SPRG Seminars
January 22, 2013:
"Density Holes, Hot Flow Anomalies and SLAMS Upstream of Earth's Bow Shock"
George Parks, Space Science Laboratory, University of California at Berkeley
Density holes (DH), Hot Flow Anomalies (HFA) and Short Large Amplitude Magnetic Structures (SLAMS) are transient structures observed in the upstream region of Earth's bow shock. The densities in these structures are depleted and in some cases as much as 99% of the ambient solar wind (SW) density. Moreover, the velocity moments of the SW is generally diminished and diverted in front of these structures. These structures, which can be as short as 4s (spin period of the spacecraft), are seen only when back-streaming particles are present. But not all backstreaming particles produce upstream structures and the conditions for forming these structures still remain unknown. In 2010 and 2011, the Cluster plasma ion experiment was configured to sample 3D distributions of the SW and the backstreaming particles with spin period time resolution (4s). Preliminary results show the SW beam in the hole is field-aligned and that evolving structures can be produced within existing DHs, HFAs and SLAMS. This seminar will discuss salient features of upstream structures and present new observations including examples of how the structures can evolve into shocks.