Wednesday

The polar electrojets (PEJs) are troublesome to describe and predict, reflecting their origin in the complex solar wind-magnetosphere interaction and subsequent magnetospheric unloading processes and coupling to varying ionospheric conductivity. They are highly variable with several different types of drivers, from partly stochastic variations in the solar wind, to seasonal effects caused by Earth's orbit and its rotational and magnetic axes, to the longer term modulation by the solar cycle. As a key component of space weather, understanding them is important both in terms of furthering space and geophysical research and for practical applications due to their role in geomagnetically induced currents (GICs) in power grids, atmospheric heating increasing drag on satellites, and disturbances to magnetic navigation systems. With regards to geophysical research, the nature of the PEJs and the associated field-aligned currents (FACs) which feed them makes them difficult to account for when modelling internal fields (from the core and the crust). As well as introducing noise, models of the core secular variation could be seriously contaminated by time-varying biases in these external fields. We present a study of the electrojet activity using magnetometer data from Swarm and older satellites. We describe the behaviour of the PEJs in response to solar wind driving and seasonal effects, identify hemispheric differences, and attempt to identify long term variation. The relation to magnetospheric processes and the implications for internal field modelling are discussed.

MIST submission (student)