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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 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
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
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
Multiple examples SA22A-02, Dec 4, 2012
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
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
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
Because it was cloudy on Feb 18 SA22A-02, Dec 4, 2012
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
Intensity of both spectrograph (zenith) and PKZ PKZ vertical velocity Ratio of I(4278) to I(6300) SA22A-02, Dec 4, 2012
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
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
Ion Upflow Semeter et al, 2003 Sadler, 2012, Echar = 150 eV, 20.5 second intervals between traces Zettergren, 2008 SA22A-02, Dec 4, 2012
Modeled speeds are lower than those we measure Volume Emission Rate SA22A-02, Dec 4, 2012
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
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