# Presentation: 943929

## Shock Geometry, Seed Populations, and the Origin of Energy-Dependent Fe/O in Large, Gradual Solar Energetic Particle Events

***Allan J. Tylka and Martin A. Lee***
***allan.tylka@nrl.navy.mil;   ******marty.lee@unh.edu***

***SHINE WG3 Invited Talk***
***Big Sky, Montana***

***2004 June 29***

## Overview / Summary

***We present calculations that describe SEP spectral & compositional variability at high energies, including***
***“******Zoo” of energy-dependent Fe/O***
***Associated morphologies in spectral shapes***
***Energy-dependent <Q******Fe******>***
***The calculations make quantitative predictions about high-energy behavior that are consistent with the data.***
***The calculations require two key ingredients:***
***Variable seed population, including both SW & flare suprathermals***
***Variable shock geometry (quasi-parallel & quasi-perp) ***
***The calculations are applicable to both SEPs and IP shocks at  1 AU.***
***The calculations are ***_***simple***_***, analytical, and ***_***heuristic:***_
***Certainly not the final word***
***Useful for developing intuition about these complex problems.***
***Encourage more rigorous investigations of these ideas.***

## SHINE Campaign Events: 2002 April 21  &  2002 August 24

***SHINE Campaign Events: ******2002 April 21  &  2002 August 24***

***Tylka et al. (2004) suggested that:***
***Events like this involve a quasi-perpendicular shock operating on a seed population containing flare suprathermals.***
***Events like this are from a solar-wind seed population, accelerated by a shock, most likely quasi-parallel.***

***We now present analysis & modeling that support these interpretations.***

## Compare Spectra:  2002 April 21 & 2002 August 24We also need to account for these spectral differences!

***Fits to “Band et al.” Functions:***
***Double power-laws***
***At high energy, Fe harder than O***

***Fits to *****F(E) ~ E****-******** exp(-E/E****0****)**
***At high energy, Fe softer than O***

## Spectral Origin of Highly Suppressed Fe/O at High Energies

**F****x****(E) ~ E****-******** exp(-E/E****0x****)****  **
**with ****E****0x**** ******** Q****x****/A****x**
**(Ellison & Ramaty 1985)**

***Data from 8 instruments, 5 satellites***

***Oxygen charge state measured by SAMPEX***
***Others inferred by scaling according to fitted E******0***

- trans-
- Fe

## Solar-wind Seed Population in the 2002 April 21 Event

***Use theoretical calculations to determine source plasma temperatures from the mean ionic charge states ***
***Arnaud & Rothenflug 1985 Arnaud & Raymond 1992***
***All species consistent with 1.4 MK, typical of the solar wind.***
***These charge states are our justification for identifying solar wind (suprathermals) as the dominant seed population in this event.***

## Are there quasi-perp shocks near the Sun?Do they make SEPs?                                                             -- almost surely!

***2001 April 15 GLE***
***(like 2002 August 24, but bigger)***

***SEP onsets & peak of ~GeV production occurred when the CME was at ~2 R******S******.***

## A Theoretical Insight about Quasi-Perp Shocks(A Suspicion?)

***   ******Rate of energy gain is higher at  quasi-perpendicular shocks. ***

***If  a shock takes on a range of ***********Bn**** *****values, high-energies will be dominated by particles produced at ***********Bn**** ~ 90****o.**

***Jokipii 1987***

-  = || / rg = 100

-  = || / rg = 10

***Similar results also derived by Webb et al. (1995).***

## Another Theoretical Insight about Quasi-Perp Shocks(Another Suspicion??)

***   ******Injection threshold is likely to be higher at quasi-perp shocks.***

- Jokipii (1987): “[Our equations] become quite stringent constraints for low-energy particles, where vparticle may not be much larger than Vshock..  These considerations lead to the expectation that low-energy injection occurs more readily when the shock is quasi-parallel.  However, if the particle velocity is much higher than the shock velocity, very efficient diffusive acceleration can occur at perpendicular shocks.”
- Webb et al. (1995):
- vparticle  >> 0.75•Vshock                  for Bn =  0o
- vparticle  >> 0.75•(1 + 2)1/2 Vshock  for Bn =  90o
- Webb et al. (1995) used   10.

***A quasi-perp shock preferentially ‘reveals’ the characteristics of the higher-speed seed particles.***

## How can we get Fe/O increasing with energy?

***These two components naturally lead to energy-dependent composition in the seed population.***
***Consider varying *********Bn****,***** including both quasi-perp and quasi-parallel.***

## Effects of Averaging over a Varying Shock AngleM.A. Lee & A.J. Tylka

***Effects of Averaging over a Varying Shock Angle******M.A. Lee & A.J. Tylka***

***Power-law index the same for all species.***
***Species “X” and **********Bn****** dependence reside in rollover, E******0X****** ***

***SW component has steeper spectrum by E******-1***
***Flare & SW components have different Q/A dependence***

***Parameters : ***
******,  E****0****,  R**

## Effects of Averaging over a Varying Shock Angle

***This simple, heuristic calculation reproduces significant features of the data:***
***Roughly double power-law spectra***
***(Nearly) power-laws at high energy, with Fe harder than O***
***Fe/O increasing with energy***

****** *****  *****=  1.5***** ***
**E****0**** = 3 MeV/nuc**
**R = 0.1**

## Energy-Dependent Fe Charge States

***2001 April 15 GLE***
***(like 2002 August 24, but bigger)***

***SAMPEX: Labrador et al. 2003***
***                   ******Mazur, private communication.***
***TTM: Dietrich & Tylka 2003***

***From these calculations***

## The “Zoo” of  Fe/O vs. Energy

***Data***

***Modeling***

*** ******vary size of flare component in seed population:  ***
***R = (Seed Pop Flare O) / (Seed Pop SW O)***

- R = 0

**Notes:**
In the modeling plot:  the dark blue curve at the bottom is a pure-parallel shock, acting on a seed population containing no flare suprathermals.
The other curves are various colors are from integrating over the full range of shock angles, including 90 degrees, but with varying amounts of flare particles in the seed population.

## Enhanced Fe/O Asymptote at High Energies

***Regardless of the size of the flare-component in the seed population, re-acceleration by a quasi-perp shock give an asymptotic Fe/O value at high-energies:***
***(Fe/O)******shock****** ******= (Fe/O)******flare******• [Q/A] ******Fe, Flare ******/ [Q/A]******O, Flare***
***                  ******=   8 • (17/56) / (8/16)***
***	******   ******=  4.8***
***using average values for impulsive events:***
***         ******(Fe/O)******flare****** = 8x   <Q******Fe******>=17   <Q******O******>=8***
***Do we see this in the data?***

***Modeling***

## Average Fe/O Enhancement at High Energies

***Based on ******average****** characteristics of flare ions, we’ve made a prediction for the ******average****** value of enhanced Fe/O at high-energies in gradual events.***

- Numbers on the datapoints tell how many events were used in the average.

## Fe/O at High Energies

***These two calculations have no flare particles in the seed population.***
***In the quasi-perp case, Fe/O plateaus at:***
***(Fe/O)******shock****** ******= ******[Q/A] ******2******Fe, SW  ******/ [Q/A] ******2******O, SW***
***                  ******= (10/56)******2****** / (6/16)******2***
***	******   ******= 0.22 x nominal value***
***(In the parallel case, Fe/O drops precipitously.)***
***Do we see this in the data?***

***Fe/O (normalized) vs. Energy***

## 2001 November 06*: A Strong Quasi-Perp Shock at 1 AU

***High-energy particle production dominated by shock’s arrival at 1 AU.***
***This is a quasi-perp shock acting on a solar-wind-like seed population:***
***ACE (Q. Hu):****** **********Bn ******= 82 ***_***+***_*** 3******o****** ***
***SAMPEX (A. Labrador):***
***Above ~25 MeV/nuc:***
***<Q******Fe******> = 12 ***_***+***_*** 1***
***<Q******O******>  = 6.6 ***_***+***_*** 0.3***
***The high-energy Fe/O “bottoms out” at 0.2 x nominal.***
***--  just as predicted for this case.***

****Event launched on 2001 November 4.***

## Compare: 2001 November 04 & 2001 September 24

## Compare: 2001 November 04 & 2001 September 24

| CME Speed | 1810 km/s | 2402 km/s |
| --- | --- | --- |
| Source Longitude | W18 | E23 |
| Sun-Earth Transit Time | 33.0 hours | 33.5 hours |
| Flare | X1.0 | X2.6 |
| SAMPEX/MAST <QFe> | 12 + 1 | 10 + 1 |
|                              <QO> | 6.6 + 0.3  | 6.3 + 0.4 |
| Fe/O/0.134 @ ~50 MeV/nuc | 0.24 + 0.04 | 0.026 + 0.014 |
| ACE Bn  (Q. Hu) | 82 +  3 o | 66 + 18 o |

- Aw shucks!

## Application to Traveling IP Shock Events near 1 AU

***In carrying out these calculations, it is not necessary to average over the full range 0 ***_***<***_*** *********Bn**** **_***<***_*** 90******o******.***
***The results may also be applicable to traveling IP shock events (Desai et al.).***
******Bn *****naturally takes on a range of values as the magnetic connection sweeps across the non-spherical front of an approaching shock.***

## Summary

***Outline of the calculation:***
*** ******Simple functional form for the shock spectra:   *****F****x****(E) ~ E****-******** exp(-E/E****0x****)**** **
*** ******Species and***** ********Bn**** *****dependence in*****  E****0x****  ~ [Q****x****/A****x****] [sec********Bn****]****2/(2********-1)**
***Average over***** ********Bn****:**** **
***Flare suprathermals are equally injectable at all***** ********Bn . **
***SW suprathermals weighted by a factor of*****  ******** = cos ********Bn .**
***Use nominal composition and charge states.***
***Variability in the relative size of flare- and SW-components of the seeds.***
*** ******These calculations qualitatively account for:***
***Spectral variability:  exponential rollovers & double power-laws.***
***Different power-laws for Fe & O at high-energies***
***“******Zoo” of energy-dependent Fe/O***
***Energy-dependent <Q******Fe******>***
***The calculations also make ***_***quantitative***_*** predictions about high-energy behavior that are consistent with the data.***

## Summary

***The calculations are applicable to both SEPs and IP shocks at  1 AU:***
***In the SEP case, the averaging over *********Bn***** may be primarily due to evolution as the shock moves out from the Sun.***
***In the ESP case, the averaging reflects changes in *********Bn***** as the magnetic connection point sweeps across the approaching shock front.***
***Given the simplicity of these calculations, they are not the final word.***
*** ******But they certainly justify more rigorous investigation of these ideas, including:***
***Time dependent simulations, with evolving *********Bn***** ***
***Compound seed populations, with both SW & flare suprathermals.***
******Bn****-*****dependence of the***** *****threshold speeds and injection efficiency.***

## Next Step:  Temporal Evolution

***Wind/LEMT: 3 energy bins, 2.5-10 MeV/nuc***

**Fe/O/corona**

**Oxygen Intensity**

**Time**

## Next Step:  Temporal Evolution

***ACE/SIS: 4 energy bins, 10-40 MeV/nuc***

**Fe/O/corona**

**Oxygen Intensity**

**Time**

## Next Step:  Temporal Evolution

***ACE/SIS: Oxygen Energy Spectra:  First Six Hours***

## 1997 November 6:  The First Very Large SEP Event of Cycle 23

## Earth’s Bow Shock

***Earth’s Bow Shock***

***Meziane, Hull, Hamza, & Lin, JGR 107, 1243 (2002)***

- Wind-3DP Bow Shock Crossings 1994 Nov 30 – 2000 Jan 25

## How fast is fast enough?

***Roussev et al., ApJ Letters  605, L73 (2004)***

***MHD simulation of a CME with peak speed of ~1200 km/s, based on observations of the 1998 May 02 GLE.***
***“******We have been able to determine that a shock can develop close to the Sun sufficiently strong to account for energetic particles up to 10 GeV.”***

## High-Energy Fe/O vs. CME Speed

## CIR Composition