space group department of physics umeå university

Space Group

Department of PhysicsUmeå UniversityStaff:

Kjell Rönnmark, prof.Patrik Norqvist, lektorMaria Hamrin, lektor

Annie Reiniusson, doktorandJörgen 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 tubesJörgen Vedin, Kjell Rönnmark.

Small scale density gradients, FrejaAnnie Reiniusson, Gabriella Stenberg, Patrik Norqvist, Kjell Rönnmark, …

Small scale density gradients, Cluster Patrik Norqvist, Gabriella Stenberg, …

Bonus project 1: Cluster passage of reconnection separatricesMaria Hamrin, Gabriella Stenberg, …

Bonus project 2: Calibration of IMA, Mars ExpressNiklas 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

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

L=100kmW=20km

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 field-aligned 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 irregular small scale density gradients.

More electrostatic waves (E/B bigger) on sharp gradients.

Dens

Grad Dens

ΣSE

SE

SB

ΣSB

Cluster data confirms this.

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