Geomagnetic Storm measured in Birr on 2nd October 2013. Thought to have been caused by the Coronal Mass Ejection released from the Sun on 29th September

1. The Coronal Mass Ejection of 29 Sep 2013
and Geomagnetic Storm of 2 Oct 2013
Peter T. Gallagher
School of Physics
Trinity College Dublin

2. 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 from22:24
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)

4. STEREO-A
STEREO-B

5. CME arrival at ACE/L1
(~20131002T01:20Z?)
Pre-CME solar
wind speed
(~375 km/s)

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

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

8. Rough IDL Arrival Time Calculation
t_sdo = '2013-09-29T21:00Z’
au = 149e6
v_cme = 1096.
v_sw = 375.
v_ave = ( v_cme + v_sw ) / 2.
dt = au / v_ave
;
;
;
;
;
km
km/s
km/s
km/s
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.

9. 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 STEREOA CME velocity of 1200 km/s to get correct
arrival time at Earth (2-Oct-2013 ~01:00 UT).