Physics Department Seminar University of Alaska Fairbanks

J O U R N A L    C L U B

Electrochemistry of Sprite Streamers
Dave Sentman
Geophysical Institute & Physics Deptartment

Electrical streamers are one stage in a sequence of events that occur in the development of sparks and lightning discharges. Sprites are very large (km-scale) streamers that form in the upper atmosphere as a secondary response to very large cloud-to-ground lightning discharges. Many macroscopic aspects of streamers are still not well understood at the microkinetic level, so the subject remains one of active investigation. Recent high speed imaging of sprites at 10,000 fps — obtained in 2005 — provide the most detailed space- and time-resolved description of streamer dynamics that have been obtained to date, equivalent to imaging at about 1 billion fps if scaled to atmospheric pressure. In this talk a preliminary model of the highly coupled local chemical processes impulsively launched by a sprite streamer is described. Results of the simulation show that the attachment-recombination lifetime of electrons created by ionization in the descending streamer head is long enough (~100s of ms at 70 km) to account for the observed "reignition" of sprites from old sprite tendrils. The principal ion remnants that survive longer than 1 second are O2- and O-, and NO+ and O4+. Subsequent interactions of the negative ion remnants with ambient CO2 and positive ion remnants with H2O could constitute a significant regional source of complex negative ions and hydrated positive ions, respectively, within the upper atmosphere.

Friday, 1 December 2006
Globe Room, Elvey Building
3:45 PM