International Polar Year (IPY)
Project Number 547 Description

Introduction

The ionised atmosphere in the polar regions is a highly structured plasma containing irregularities in electron density over a wide range of horizontal scale-sizes. The structure is influenced largely by the solar wind as it sweeps past the Earth, with the coupling of the interplanetary magnetic field to the magnetospheric field leading to a series of complex processes that result in a dynamic and structured ionospheric plasma. During times of disturbed geomagnetic activity, enhancements and gradients in the plasma density can cause severe disruption to transionospheric radio signals, affecting communications and navigation systems.

Radio tomography

Radio tomography is a relatively new technique for imaging the ionospheric plasma over extended height-versus-latitude planes. In essence, radio transmissions from polar-orbiting satellites are monitored at a chain of receivers aligned in longitude but separated in latitude. Measurements of the line integral of the electron density along satellite-to-receiver ray paths, the so called total electron content, are inverted in a reconstruction algorithm to yield an image of the spatial distribution of the density over the region of interest. Routine monitoring of transmissions from satellites over an extended period of time leads to coverage of the ionosphere at all Universal Times, seasons, geomagnetic and solar conditions. The technique gives wide spatial coverage from a limited number of ground stations and so is ideal for remote inaccessible polar regions.

Multi-chain tomography

Observations from a single tomography chain can of necessity reveal only a localised, limited view of the density distribution. However, observations from several chains separated in longitude have the potential to provide the spatial distribution of plasma over an extended geographic region. The International Polar Year opens the unique opportunity for increased collaborative tomographic observations of the distribution of the polar ionospheric plasma over large geographic regions and long time intervals, to study signatures of space weather in the Arctic ionosphere.

Collaborating research groups

The collaborating research groups, with co-ordination under the International Ionospheric Tomography Community (IITC), are:

• University of Wales Aberystwyth, Wales
• Sodankylä Geophysical Observatory, University of Oulu, Finland
• NorthWest Research Associates, USA
• University of Alaska Fairbanks, USA
• Applied Research Laboratories, University of Texas, USA
• Polar Geophysical Institute of Russian Academy of Sciences, Russia
• M.Lomonosov Moscow State University, Russia

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