Themis Substorm 1118 March 23, 2007

1. Themis Substorm1118 March 23, 2007 Pi 2 Analysis by McPherron Data provided by Kazuo Shiokawa and Shasha Zhou

2. The H and D Components at Japanese Stations – March 23, 2007 • The H and D components show weak perturbations a little after 11 UT • Honolulu is near midnight at 10 UT and Japan stations are near midnight at 14 UT • The Japan stations are probably west of substorm current wedge

3. Expanded Japanese Magnetograms • Expanded views of the raw H and D components show Pi 2 pulsations about 11:20 UT • The perturbations are strongest in the D component suggesting that the Japanese stations are near the outward current of the current wedge • There are weaker pulsations that begin earlier

4. Horizontal Pi 2 Power in Japan • Band pass filter the H and D components at three stations in Japan to Pi 2 band • Create instantaneous power in the horizontal plane (doubles frequency) • Determine times at which first half cycle emerges from background • There were two very weak bursts (P<0.4) at 11:11:57 and 11:14:08 followed by strong burst (P~12) at 11:18:08 (See following slide for comparison of strength)

5. Procedure for Alaska Pi 2 • Detrend and Pi 2 band pass filter the H and D components at every station • Calculate magnitude of the horizontal perturbation vectors • Make stack plot of amplitude of horizontal components • Normalize each station amplitude by its standard deviation in the interval 11-12 UT • Create a wig plot of the normalized amplitude traces • Create and plot upper envelope of the normalized Pi 2 horizontal amplitude

6. Horizontal Pi 2 Power at Alaska StationsMarch 23, 2007

7. Upper Envelope of Normalized Pi 2 Power for Alaska Magnetometers - March 23, 2007

8. Alaska Summary • The Pi2 power envelopes from stations in Alaska chain are not coherent as they are at midlatitudes in Japan • The obvious onsets determined at midlatitudes are not clearly seen in the auroral zone • The onset of activity in Alaska is about 87 seconds earlier than in Japan • The Alaska data confirms that 11:18 is the major substorm onset • The highest latitude station recorded two intensifications not seen at other stations [11:30 and 11:43]

9. Relation of Propagated Solar Wind to Pi2 in Japan – March 23, 2007

10. Relation of Northward Turning to Pi 2 Onsets • The propagated solar wind turns sharply northward ahead of the bow shock at 11:07 UT • Add ~ 5 minutes delay in magnetosheath to obtain 11:12 which is the time of the first Pi 2 burst • A comparison of propagated wind with Cluster just ahead of the bow shock show only 1-2 min offset of the Bz traces • Wind was several hundred Re upstream near the Earth-Sun line

11. Compare Propagated Wind and Cluster • Use the OMNI 1-min Weimer propagated IMF and solar wind from Wind (blue) spacecraft • Compare to Cluster (red) just ahead of the bow shock • Only 1-2 minutes difference in the two signals

12. LANL Electron Flux for March 23, 2007

13. LANL 97A Proton Fluxes for March 23, 2007

14. Summary of LANL Particle Observations • Spacecraft 1989-046 located at about 0140 LT observed a large dispersionless electron injection at 11:21:44 UT • This was preceded by two small injections seen only in the first two energy channels at 11:15:30 and 11:18:28 • The large electron injection was delayed by nearly 4 minutes from the largest Pi 2 event seen at midlatitudes • Spacecraft LANL 97-A located at about 21:02 LT observed a proton injection beginning at 11:19:03 or 11:20:00 • There was a large dispersionless injection in all channels at 11:21:31 • The largest electron and proton injections seem to be ~11:22 about 4 minutes after the largest midlatitude Pi 2