PIXIE/Polar A Success Story! PIXIE (Polar Ionospheric X-ray Imaging Experiment)

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Gerald Gilmore
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1 PIXIE/Polar A Success Story! PIXIE (Polar Ionospheric X-ray Imaging Experiment)

2 Norsk Romsenter 8 mai 2008 Polars siste runddans Professor Johan Stadsnes ved 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.

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

3 Celtic Mythology Creatures Elves PIXIE Banshee Gnome

4 28 papers in peer-reviewed journals (between 1995 and 2007). Note: In 23 of these papers, the first author is a member of the 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

5 Toni Silvennoinen, Finland.

6 Weak aurora An intense auroral substorm Images from the POLAR VIS instrument

7 Comparison of remote sensing methods. From Robinson and Vondrak [1994]. X-ray UV Visible Temporal coverage Day and night Day and night Night only Albedo corrections Unnecessary Unnecessary Needed Absorption corrections Usually unnecessary Often necessary Usually unnecessary Emission processes Well understood Somewhat understood Somewhat understood Atmospheric background Negligible Negligible Simetimes significant Derivation of geophysical parameters Straight-forward Chemistry-dependent Chemistry-dependent Electron spectral information Multi-parameter Two-parameter Two-parameter Characteristic electron energy sensitivity kev < 10 kev < 10 kev Validation Proven Proven Proven

Often necessary Usually unnecessary Emission processes Well understood Somewhat understood Somewhat understood Atmospheric background Negligible Negligible Simetimes

8 Precipitating electrons with energy [kev]: Altitudes 160 km 140 km 120 km 100 km 80 km An X-ray camera is needed to capture the most energetic electrons

9 The PIXIE group in Bergen Jon Bjordal and Johan Stadsnes (co-investigators) Kåre Slettebakken (project engineer, mechanical) Kåre Njøten (project engineer, electronics) 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

cooperation between: Lockheed Palo Alto Space Sciences Laboratory The Aerospace Corporation, Los Angeles University

11 PIXIE was launched on NASA s Polar satellite in February 24, Estimated life: ~2 years PIXIE was operating till November 9, 2002.

13 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

14 PIXIE research 1. Energy deposition by precipitating electrons and how it affects ionospheric 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)

electrodynamics 2. Electron precipitation - dynamics and special features 3.

15 The electric current density in the ionosphere ~ km j = σ P (E pp + v n xb) + σ H Bx(E pp + v n xb)/b + σ E The Pedersen conductivity σ P is largest around 125 km. The Hall conductivity σ H is largest below 110 km. Conductance = Height-integrated conductivities Σ P = Pedersen conductance i.e. height-integrated σ P Σ H = Hall conductance i.e. height-integrated σ H

The Hall conductivity σ H is largest below 110 km.

16 Σ H,P < 10 S

17 Σ H,P = 10 S? 20 S? 50 S? 100 S? Σ H,P < 10 S

18 Formulas for the Hall σ H and Pedersen σ P conductivities σ H = - (ω ge /(ν en2 +ω ge2 ) + m e /m i (ω gi /ν in2 +ω gi2 )) * N e e 2 /m e σ P = (ν en /(ν en2 +ω ge2 ) + m e /m i (ν ni /ν in2 +ω gi2 )) * N e e 2 /m e

19 Precipitating electrons with energy [kev]: Altitudes UVI 160 km 140 km 120 km PIXIE 100 km 80 km

20 Instantaneous Global Conductance Maps UVI PIXIE nm nm ~ 2 8 kev ~ 8 22 kev ~ kev ~ kev [S] Pedersen Conductance Hall Conductance > < 2

21 31 July 1997 Global Hall conductances 0230 UT 0245 UT 0300 UT [S] UT 0330 UT 0345 UT

22 Different statistical conductance models based on particle precipitation data Model Data Satellite Organization Wallis and Budzinski (1981) Average elektron fluxes of 0. 15, 1.27, 9.65 and > 22 kev ISIS-2 Kp Spiro et al. (1982) Electrons kev AE-C AE-D AE Fuller-Rowell and Evans (1987) Electrons and ions kev NOAA 6 NOAA 7 HPI Hardy et al. (1987) Electrons kev DMSP F2 DMSP F4 P78-1 Kp Gjerloev and Hoffman (2000) Electrons kev DE-2 Substorm feature

23 9 July, 1997 Prior to onset Onset +15 min + 45 min 24 July, 1997 Prior to onset Onset +15 min + 45 min [S]

24 Electron spectrum from UVI ( kev) J exp = exp(-e/5) Electron spectrum from PIXIE (5-100 kev) J exp = exp(-e/10) exp(-e/60) 10 8 Electronflux [s. cm 2. kev] UVI PIXIE Do we really need the X-ray data? 20 Energy [kev]

25 UVI UVI + PIXIE [S] S 51 S 0

26 The AMIE procedure An optimally constrained, weighted, least squares fitting of coefficients to measurements of different electrodynamical quantities The purpose of AMIE is to obtain the best possible estimate of the electrodynamics in the ionosphere by combining all available observations We have used AMIE to study effects of energetic electrons on the electrodynamics in the ionosphere by running AMIE with and without the PIXIE data PIXIE

27 26/06/ :43 UT Hall (UVI) Hall (UVI+PIXIE) [S] Difference [%] Pedersen (UVI) Pedersen (UVI+PIXIE) [S] Difference [%]

28 26/06/ :43 UT Joule Heating Q J = S P E 2 UVI UVI+PIXIE [mw/m 2 ] Difference [%]

29 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 AMIEinvestigation.

Unusual declining phase of solar cycle 23: Weak semi-annual variations of auroral hemispheric power and geomagnetic activity

Click Here for Full Article GEOPHYSICAL RESEARCH LETTERS, VOL. 36, L22102, doi:10.1029/2009gl040825, 2009 Unusual declining phase of solar cycle 23: Weak semi-annual variations of auroral hemispheric power