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Sustained Vertical Thermospheric Winds in the Auroral Zone

Sustained Vertical Thermospheric Winds in the Auroral Zone. Don Hampton(1) John Meriwether(2), Miguel Larsen(2) Aaron Ridley(3) and Mark Conde (1) (1) Geophysical Institute, UAF (2) Clemson U . (3) U. Michigan. Instrumentation & Operations Poker Zenith FPI (PKZ).

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Sustained Vertical Thermospheric Winds in the Auroral Zone

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  1. Sustained VerticalThermospheric Winds in the Auroral Zone Don Hampton(1) John Meriwether(2), Miguel Larsen(2) Aaron Ridley(3) and Mark Conde(1) (1) Geophysical Institute, UAF (2) Clemson U. (3) U. Michigan SA22A-02, Dec 4, 2012

  2. Instrumentation & OperationsPoker Zenith FPI (PKZ) • 7 cm aperture etalon with 1.5 cm plate spacing • Originally 75 mm focal length results in 3 full fringesof 630 nm O(1D) emission. • Upgraded Jan 2011 resulting in 9 full fringes • Field of view ~1° • Etalon thermal drift tracked with frequency stabilized HeNe laser • Nine 90-second zenith images followed by laser image and dark image • Total cycle time 900+ second SA22A-02, Dec 4, 2012

  3. 11 Jan, 2010 • Consistent vertical wind coincident with enhanced 630 nm emission due to auroral activity • Sustained vertical wind as long as 4 hrs • No obvious increase in temperature Vertical Wind (m/s) 03 05 07 09 11 13 UT 11 Jan Temp. (K) Intensity (R) SA22A-02, Dec 4, 2012

  4. Multiple examples SA22A-02, Dec 4, 2012

  5. Can we believe the measurements? • Enhanced sensitivity could also render the instrument susceptible to contamination • Two possible sources: • Scattered light from the troposphere or observatory dome • N2 First Positive emission band (10,7) contains one emission line within 0.02 nm of the 630.03 nm 1D emission Airglow/Aurora SA22A-02, Dec 4, 2012

  6. Scattered Light Analysis • Need a record of the net Doppler shift of the 630.0 nm emission outside of the PKZ field of view 115 Cells over 160° of the sky. Scanning Doppler Imager (SDI) SA22A-02, Dec 4, 2012

  7. Intensity of both SDI (zenith) and PKZ PKZ vertical velocity Sum of the product of line-of-sight velocity and intensity for each cell from SDI Temp from both SDI and PKZ This plot shows that the technique works. Why? SA22A-02, Dec 4, 2012

  8. Because it was cloudy on Feb 18 SA22A-02, Dec 4, 2012

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  12. N2 Contamination Analysis • Need an instrument that measures N2 and O(1D) emissions simultaneously Meridian Spectrograph All-sky lens Slit Andor CCD Collimating lens Filter Wheel Grating SA22A-02, Dec 4, 2012

  13. Intensity of both spectrograph (zenith) and PKZ PKZ vertical velocity Ratio of I(4278) to I(6300) SA22A-02, Dec 4, 2012

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  17. Contamination Conclusions • Upward vertical signal is not correlated with intensity of N2 emissions • For clear skies, there is no consistent correlation with net out-of-field line-of-sight Doppler shift • Upward vertical motion correlated to auroral red-line emission is a real phenomenon. SA22A-02, Dec 4, 2012

  18. Ion Neutral Connection? • Aruliah et al. (2012) found a similar vertical signature in association with soft precipitation on the dayside • The PKZ events are correlated with soft precipitation • When I(4278)/I(6300) > ~0.5 the vertical signature dissipates • Papers by Su (1999), Clemmons (2008), and Sadler(2012) relate soft e- precipitation with ion upflow/outflow • Ion motion will produce a population of fast neutral oxygen via charge exchange and other collisions SA22A-02, Dec 4, 2012

  19. Ion Upflow Semeter et al, 2003 Sadler, 2012, Echar = 150 eV, 20.5 second intervals between traces Zettergren, 2008 SA22A-02, Dec 4, 2012

  20. Modeled speeds are lower than those we measure Volume Emission Rate SA22A-02, Dec 4, 2012

  21. Summary • Sensitive vertical measurements of thermo-spheric630 nm emission commonly show vertical motion correlated with soft electron precipitation in the auroral zone • Contamination is no longer suspected • Upward vertical motion can last for hours • Speeds typically 20 m/s, but ~60 m/s in some cases • Current models of ion upflow don’t reproduce the measured neutral vertical speeds SA22A-02, Dec 4, 2012

  22. Future Work • Continue to mine past three years of PKZ data and continue to correlate with complementary measurements (PFISR, SDI, N2 1P intensity, SuperDARN) • Current season will use three stations in AK in vertical mode • Probe the MLT and latitude dependence of the vertical winds Use method of Zettergren et al (2008) and narrow-field spectrograph at Poker to estimate the ion upflowcharac-teristics SA22A-02, Dec 4, 2012

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