SOLPENCO: An ongoing example of the transition from scientific models to prediction tools

SOLPENCO:SOLPENCO: An ongoing An ongoing example of the transition example of the transition from scientific models to from scientific models to

prediction toolsprediction tools

SOLPENCO:SOLPENCO: An ongoing An ongoing example of the transition example of the transition from scientific models to from scientific models to

prediction toolsprediction tools

Solpenco.pro

ESWW5,Brussels, 19 November 2008

A. Aran(1), B. Sanahuja(1) & D. Lario(2)

(1) Dep. d’Astronomia i Meteorologia, Universitat de Barcelona

(2) Applied Physics Laboratory, The Johns Hopkins University

OUTLINE:

1. What is SOLPENCO?

2. How we built it up?

3. Fluxes & fluences of SEP events from SOLPENCO

4. Comparing the outputs with measurements

5. What must be improved?

6. Toward an improved version of SOLPENCO: SOLPENCO2 (within the SEPEM project)

SOLPENCO (The SOLar Particle ENgineering COde)SOLPENCO (The SOLar Particle ENgineering COde)

Long-term objective: development of a tool to characterize SEP events at user-specified locations, from outside the solar corona up to the orbit of Mars.

Main challenges: - knowledge of the underlying physics is incomplete - the scarce number of observations out of 1 AU.

SOLPENCO is a first step. Its main purpose is:To provide the capability to quantitatively and to rapidly predict SEP time-dependent upstream proton fluxes and fluences generated by interplanetary shocks, for 50 keV < E < ~100 MeV protons

1. What’s SOLPENCO? 4. Comparing with data

2. How is it built? 5. Improvements3. Fluxes & Fluences 6. Toward

SOLPENCO2

SOLPENCO allow us to analyze the aspects of SEP gradual events modeling that must be improved in order to produce useful space weather predictions.

How does SOLPENCO work?How does SOLPENCO work?



SOLPENCO2

Outputs of SOLPENCO. ExamplesOutputs of SOLPENCO. Examples



SOLPENCO2

Western event at 0.4 AU

Flux at 0.5 MeV

Shock

Flux at 0.5 MeV

Shock

Fluence E > 0.5 MeV Fluence E > 0.5 MeV

Central Meridian event at 1 AU

SOLPENCO consists of:1. A data base of pre-built SEP events2. A user-friendly interface 3. A module that interpolates between the events in

the database to obtain intermediate cases

The SOLPENCO toolThe SOLPENCO tool



SOLPENCO2

Note that:Modelling a given SEP event (e.g. with our Shock-and-

Particle model, Lario et al., 1998) requires expertise and heavy computation (time).

Thus, At present models cannot be directly applied for near-

real time or rapid estimations of a given event eventually produced at the Sun.

Spacecraft Location a) Heliocentric distance, r: 1 AU and 0.4 AU b) Angular position: from W90 to E75 (14 values)

The database: brief descriptionThe database: brief description



SOLPENCO2

Shock parameters: a) Initial pulse speed, vs: from 750 to 1800 km s-1 (8 values) b) Initial pulse width, : 140° (fixed)

Transport conditions: a) Proton mean free path (at 0.5 MeV), λ║: 0.2 AU and 0.8 AU.

Scaled with proton rigidity λ║= λ║ (R/R0.5)2-q, q=1.5 b) Turbulent foreshock region: Yes/No option. (width = 0.1 AU; λ║c=0.01 AU (at 0.5 MeV); λ║c= λ║c (R/R0.5)-

0.6

Proton energies: from 0.125 to 64 MeV (10 values)

Therefore, the data base contains:

The flux and fluence computed for 10 energy channels, and 448 possibilities for the combined shock-particle scenario (8 shocks x 14 observers x 4 transport conditions) at 1 AU and at 0.4 AU.

Taking into account the interpolated scenarios, SOLPENCO can provide the flux and fluence profiles for at least 697,800 different events (Aran et al. 2006).



SOLPENCO2

We assume that the source of shock-accelerated particles Q is given by:

log Q (t, E) = log Q0(E) + k VR (t),

Based on the previous modelling of actual SEP events, we adopted:

k = 0.5

Q0 (E) = C E where γ is the spectral index:

γ = 2 for E < 2 MeV, and γ = 3 for E ≥ 2 MeV.

The database: synthesising the flux profilesThe database: synthesising the flux profiles



SOLPENCO2

-γ

By taking γ = 3 at high energy, we might be overestimating the fluence of a given event, in some cases.

At high energies the spectral index, γ, varies from 2 to 7 (Cane et al, 1998)

This is a wide range!

The database: A note on energy dependenceThe database: A note on energy dependence



SOLPENCO2

Interpolation procedureInterpolation procedure



SOLPENCO2

1. The code searches for both the initial speeds of the shock and s/c angular positions closest to the selection of the user

Intermediate case 1200 km s-1 and W30

2. First, the code interpolates between S/C locations for the same shock (upper plots) and then, it interpolates between the two initial speeds (bottom plot).

Interpolation procedureInterpolation procedure



SOLPENCO2

W001450W10 0.5 MeV

Relative differences between simulated-interpolated events are less than a 10 %, except for the beginning of the event. Differences are much smaller.

Intermediate case obtained between correlative grid points:

(1500 km s-1, W00) and (1350 km s-1, W00)

Flux profiles Flux profiles

The difference between the profiles corresponding to the same initial shock speeds in the top and bottom panels is a direct consequence of the different conditions for the particle acceleration and injection in the regions scanned by the cobpoint.



SOLPENCO2

The faster the shock the higher the peak flux, for the same angular position.

At 1 AU, for each interplanetary shock, western central meridian events (W00-W15) have the higher peak fluxes.

Shock strength

Observer’s location



SOLPENCO2

Peak Fluxes Peak Fluxes

Shock strength

Observer’s location

Two factors determine the fluence: (1) the duration of the injection of shock-accelerated particles and (2) the efficiency of the shock as a particle accelerator.



SOLPENCO2

Fluences Fluences

A relevant result: the fluence derived for SEP events at 1 AU are higher than those obtained at 0.4 AU. This is against the inverse squared power law

dependence of the fluence with the heliocentric distance, usually assumed.

This is a consequence of the contribution to the fluence of the interplanetary shock which is more important as longer the duration of the particle event is and stronger the shock is. But, the shock-and-particle model does not consider the contribution of the downstream region of the SEP events. In certain scenarios, this could lead to higher cumulate fluences than those predicted by the model.


2. How is it built? 5. Improvements3. Fluxes & Fluences 6. SOLPENCO2

Fluences Fluences

Let’s assume for a pair of observers that: F(0.4)/F(1.0) = 0.4β

where F is the fluence or the peak intensity and β is the radial index

IMF

W00, 1AU

E30,0.4 AU

Radial dependencesRadial dependences



SOLPENCO2

PEAK INTENSITIES

Even for observers located along the same IMF line the radial dependence of the peak flux depends on:

(1) the longitudinal separation between the spacecraft’s and the direction toward the shock expands and

(2) the shock front region along which the observer is connected (i.e. the regions scanned by the cobpoint).

For well-connected events: The higher the shock speed, the fastest the decrease of the peak flux with the heliocentric distance.

Event fluences are calculated here up to the arrival of the shock. Their radial dependence are positive because the duration of the SEP events is longer at 1 AU than at 0.4 AU.

Radial dependencesRadial dependences



SOLPENCO2

Selection of the SEP events We identified the solar origin of 115 interplanetary shocks associated with proton events (SEP events) between January 1998 and October 2001.

We used observations of ten (47 keV < E < 440 MeV) channels from ACE/EPAM and IMP8/CPME instruments.

Selection criteria: SEP events for which

1. The association between the shock and a parent solar activity is well established and unique

2. The proton intensity-time profiles show a significant increase of the flux profiles for E < 25 MeV and there is a noticeable enhancement up to 96 MeV

3. The SEP event is not superimposed on a preceding event.

Comparison with observationsComparison with observations



The output is a set of 16 SEP events:8 Central meridian events (E30 – W30)

and



SOLPENCO2

Comparison with observationsComparison with observations

7 Western events (W30 – >W90) and 1 Eastern event

Weste

rn

even

ts



SOLPENCO2

Example of a central meridian event

An example: 12 – 15 Sep 2000, W09 SEP event

Peak fluxAnalysis of the peak intensitiesAnalysis of the peak intensities

Flux at shock arrival



SOLPENCO2

Analysis of the peak intensitiesAnalysis of the peak intensities



SOLPENCO2

The peak fluxes of the analyzed central meridian (western) SEP events are well predicted at E < 2 MeV.

Predictions of central meridian events are still valid at high energies for the events with a relatively poor contribution of a particle population accelerated when the shock is still close to the Sun.

For events displaying a strong prompt component predictions do not match observations at E > 2 MeV.

Analysis of the peak intensitiesAnalysis of the peak intensities



SOLPENCO2

The reason is twofold:

1. The initial conditions of the MHD code are placed at 18R, thus above the region where the injection of the high-energy particles is assumed to take place; and

2. the constant of proportionality between Q and VR (k = 0.5) has been derived from modeling actual SEP events at low energies.

Main (internal) difficulties when building SOLPENCO:● The slope k in Q(VR)● The spectral index, γ

Main (external) shortcomings:

● MHD modeling and initial conditions

● Proxy solar indicators/conditions (type II, CME speed,…)

● Lack of observational data out of 1 AU (i.e., 0.3 AU and

1.5 AU) to study radial gradients

What must be improved?What must be improved?



( ( a lot of work to do!) a lot of work to do!)

Shock

MeV

Contribution of shock-accelerated particles to the flux during the prompt phase of the event

The conclusion: A MHD shock propagation model with an inner boundary near 3-4 R would represent a large improvement of the present version of SOLPENCO.

Improving the code Improving the code What would happen if the cobpoint could be tracked closer to the Sun?



SOLPENCO2

An example western event of 2 October 1998

We are collaborating with the group in the Center for Plasma Astrophysics (CPA), Leuven (Belgium).

They have a 2D MHD model to simulate the propagation of CME-driven shocks from the inner corona to 1.7 AU.

Its initial boundary at ~3 R will allow us to track the initial stages of SEP events where the acceleration of particles in more efficient.

Improving the code Improving the code



SOLPENCO2

An example of a CME-driven shock simulation: Observer at W60

MHD simulation by Carla Jacobs (CPA, K.U.Leuven)

The April 2000 SEP event: an example

Changing the shock-and-particle model Changing the shock-and-particle model



SOLPENCO2


ACE/MAG and SWEPAM data

Simulation




SOLPENCO2


Fitting plasma parameters at 1 AU:

Position of the COBPOINT

time r-distance

Run1 0.17 h 4.3 R

Run2 0.33 h 5.3 R

MHD old 1 3.4 h 25.5 R

MHD old 2 3.5 h 25.0 R

The magnetic connection of the observer with the shock front is established at:




SOLPENCO2

VR (t)

Source of shock-accelerated particles Q is given by: log Q (t, E) = log Q0(E) + k VR (t)

ACE/EPAM data

Simulation




SOLPENCO2

Fitting particle fluxes at 1 AU

The only assumed source of particles is the coronal/IP CME-driven shock.



SOLPENCO2

Conclusion: Toward SOLPENCO2 Conclusion: Toward SOLPENCO2

We are working to produce an improved shock-and-particle model to built a new particle flux and fluence data base for SOLPENCO SOLPENCO2

This is part of the Solar Energetic Particle Environment Modelling (SEPEM) Project sponsored by ESA in which we (STP/SW Group/CPA) are involved.

SOLPENCO2 must provide rapid and improved synthetic particle flux profiles for observers located from ~0.1 AU up to 1.7 AU and covering a wider range of heliolongitudes.

See the poster by P.T.A Jiggens et al. “The ESA SEPEM Project: Database and Tools”

“The two extremes”


2. How is it buit? 5. Improvements3. Fluxes & Fluences 6. SOLPENCO2

THANKS!!

Prediction

three

Documents

SOLPENCO: An ongoing example of the transition from scientific models to prediction tools