The Coronal Mass Ejection of 29 Sep 2013 and Geomagnetic Storm of 2 Oct 2013

Peter T. GallagherSchool of Physics

Trinity College Dublin

Event Summary• SDO observed a filament lift-off in the northwest quadrant of the Sun

(~W40) starting at ~2013-09-29T21:00Z.

• An asymmetric halo CME was observed in SOHO/LASCO images from 22:24 UT. Apex velocity of ~897 km/s (LASCO) and 1097 km/s (STEREO B).

• ACE arrival time (L1): 2013-10-02T01:20Z

• GOES arrival time (1AU): 2013-10-02T02:00Z

• Geomagnetic storm start (Ireland): 2013-10-02T01:58Z

• Earth arrival times (models):– NASA/GSFC SWRC Ensemble: 2013-10-02T04:1Z (+8/-12 hours)– STOA: 2013-10-02T06:15Z (+/-10 hours)

STEREO-BSTEREO-A

CME arrival at ACE/L1(~20131002T01:20Z?)

Pre-CME solar wind speed(~375 km/s)

CME arrival at Earth(~20131002T02:00Z?)

CME arrival at Earth(~20131002T02:00Z?)

Rough IDL Arrival Time Calculation

t_sdo = '2013-09-29T21:00Z’au = 149e6 ; kmv_cme = 1096. ; km/sv_sw = 375. ; km/sv_ave = ( v_cme + v_sw ) / 2. ; km/s dt = au / v_ave ; s

t_au = anytim( anytim( t_sdo ) + dt, /vms ) print, t_au 2-Oct-2013 05:14:05.656

This is ~4 hours later than observed arrival.

Conclusions

• STEREO –B CME velocity of 1097 km/s is less than actual CME velocity as CME was directed away from STEREO-B.

• STEREO-A CME velocities therefore likely to be > STEREO-B velocities.

• From radial propagation model, need STEREO-A CME velocity of 1200 km/s to get correct arrival time at Earth (2-Oct-2013 ~01:00 UT).