Physics
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufmsa24a..02a&link_type=abstract
American Geophysical Union, Fall Meeting 2011, abstract #SA24A-02
Physics
[2409] Ionosphere / Current Systems, [2431] Ionosphere / Ionosphere/Magnetosphere Interactions, [2721] Magnetospheric Physics / Field-Aligned Currents And Current Systems
Scientific paper
The Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) uses the constellation of Iridium Communications satellites in 780-km-altitude, circular, polar orbits to monitor the global Birkeland currents with a nine-minute cadence. This allows us to follow the development of these currents through transitions from quiescent conditions to moderate driving as indicated by rotations of the interplanetary magnetic field (IMF) from northward to southward. AMPERE data are available beginning on October 2009 for development testing purposes and for continuous science observations starting in June 2010. Data are processed in 10-minute windows stepped by two minutes to derive global Birkeland currents with a minimum intensity of 0.2 mirco-A/m2. A transition event ocurred on 24 February 2010, which illustrates one type of systematic behavior found. As measured by ACE at the first Langrangian point, L1, the IMF was northward and sunward from 1300 to 1420 UT with a BZ component of +2 to +3 nT. At 1420 UT, the IMF began rotating southward reaching -2 to -3 nT by 1510 UT. At Earth, the first enhancement in Birkeland currents occurs at 1524-1534 UT on the dayside, reflecting reconnection driven convection associated with the positive IMF BY that persisted through the event. The dayside currents continued to intensify through 1540-1550 UT and extended from mid-morning to dusk. At 1542-1552 UT, isolated nightside currents appear at midnight and are localized in latitude and longitude, extending less than one hour pre or post-midnight. Ten minutes later the nightside currents expand to most of the nighside and merge with the dayside system. The nightside currents then continue to intensify, first near midnight and expand toward both dawn and dusk, resulting in a fully formed classic Region 1/Region 2 current system by 1640-1650 UT. The results indicate that dayside reconnection drives both Region-1 and Region-2-sense currents, whereas the nightside currents are driven by convection closure from the nightside. Significantly, we do not observe Region-1 and Region-2-sense currents driven independently and conclude that the paradigm that the Region-1 system is driven by magnetopause reconnection while Region 2 is a response due to return convection in the magnetosphere is not consistent with the observations. Rather, the entire dayside Birkeland current system appears to be driven by reconnection, whereas the nightside Birkeland currents are completely driven by the magnetospheric return flows that close the Dungey convection cycle.
Anderson Benjamin J.
Barnes James R.
Dyrud Lars P.
Green D. L.
Korth Haje
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