# Presentation: 482062

## 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*

## 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
- in solar wind at ACE, Wind, and STEREO
- in polar cap (PC) at Polar HIST
- Different signature at GEO raises questions

## Polar High Sensitivity Telescope HIST

- HIST contains a ~3.5 x 5 cm plastic scintillator (large omni-directional 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

## GCR Modulation on 06-15-99 seen by HIST

**GCR Modulation on 06-15-99 seen by HIST**

- 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

## GCR Modulation on 06-15-99 seen by Wind

- 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

## ACE Solar Wind Observations 06-15-99

- 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

## Polar HIST in High-Statistics (HS) Mode

- 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

**Polar HIST in High-Statistics (HS) Mode**

## Opportunity in SEP Events of Dec 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

## 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

**Spacecraft Orbit Geometries**

## Observations of the Electron Precursor to 12/13 Ground Level Event

- 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

**Observations of the Electron Precursor to 12/13 Ground Level Event**

## Polar HIST HS Mode Response

- 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

**Polar HIST HS Mode Response**

## ICME Shock Particles on 12/14  Polar and STEREO

- 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

**ICME Shock Particles on 12/14  Polar and STEREO**

**shock**

## SEP Within an ICME on 12/15

- 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)

**SEP Within an ICME on 12/15**

## Satellite Orbit Geometries

- 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?

**Satellite Orbit Geometries**

## 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
- Need to exercise some caution using GEO data in IPM models
- Did Comet McNaught play a role?

## Supplemental Charts

## Polar HIST in High-Statistics (HS) Mode

- 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

**Polar HIST in High-Statistics (HS) Mode**

## GOES Differential Proton Fluxes

- 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?

**GOES Differential Proton Fluxes**

## GOES Integrated Proton Fluxes

- 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

**GOES Integrated Proton Fluxes**

## ACE Solar Wind and Flux Rope Fit