The July 2012 STEREO-A Extreme
Event SEPs:
Solar and Heliospheric Context,
1 AU Observations
and a Model
J.G. Luhmann (SSL U of California, Berkeley)
C.T. Russell (IGPP UCLA), Ying Liu (Chinese Acad. Sciences)
D. Odstrcil (GMU, GSFC), M.L. Mays (CUA, GSFC), H. Bain,
Y. Li (SSL, University of California) and the STEREO Teams
LWS ESWE Meeting 2014, Boulder
We consider the context of the July 2012 STA extreme SEP event period. This included
a very fast backsided halo CME for Earth that was a frontside halo at STA
STEREO Science Center
Locator plot (center); SECCHI
COR and LASCO C2 images
SECCHI images
On STEREO-A
July 23, 2012
CME speed
Near Sun
~3500 km/s
ICME speed
at STEREO-A
~2000 km/s or
greater
Major Solar
Energetic Particle
Events
Large interplanetary
fields (>100 nT)
Described in Liu et al.
Nature Comm., 2014
The July 23, 2012 event produced SEPs seen at widespread locations
STEREO-B
MEX backgnd
STEREO-A
VEX backgnd
MESSENGER (above) and ACE and GOES (below)
July 23, 2013 Event: Energetic Proton Flux,
Magnetic Field and Speed
• On July 23, 2013, a strong burst of solar
activity began shortly after 0200 UT.
• Four times of interest are marked
1.
At about 1630 UT, the speed jumped; the
magnetic field increased in several steps.
This field behavior was not shock-like.
2. At 1920 UT, the magnetic field slowly began
to drop to very low values while the
energetic particle flux rose sharply. This has
the characteristics of a slow-mode wave.
3. The solar wind slowly increased in speed
until 2100 UT, when it jumped to about
2400 km/s. The 0.4-0.6 MeV protons and
the 4-6 MeV protons increased in flux but
the 40-60 MeV protons dropped.
4. The magnetic cloud was entered at 2300 UT
and the energetic proton fluxes all dropped.
NOTE: This event was ~1000x more intense than
the average SEP event
From Russell et al., ApJL, 2013
5
The July 23, 2012 energetic proton
fluence at STA was also comparable
to that of the largest events of cycle
23. It certainly would have caused a
Ground-Level Enhancement (GLE). A
fit to July 23rd fluence is remarkably
similar to fits to 3 of the 4 largest
events of cycle 23.
(Mewaldt et al.; Fall AGU 2013 SH33B-2068)
Had the July 23, 2012 Proton Event occurred at Earth, it would
place 3rd on NOAA’s list of major Solar Proton Events since 1976
08/2328
Note that 8 of the events are
from Cycle 23. So far only
two Cycle-24 events rank in
the top 20.
(Mewaldt et al.; Fall AGU 2013
SH33B-2068)
This was an example of ‘extreme events’
that seem to occur ~once a cycle
SECCHI images
On STEREO-A
July 23, 2012
CME speed
Near Sun
~3500 km/s
ICME speed
at STEREO-A
~1400 km/s or
greater (TBD)
Major Solar
Energetic Particle
Events
Somehow conditions conspire to produce
these rare exceptional outbursts-but how?
Large interplanetary
fields (>100 nT)
and large longduration southward component
The related flare site: AR1520 activity summary
(from Hyesook Lee et al., CCMC, personal comm.)
X-ray Event
Date
06
06
07
09
10
10
12
14
17
19
Max Dur.
Time (min)
Jul
Jul
Jul
Jul
Jul
Jul
Jul
Jul
Jul
Jul
1330
1855
0828
2307
0514
0627
1649
0458
1715
0558
Xray
class
6 M1.2
17 M1.3
21 M1.0
8 M1.1
33 M1.7
42 M2.0
41 X1.4
11 M1.0
301 M1.7
159 M7.7
Coronal Mass Ejection
First
Type Initial Direction Full Ang.
Appearance
Speed (Lon/Lat) Width
(day/time)
(km/s)
12/1654
17/1423
19/0536
23/0236
O
O
O
ER
1400 -6/-17 140
1100 54/-30 90
1200 100/-20 100
3435 138/-10 160
Solar Energetic Particle E
vent
Start
Peak
Channel
Time
Flux (pfu) (S/C)
(day/time)
12/1750
12/1818
12/1835
17/1630
17/1705
23/0359
This event was
not alone!
23/1400
24/1827
>1 >15.8 MeV
(SOHO)
~0.17 13-100 MeV
(STEREO B)
~96.1 > 10 MeV
(GOES-13)
>1 >15.8 MeV
(SOHO)
~110 > 10 MeV
(GOES-13)
~446 13-100 MeV
(STEREO A)
~12.8 > 10 MeV
(GOES-13)
~0.26 13-100 MeV
(STEREO B)
Was it a single or multiple event?
The SEEDS search algorithm identifies a second CME in
essentially the same sector in STA COR2 difference images
that took off a few hours after the fastest CME.
Was it a single or multiple event?
The SEEDS CME catalog automated search also finds
2 events in LASCO C2 images, supporting the idea of
co-located eruptions ~hours apart
Cause of minimal slowdown ?
LASCO
• A series of preceding eruptions
occurred on the Sun including a July 19
CME (from the same active region);
• The July 23 event was moving through
a density depletion region (as low as 1
cm^-3) with radial magnetic fields,
created by the earlier eruption..
The Images also allowed triangulation and event tracking of
such a major event for the first time.
STEREO-A
STEREO-A
SOHO-LASCO
Images from
the GMU
SEEDS site
STEREO-B
An ENLIL model was produced that captured some of the background behavior
in the plasma and field, including the presence of multiple CME shocks
ENLIL model results support the suggested influences on the July 23, 2012 event
Multiple eruptions are introduced
Into the model solar wind several
days ahead (Model: D. Odstrcil, GMU)
The earlier events merged to form a wide front followed by rarefaction
The July 23 event(s) thus traveled outward relatively unimpeded
Here time series of the observer-connected shock locations for several sites in
ENLIL’s domain are shown. Connected shock strength is indicated by color-fill.
This CISM SEP event model (JASR 2010) uses these
ENLIL results :
-assumes the ENLIL shocks are moving SEP sources
-assumes field-aligned transport only, here w/o scattering
except close to the shock source
-uses guiding center particle tracing on ‘snapshots’ of
ENLIL observer-connected field lines-sampled every ~5
minutes
STEREO-A SEP Event observations from the IMPACT LET. SEPT and HET
instruments (top) and STEREO-A ICME shock connection locations along
field lines for 6 CMEs In the ENLIL run (bottom), distinguished by color..
In this SEP event model the SEP onsets are determined by the shock
connection times and shock strengths. Thus its performance depends
on ENLIL’s capturing those accurately.
The event character and duration is also significantly affected by the
ENLIL field and shock source evolution, Both mirroring in the heliospheric field and post-shock passage shock connections matter.
Magnetic mirroring in the model occurs due to field compressions
like these along the observer connected field lines
Each of the CME/ICME shocks in ENLIL creates a distinct event.
These merge together to produce the final, extreme event
The results of the complete event model for STEREO A (bottom), compared
with STEREO IMPACT SEP data from LET, SEPT and HET instruments (top).
Lessons learned from the July 2012 Observations::
-The ability of a CME to produce an extreme SEP event depends on
context (solar, solar wind), including timing (previous and following activity)
and proximate (same or nearby active region) and also global activity.
-Widespread/Extreme SEP events like this one are likely often affected
by multiple CME-created shocks and compressions, by field geometries
that allow mirroring/trapping , as well as by SEPs heading back toward
the Sun from a still-strong shock source that has already passed.
-Looking at SEPs in isolation is probably not going to reveal the physics!
One needs to consider solar conditions (even farside) and heliosphere
conditions (from corona to well beyond 1 AU)
-
Lessons learned from the July 2012 model tests:
-The ability to model a SEP event at any spacecraft location requires
modeling shock source injections and field line connectivity and
evolution in sufficient detail to capture all sources and magnetic mirrors
affecting the site. A deficient heliospheric background description will
prevent the accurate interpretation of the SEP events generation.
notes:
>> ENLIL does not include the domain inside 20Rs, precluding
coronal shock portion inclusion)
>> ENLIL’s outer boundary is set at 5.5 AU, and the run at ~20 days
duration in order to include the full heliospheric history involved
-Widespread/Extreme SEP events like this one are likely often affected
by multiple CME-created shocks and compressions, by field geometries
that allow mirroring/trapping , as well as by SEPs heading back toward
the Sun from a still-strong shock source that has already passed.
-