Time plan Project "Parallel electric fields in space" Subtitle "Observations by Cluster satellites inside the auroral zone at altitudes above the main acceleration region" --------------------------------------------------------------------- Exjobbare Erik Bergman tel:070-2211963, email:erikbergman@home.se Handledare Andris Vaivads 018-4715904, andris@irfu.se Granskare Annika Olsson 018-4715904, ao@irfu.se --------------------------------------------------------------------- Motivation: Electric fields parallel to the ambient magnetic field are very important for energy conversion inside the magnetosphere and for the ionosphere- magnetosphere coupling. In addition, they are one of the most efficient ion and electron accelerators inside our magnetosphere as well as in other places of the universe. Allthough the studies of parallel electric fields are very important, the direct measurements of the parallel electric fields can be very difficult. One has succeeded in measuring parallel electric fields of large amplitude at distances of about 1 R_E where most of the auroral acceleration takes part. However, there is a lack of knowledge regarding the parallel electric field amplitudes and their distribution at distances well above the main acceleration region that should be explored. Polar is one satellite which has studied electric fields at large distances. In some cases its data have shown indications of small parallel DC electric field in the regions where electrostatic waves in the 1-10 Hz frequency range can have a significant parallel component. This happens in the auroral region (invariant latitudes ILAT that correspond to the visible auroral oval). However, the quality of Polar electric field instrument may not be sufficient to reliably measure the parallel E-field in this case. Cluster has significantly better electric field instrument that can allow reliable measurement of the parallel electric field. In this project we use the Cluster data to study parallel electric fields in the auroral region. Week 34, Litterature study (auroral zone) Week 35, Getting used to the analysis package ISDAT and its implementation in Matlab Week 36, Litterature study (Cluster + in depth auroral zone) Weeks 37-39, - To identify time periods when to look for parallel electric fields in Cluster data - To write a small program which computes the angle between the spin plane and the magnetic field along Cluster orbit. - Search for cases where DC magnetic field is in the spin plane (smaller than some threshold, e.g. 1 degree) and Cluster is in the auroral zone (ILAT range 65..74 degrees; the best ~69.5) at about 4-5 R_E radial distance. - Limit events only to months Jan-Feb-Mar-Apr-May that correspond to nightside auroral crossings. - All four satellites should be taken into the search. It can be that only one of them detects the feature. Or, in the best case, it can be that several detect it, in which case one can study the lifetime and speed of the region containing the downward electric field. - Any events where we find downward/upward parallel electric fields during these conditions, would be important result. The expected magnitude of the downward electric field is something like 1-10 mV/m. Probably closer to 1 mV/m, or even less, but it may not be possible to reliably detect fields smaller than 1 mV/m under these conditions. Weeks 40-43, - When suitable events of parallel electric fields are found, they must be critically examined for possible instrumental effects. For example, the wake effect can show up as a spurious, non-physical parallel electric field (one or more of the probes is in the wake of the spacecraft body in the field-aligned plasma flow, in which case it measures a different density than the other probes, which causes its potential to differ). Perhaps one has to avoid cases where the probes are exactly in the field-aligned direction, although we require them to be close. One has to analyze the data at high time resolution to see if wake effect exists and what part of the data has to perhaps be taken away. The status of the satellite potential controlling device also can affect the electric field measurements and care should be taken for that. - Parallel static electric fields at this altitude (or at any altitude, for that matter) should be a rare phenomenon. One should see the measured parallel field to go from zero to some value, perhaps in a fluctuating way, and back to zero again. Week 44, - One or two of the identified events of parallel electric field should be compared to the data from other Cluster instruments, as parallel currents from magnetometer and, if time allows, also electron and ion data from particle instruments. In addition, for these events data should be compared to the theoretical models of acceleration region formation. Weeks 45-50, Writing the report