Testing Cloud Seeding

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BillTre
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Here is a Science magazine News Report
on some clever (to me anyway) testing of seeding clouds with Silver Iodine vs. induced snow formation.
 

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davenn
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Here is a Science magazine News Report
on some clever (to me anyway) testing of seeding clouds with Silver Iodine vs. induced snow formation.

where's the report or link to it ? :wink:
 
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BillTre
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Opps.
It be here.
 
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At -45C or colder, especially in relatively still air (no matter how you cut it, the air can hold very little moisture here), we can easily cloud seed by boiling a pot of water, throwing it up into the air... The liquid vaporizes with a loud hiss into tiny droplets that remain super cooled for a time, especially if there is low particulate in the air. It can take a long time to nucleate, and will often form SF (Stratus Fractus) clouds that can deposit rime as it passes objects. Later on, it will drift or fall back to earth as IC (ice crystals). Kids stuff, but still a neat experiment. One time, i created a cloud that drifted over the met compound and became stationary due to shoreline effect, thus raising the official temperature by 6 degrees locally... I said it wasn't me...
 
  • #5
I will also add, cloud seeding, while possibly important in some areas, poses an ethical question in some geographic regions. Towards the poles, particularly in very cold weather (<40C), we see a temperature rise that is remarkable and is most drastic with low cloud. What happens here is the cloud traps radiation from the earth, warming the air. This can be an increase by as much as 10-12C at (-47C to -50C) initial temperature. This is the obvious reason we see a a ten degree warming trend in dark season in the arctic (open water~more low cloud cover). Back in the 40s the Americans did a lot of work in cloud seeding in the Canadian Arctic, I expect they abandoned it for this reason alone... (the increase in temperature I mention in my last post is due to this heat trapping).
 
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At -45C or colder, especially in relatively still air (no matter how you cut it, the air can hold very little moisture here), we can easily cloud seed by boiling a pot of water, throwing it up into the air... The liquid vaporizes with a loud hiss into tiny droplets that remain super cooled for a time, especially if there is low particulate in the air. It can take a long time to nucleate, and will often form SF (Stratus Fractus) clouds that can deposit rime as it passes objects. Later on, it will drift or fall back to earth as IC (ice crystals). Kids stuff, but still a neat experiment. One time, i created a cloud that drifted over the met compound and became stationary due to shoreline effect, thus raising the official temperature by 6 degrees locally... I said it wasn't me...
Interesting. Could it be done at high altitude (say 5-10 km), where temperatures are lower and there are probably not enough particles for clouds to form? A high cloud may also last longer, especially if it borders or is inside the stratosphere.
 
  • #7
Interesting. Could it be done at high altitude (say 5-10 km), where temperatures are lower and there are probably not enough particles for clouds to form? A high cloud may also last longer, especially if it borders or is inside the stratosphere.
Absolutely. I am not sure how practical it is, however. The higher we go, especially in dry air, the more likely the frozen precipitation will sublimate before it becomes a liquid or if it warms, evaporates before it hits the ground. We also have the problem of generally much higher wind velocity in the air columns. When we go very high (45,000 feet or higher), we risk forming nacreous clouds which are a very very bad thing. Nacreous clouds work as a catalyst for ozone destruction that leave gaping holes where they form!

But ice crystals do form at the altitudes you mentioned, and higher. Super cooled water nucleates on dust particles... sometimes can fall to earth (such as in cold climes). Often the dust for nucleation is from sandstorms in Africa, or volcanic activity somewhere in the world. The is actually quite a bit of particulate up there.
 

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