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Space Group Department of Physics Umeå University Staff: Kjell Rönnmark, prof. Patrik Norqvist, lektor Maria Hamrin, lektor Annie Reiniusson, doktorand Jörgen Vedin, doktorand Niklas Melander, exjobbare Current research topics Tracking down the (auroral) generator and load regions Maria Hamrin, Octav Marghitu (MPI-Garching & Bucharest), … Method development, GALS Maria Hamrin, Kjell Rönnmark, Jörgen Vedin. Numerical simulations of auroral flux tubes Jörgen Vedin, Kjell Rönnmark. Small scale density gradients, Freja Annie Reiniusson, Gabriella Stenberg, Patrik Norqvist, Kjell Rönnmark, … Small scale density gradients, Cluster Patrik Norqvist, Gabriella Stenberg, … Bonus project 1: Cluster passage of reconnection separatrices Maria Hamrin, Gabriella Stenberg, … Bonus project 2: Calibration of IMA, Mars Express Niklas Melander, Maria Hamrin, Patrik Norqvist, Rickard Lundin, … Hamrin, Uppsala, May 2006 Generator and load regions in the plasma sheet (Cluster+FAST) Earlier study on auroral generator (Cluster + FAST). Now: Cluster plasma sheet crossings, fall 2001. E·J signatures → concentrated loads and generators found (CLR, CGR). CLR more common. Often close to the neutral sheet. CGR often in PSBL. Good agreement with simulations (Birn & Hesse 2005). Many future prospects… GALS: Gradient Analysis by Least Squares L=100km W=20km Method for reconstructing the (B-) field and its gradients at an arbitrary point in space-time by using multispacecraft observations. Current density from Ampere’s law. Not very sensitive to the s/c configuration. Comparable or better than the Curlometer. Hamrin, Uppsala, May 2006 Reasonable measures of quality. Hamrin, Uppsala, May 2006 Numerical simulations of auroral flux tubes Numerical model: auroral current circuit. Electrons both modeled as fluid and individual particles (→temperature). Driving mechanism: applied generator in the equatorial magnetotail → Alfvén waves propagating towards the ionosphere. Electrons are strongly heated (parallel and perpendicularly) in the acceleration region. The model explains how fieldaligned potential drops of several kV are supported by gradients in the electron temperature (pressure). Hamrin, Uppsala, May 2006 Small scale density gradients, Freja + Cluster Previous studies: increased E in lower hybrid cavities. Now: increased E and B is found on Dens Grad Dens irregular small scale density gradients. More electrostatic waves (E/B bigger) on sharp gradients. Cluster data confirms this. SE SB ΣSE ΣSB Bonus projects Bonus project 1: Cluster passage of the separatrices of a distant reconnection site. Bonus project 2: Calibration of IMA, Mars Express.. Hamrin, Uppsala, May 2006