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Space Group Department of Physics Umeå University

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.

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Space Group Department of Physics Umeå University

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  1. 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

  2. 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, ClusterPatrik 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

  3. 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…

  4. GALS: Gradient Analysis by Least Squares L=100kmW=20km • Method for reconstructing the (B-) field and its gradients at an arbitrary point in space-time by using multi-spacecraft 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

  5. Reasonable measures of quality. Hamrin, Uppsala, May 2006

  6. 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 field-aligned potential drops of several kV are supported by gradients in the electron temperature (pressure). Hamrin, Uppsala, May 2006

  7. Small scale density gradients, Freja + Cluster Dens • Previous studies: increased E in lower hybrid cavities. • Now: increased E and B is found on irregular small scale density gradients. • More electrostatic waves (E/B bigger) on sharp gradients. Grad Dens SE SB • Cluster data confirms this. ΣSE ΣSB

  8. 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

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