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Does rain wash the sky clean ???


WayBig
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I've noticed when the skies have cleared after rain stars appear brighter and steadier.

At 6am this morning after rain in the night, m42 looked fantastic in my 15x70s and it was so easy to pick out the winter constellations, incl orions bow (I think it's a bow) leo, all of gemini's limbs etc for the first time this year.

So does the rain wash all the crud out of the air?

If so...pray for rain...but only up to about 8pm

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Rain will clear alot of the particles out of the atmosphere at times that can make visibility better.

Generally yes, a good rain shower before darkness, as long as clear cloudless skies is almost a perfect situation.

Edited by Catanonia
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Hi,

When there is a high pressure area over the country you get progressively more stable air and a temperature inversion may occur where there is a layer of warm air above the surface layer which traps the crud from emissions etc in the base layer. If your flying gliders this layer shows as a dark band on the horizon at the height of the inversion.

When a cold front moves through the air-mass changes and becomes unstable allowing convection . There is cold air on the front meeting warm moist air causing rain. So yes the air clears with the rain but its the airmass changing that produces the lovely seeing we want. The rain doesnt wash the air clean.

Hope that helps

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..a third factor is that the moisture in the air itself defracts light causing loss of transparency creating 'skyglow'.. all three effects are real and add to the improvements after rain..

the rain is water vapour removed from the atmosphere

the rain does clear particulate matter

the passing system-front can consolidate a steady airmass

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exactly right...

rain needs particulate matter to form...

same for bubbles in beer glasses.

Try rinsing the inside of a beer glass before pouring....the water fills in much of the roughness of the glass, meaning less bubbles form.

paul

Yes you do need particles for rain to form but there is normally plenty of that.

The reason the rain cant have washed out the particles from the air is that the air with the bad seeing and the post frontal air-mass (cold sector air) are different air-masses. The muck has moved away......

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Brilliant, I ask a question that might, in the wrong company, be seen as a daft question and not only do I get told that It's a sensible question, but I get advised to do further research involving drinking beer.

I love you guys!!!

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The transparency improves with passage of the cold front, every yachtsman knows that. The seeing is another matter altogether unfortunately. Seeing tends to be good when there is a lot of crud in the atmosphere (although that's far from consistent!)

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this is why I stated that a passing front CAN consolidate a stable airmass... the opposite can also be true. :)

The transparency improves with passage of the cold front, every yachtsman knows that. The seeing is another matter altogether unfortunately. Seeing tends to be good when there is a lot of crud in the atmosphere (although that's far from consistent!)
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this is why I stated that a passing front CAN consolidate a stable airmass... the opposite can also be true. :)

Nope....by definition a front is a boundary between different airmasses either cold or warm.

A different airmass cant consolidate anything that it has replaced at that location.

I both sail and instruct glider pilots.

Now if you want to get difficult we could talk about troughs.....

perhaps not:D

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Pedantic twaddle and semantics... the movement of a frontal system leaves in its wake a changed atmosphere.. that can be a 'consolidation' of the airmass characteristics, or a disruption of the atmospheric stability over that location.... whether the air molecules have been replaced by others is irrelevant to the topic of the the perceived improvement of the observed sky over that location.

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Pedantic twaddle and semantics... the movement of a frontal system leaves in its wake a changed atmosphere.. that can be a 'consolidation' of the airmass characteristics, or a disruption of the atmospheric stability over that location.... whether the air molecules have been replaced by others is irrelevant to the topic of the the perceived improvement of the observed sky over that location.

Just trying to help.

When a front goes through the air mass changes, the pressure changes, the temperature changes, the air quality changes , the wind direction changes. The only constant is the partial pressures of gasses making up the air but thats not consolidation......

Well as they say in Dragons Den.....I'm Out.

Hope the original post found it usefull and enjoys his beer:D

Edited by Bigwings
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For all you beer drinkers ,PS sorry to go off the subject of rain, When you pour a pint of Guinness do the bubbles go up or do they go down.

Locally relative to the stout around the bubbles, the bubbles *always* rise. However, as the currents in the stout mean that there is an 'eddy' at the sides of the glass, the stout is sinking faster than the tiny bubbles can rise, giving the appearance of sinking bubbles.

Picture trying to walk up a down-escalator, you are moving up relative to the steps, but you might be actually going down relative to the floors..

Back on topic, when there's a decent cold front after passing, the cold air mass is usually much less in water content, and given that the airmass would have originated over either ice or water, it'll have much less particulates than a usually warmer airmass that originated over e.g. the Sahara or Europe. This means less skyglow, and less scatter from particulates.

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