Atmospheric electricity

Earth's atmosphere is partially ionised from the effects of Galactic Cosmic Rays (GCRs), and near the continental surface, natural radioactivity. This ionisation gives rise to a finite electrical conductivity of atmospheric air, which permits a small vertical current (of density Jz) to flow between the conducting regions of the ionosphere and Earth's surface. There is a large (≈ 250kV) voltage difference between the ionosphere and the Earth's surface, associated with charge transfer from the ≈ 1000 thunderstorms and rain clouds continuously active around the globe, in a framework known as the Global Electric Circuit (GEC). For a more detailed summary of the GEC, as well as the development of this framework, please see the following document.

Modulation of global atmospheric electricity depends on several factors including thunderstorm variability, Pacific Ocean temperatures and aerosol particle concentrations, which represent "internal" sources of variability. As well as internal sources of variability, there also exist "external" sources such as changes in the space weather environment. Such changes in space weather can affect the atmospheric ionisation rate (through modulation of the GCR flux and generation of Solar Energetic Particles (SEPs)), geomagnetic field and value of the Earth-Ionosphere potential difference, VI, all of which can affect atmospheric electrical parameters.

The SPATE group at the University of Reading investigates the effect of space weather on atmospheric electricity through surface observations made on its meteorological enclosure (the Reading University Atmospheric Observatory, RUAO), and balloon borne observations using a suite of specially developed sensors carried by conventional weather balloons (meteorological radiosondes).

Research at Reading also focuses on how space weather can affect tropospheric weather processes, such as through investigating the electrification of non-thunderstorm cloud edges which arises from vertical current flow in the global electric circuit.

Ionospheric physics

The Earth's upper atmosphere (the thermosphere) and the weakly ionised plasma within it (the ionosphere) are sensitive to influences from above and below. The ionosphere is created when extreme ultra violet and x-ray radiation from the Sun is absorbed by thermospheric gases leading to their ionisation. In addition, the arrival at Earth of solar wind transient structures accelerates energetic particles into the upper atmosphere, enhancing ionisation at the poles and heating the thermosphere, which then expands.

At the same time, influences from the troposphere below, such as waves and ionisation generated by thunderstorms, add to the ionospheric variability.

Our work focuses on detecting the mechanisms by which the upper and lower atmospheres are connected, from solar wind modulation of the ionosphere to enhancement of the ionosphere by tropospheric lightning. In addition we are investigating long term changes in the ionosphere to infer compositional changes in the thermosphere in response to geomagnetic activity.

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