Dr Iannis Dandouras from the Research Institute in Astrophysics and Planetology in Toulouse, France, has found the first conclusive proof of the existence of a space wind first proposed about 20 years ago.

Dr Dandouras, who reported the finding in the journal Annales Geophysicae, explained: “after long scrutiny of the data, there it was, a slow but steady wind, releasing about 1 kg of plasma every second into the outer magnetosphere: this corresponds to almost 90 tones every day. It was definitely one of the nicest surprises I’ve ever had!”

The plasmasphere is a region filled with charged particles that takes up the inner part of the Earth’s magnetosphere, which is dominated by the planet’s magnetic field.

To detect the space wind, Dr Dandouras analyzed the properties of these charged particles, using information collected in the plasmasphere by ESA’s Cluster spacecraft.

Further, he developed a filtering technique to eliminate noise sources and to look for plasma motion along the radial direction, either directed at the Earth or outer space.

The data showed a steady and persistent wind carrying about 1 kg of the plasmasphere’s material outwards each second at a speed of over 5,000 km/h. This plasma motion was present at all times, even when the Earth’s magnetic field was not being disturbed by energetic particles coming from the Sun.

“The plasmaspheric wind is a weak phenomenon, requiring for its detection sensitive instrumentation and detailed measurements of the particles in the plasmasphere and the way they move,” Dr Dandouras said.

The wind contributes to the loss of material from the Earth’s top atmospheric layer and, at the same time, is a source of plasma for the outer magnetosphere above it.

“The plasmaspheric wind is an important element in the mass budget of the plasmasphere, and has implications on how long it takes to refill this region after it is eroded following a disturbance of the planet’s magnetic field. Due to the plasmaspheric wind, supplying plasma – from the upper atmosphere below it – to refill the plasmasphere is like pouring matter into a leaky container,” Dr Dandouras explained.

______

Bibliographic information: Dandouras I. 2013. Detection of a plasmaspheric wind in the Earth’s magnetosphere by the Cluster spacecraft. Ann. Geophys., 31, 1143-1153; doi: 10.5194/angeo-31-1143-2013