# Presentation: 177485

## NASA NAG5 13488Structure and Dynamics of the Near Earth Large-Scale Electric Field During Major Geomagnetic Storms

- P-I John R. Wygant
- Assoc. Professor of Physics
- University of Minnesota
- Grant Term : 4/31/2003 to 5/2006
- Yearly Report 4/31/04 to 5/01/05

## Experimental Evidence Implicating Convection Electric Field in the Energization of Ring Current Plasma 

- The signature feature of major geomagnetic storms in the inner magnetosphere is the energization of ring current plasma (10-300 keV ions) which forms a hot torus of plasma surrounding Earth at 2-6 Re (L=2-6].
- It has been estimated that 30-50% of the energy extracted from the solar wind during major geomagnetic storms is dissipated in this process. The primary agent for this energization is believed to be particle injection by the large scale electric field,  but there is no previous statistical  and systematic evidence that enhanced large scale electric fields are specifically associated with the actual process of  injection and energization of ring current plasma.
-  CRRES measurements in the inner magnetosphere from ~400 orbits  show the dawn-dusk component of the electric field is strong  enhanced over radial distances of  L=2-6 when the ring current is being injected into the inner magnetosphere (dDst/dt<-10nT).
-   The CRRES electric field measurements have been binned by radial position horizontal scale, by  intensity of the ring current (as monitored by its magnetic field perturbation at the surface of the Earth- the Dst index indicated by the different color traces), and separated into four plots corresponding to the rate of the ring current injection. The plot corresponding to the largest injection rate (upper RHS) shows the electric field is larger for each value of Dst by a factor of 2-3 and this enhancements extends deep into the inner magnetosphere.
- Rowland and Wygant (in preparation, 2005) also present the first two dimensional mapsof this electric field  in the equatorial plane of the inner magnetosphere  for conditions ranging from queite to very active(Kp 6-8). Polar and Cluster data is also being studied in the tail and inner magnetosphere during storm periods and compared to IMAGE data in order to understand the dynmamics of this energization process..

## Observations of spatial extensive regions of strong wave Poynting flux parallel to the magnetic field in the inner magnetosphere during major geomagnetic storms 

- The first measurements of electromagnetic energy flow due to MHD waves, electron energy flux and ion energy flux parallel to the magnetic field in the inner magnetosphere  during a major geomagnetic storm are provided from a Polar spacecraft pass during May 3, 1998.
- Polar passes from L=20 at beginning of interval  to L=3.7 near the end of the the 90 minute interval.  Spacecraft is in pre-midnight local time sector
- The data shows dynamically significant wave Poynting flux present over the entire interval extending deep into the inner magnetosphere to L=3.7. The largest bursts of Poynting flux exceed 0.1 ergs/cm^s at the Polar position. When mapped along converging magnetic field lines to 100 kms altitude this corresponds to 50 ergs/cm2 s (at the magnetic foot of the  outer boundary of plasma sheet) to 10 ergs/cm2 s (at the magnetic foot of  L=3.7). ..
- Data shows that the Poynting flux typically ranges between 25% and 100% of the total  energy flux along the flux tube.