will reach multiple science objectives mentioned under Theme 3 in the SoW. The project will characterize the coupling between the different layers of the ionosphere and the thermosphere during different levels of geomagnetic activity and in different phases of the solar cycle. Neutral density variations due to Joule heating and energy transfers during geomagnetic storms will be investigated in detail, taking into account the different interplanetary drivers behind the storms. The unique opportunities offered by the co-planarity periods (i.e., two satellites at different altitudes in nearly the same orbital plane) between the Swarm, GRACE and GRACE-FO missions will be utilized to probe the vertical variations in the thermospheric structure and composition. Conjunctions between the Swarm spacecrafts and the EISCAT incoherent scatter radars give the spatial and temporal resolution required for investigating the ionosphere-thermosphere coupling in a multi-satellite and multi-source context.