Auroral dynamics EISCAT Svalbard Radar: field-aligned beam  complicated spatial structure (<1 km)  fast temporal variations (<1 second) 17 Jan ° x 31° white light 25 fps  coherent scatter from ion acoustic waves  structure size under 300 m at 500 km altitude  varying on 0.2 second time scale

North West Auroral dynamics EISCAT Mainland Radar: position of field-aligned beam 64° x 86° cut-off filter 1 frame/3s 30 Jan 1995  dynamic range problems  geometry of 3 D multiple structures seen in 2 D  white light or cut-off filter density depletion? PULSE experiment

Auroral fine structure examples of discrete auroral structures 0.1 to 1 km wide T.Trondsen (Univ of Calgary)  few instruments can measure it well  few theoretical models can account for it

What are the unsolved problems?  The big one: how are particles accelerated?  Is the filamentary structure important, especially for field- aligned currents?  How well do theories account for the dynamics observed?  Are rays just curls seen from the side?  etc.

Why does it matter? fundamental plasma physics implications for macroscopic processes (photo: Jouni Jussila)

Observations some properties of discrete aurora multiple (parallel) curtains or filaments (< 1km) dynamic rayed aurora large amplitude spiky electric fields in the acceleration region time scales between fractions of seconds and minutes strong velocity shear near discrete aurora major portion of current carried by low energy electrons

Our approach to the problem -fit measurements to theory 1. Optical and radar observations 2. Modelling (1D, 2D and 3D) 3. New ASK instrument to measure plasma flows at high resolution, and low energy precipitation

1. Radar and optical observations From ground we have three sorts of instruments  field-aligned, eg radars and photometers (temporal)  2D imagers (spatial, with geometrical constraints)  spectral imagers (energy information) Combination of all three in the Spectrographic Imaging Facility (SIF) at Longyearbyen…but we are going back with ASK to…

EISCAT mainland 30 Jan 1995 density depletions?

3 seconds integration

horizontal velocity (km/s) V north V east 3 s vectors from 1837 to 1840 UT angle of maximum variance,  = 61  E of N

density maximum lags light intensity N W radar beam 20 km at 100 km electric field vectors

2. Modelling 3D plasma-neutral fluid model Can operate at several heights depending on local plasma conditions multiple current layers (current striation) auroral filaments

perturbation travels along field as Alfvén waves strong deformation and filamentation of field-aligned current km Slice through at the acceleration region (about 1R E ) - the height of maximum E parallel Field-aligned current density and velocity upward downward

In the ionosphere: size of radar field of view large and variable horizontal velocities (> 2 km/s) filamentary parallel currents (> 50 μA/m 2 )

upward In the ionosphere: after 4.5 s Maximum of precipitating energy (ie auroral emission) is not coincident with field-aligned current layer.

Ionospheric precipitation energy  simulated auroral image

How to generate large velocities 100 nT + average plasma density (1-2 km/s) 400 nT or low density plasma (4-8 km/s) only very fast time variation can generate high speed flows

To image aurora in the magnetic zenith in forbidden ion line and directly observe plasma drifts, with sub-km and sub-sec resolution. Concurrent imaging in other lines characterises the production of the metastable ions. 3. The ASK concept ASK stands for the ”Auroral Structure and Kinetics” So....

Physics summary how to generate auroral structure- top to bottom structure and processes at magnetospheric boundaries solar wind dynamic pressure changes, magnetic reconnection, Kelvin Helmholtz instabilities, diffusion by micro turbulence physical mechanism for transport of information field-aligned currents and Alfvén waves, fast waves or beams of particles field-aligned currents – magnetic field geometry altered If processes lead to a violation of frozen-in condition magnetic field lines have no identity transport of information not linear physical processes in the inner magnetosphere could alter the magnetic topology, violate the frozen-in condition and generate structures in addition to those of the source at the magnetospheric boundary effect of ionosphere changes in ionospheric conductivity from particle precipitation will have a significant influence on magnetosphere-ionosphere coupling