
The impact of water vapor on afternoon rainfall - dnetesn
https://phys.org/news/2020-05-decoding-impact-vapor-afternoon-rainfall.html
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mikhailfranco
This rambling account may not do justice to the original research, but I found
it just another example of how naive ML correlations find it
impossible/difficult/laborious to re-discover basic platitudes of a specialist
field.

If you discretize features from a continuous domain, like space-time chunking
of "afternoon rain", then it will degenerate into a hybrid CNN-RNN ML system.
Wet soil in the morning will depend on "overnight rain" and "morning dew".
Then "overnight rain" might suppress afternoon rain, if it drains moisture
from the atmosphere etc. etc. There will be various spatial and temporal
influences expressed as Bayesian priors.

One fact that I found surprising when I first heard it, but within 10 seconds
realized was obvious, is that water is lighter than air (N2 O2 v. H2O). I
imagined that clouds need convection currents from hot land causing
temperature gradients, for moisture to rise into cooler layers, then condense
and rain. But water (MW 18 g/mol) is lighter than air (MW 29 g/mol), so it
just rises and rains (unless there is a temperature inversion anti-convection
barrier). I imagine many such 'obvious' facts of fluid dynamics that elude CS
ML hammer-nail practitioners.

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stirbot
Sadly the active radar sensor on the pictured SMAP satellite failed shortly
after launch [0]. I've been looking for news on NASA's NIAC Phase 2 R-MXAS
studies which, while it looks like it would require some serious material
science breakthroughs, could provide near-continuous soil moisture data over
an entire continent which suddenly seems even more useful [1].

[0] [https://www.nasa.gov/press-release/nasa-soil-moisture-
radar-...](https://www.nasa.gov/press-release/nasa-soil-moisture-radar-ends-
operations-mission-science-continues)

[1]
[https://www.nasa.gov/directorates/spacetech/niac/2019_Phase_...](https://www.nasa.gov/directorates/spacetech/niac/2019_Phase_I_Phase_II/Rotary_Motion_Extended_Array_Synthesis/)

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lolc
I can rationally appreciate that creating a weather model is an iterative
process but still it does weird me out that something as basic as this is
being actively researched. Even after reading this I still have trouble saying
"we're just figuring out how moist air leads to precipitation".

~~~
wcarss
"Over the Southern Great Plains, we found that when the wind brings less
moisture, dry soils are associated with increases in rainfall amount; and when
the wind brings greater moisture, wet soils are associated with increases in
rainfall amount. In the current study, we find that, actually, in many
regions, the opposite is true for the likelihood of afternoon rainfall," Welty
said.

I'm certainly surprised that it's _so_ nuanced as to be completely the
opposite in different areas.

