PIXIE/Polar – A Success Story!

PIXIE (Polar Ionospheric X-ray Imaging Experiment)

Norsk Romsenter 8 mai 2008

Polars siste runddans

Professor Johan Stadsnesved Universitet i Bergen er vemodig, men mest stolt over Norges bidrag til satellitten som ender sine dager i kamp mot solen.

Dette bildet av nordlyset er det siste bildet Polar sendte hjem før instrumente ble skrudd av. Foto: Nasa.

Siden oppskytningen i 1996 har Polar jobbet jevnt og trutt og levert resultater som NASA og samarbeidspartnerne bare kunne drømme om.

Satellitten har levd ti år lenger enn forventet.

…kameraet fikk akronymet PIXIE (Polar Ionospheric Xray Imaging Experiment) og henspeiler til figurer fra den keltiske mytologien. Det nærmeste vi kan sammenligne dem med i Norge er trolig smånisser, eller huldrer.

PIXIE

Elves

Banshee

Gnome

Celtic Mythology Creatures

28 papers in peer-reviewed journals (between 1995 and 2007). Note: In 23 of these papers, the first author is a member ofthe Space Physics Group in Bergen.

6 PhD based on PIXIE data(Nikolai Østgaard, Stein Håland, Arne Aasnes, Arve Aksnes, Camilla Sætre, Hilde Nesse)

Numerous master student degrees

Toni Silvennoinen, Finland.

Images from the POLAR VIS instrument

Weak aurora An intense auroral substorm

ProvenProvenProvenValidation

< 10 keV< 10 keV1-100 keVCharacteristic electronenergy sensitivity

Two-parameterTwo-parameterMulti-parameterElectron spectralinformation

Chemistry-dependentChemistry-dependentStraight-forwardDerivation ofgeophysical parameters

Simetimes significantNegligibleNegligibleAtmosphericbackground

Somewhat understoodSomewhat understoodWell understoodEmission processes

Usually unnecessaryOften necessaryUsually unnecessaryAbsorption corrections

NeededUnnecessaryUnnecessaryAlbedo corrections

Night onlyDay and nightDay and nightTemporal coverage

VisibleUVX-ray

Comparison of remote sensing methods. From Robinson and Vondrak [1994].

Altitudes

160 km

140 km

120 km

100 km

80 km

Precipitating electrons with energy [keV]:1 3 10 30 50 100

”An X-ray camera is needed to capturethe most energeticelectrons”

Jon Bjordal and Johan Stadsnes(co-investigators) Kåre Njøten

(project engineer, electronics)

Kåre Slettebakken(project engineer,

mechanical)

The PIXIE group in Bergen

The X-ray camera PIXIE was developed and built in a cooperation between: • Lockheed Palo Alto Space Sciences Laboratory• The Aerospace Corporation, Los Angeles• University of Bergen

The following institutions were also involved in the project:• University of California Los Angeles• University of Maryland

PIXIE was launched on NASA’s Polar satellite in February 24, 1996.

Estimated life: ~2 years

PIXIE was operating till November 9, 2002.

A movie showing the PIXIE X-ray aurora between 17:30 and 21:30 UT on February 9, 1997, over the Northern Hemisphere

Low Intensity High Intensity

PIXIE research

1. Energy deposition by precipitating electrons and how it affectsionospheric electrodynamics

2. Electron precipitation - dynamics and special features

3. Energy flow - Solar wind -> ionosphere

4. Chemical effects of electron precipitation

5. Substorms

6. Auroral signatures from the X-line? (Cluster and PIXIE)

j = σσσσP(Epp + vnxB) + σσσσHBx(Epp + vnxB)/B + σ||E||

The electric current density in the ionosphere~ 70 – 160 km

ΣΣΣΣP = Pedersen conductance i.e. height-integrated σσσσPΣΣΣΣH = Hall conductance i.e. height-integrated σσσσH

Conductance = Height-integrated conductivities

The Pedersen conductivity σσσσP is largest around 125 km.The Hall conductivity σσσσH is largest below 110 km.

ΣΣΣΣH,P < 10 S

ΣΣΣΣH,P < 10 S

ΣΣΣΣH,P = 10 S? 20 S? 50 S? 100 S?

Formulas for the Hall σσσσH andPedersen σσσσP conductivities

σσσσH = - (ωge/(νen2+ωge2) + me/mi (ωgi/νin2+ωgi2)) * Ne e2/me

σσσσP = (νen/(νen2+ωge2) + me/mi (νni/νin2+ωgi2)) * Ne e2/me

Altitudes

160 km

140 km

120 km

100 km

80 km

Precipitating electrons with energy [keV]:1 3 10 30 50 100

UVI

PIXIE

UVI PIXIE140-160 nm 160-180 nm ~ 2–8 keV ~ 8–22 keV

Pedersen Conductance Hall Conductance

Instantaneous Global Conductance Maps

~ 0.1-20 keV ~ 5-100 keV [S]

> 50

40

25

10

< 2

0230 UT 0245 UT 0300 UT

0315 UT 0330 UT 0345 UT

[S]

50

40

30

20

10

0

31 July 1997 Global Hall conductances

Substorm featureDE-2Electrons0.005-32 keV

Gjerloev and Hoffman (2000)

KpDMSP F2DMSP F4P78- 1

Electrons0.05-20 keV

Hardy et al. (1987)

HPINOAA 6NOAA 7

Electrons and ions0.3-20 keV

Fuller-Rowell and Evans (1987)

AEAE-CAE-D

Electrons 0.2-27 keV

Spiro et al. (1982)

KpISIS-2Average elektron fluxes of 0. 15, 1.27, 9.65 and > 22 keV

Wallis and Budzinski(1981)

OrganizationSatelliteDataModel

Different statistical conductance modelsbased on particle precipitation data

[S]3530252015105

9 July, 1997

Prior to onset Onset +15 min + 45 min

24 July, 1997

Prior to onset Onset +15 min + 45 min

PIXIE

Electron spectrum from UVI (0.1-15 keV)Jexp = 4.0.107.exp(-E/5)

Electron spectrum from PIXIE (5-100 keV)Jexp = 8.5.106.exp(-E/10) + 8.0 .104.exp(-E/60)

108

106

Electronflux[s.cm2.keV]-1

102

20 Energy [keV] 80 100

UVI

Do we really needthe X-ray data ?

UVI UVI + PIXIE

[S]

50

40

30

20

10

051 S41 S

The AMIE procedureAn optimally constrained, weighted, least squares fitting of coefficientsto measurements of different electrodynamicalquantities

The purpose of AMIE is to obtain the best possible estimate of the electrodynamics in the ionosphere by combining all availableobservations

We have used AMIE to studyeffects of energetic electronson the electrodynamics in theionosphere by running AMIE with and without the PIXIE data

PIXIE

Hall (UVI) Hall (UVI+PIXIE) [S ] Difference [%]

20

15

10

5

0

-5

50

40

30

20

10

0

60

40

20

0

-20

20

15

10

5

0

Pedersen (UVI) Pedersen (UVI+PIXIE) [S] Difference [%]

26/06/1998 05:43 UT

UVI UVI+PIXIE [mW/m 2] Difference

[%]

Joule Heating QJ = SP E2

26/06/1998 05:43 UT

40

30

20

10

0

- 35

- 25

- 15

- 5

5

Summarize• PIXIE was the first (and only) genuine 2D auroral X-ray imager to fly on

a satellite in space

• PIXIE was the only instrument which provided instantaneous global maps of the energetic electrons up to 100 keV

• Using remote sensing from space of UV and X-ray emissions, we developed a technique to derive instantaneous global conductance maps.

• In contrast to statistical models, the technique developed provided realistic large-scale conductance patterns during individual geomagnetic substorms, crucial to understand the electrodynamics in the ionosphere and the MI-coupling.

• We have also seen that X-ray measurements are needed to capture the most energetic electrons affecting the Hall conductance. These energetic electrons can have a significant effect on different electrodynamical parameters, as demonstrated in the AMIE-investigation.