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© 2008 The Aerospace Corporation Workshop on Coupling of Thunderstorms and Lightning to Near-Earth Space University of Corsica, 23-27 June 2008 SAMPEX.

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Presentation on theme: "© 2008 The Aerospace Corporation Workshop on Coupling of Thunderstorms and Lightning to Near-Earth Space University of Corsica, 23-27 June 2008 SAMPEX."— Presentation transcript:

1 © 2008 The Aerospace Corporation Workshop on Coupling of Thunderstorms and Lightning to Near-Earth Space University of Corsica, 23-27 June 2008 SAMPEX - Searches for Lightning-Induced Relativistic Electron Precipitation J. B. Blake 1 and U. Inan 2 1 The Aerospace Corporation 2 Stanford University

2 © 2008 The Aerospace Corporation Workshop on Coupling of Thunderstorms and Lightning to Near-Earth Space University of Corsica, 23-27 June 2008 Objective of Talk SAMPEX has observed trapped and precipitating magnetospheric electrons on a continuous basis since launch in July 1992 –Precipitation from interactions with the residual atmosphere –Precipitation by magnetospheric waves –Scattering by whistlers generated by lightning However SAMPEX searches for energetic electrons (several MeV and above) accelerated by lightning have not resulted in convincing evidence for their existence in the magnetosphere What are the strengths/weaknesses of the SAMPEX search

3 © 2008 The Aerospace Corporation Workshop on Coupling of Thunderstorms and Lightning to Near-Earth Space University of Corsica, 23-27 June 2008 Outline SAMPEX as a detector of rapidly varying relativistic electron fluxes in near-Earth space –Sensor characteristics –SAMPEX coverage in B, L space Microbursts - relativistic electron precipitation on sub- second timescales –Commonly observed phenomena illustrating SAMPEX performance Gammaburst Observation Thunderstorm/Lightning associated electron precipitation

4 © 2008 The Aerospace Corporation Workshop on Coupling of Thunderstorms and Lightning to Near-Earth Space University of Corsica, 23-27 June 2008 SAMPEX Launched July 1992 Duty cycle well over 90%, still in operation Altitude 500-600 km Inclination 82 degrees Zenith pointing at high latitudes, field-line pointing at low L Four energetic particle detectors

5 © 2008 The Aerospace Corporation Workshop on Coupling of Thunderstorms and Lightning to Near-Earth Space University of Corsica, 23-27 June 2008 SAMPEX For present purposes only two instrument/channels need be considered: –PET/P1 Electrons > 500 keV, eG ~ 5 cm 2 sr, sampled 10 times/sec –HILT/SSD Electrons > 1.05 MeV, eG ~ 100 cm 2 sr, sampled 50 times/sec

6 © 2008 The Aerospace Corporation Workshop on Coupling of Thunderstorms and Lightning to Near-Earth Space University of Corsica, 23-27 June 2008 HILT Sensor

7 © 2008 The Aerospace Corporation Workshop on Coupling of Thunderstorms and Lightning to Near-Earth Space University of Corsica, 23-27 June 2008 Key Facts About SAMPEX The altitude of SAMPEX is such that the spacecraft is in the Drift-Loss-Cone (DLC) ~ 85% of the time –In the DLC only recently scatter or injected electrons can be seen –The lifetime of these electrons is no more than tens of minutes and they will be lost after longitudinal drift to the western edge of the South Atlantic Magnetic Anomaly

8 © 2008 The Aerospace Corporation Workshop on Coupling of Thunderstorms and Lightning to Near-Earth Space University of Corsica, 23-27 June 2008 Drift Loss Cone Issues

9 © 2008 The Aerospace Corporation Workshop on Coupling of Thunderstorms and Lightning to Near-Earth Space University of Corsica, 23-27 June 2008 Drift Loss Cone Issues

10 © 2008 The Aerospace Corporation Workshop on Coupling of Thunderstorms and Lightning to Near-Earth Space University of Corsica, 23-27 June 2008 Microburst Examples

11 © 2008 The Aerospace Corporation Workshop on Coupling of Thunderstorms and Lightning to Near-Earth Space University of Corsica, 23-27 June 2008 Microburst Examples

12 © 2008 The Aerospace Corporation Workshop on Coupling of Thunderstorms and Lightning to Near-Earth Space University of Corsica, 23-27 June 2008 Microburst Examples

13 © 2008 The Aerospace Corporation Workshop on Coupling of Thunderstorms and Lightning to Near-Earth Space University of Corsica, 23-27 June 2008 Microburst Examples

14 © 2008 The Aerospace Corporation Workshop on Coupling of Thunderstorms and Lightning to Near-Earth Space University of Corsica, 23-27 June 2008

15 © 2008 The Aerospace Corporation Workshop on Coupling of Thunderstorms and Lightning to Near-Earth Space University of Corsica, 23-27 June 2008

16 © 2008 The Aerospace Corporation Workshop on Coupling of Thunderstorms and Lightning to Near-Earth Space University of Corsica, 23-27 June 2008 Microburst Probability, f(L) Peak probability for L values between 5 & 6 In the slot region (2<L<3) probability is very low In the inner zone (L<2) no events seen

17 © 2008 The Aerospace Corporation Workshop on Coupling of Thunderstorms and Lightning to Near-Earth Space University of Corsica, 23-27 June 2008 Low-Latitude Microbursts Found by a statistical search Trio of bursts at unusually low L, ~ 2 Spectral information indicates no electrons at several MeV

18 © 2008 The Aerospace Corporation Workshop on Coupling of Thunderstorms and Lightning to Near-Earth Space University of Corsica, 23-27 June 2008 Low-Latitude Microbursts Typical isolated microburst –Periodicity at bounce frequency Observed periodicity agrees with calculated to better than 1% –Amplitude decreases with time –Other smaller features often seen

19 © 2008 The Aerospace Corporation Workshop on Coupling of Thunderstorms and Lightning to Near-Earth Space University of Corsica, 23-27 June 2008 SGR 1806-20 An intense gammaburst is easily seen in the SAMPEX high rate channels Single events can be easily found by a computer search for statistically significant variations

20 © 2008 The Aerospace Corporation Workshop on Coupling of Thunderstorms and Lightning to Near-Earth Space University of Corsica, 23-27 June 2008 Storm-Associated Electron Precipitation Electrons > 150 keV observed in DLC over three day period associated with storms/lightning at low latitude J. B. Blake, U. S. Inan, M. Walt, T. F. Bell, J. Bortnik, D. L. Chenette, H. J. Christian,, Lightning-induced energetic electron flux enhancements in the drift loss cone, J. Geophys. Res 106, 2001.

21 © 2008 The Aerospace Corporation Workshop on Coupling of Thunderstorms and Lightning to Near-Earth Space University of Corsica, 23-27 June 2008 Storm-Associated Electron Precipitation Precipitation took place in multiple L-shells Precipitation shells seen at same L shells and with comparable magnitude in both hemispheres

22 © 2008 The Aerospace Corporation Workshop on Coupling of Thunderstorms and Lightning to Near-Earth Space University of Corsica, 23-27 June 2008 Summary SAMPEX observes relativistic electron fluxes with a 20 ms temporal resolution SAMPEX database now is 16 years long with almost continuous coverage SAMPEX database has been search by several scientists using a variety of techniques to find short, energetic transients There are no cases where convincing observations were made of highly relativistic electrons (several MeV and above)

23 © 2008 The Aerospace Corporation Workshop on Coupling of Thunderstorms and Lightning to Near-Earth Space University of Corsica, 23-27 June 2008 Summary SAMPEX is very sensitive to relativistic electrons –~ 100 cm 2 sr at 1 MeV –Several hundred cm 2 sr at several MeV However SAMPEX is not very sensitive to gammas, by design. SAMPEX observations set stringent conditions upon a hypothesis that lightning accelerates and injects multi-MeV electrons into the magnetosphere

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