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1、Leiden October 2007,High Time-Resolution Sprite Imaging:Observations and Implications,H.C.Stenbaek-NielsenGeophysical InstituteUniversity of Alaska FairbanksM.G.McHargU.S.Air Force Academy,Leiden October 2007,This ppt version was prepared for conference web site posting.There are no animations in th
2、is version.Animations havebeen replaced with a representative image,and some additionalexplanatory text has been added.I will be preparing compressed version of animations.(Most are too large for email)Some are available with our publications through AGUs journal website:McHarg et al.GRL,34,L06804,d
3、oi:10.1020/2006GL027854,2007Stenbaek-Nielsen et al.,GRL,34,L11105,doi:10.1029/2007GL029881,2007For further info contact us by email:hnielsengi.alaska.edu,Leiden October 2007,Trans Luminous Events(TLE),Elve:1 ms E&M pulse,Halo:1-5 ms:glow discharge,Sprite:1-10 ms;streamer discharge Afterglow:1-200 ms
4、 chem.processes,Blue jets,beads,crawlers,ambers etc.:5-1000ms process?,Leiden October 2007,2 examples at 1000 fps,Sprite dynamicsImages show features well known from TV image sequences with better detailHalo,tendrils,branches,and beadsImages colorized for emphasisAltitude scale derived assuming spri
5、te to be at lightning strike(NLDN),Leiden October 2007,Sprite at 1000 fps,Sequence:15 ms.,Selected frames from animation,Animation,Leiden October 2007,Sprite at 1000 fps,Sequence:30 ms.Note:No halo with second sprite,Animation,Selected frames from animation,Leiden October 2007,Rebrightening,Leiden O
6、ctober 2007,Features to be addressed,Time scales Branches 1 msTendrils 1 ms(not resolved at ms)Image:18 Aug 1999,WIRO,Wy.,Leiden October 2007,Effect of frame rate9 July 2005 06:06:46 UT,Streamers(almost)resolved at 50 s(20,000 fps),33 ms video,1 ms,50 ms,10,000 fps makes a lot of difference.,Leiden
7、October 2007,Link to streamers in the lab,Exposure:300 ns 50 ns 10 ns 2 ns,Courtesy of Prof.Ute Ebert and T.Briels of TU Eindhoven,Netherlands,Leiden October 2007,Scaling of process time,Time development scales as 1/nDensity at ground level:3 1019/ccDensity at 80 km altitude:3 1014/ccScaling factor:
8、105,Leiden October 2007,Scaled to 80 km altitude,30 ms(TV)5 ms 1 ms 0.2 ms 33 fps 200 fps 1000 fps 5000 fps,Leiden October 2007,Scaled to 80 km altitude,30 ms(TV)5 ms 1 ms 0.2 ms 33 fps 200 fps 1000 fps 5000 fps,10,000 fps makes a lot of difference.,Leiden October 2007,Streamer head formation,First
9、downward,later upwards moving streamer headsUpward starts fromLower altitude Existing luminous sprite structures(animation:GRL,34,11,2007),9 ms image sequence,Animation,Leiden October 2007,Streamer head formation,9 July 2005 06:33:11 UT:10,000 fps Gating 50 s Duration 5.0 ms,Downward streamers first
10、Upwards streamers later and-from lower altitude-from existing structureStreamer velocity up to 0.3 c,Animation,Leiden October 2007,Streamer head formation,Downward streamers firstUpwards streamers later and-from lower altitude-from existing structureStreamer velocity up to 0.3 c,7 July 2005 08:31:20
11、 UT:5,000 fps Gating 100 s Duration 5.0 ms,Animation,Leiden October 2007,Downward Streamer,Summary of downward streamers:Streamer head starts 70-90 km altitudeHalo may or may not be presentStreamer head brightens as it moves downDirection largely straight downVelocity up to 6 107 m/sBoth increase an
12、d decrease in speed observed,Leiden October 2007,Upward Streamer,9 July 200504:15:17 UT 10,000 fps,Animation,Leiden October 2007,Upward Streamer,Summary of upward streamers:Not present in all eventsStarts later than downward streamersStarts at lower altitude than downward streamersStarts from bead s
13、tructuresEnds with a“puff”and upward motion stopsVelocities similar to downward streamersSignificant horizontal velocity component,Leiden October 2007,Morphology,C-spriteDownward streamersNo upward streamers,Carrot spriteDownward streamersUpward streamers,Leiden October 2007,Main Points,All sprites
14、start with downward moving streamer headsStreamer heads are small.Appear in images just like background starsIndividual streamer heads move in one direction onlyNo example of double headed streamersNo evidence of geomagnetic field effects,Leiden October 2007,Streamer head brightness,Streamer heads:G
15、aussian profileSimilar to stars Smaller than spatial resolution Point sources Stellar mag-6Emission rates:5 1021 to 3 1024 phot/s,Leiden October 2007,Size,Smaller than our 150 m resolutionTelescope obs:10-200 m(Gerken et al.)Models 25 m(Liu and Pasko)Assuming 25 m size:Average brightness:1 100 GR,Le
16、iden October 2007,Size,Assuming 8 1011#/cm3/s(Sentman et al.):Size from 30 300 m,Leiden October 2007,Streamer brightness presented is in the June 16 issue of GRL.Reprints available here at meeting,Leiden October 2007,Implications,Streamer heads very brightSource of energy for local chemical processe
17、s(talk Friday by D.Sentman)Longer lasting effects?Significant effects on the mesosphere?,Leiden October 2007,Streamer head splitting,9 July 200506:33:11 UT 10,000 fps,Animation,Leiden October 2007,Streamer head splitting,Splitting on the run2005 data show splitting a slow process:Individual streamer
18、 heads propagate 30 km,but only a few splitting events observedOnly 1 or 2 new streamer heads formed in each splittingNo slow down while splittingBut 2007 telescopic images show many and multiple streamer heads forming,Leiden October 2007,Streamer head splitting,23 June 2007 07:01:01 UT,Langmuir,NM1
19、0,000 fps,50 s exposuresField of view:2.12x1.58 degreesAltitude 80 km at 600 km rangeVelocity:3 107 m/s;Size:0.1 to 2 km,Animation,Leiden October 2007,Streamer head splitting,23 June 2007 04:22:49 UT10,000 fps,50 s exp.Field of view:2.12x1.58 degAltitude 80 km at 600 kmVelocity:107 m/s;Size:0.1 to 2
20、 km,Leiden October 2007,Streamer head splitting,Preliminary analysisDifficult to match with earlier larger FOV imagesMore splitsMore streamer headsMaybe the sequences are from the central part of the sprite,Animation,Leiden October 2007,Afterglow,9 July 200504:38:00 UT 10,000 fps,Leiden October 2007
21、,Afterglow,Very little spatial motionVertical structure and brightness not as expected from streamer head brightnessDuration of afterglow vary between eventsEnergy beyond streamer heads aloneCan last from a few ms to several 100 msTotal optical power may be larger than for streamer heads,Leiden Octo
22、ber 2007,Afterglow spectrum(300 fps),N2 1P spectra.Some altitude differences indicating additional local processes(Kanmae et al.,GRL,2007).,Leiden October 2007,Streamer head spectrumSlitless spectroscpy,Star background.0th and 1st order spectra clearly seen.Wavelength coverage 400-900 nm,Leiden Octo
23、ber 2007,Streamer head spectrum50 s(20,000 fps),Primarily N2 1P,Leiden October 2007,Atmospheric effects,Sprites were at 600-700 km so blue attenuated by x100,Leiden October 2007,Optical spectra,Primarily N2 1P band emissions in both streamer heads and afterglowSpectral altitude differences in afterg
24、lowNo N2 ion emissions detected(yet)Would expect differences between streamer heads and afterglow(not proven yet we are working on it)Chemical processes and their consequences,Leiden October 2007,Delayed Sprite,Video(30 fps).FOV:21x16 degreesNote:First one sprite then a large carrot sprite and final
25、ly some activity at lower altitude,1000 fps images covering the first sprite to the onset of the carrot sprite(Left-right reversed.Sorry!),Animation,Animation,Leiden October 2007,Lightning,Lightning at USAFA66,000 fps(15 s)Distance?(very close!)Field of view:8x8 degPix size:0.2 m(200 m range)Thanks for your attention.,
