Examples of studies made with IMPTAM


Role of Variable Electric Fields for the Ring Current in Storm Times:

See the scientific article

"Particles with different energies produce varying contributions to the total ring current energy density as the storm progresses. Ring current energy densities and total ring current energies were obtained using particle data from the Polar CAMMICE/MICS instrument during several storms observed during the years 1996–1998. Four different energy ranges for particles are considered: total (1-200 keV), low (1-20 keV), medium (20-80 keV) and high (80-200 keV). Evolution of contributions from particles with different energy ranges to the total energy density of the ring current during all storm phases is followed.

To model this evolution we trace protons with arbitrary pitch angles numerically in the drift approximation. Tracing is performed in the large-scale and small-scale stationary and time-dependent magnetic and electric field models. Small-scale time-dependent electric field is given by a Gaussian electric field pulse with an azimuthal field component propagating inward with a velocity dependent on radial distance. We model particle inward motion and energization by a series of electric field pulses representing substorm activations during storm events.

We demonstrate that such fluctuating fields in the form of localizedelectromagnetic pulses can effectively energize the plasma sheet particles to higher energies (above 80 keV) and transport them inward to closed drift shells. The contribution from these high energy particles dominates the total ring current energy during storm recovery phase. We analyse the model contributions from particles with different energy ranges to the total energy density of the ring current during all storm phases.
By comparing these results with observations we show that the formation of the ring current is a combination of large-scale convection and pulsed inward shift and consequent energization of the ring current particles.
--

Measurements from Polar CAMMICE/MICS instrument showed that the medium energy protons are the main contributors to the total ring current energy during the storm main phase. During the recovery phase the high energy protons play a dominant role.

The modeling showed that the dominant role of the high-energy ions during the storm recovery phase cannot be obtained by simply using variable intensity of the large-scale convection electric field or by changing the initial distribution density and/or temperature. Only the impulsive localized substorm-associated electric fields were strong enough to yield the observed fluxes of high-energy particles. These results indicate that the formation of the ring current is a combination of enhanced largescale convection and pulsed inward shift and consequent energization of the ring current particles.
"

Measurements

Modeling

Polar CAMMICE/MICS measurements as
energy-time spectrogram and pitch-angle
distributions for protons, He and O on 4 May 1998.

click for a popup
Solar wind parameters and AE and Dst indexes.


click for a popup
The effect of added submodels to total ring current proton energies. Plotted are all (black) and low (blue), mid (green) and high (red) energies.
Note correspondence of the full model to the Dst index in the bottom panel.
click for a popup

Time series of modeled energy densities in the equatorial plane

Energy density for high energy protons (80-200 keV).


click for a popup
Energy density for medium energy protons (20-80 keV).


click for a popup


An example of time series of meridianal cuts during a space storm showing modeled electron fluxes