Upstream effect on fluid thread

[Keith_McClary]

I adjust my tap to produce a thread of water about 2 mm in diameter. It breaks up into droplets about 10 cm below the spout. I touch the thread near the spout with the tip of a single hair (from my head). I see ripples (standing, not travelling) on the thread 1-2 cm below the hair. The strange thing is, there are also ripples 1-2 cm ABOVE the hair.

I Googled up
Break-up dynamics of fluctuating liquid threads.

Just reading the abstract tells me that this is not simple.

Can the upstream ripples be explained on general principles without getting into these complications?

(This was inspired by a question by 23scurtu on http://.com/questions/200815/why-does-a-continuous-water-stream-form-ripples-when-colliding-with-a-surface/200943#200943 with videos of the effect. )

 

[Andy Resnick]

The group velocity of capillary-gravity waves exceed the phase velocity, so energy is transported 'upstream' as well as downstream.

http://math.mit.edu/classes/18.376/TermPapers/18376_Term_Paper_Fan.pdf

 

[Keith_McClary]

Corrected link to the physics.stackexchange question:
Why does a continuous water stream form ripples when colliding with a surface?