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Project Highwater (wikipedia.org)
66 points by benbreen 7 months ago | hide | past | favorite | 9 comments

> The Highwater experiment sought to determine the effect of a large volume of water suddenly released into the ionosphere.

and they really just went ahead and called it that

I presume they were also punning off "high water mark".

The ionosphere is a cool subject. As an undergrad, I worked on a sounding rocket payload under a man named Mike Kelley[1] (rest in peace) who did a lot of work in this area. Our mission was to launch a sounding rocket from PFRR during an aurora to catch and return particles in situ a la Stardust. Our payload never flew, but I learned a lot.

I was invited to help collect data on noctilucent clouds[2] (NLC) at PFRR with one of his collaborators. NLCs are due to the presence of upper atmospheric water vapor. The transport of water vapor into this region is usually by some interesting process (e.g. volcanic explosions, rocket launches, Project Highwater). The sun is still shining through that very high, thin atmosphere when nighttime has already taken hold on Earth's surface, so the clouds formed from (very rare) water vapor at this altitude appear to glow at night. It's easiest to observe in the extreme latitudes (where we were in Alaska for instance), because the late twilight period is extended. In addition, closer the Earth's poles, NLC are more common for some reason I don't remember. To measure NLC density, we aimed a laser into the ionosphere and imaged the same region via telescope, counting the photons returned as a measure of NLC density.

Dr. Kelley postulated that the Tunguska Event[3] was actually an icy comet (rather than a rocky meteor) based on NLC sightings published in newspapers around the same time, thinking the injected water vapor induced the NLC.

[1]: https://cpb-us-e1.wpmucdn.com/blogs.cornell.edu/dist/3/6798/...

[2]: https://en.wikipedia.org/wiki/Noctilucent_cloud

[3]: https://en.wikipedia.org/wiki/Tunguska_event

>For both of these experiments, the resulting ice clouds expanded to several miles in diameter and lightning-like radio disturbances were recorded

Would you be able to elaborate on this line from TFA? How does this happen? I'm assuming the answer is "the same thing that causes internal lightning in big thunderheads", but I don't think of ice as being particularly conductive...

I can't explain authoritatively, as I am several years out of this subject and have never been an expert. But I have a few thoughts that may help you uncover a satisfying answer. The NASA report on Project Highwater[1] might also help.

The atmosphere is stratified in steady-state and separated by "pauses" that form boundaries[2]. These pauses are stabilized by various phenomena include gravity, chemistry, inertia, solar warming, radiative cooling, convection. It's all a big fun cesspool of physics that lots of people study. Noting when the test took place, one could imagine a lot of scientific interest motivated by surveillance of space-bound launch vehicles, which were otherwise very difficult to observe. Also, of course, HAMs have a history of observing the ionosphere indirectly with communication[3], think surveillance applications too (not to mention installations like PFRR).

I suspect the phrasing in that Wikipedia article is summarizing a few things that occurred in sequence, eventually resulting in lightning-like phenomena (i.e. rapid electric field equalization over long distances, or noise) on some sensor somewhere:

1. The water launched to that altitude would have still been near STP upon arrival. Relatively speaking, it would have been warmer and released into a lower pressure environment. It's possible the launch could have cooled the water somewhat, but you can only dump so much heat on a short flight! The water was probably packed in some low surface area shape---at least radially circular to conform to the rocket body, and potentially closer to say spherical to aid in stability of flight, to reduce fluid sloth dynamics, make tank strength more manageable with fewer force concentration points, and/or to make the explosion easier to model---so I'm comfortable thinking of it as "hot" water discharged into a "cold" vacuum (around 1e-5 atm at 80km).

2. The water was likely released with some engineered pyrotechnic mechanism that would spread it out as widely as possible and in some tractable shape. I bet a spherical blast would have been the simplest and easiest to achieve, though shaped or staged charges are imaginable, or perhaps they were testing the risk to humans if it were fuel so they had a directional explosion starting from the engine. I didn't do any research down this line.

3. This hot water hits the vacuum with greatly multiplied surface area (from the explosion). The vapor pressure of water would push it into a second stage of evaporative expansion, and it would still also carry most of the momentum of the launch vehicle. I have no idea how to model this, but I am guessing it would be really big and begin to interact with the stratification of the atmosphere and any transport phenomena stabilizing it.

4. The atoms have to go somewhere, at at this altitude they would have had to expand many orders of magnitude. This implies large distances. Also, water is typically not stable at these altitudes, so I'm guessing it decomposed in a way that resulted in the creation of ionized gas.

5. Ionized gas can act as a conductor, and with all kinds of crazy atomspheric stuff happening up there, perhaps it shunted two areas of the atmosphere with significant difference in potential, short of causing visible lightning (see section 5.3 of the report). This would have been resolvable on various instruments and could have resembled lightning on some.

[1]: https://ntrs.nasa.gov/citations/19650011729

[2]: https://www.weather.gov/jetstream/layers

[3]: https://www.hamradiosecrets.com/ionospheric-propagation-of-r...

Nature provided a much better reference point, this year, with the Hunga-Tonga-Hunga Ha’apai eruption, which launched truly enormous volumes of water vapour into the ionosphere. It may be in part responsible for the rather sudden acceleration of global heating we are witnessing this year.


The article is extremely sparse on the results/findings of the experiments :(

Read the paper: Woodbridge, David D; Lasater, James A; et al. (October 25, 1963). An Analysis of the Second Project High Water Data. NASA. hdl:2060/19790078055. NAS10-841

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