Alfvén wave modulation of Substorms and outflowing O+ ions Observed by Cluster: Bulk Parameter View

Details Alfvén wave modulation of Substorms and outflowing O+ ions Observed by Cluster: Bulk Parameter View Alfvén wave modulation of Substorms and outflowing O+ ions Observed by Cluster: Bulk Parameter View

Dec 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003agufmsm21c..06p&link_type=abstract

American Geophysical Union, Fall Meeting 2003, abstract #SM21C-06

Physics

2431 Ionosphere/Magnetosphere Interactions (2736), 2471 Plasma Waves And Instabilities, 2736 Magnetosphere/Ionosphere Interactions

Scientific paper

The Cluster spacecraft often encounters the current sheet in the geomagnetic tail. This talk will discuss the behavior of a substorm that occurred on October 1, 2001. Cluster observed the substorm from onset through the recovery phase. This talk will highlight the behavior of bulk parameters (density, mean velocity annd temperature) and the subsequent talk by E. Lee et al. will expand the discussion to kinetic features.The substorm onset occurred ≈0927 UT (AE index) and at synchronous altitude it was signified by large pulse-like variations in the magnetic field at ≈0930 UT. Cluster detected the onset signature at ≈0927 UT at geocentric coordinates (-16.1, 6.2, 4.9)RE. Cluster first crossed the current sheet at ≈0938 UT and subsequently Alfvén waves modulated the tail allowing Cluster to move back and forth across the current sheet several times. Outflowing ionospheric O+ show periodic bursts of ≈1-2 minutes associated with the Alfvén wave oscillation indicating strong MI coupling. Longer period modulations (≈6-10 minutes) were observed in energetic particles injected at synchronous altitudes. Prior to the first current sheet crossing, mean velocities of ion distributions were ≈500 km/s in the tailward direction. As Cluster crossed into the southern hemisphere, mean ion velocities reached values of ≈1000 km/s but in the earthward direction, and remained in that direction through the end of the recovery. However, these velocity moments do not mean the plasma was flowing because kinetic features show Cluster was close to the high latitude boundary of the plasma sheet. The time delay between the synchronous altitude and Cluster indicates that the substorm onset was located between the synchronous altitude and the Cluster orbit.

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