Available projects – Space plasma physics (Uppsala)

High fluxes of suprathermal electrons in the Earth magnetotail

Study the source regions of high energy suprathermal electrons in the Earth magnetotail using ESA Cluster satellite observations during 12 years of its mission.

Background

Cluster consists of 4 spacecraft with orbit apogee at 19 Earth radii. Since 2001 Cluster has collected large database of Earth magnetotail observations under different conditions (different phases of solar cycle, different solar wind conditions, different stages of reconnection, etc.).

This allows to address statistically many important science topics where previously mainly event based studies have been carried out.

Cluster spacecraft allow the most detailed 3D in situ observations of plasma that are accessible experimentally and the obtained knowledge can be of importance not only understanding Earth magnetosphere but even understanding such physically very distant phenomena as solar flares.

Project

One topic of very high importance is the suprathermal (energies manyfold larger than thermal energies) electron acceleration in the Earth magnetotail. For example, much of our knowledge on distance solar flares, is based on X-ray emissions generated by similar suprathermal electrons in the Suns corona.

The suprathermal electrons can be observed in situ in the Earth magnetotail and are believed to be created due to magnetic reconnection and associated physical processes.

There have been detailed event studies of such suprathermal electron acceleration within magnetic islands of tail current sheet during magnetic reconnection, or magnetic flux pile up regions created due to reconnection jets.

Numerical simulations have suggested different possible acceleration mechanisms. However, statistically it has not been resolved what is the most efficient mechanism generating these electrons in the Earth magnetotail.

The large database of Cluster would allow to address this question.

The goal of the project would be to identify all Cluster events where suprathermal electrons show localized high fluxes, thus suggesting that Cluster is passing through the electron generation region, and classify these regions based on the properties of the magnetic field and plasma. For example, are these regions in the center of current sheet, at the front of magnetic pile up regions, within magnetic islands etc.

Plan

Contact person: Yuri Khotyintsev, yuri@irfu.se

Timing analysis using multi-spacecraft data

To develop a better method to estimate velocities using multi-spacecraft data and apply it study the distribution of scales and orientations of current sheets for the current sheets observed in the Earth’s magnetosheath.

Background

Estimating scales and speeds of plasma structures is crucial for understanding of many plasma phenomena. One such plasma structure are the current sheets forming in different parts of the magnetosphere as magnetotail, magnetopause, turbulent magnetosheath and knowledge of their scale, speed and orientation from observations is important for comparisons with theories of magnetic reconnection and plasma turbulence. For true quantitative comparisons one needs to have full control of the uncertainties.

Based on data from one spacecraft, it is generally not possible decide whether an observed variation is coming from temporal or spatial changes.

To resolve this ambiguity, ESA launched a multi-spacecraft Cluster mission, which consists of 4 spacecraft flying in a constellation with orbit apogee at 19 Earth radii.

So, if 4 spacecraft (located in corners of a tetrahedron) observe the same plasma structure, we can assume the structure is planar and moving at a constant speed and it straightforward to compute the velocity of the structure.

But what if the observed profiles are similar and not identical? How can we quantify the error?

Project

In this project we will extend the existing methods for timing analysis of multi-spacecraft to provide quantitative estimates of the error for the both the magnitude and direction of the velocity vector.

We will test the method on surrogate data wich can simulate background noise and accelerated motion of current sheets, but also on several cases of real current sheet observed by Cluster.

As the last part of the project we will apply the method to a large number of small-scale current sheets observed in magnetosheath.

The method developed will have important implication for analysis of multi-spacecraft data from the Cluster mission as well as from the future NASA MMS mission.

Plan

Contact person: Yuri Khotyintsev, yuri@irfu.se