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1、Leiden October 2007,High Time-Resolution Sprite Imaging: Observations and Implications,H. C. Stenbaek-Nielsen Geophysical Institute University of Alaska Fairbanks M. G. McHarg U.S. Air Force Academy,Leiden October 2007,This ppt version was prepared for conference web site posting. There are no anima
2、tions in this version. Animations have been replaced with a representative image, and some additional explanatory 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
3、 al. GRL, 34, L06804, doi:10.1020/2006GL027854, 2007 Stenbaek-Nielsen et al., GRL, 34, L11105, doi:10.1029/2007GL029881, 2007 For 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;
4、 streamer discharge Afterglow: 1-200 ms chem. processes,Blue jets, beads, crawlers, ambers etc.: 5-1000ms process ?,Leiden October 2007,2 examples at 1000 fps,Sprite dynamics Images show features well known from TV image sequences with better detail Halo, tendrils, branches, and beads Images coloriz
5、ed for emphasis Altitude scale derived assuming sprite 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
6、from animation,Leiden October 2007,Rebrightening,Leiden October 2007,Features to be addressed,Time scales Branches 1 ms Tendrils 1 ms (not resolved at ms) Image: 18 Aug 1999, WIRO, Wy.,Leiden October 2007,Effect of frame rate 9 July 2005 06:06:46 UT,Streamers (almost) resolved at 50 s (20,000 fps),3
7、3 ms video,1 ms,50 ms,10,000 fps makes a lot of difference,Leiden 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/n Density at g
8、round level: 3 1019 /cc Density at 80 km altitude: 3 1014 /cc Scaling factor: 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
9、 fps makes a lot of difference,Leiden October 2007,Streamer head formation,First downward, later upwards moving streamer heads Upward starts from Lower altitude Existing luminous sprite structures (animation: GRL, 34, 11, 2007),9 ms image sequence,Animation,Leiden October 2007,Streamer head formatio
10、n,9 July 2005 06:33:11 UT: 10,000 fps Gating 50 s Duration 5.0 ms,Downward streamers first Upwards streamers later and - from lower altitude - from existing structure Streamer velocity up to 0.3 c,Animation,Leiden October 2007,Streamer head formation,Downward streamers first Upwards streamers later
11、and - from lower altitude - from existing structure Streamer velocity up to 0.3 c,7 July 2005 08:31:20 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 altitude Halo may or may not be present Str
12、eamer head brightens as it moves down Direction largely straight down Velocity up to 6 107 m/s Both increase and decrease in speed observed,Leiden October 2007,Upward Streamer,9 July 2005 04:15:17 UT 10,000 fps,Animation,Leiden October 2007,Upward Streamer,Summary of upward streamers: Not present in
13、 all events Starts later than downward streamers Starts at lower altitude than downward streamers Starts from bead structures Ends with a “puff” and upward motion stops Velocities similar to downward streamers Significant horizontal velocity component,Leiden October 2007,Morphology,C-sprite Downward
14、 streamers No upward streamers,Carrot sprite Downward streamers Upward streamers,Leiden October 2007,Main Points,All sprites start with downward moving streamer heads Streamer heads are small. Appear in images just like background stars Individual streamer heads move in one direction only No example
15、 of double headed streamers No evidence of geomagnetic field effects,Leiden October 2007,Streamer head brightness,Streamer heads: Gaussian profile Similar to stars Smaller than spatial resolution Point sources Stellar mag -6 Emission rates: 5 1021 to 3 1024 phot/s,Leiden October 2007,Size,Smaller th
16、an our 150 m resolution Telescope obs: 10-200 m (Gerken et al.) Models 25 m (Liu and Pasko) Assuming 25 m size: Average brightness: 1 100 GR,Leiden 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
17、 of GRL. Reprints available here at meeting,Leiden October 2007,Implications,Streamer heads very bright Source of energy for local chemical processes (talk Friday by D. Sentman) Longer lasting effects? Significant effects on the mesosphere?,Leiden October 2007,Streamer head splitting,9 July 2005 06:
18、33:11 UT 10,000 fps,Animation,Leiden October 2007,Streamer head splitting,Splitting on the run 2005 data show splitting a slow process: Individual streamer heads propagate 30 km, but only a few splitting events observed Only 1 or 2 new streamer heads formed in each splitting No slow down while split
19、ting But 2007 telescopic images show many and multiple streamer heads forming,Leiden October 2007,Streamer head splitting,23 June 2007 07:01:01 UT, Langmuir, NM 10,000 fps, 50 s exposures Field of view: 2.12x1.58 degrees Altitude 80 km at 600 km range Velocity: 3 107 m/s; Size: 0.1 to 2 km,Animation
20、,Leiden October 2007,Streamer head splitting,23 June 2007 04:22:49 UT 10,000 fps, 50 s exp. Field of view: 2.12x1.58 deg Altitude 80 km at 600 km Velocity: 107 m/s; Size: 0.1 to 2 km,Leiden October 2007,Streamer head splitting,Preliminary analysis Difficult to match with earlier larger FOV images Mo
21、re splits More streamer heads Maybe the sequences are from the central part of the sprite,Animation,Leiden October 2007,Afterglow,9 July 2005 04:38:00 UT 10,000 fps,Leiden October 2007,Afterglow,Very little spatial motion Vertical structure and brightness not as expected from streamer head brightnes
22、s Duration of afterglow vary between events Energy beyond streamer heads alone Can last from a few ms to several 100 ms Total optical power may be larger than for streamer heads,Leiden October 2007,Afterglow spectrum (300 fps),N2 1P spectra. Some altitude differences indicating additional local proc
23、esses (Kanmae et al., GRL, 2007).,Leiden October 2007,Streamer head spectrum Slitless spectroscpy,Star background. 0th and 1st order spectra clearly seen. Wavelength coverage 400-900 nm,Leiden October 2007,Streamer head spectrum 50 s (20,000 fps),Primarily N2 1P,Leiden October 2007,Atmospheric effec
24、ts,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 afterglow Spectral altitude differences in afterglow No N2 ion emissions detected (yet) Would expect differences between streamer heads and afterglow
25、 (not proven yet we are working on it) Chemical processes and their consequences,Leiden October 2007,Delayed Sprite,Video (30 fps). FOV: 21x16 degrees Note: First one sprite then a large carrot sprite and finally 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 USAFA 66,000 fps (15 s) Distance? (very close!) Field of view: 8x8 deg Pix size: 0.2 m (200 m range) Thanks for your attention.,