Student project at IRF Uppsala
| INSTITUTET FÖR RYMDFYSIK
| Swedish Institute of Space Physics
|| (59o50.272'N, 17o38.786'E)
Project work (30 c)/Examensarbete (30 hp)
Drift lower hybrid wave properties in space plasma
Student: Cecilia Norgren,
To identify fundamental properties of drift lower hybrid waves in space plasma using interferometry between closely separated Cluster C3 and C4 spacecraft.
ESA's Cluster II mission consists of four identical spacecraft flying in formation high above the Earth's poles. The Cluster mission was launched in 2000. Due to its success, the original two-year mission has been extended several times, latest until 2012. Flying in a formation, the four spacecraft collect the most detailed data yet on small-scale 3D structure of the near-Earth space and the interaction between the gas of charged particles (plasma) and electromagnetic fields there. This enables scientists to better understand the processes occurring inside plasmas, processes that are commonly taking place in many places of the Universe. Most of the mission, Cluster spacecraft have flown in a tetrahedral (triangular pyramid) constellation with separation between all spacecraft being roughly the same. The separation has been varied throughout the mission in the range between 100km and 10,000km. However, during shorter periods, Cluster has had constellation very different from a tetrahedron. Particularly, during several months in 2007, the distance between two of spacecraft was the smallest during the whole mission, as little as 17km, while other were at 10,000km distance. This allows exploring the smallest scales in the space plasma.
Drift lower hybrid waves are in most cases the waves with strongest electric field amplitude that are present in space plasma and they are involved everywhere where energetic plasma energization processes occur. Due to their very small perpendicular scales, the possibility to study them has been limited. However, exploring the data set when the two spacecraft have been at the shortest separation can allow finally studying these waves in unprecedented detail.
For the first time we are able to make very detailed studies of the LHDW using observations by the Cluster spacecraft in the plasma surrounding Earth. By making cross spacecraft correlations of the electric field and examining existence conditions, we were able to determine the velocity of propagation and wavelength of the waves and thereby identify them as LHDW. We also calculate the electrostatic potential and find that it corresponds to about a third of the electron temperature. This indicate that they might be able to affect the electrons and thus take part in the processes within the boundary layer. By deriving a linear relation between the electrostatic potential, and the wave magnetic field, we compare them both and find that they correspond very well. We can use this to estimate the electrostatic potential in cases when cross spacecraft correlation is not possible.