Lower hybrid drift wave properties in space

Abstract: The whole universe is filled with plasma. There are different kinds of plasmas filling large volumes, separated by distinct boundaries. Many important energy conversion, particle acceleration and plasma transport processes occur at these boundaries, and therefore it is important to study the plasma processes there. It will for example help us to better understand the interaction and energy exchange between the Sun and the Earth. The lower hybrid drift waves (LHDW) are strong plasma waves that are often excited within boundaries, but their role in different plasma processes are still unclear. Many studies of the LHDW have been done, both in space and in laboratory. However, the LHDW are electron scale waves, and due to their small wavelength it has been difficult to study them in detail experimentally. 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.