# Presentation: 336662

## SAMPEX/PET proton model

**D. Heynderickx****1****, M.D. Looper****2****, J.B. Blake****2**
***1******BIRA, Belgium***
***2******Aerospace Corp., U.S.A.***

- Belt models - Protons

- 5 October 2004

## Overview

**Variability of the low altitude trapped proton environment**
**Strengths and shortcomings of AP-8**
**SAMPEX mission and PET instrument**
**New model development**
**Coordinate system**
**Data binning**
**Solar cycle dependence and seasonal variations**
**Sample model outputs and comparison to AP-8**
**Work to do**
**Model software and distribution issues**

- Belt models - Protons

- 5 October 2004

## Low altitude proton flux variations

**Geomagnetic secular variation**
**Solar cycle activity**
**Solar proton events**
**Changes in atmospheric density**

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## AP-8 strengths and shortcomings

**Strengths**
**Widely known and used, integrated in existing applications**
**Provides (nearly) full energy range 100 keV – 400 MeV**
**Provides complete spatial coverage**
**Reasonably straightforward to use with TRARA**
**Shortcomings**
**No updates since 1970; would be very difficult to do**
**No real solar cycle dependence**
**No error bars (“probably a factor of two”)**
**TRARA doesn’t work well at low altitude**

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## SAMPEX mission

**SMEX mission**
**Launched in 1992**
**Still operational?**
**Orbit: 520 x 670 km, 82****o, Sun pointing**
**3 month periodicity in orbit configuration**
**Most of the time in non-spinning mode**
**For this study: proton/electron telescope (PET)**

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## Proton/Electron Telescope

**Array of Si solid state detectors**
**Passive shielding + anti-coincidence through guard rings**
**dE/dx – total energy technique + coincidence logic -> 15 channels**
**Opening angle: 58****o**** -> large geometric factor**
**Counts and livetimes over 6s are stored because of telemetry limits**

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## PET Channels

| Channel | El (MeV) | Eh (MeV) | Emid (MeV) | G. F. (cm2 sr) |
| --- | --- | --- | --- | --- |
| 1 | 18.5 | 20.5 | 19.5 | 1.792 |
| 2 | 20.5 | 22.5 | 21.5 | 1.792 |
| 3 | 22.5 | 24.5 | 23.5 | 1.792 |
| 4 | 24.5 | 27.2 | 25.8 | 1.792 |
| 5 | 27.2 | 37.4 | 32.3 | 1.714 |
| 6 | 37.4 | 45.8 | 41.6 | 1.526 |
| 7 | 45.8 | 53.0 | 49.4 | 1.356 |
| 8 | 53.0 | 65.4 | 59.2 | 1.146 |
| 9 | 65.4 | 71.0 | 68.2 | 0.477 |
| 10 | 71.0 | 76.3 | 73.7 | 0.420 |
| 11 | 76.3 | 86.1 | 81.2 | 0.341 |
| 12 | 86.1 | 120.0 | 103.0 | 0.276 |
| 13 | 120.0 | 200.0 | 160.0 | 0.276 |
| 14 | 200.0 | 300.0 | 250.0 | 0.276 |
| 15 | 300.0 | 500.0 | 400.0 | 0.276 |

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## Coordinate system

**(*****B*****,*****L*****) type coordinates not well suited for low altitudes**
**Alternatives: Kaufmann *****K = I*****√*****B*****; minimum altitude on drift shell**

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## Proton flux time series

**Proton flux time series**

**Monthly averages + *****F*****10.7**
**Averages + inverse *****F*****10.7**
**Averages + inverse *****F*****10.7 ****+ inverse MSIS atmospheric density**

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## Solar cycle dependence

**Monthly averages grouped by month**
**Hysteresis effect**
**Different behaviour for descending and ascending phases**
**Two separate fits work better**

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## Seasonal variations

**Seasonal variations**

**Annual variation of *****F*****10.7 ****fit parameters (coloured lines)**
**Sine fit with fraction of year (black lines)**
**MSIS total mass density**
**Inverse density**

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## Model fluxes

**Fit was applied to all energy, *****K***** and *****h*****min**** bins**
**Model consists of tables of fit coefficients**

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## Slide 13

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## Work to do

**Further validation of fitting procedure**
**Smoothing in (*****h*****min****,*****K*****) plane**
**Spectrum fits**
**Elimination of data contaminated by SEP events**
**Validation with AZUR, CRRES, ... data**

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## Final model format

**Presently: tabel of sine fit coefficients for (*****E*****,*****h*****min****,*****K*****,*****F*****10.7****,DOY)**
**Sine fit parameters are extracted from (*****E*****,*****h*****min****,*****K*****) bin**
**DOY is used with sine fit to generate coefficients for parabolic *****F*****10.7**** function**
***F*****10.7**** function yields flux**
**Energy dependence could also be fitted**
**Low altitude proton model is probably not far away from standardization**

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## Software and distribution issues

**Software implementation**
**Currently in IDL, will be ported to Fortran**
**Stand-alone version for use with SPENVIS**
**“****library” type version as a subroutine callable from IDL, Fortran, C, ...**
**Distribution**
**Model source code and coefficients on web site, downloadable after user identification**
**Regular updates when new data become available or fitting improves; notification of registered users**
**Code for calculating magnetic coordinates must be available as well (UNILIB, ...)**

- Belt models - Protons

- 5 October 2004