Electrodynamics is far from my field, but I was struck by the great interest NASA took in a series of photographs taken in San Francisco as Columbia was flying overhead, and which MAY show a purple streak striking the spacecraft.
Excerpts from the story in today's San Francisco Chronicle:
Of particular interest is a startling image taken by an amateur astronomer in San Francisco, which appears to show a purplish bolt of lightning striking Columbia at it streaked across the predawn skies.
NASA dispatched former astronaut Tammy Jernigan, who has flown five times on the shuttle, to pick up the photos and the camera itself. She delivered them to a NASA jet at Moffett Field, where they were to be flown to Texas on Wednesday. Jernigan said she did not know what to make of the image but agreed it needed to be analyzed.
"We sure will be very interested in taking a very hard look at this," she said while examining the picture in the photographer's San Francisco home.
The images could turn out to be the result of a subtle jiggle of the
camera or might depict some rare electrical phenomenon in the zone known as the ionosphere, more than 40 miles above Earth.
Photo analysts should be able to match the location of the strange lightning-like image with a precise point in space and time during the orbiter's descent. That's because the photograph also depicts a crisp field of stars in the background, which provide astronomical reference points.
The amateur astronomer, who does not want his name released, said he believes he snapped the images at 5:53 a.m. Saturday.
Scientists at the University of Alabama at Huntsville published a paper on plasma jets is space. See:
http://bex.nsstc.uah.edu/RbS/UGRANT/ugrant.html
A paragraph from the paper says thus in discussing ionospheric jets:
Note that charge separation occurs as soon as the dipole gradients are seen by the sunward convecting neutral plasma. It is generally assumed that the high conductivity of the cold plasma (assumed to be zero temperature, and therefore oblivious to magnetic gradients) allows the electrons to be redistributed in a
way to maintain quasi-neutrality. Recent observations show that this assumption of sufficient cold plasma fails during a magnetic storm, and real charge separation may occur. Under these conditions, cold plasma from distant regions is required, and indeed accelerated to shield the space charge. POLAR made
recent measurements of a 30 keV field-aligned potential drop during a small storm, that populated the ring current with accelerated ionospheric plasma (Sheldon98a). Thus the ring current can be explosively driven on timescales of minutes by upward ionospheric jets, as is evident in high time resolution
magnetograms.
The weblink containing the full paper includes a photograph of a plasma jet that was created in a laboratory chamber. Care to guess what color the plasma jet was?
I also came across a reference in a paper on space weather to temporal changes in ion density depending on the season and time of day. At northern mid-latitudes, the ion density is most negative in mid-winter and just before dawn. Columbia transited the San Francisco Bay area in the hour before dawn (PST).
http://www.agu.org/sci_soc/eosbuon.html
I did come across several papers by Russian scientists on kinetic forces associated with plasma jets, but didn't grasp a good sense of how weak or powerful such jets might be.