Jump to content

Welcome to our forums!

Sign In or Register to gain full access to our forums. By registering with us, you'll be able to discuss, share and private message with other members of our community.

Welcome!

Thanks for stopping by the Weather Forums! Please take the time to register and join our community. Feel free to post or start new topics on anything related to the weather or the climate.


Photo

Bizarre science fiction hypothetical


  • Please log in to reply

#1
Redsheep

Posted 05 June 2017 - 07:04 AM

Redsheep

    Forum Newbie

  • Members
  • Pip
  • 4 posts

So, I'm a science-fiction writer, and I've got a weird one here: suppose you've got a planet that's mostly barren, with viable atmosphere, etc. conditions confined to a series of extremely deep rifts and depressions.  Within those depressions, basically normal earthlike conditions prevail, so 21% oxygen, abundant water.  They're up to sixteen kilometers deep, and outside of them the atmosphere as I conceive of it is quite rarified (i.e. top of Everest conditions).  Of course, I am not a meteorologist, which is why I'm here, so possibly my picture there is implausible.  For full disclosure, in case it matters, the planet is half earth mass, 80% earth gravity.  The contiguous region of rifts and basins I am concerned with makes up ten percent of its surface, but spread out over most of a hemisphere (picture a gigantic spiderweb).

 

This is awkward without a map, but basically the "spiderweb" is divided in half, north to south, and those halves connected by a three thousand kilometer rift (closer to 2200 north-to-south, since the rift winds a lot).  At either end of the rift stand two large basins; the southern one is roughly the size of Peru, with many connections to other basins, while the northern is more Iran-sized.  The southern basin straddles the planet's equator and has a large sea in it.  The northern also has a significant sea, but is naturally much cooler.  An artificial canal runs through the connecting rift for trade purposes.

 

Now, by my primitive understanding of climate science, the southern basin should have much lower air density than the northern due to its receiving far more solar radiation.  The differential will cause the basin to suck cold air through the connecting rift like a straw, generating a constant cool wind.  Once that wind hits the warmer air in the south, it will precipitate moisture in the air, making the spot where the rift meets the southern basin extremely rainy.  I'm guessing, based on vague intuition alone, that the overall balance of air in the system will then be maintained by the warmed air returning along the rift it came from, but at a significantly higher elevation.  Is any part of this plausible?

 

Sorry for making it so complicated.  This isn't the sort of thing I can just consult library books about, obviously.  Thanks for reading!


  • iFred, happ and tenochtitlan like this

#2
Redsheep

Posted 10 June 2017 - 06:01 PM

Redsheep

    Forum Newbie

  • Members
  • Pip
  • 4 posts

. . . I take it there are too many unknowns to even guess?  I understand that meteorology depends on a billion different factors, changing one slightly can produce drastically different results, and I've changed dozens with this scenario.  That would be good news for me too, as a science-fiction author with only a broad general knowledge of science.  I love "plausible deniability."  But is that the case?



#3
wx_statman

Posted 05 July 2017 - 09:29 PM

wx_statman

    Advanced Member

  • Members
  • PipPipPipPipPipPip
  • 3491 posts
  • LocationPortland, OR

. . . I take it there are too many unknowns to even guess?  I understand that meteorology depends on a billion different factors, changing one slightly can produce drastically different results, and I've changed dozens with this scenario.  That would be good news for me too, as a science-fiction author with only a broad general knowledge of science.  I love "plausible deniability."  But is that the case?

 

You could always just make a bunch of stuff up and make it sound good. I'm thinking Douglas Adams and the Hitchhiker series. I don't think he had any training in the sciences either?



#4
wx_statman

Posted 05 July 2017 - 09:38 PM

wx_statman

    Advanced Member

  • Members
  • PipPipPipPipPipPip
  • 3491 posts
  • LocationPortland, OR

So, I'm a science-fiction writer, and I've got a weird one here: suppose you've got a planet that's mostly barren, with viable atmosphere, etc. conditions confined to a series of extremely deep rifts and depressions.  Within those depressions, basically normal earthlike conditions prevail, so 21% oxygen, abundant water.  They're up to sixteen kilometers deep, and outside of them the atmosphere as I conceive of it is quite rarified (i.e. top of Everest conditions).  Of course, I am not a meteorologist, which is why I'm here, so possibly my picture there is implausible.  For full disclosure, in case it matters, the planet is half earth mass, 80% earth gravity.  The contiguous region of rifts and basins I am concerned with makes up ten percent of its surface, but spread out over most of a hemisphere (picture a gigantic spiderweb).

 

This is awkward without a map, but basically the "spiderweb" is divided in half, north to south, and those halves connected by a three thousand kilometer rift (closer to 2200 north-to-south, since the rift winds a lot).  At either end of the rift stand two large basins; the southern one is roughly the size of Peru, with many connections to other basins, while the northern is more Iran-sized.  The southern basin straddles the planet's equator and has a large sea in it.  The northern also has a significant sea, but is naturally much cooler.  An artificial canal runs through the connecting rift for trade purposes.

 

Now, by my primitive understanding of climate science, the southern basin should have much lower air density than the northern due to its receiving far more solar radiation.  The differential will cause the basin to suck cold air through the connecting rift like a straw, generating a constant cool wind.  Once that wind hits the warmer air in the south, it will precipitate moisture in the air, making the spot where the rift meets the southern basin extremely rainy.  I'm guessing, based on vague intuition alone, that the overall balance of air in the system will then be maintained by the warmed air returning along the rift it came from, but at a significantly higher elevation.  Is any part of this plausible?

 

Sorry for making it so complicated.  This isn't the sort of thing I can just consult library books about, obviously.  Thanks for reading!

 

From what I understand, you're basically describing a variation of the Hadley Cell/ITCZ. At the ITCZ, air converges and lifts, and constant year-round convection results as the air rises and condenses. It cools and dries, and travels north and south away from the equator at high altitude before descending in the subtropical latitudes. It then travels back toward the equator/ITCZ via the trade winds, which are deflected due to the Coriolis force (which is why they don't blow straight toward the equator). They converge and lift at the ITCZ, starting the process all over. This circulation is known as the Hadley Cell. 



#5
Redsheep

Posted 06 July 2017 - 06:03 AM

Redsheep

    Forum Newbie

  • Members
  • Pip
  • 4 posts

Thank you very much!  It sounds like this is at least plausible enough that any readers with a meteorology background won't roll their eyes with disgust and throw the book across the room.  Would you expect anything in particular to happen when the circuit is completed--when the warm air streaming north at high altitude sinks back down?  Would the meeting of hot and cold make it rainy at the top end as well?



#6
wx_statman

Posted 06 July 2017 - 04:17 PM

wx_statman

    Advanced Member

  • Members
  • PipPipPipPipPipPip
  • 3491 posts
  • LocationPortland, OR

Thank you very much!  It sounds like this is at least plausible enough that any readers with a meteorology background won't roll their eyes with disgust and throw the book across the room.  Would you expect anything in particular to happen when the circuit is completed--when the warm air streaming north at high altitude sinks back down?  Would the meeting of hot and cold make it rainy at the top end as well?

 

No, when the air descends back down in the subtropical latitudes (around 25-35 degrees latitude on either side of the equator) it creates a stable and dry environment.

 

I didn't properly explain what happens to the air when it rises and cools at the Intratropical Convergence Zone (ITCZ). The air parcels expand and cool as they rise higher. Eventually the dropping temperature meets the dewpoint, and the water content in the air parcel condenses into liquid form. This falls downward as rain. So when I said the air "cools and dries" it was quite a shortcut on my part!

 

These cool air parcels stream north and south away from the equator at high altitude before descending as explained before. When air parcels descend, they begin to contract - get smaller - as they encounter higher and higher pressure on their way down into the lower atmosphere. This compression pushes the air molecules closer together and causes "compressional heating," also known as adiabatic warming. When this air reaches the surface, it is warm (from the descent) and dry (after having dropped its water content as rain earlier). That is why you see most of the world's deserts in the subtropical zone around latitude 25-35. Think Sahara, the Australian outback, northwestern Mexico, etc. Descending air, by its nature, isn't conducive to precipitation since it already dropped its water on its way up, earlier.

 

I hope that clears things up a little bit. 



#7
Redsheep

Posted 06 July 2017 - 07:54 PM

Redsheep

    Forum Newbie

  • Members
  • Pip
  • 4 posts

Yes, thank you.  The picture is complicated here by the planet not being earthlike; since the terrain is broken up into modest-sized blocks, really enormous weather patterns can't form.  I imagine this would also mean greater extremes in local climate, since you can't have moderating effects like the Gulf Stream on the same scale.  So the northernmost basin is much cooler than it would be on Earth at equivalent latitude, etc.



#8
Swayseeker

Posted 20 July 2017 - 01:15 PM

Swayseeker

    Forum Newbie

  • Members
  • Pip
  • 5 posts

Air with a lower density will rise, but if the pressure exerted by the less dense air is the same as the pressure of the surrounding air, which it usually is, air cannot rush in to the space occupied by the less dense air. For instance if you warm up the air in a house to hundreds of degrees above outside temperature, the air is far less dense inside, but the molecules are moving faster and the pressure inside the house is the same as that outside if you keep windows open. Air does not move into the house (except for some mixing, etc).