March 19, 2010, 12:00 pm - 1:00 pm
March 19, 2010, 12:00 pm - 1:00 pm
Cluster observation of multiple Dipolarization Front (DF) events deforming mid-tail magnetic topology
Joo (Kyoung-Joo) Hwang (Code 673, Geospace Physics Laboratory
We present Cluster observation of a series of a dipolarization front (DF) at the central current sheet in the Earth’s magnetotail. The fast earthward flow observed behind each DF with a velocity corresponding to the Alfvén velocity indicates that the flow bursts might have been generated by bursty reconnection that occurred tailward of the spacecraft. Based on the multi-spacecraft timing analysis, the DFs are found to propagate mainly earthward at ~160-335 km/s with a thickness of 900-1500 km, similar to the ion inertial length. The third DF is, however, found to move mainly dawnward, possibly due to the pre-existing plasmas compressed by preceding two DFs, and the last, week DF is found to retreat tailward. Each DF is followed by significant fluctuations in the x- and y- components of the magnetic field with an about 1 minute delay. These Bxy-fluctuation structures propagate dawnward (mainly) and earthward, and their normal directions make an oblique angle to the equatorial plane. Strongly enhanced field-aligned beams are observed coincidently with Bxy fluctuations, while an enhancement of tail currents is associated with DFs. From the observed pressure imbalance and flux-tube entropy changes between the two regions separated by the DF, we speculate that interchange-instability-unstable DF might have caused the deformation of the mid-tail magnetic topology, which generates significant field-aligned currents, and, possibly, powers the auroral arc during the substorm processes. The dawn-dusk (earthward) propagation of the structure associated with the development of interchange-unstable DF can explain the azimuthal (north-to-south, streamer) drift of the arc during the growth phase of substorm.
Understanding and Modeling Radiation Belt Enhancement During a Geomagnetic Storm
Alex Glocer (Code 673, Geospace Physics Laboratory
On September 4, 2008, an enhancement of the outer radiation belt electron flux was observed by the Akebono spacecraft. At the same time, the magnetospheric magnetic field experienced very disturbed conditions, including a dipolarization coincident with the radiation belt enhancement. We utilize the Radiation Belt Environment (RBE) model coupled to the BATSRUS MHD model of the magnetosphere to simulate the observed electron flux in a realistic storm-time magnetic field. Particularly, we focus on the relative contribution of whistler mode wave-particle interactions and radial diffusion associated with rapid changes in the magnetospheric magnetic field. In our study, the RBE model obtains a realistic magnetic field from the BATS-R-US magnetosphere model at a regular, but adjustable, cadence. The results and analysis of our simulations will be presented including data model comparisons. We will also present a brief description of our modeling methodology.
New satellite mission with old data - key element of four decades of space-borne radio sounding
Robert F. Benson (Code 673, Geospace Physics Laboratory)
A GSFC data restoration and transformation effort has converted more than 16,000 original 7-track Alouette/ISIS analog telemetry tapes into a digital format and has produced more than 1/2 million digital topside ionograms. Since many of the tapes were not previously processed to produce the original ionogram format (on 35-mm film) the end result is equivalent to a new satellite mission with old data. Some of the scientific results from these data, and other space-borne radio sounders launched over an interval spanning more than 4 decades, will be briefly reviewed and some outstanding basic space plasma-physics questions will be identified.