Transcript Transient IP Structures Associated with Short-Scale T. Mulligan, B. Blake

Transient IP Structures Associated with Short-Scale
Variations in the SEP and GCR Flux
T. Mulligan, B. Blake
The Aerospace Corporation
H. Spence, and A. Jordan
Boston University
D. Shaul and J. Quenby
Imperial College
Acknowledgement to R. Mewaldt for providing STEREO B LET data
Polar Telecon
February 23, 2006
1
Introduction
•
Brief description of Polar HIST sensor
•
Switch to a high-statistics (HS) science mode on HIST
motivated by coherent variations in GCR frequently observed
at Polar, Wind, ACE, and INTEGRAL s/c during heliospheric
current sheet (HCS) crossings and Interplanetary CME transits
and need to better understand energy response of HIST to
high-energy protons
•
Active Sun in December 2006 gave multiple SEP events to
cross-calibrate high-statistics mode
•
Observation of electron precursor to Dec 13th SEP and GLE
•
Unusual SEP signatures observed inside ICME on Dec 15
Polar Telecon
February 23, 2006
–
in solar wind at ACE, Wind, and STEREO
–
in polar cap (PC) at Polar HIST
–
Different signature at GEO raises questions
2
Polar High Sensitivity Telescope HIST
Polar Telecon
February 23, 2006
•
HIST contains a ~3.5 x 5 cm
plastic scintillator (large omnidirectional geometric factor
for penetrating particles)
•
Designed for relativistic
electron radiation-belt studies
•
Large omni-directional
geometric factor is well suited
for studying short-period
variations
•
In December 2006 GLE event
the count rate exceeded 105
during a six-second rotation
of Polar
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GCR Modulation on 06-15-99 seen by HIST
Polar Telecon
February 23, 2006
•
HIST scintillator data
shows short-period
GCR beginning shortly
before 14:00 UT
•
Observation lasts
approximately 5 hours
•
Polar passing through
polar cap (PC) region
•
MTM and MEM
analyses show strong
coherence at 1.5 mHz
•
HIST count rates in
normal science mode
are too low to perform
rigorous analysis
4
GCR Modulation on 06-15-99 seen by Wind
Polar Telecon
February 23, 2006
•
Wind Epact data also
shows short-period
GCR variability on
similar time-scales
•
Observation lasts
throughout the day
•
Wind is located in
upstream solar wind
near L1 at this time
•
MTM, MEM analyses
indicate coherence at
similar and slightly
lower frequencies than
HIST data, strongest
coherence at < 1mHz.
•
Again, low GCR count
rates make analysis
difficult
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ACE Solar Wind Observations 06-15-99
Polar Telecon
February 23, 2006
•
Shock, low field strength
and variance prior to
GCR variability onset
•
HCS sector boundary
crossing with sharp
change in field strength
and variance
•
Numerical particle
tracing of GeV protons
IP fields show oscillation
in downstream local
magnetic mirror (green)
•
Oscillation is along radial
direction at multiple
frequencies over large
fraction of AU
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Polar HIST in High-Statistics (HS) Mode
Polar Telecon
February 23, 2006
•
HIST HS mode has 256
digitized bins (0-255)
•
Bins 0-254 range from
comfortably above noise
up to ~10 MeV
•
All pulses >10 MeV
appear in the “overflow”
bin 255 (magenta trace).
As expected, most
counts are in overflow
bin
•
December 2006 SEP
event data shown are
divided into four sums of
64 bins plus the overflow
bin 255
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Opportunity in SEP Events of Dec 2006
Polar Telecon
February 23, 2006
•
Dec 13, 2006 SEP observed
at ACE, Wind, STEREO B,
GOES, and Polar
•
Satellites in magnetosphere
see similar signatures as s/c
in solar wind
•
Polar is in southern polar cap
during declining phase of
SEP
•
Long SEP decay time allows
intercalibration of HS mode
•
Ensuing days bring IP shock
and ICME with rise in
energetic particles and an
additional SEP on Dec 15
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Spacecraft Orbit Geometries
•
Movie of orbit tracks for the spacecraft
during the interval from 12/13 to 12/16
(same interval as the time series plot)
•
Top panel is GSE ecliptic plane; bottom
panel is plane of sky as viewed from Sun
Top(bottom) tick marks every 20(15)Re;
grid lines every 40(30)Re
•
Wind and ACE are on opposite sides of the
Earth-Sun line and above the neutral
sheet; Wind is ~250 Re sunward.
•
GOES 10 is at dusk, GOES 11 at dawn,
and GOES 12 is at subsolar region during
the short-scale particle variation
•
Gyroradii of 40 MeV proton (8 Re) and 100
MeV proton (16 Re) shown for leading
edge ICME field
•
ACE and Wind separated azimuthally by
6x-12x proton gyroradii in energies of
interest
100 MeV proton gyroradius
40 MeV proton gyroradius
Y
Wind
X
ACE
STEREO
Z
Wind
ACE
Y
STEREO
100 MeV proton gyroradius
40 MeV proton gyroradius
Polar Telecon
February 23, 2006
9
Observations of the Electron Precursor to
12/13 Ground Level Event
Polar Telecon
February 23, 2006
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HEO4 shows electron
precursor >300 keV arrives
~13 minutes earlier than
the GeV protons causing
the GLE, shown here by
Polar HIST and the Oulu
Neutron Monitor
•
These electron precursors
can be over 60 minutes in
advance of solar protons
(Posner et al 2006)
•
Important fact is that the
precursor electrons do NOT
have a higher velocity than
relativistic protons
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Polar HIST HS Mode Response
•
•
•
•
•
•
•
•
Polar Telecon
February 23, 2006
SEP on 12/13 provides unique opportunity for
cross-calibration of Polar HIST with GOES
Decay of event was exponential with large
number of protons >100 MeV
Using 0600 UT –1200 UT on Dec 13 as
calibration interval
Interval was chosen to maximize the decay
data and minimize the influence of the
radiation belts. The data was truncated 1 hr
prior to radiation belt passage
HS mode digitized bins 0-254 range from
threshold of noise up to10 MeV
These data are divided into 4 sums of 64 (bin
sums [0, 63] and [64,127] are shown)
All pulses larger than 10 MeV appear in
overflow bin 255
e-fold time of HIST is 3.65 hrs similar to
GOES 100 MeV channel with e-fold time of
3.37 hrs
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ICME Shock Particles on 12/14 Polar and STEREO
shock
Polar Telecon
February 23, 2006
•
HS mode high count rates
at 6-second intervals
complements STEREO high
resolution solar wind flux
measurements
•
Top panel shows December
events at Polar and
STEREO
•
Bottom panel shows fine
structure observed at HIST
near the IP shock on 12/14
•
GOES 100 MeV channel
does not have the counting
statistics to resolve the fine
structure of the shock
observed at Polar and
STEREO
12
SEP Within an ICME on 12/15
Polar Telecon
February 23, 2006
•
IP shock on Dec 14th driven by
ICME (between solid lines)
•
Classic particle decrease in ICME
magnetosheath same at all s/c
•
Just inside ICME leading edge
SEP is observed, caused by a
solar flare near center disk
•
Polar is exiting southern PC after
shock passage and beginning of
SEP on 12/15
•
ACE, Wind, STEREO, and Polar
observe short-scale modulation of
particle signature within the ICME
•
GOES 10 &11 integral fluxes do
not show this signature at GEO
(GOES 12 data unavailable)
13
Satellite Orbit Geometries
Polar Telecon
February 23, 2006
•
Movie of orbit tracks during 12/14 1400 UT to
12/15 0600 UT (from the IP shock through the
1st half of the ICME)
•
Top panel is GSE ecliptic plane; bottom panel
is plane of sky as viewed from Sun (tick marks
1 Re apart; grid lines 2 Re apart)
•
GOES 12 (red) leads GOES 11 (yellow) by
~4 hrs MLT ; GOES 10 lags GOES 11 by same
amount (not shown)
•
GOES 10 is pre-noon, GOES 11 is post-noon
region, and GOES 12 is near dusk when
leading edge of ICME hits Earth; Polar (green)
in southern auroral oval during this time
•
The short-scale particle variation inside the
ICME exists at Polar so why not at GOES 10
and GOES 11?
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Summary & Conclusions
•
Large geometric factor of Polar HIST plastic scintillator is well suited for
obtaining high count rate statistics at high energies and high cadences
needed to reliably measure shot-scale SEP and GCR variability
•
Cross-calibration of HIST HS mode during long decay of SEP on
12/13/06 shows overflow bin 255 on HIST has similar e-fold time as
GOES 100 MeV integral flux channel
•
SEP and GCR observations show short-scale energetic particle
modulation occurs when in Earth is downstream of shocks, near HCS
boundaries and ICMEs
•
Best observation periods are when Polar is on open field lines either
crossing through the PC or in the auroral oval
•
Electron precursor to December 13th SEP observed ~13 minutes prior to
ground level event at Oulu Neutron Monitor, requires more study
•
Unusual SEP signatures observed inside ICME on 12/15 evident at ACE,
Wind, and STEREO in solar wind and at Polar HIST, but signature
observed at GEO orbits remains ambiguous
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Need to exercise some caution using GEO data in IPM models
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Did Comet McNaught play a role?
Polar Telecon
February 23, 2006
15
Supplemental Charts
Polar Telecon
February 23, 2006
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Polar HIST in High-Statistics (HS) Mode
•
In HS mode all pulses
>10 MeV appear in
the “overflow” bin 255
•
Bin 255 has similar
energy response as
GOES >100 MeV
channel
•
Direct comparison of
GOES > 100 MeV and
HIST bin 255 clearly
shows lack of
variability at GOES
•
Variation at HIST seen
during other passes
currently under study
Radiation Belt Passes
Polar Telecon
February 23, 2006
17
GOES Differential Proton Fluxes
Polar Telecon
February 23, 2006
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Differential proton flux data
shown at ~1 MeV to 80 MeV
energies for GOES 10, 11,
and 12, respectively.
•
GOES 10 and 11 show little if
any short-scale modulation
•
GOES 12 15-40 MeV energy
band shows clear short-scale
modulation
•
Flare region on 12/15 is near
center of solar disk
•
Better connectivity expected
at dawn due to nominal
Parker spiral field direction,
but this is not observed– is
this an ICME connectivity
issue?
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GOES Integrated Proton Fluxes
Polar Telecon
February 23, 2006
•
Top panel shows differential
proton flux at GOES 12
integrated over 2 energy bands
•
Similar short-scale particle
variation as seen at Polar and
in the solar wind observed in
15-80 MeV energy band at
GOES 12 (located near dusk)
•
IP shock passage marked by
vertical lines
•
Bottom two panels compare
the 15-80 MeV energy band at
GOES 12 with GOES 10 and
GOES 11, respectively
•
Again, GOES 10 (pre-noon) or
GOES 11 (post-noon) do not
show this feature
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ACE Solar Wind and Flux Rope Fit
Polar Telecon
February 23, 2006
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