International Heliophysical Year (IHY) celebrates 50 years of space exploration and marks the 50th anniversary of International Geophysical Year (IGY). The aim of IGY in 1957 was to understand the Earth's atmosphere and oceans and it required scientists from countries all over the world to co-ordinate their efforts. It was a monumental year which saw the launch of the first artificial satellite, Sputnik 1, and observations that confirmed the theory of plate tectonics.

IHY expands the science of IGY out into the Solar System. Our Sun is a magnetic star and creates a gigantic magnetic bubble which surrounds all the bodies in the Solar System. The magnetic bubble is called the heliosphere and it gives its name to International Heliophysical Year.

The scientific aims of IHY are to:

• understand how the planets respond to emissions from the Sun
• study fundamental processes which occur throughout the heliosphere
• study how the Sun and the heliosphere interact with the interstellar medium which surrounds it

IHY in the UK

UK scientists are world leaders in the area of heliospheric research. Starting from the interior of the Sun through to looking at the furthest reachces of the Solar System, UK scientists are building the necessary instrumentation and analysing the data.

The main focus of the science during IHY is based around emissions from the Sun and how they effect the Earth's environment. In particular the ionosphere, the layer of the Earth's atmosphere that is ionised by the Sun's radiation, and the magnetosphere, the magnetic bubble that lies on the outer edge of the ionosphere. The main question being how these layers vary over time due to effects from the Sun; an area of science now known as Space Weather.

The Sun produces a constant solar wind that blows with speeds of between 400-800 km/s and carries charged gases and magnetic fields toward the Earth. Under certain conditions the magnetic field lines of the solar wind join together with the Earth's magnetic field lines, in a process called reconnection. When this happens the Earth's magnetosphere becomes open and solar wind particles penetrate into the magnetosphere. Injection of the solar wind particles causes wave activity along the Earth's open field lines and produces heating in the ionosphere; this in turn leads to ions moving up into the magnetosphere. A new project led by UCL's Mullard Space Science Laboratory will monitor this ionospheric ion outflow using the EISCAT ground based radar in Norway to observe the heated region in the ionosphere and the four Cluster spacecraft to observe the waves and ion heating along the magnetic field lines in the magnetosphere. The aim of the project is to understand the exact mechanism of energy transfer from the solar wind into the ionopsheric ion outflow.

Some novels methods are being employed during IHY to further understand the ionosphere. At the University of Bath scientists are using GPS technology as a diagnostic tool. GPS signals can be used to probe the ionosphere and study its structure and electron content. The signal sent between the satellite and the ground station travels through the ionosphere and on the way becomes distorted. The changes in the signal can be used to produce near real-time imaging of the ionosphere. At Aberystwyth University radio signals received from satellites that are in polar orbits are also being used to produce tomographic maps of the ionosphere above the Artic where measurements are normally scarce. The aim of these projects is to understand how the variability in the ionosphere is related to (or driven by) the solar wind and magnetospheric phenomena.

Imbedded in the solar wind are sporadic expulsions of vast magnetic bubbles called coronal mass ejections (CMEs). These events have their origin in the atmosphere of the Sun and will be studied during IHY using instruments onboard two missions called Hinode and STEREO, both launched in the latter part of 2006. In the future scientists hope to have an accurate prediction of CME arrival times at the Earth providing a reliable warning system.

Using the Hinode spacecraft a new tool will be developed at the Rutherford Appleton Laboratory that will allow the prediction of CMEs that are Earth directed. These CMEs are then tracked along their journey to the Earth using the STEREO spacecraft. Both missions carry instruments supplied by the UK.

---

For further information please contact Lucie Green
Last modification: October, 11, 2006