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JimboOmega

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Triple Point Of Water
« on: May 12, 2016, 11:14:15 PM »
I've been pondering arctic phase changes and etc for a while and kept getting confused by one thing...

If you have an ice floe or similar condition of both ice and liquid existing close to the freezing point, you also have water vapor existing, right?  But as I understand the usual phase diagram, in normal conditions (e.g., ~100kpA/1ATM pressure) you should only have liquid and solid states, the triple point being much lower.

What am I missing?

What I ultimately want to know is the equation for the water vapor capacity of air vs temperature even well below 0C.

Another thing I've  been pondering, and quite related, is where the extra heat goes as one approaches a state where the arctic is increasingly ice free (since it doesn't go into melting the ice any more). The sun shines on the water and it absorbs heat (in the summer).  Presumably it loses heat to the atmosphere via evaporation, albeit at a much lower rate than would be the case in the tropics, but is this a meaningful number? And even if it is, where else can that heat go?  I assume the extra longwave radiation is not that significant. 

In other words, how much heat could be retained in the cryosphere season-to-season? 

ktonine

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Re: Triple Point Of Water
« Reply #1 on: May 13, 2016, 12:40:06 AM »
Jimb0 - I think you're misreading your references.  The triple point of water is 32F or 0C.  The pressure of interest is not atmospheric pressure, but the partial pressure.

Quote
Even if the total pressure of a system is well above triple point of water, provided the partial pressure of the water vapor is 611.657 pascals then the system can still be brought to the triple point of water.

oren

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Re: Triple Point Of Water
« Reply #2 on: May 13, 2016, 11:12:47 AM »
I've been pondering arctic phase changes and etc for a while and kept getting confused by one thing...

If you have an ice floe or similar condition of both ice and liquid existing close to the freezing point, you also have water vapor existing, right?  But as I understand the usual phase diagram, in normal conditions (e.g., ~100kpA/1ATM pressure) you should only have liquid and solid states, the triple point being much lower.

What am I missing?

What I ultimately want to know is the equation for the water vapor capacity of air vs temperature even well below 0C.

Another thing I've  been pondering, and quite related, is where the extra heat goes as one approaches a state where the arctic is increasingly ice free (since it doesn't go into melting the ice any more). The sun shines on the water and it absorbs heat (in the summer).  Presumably it loses heat to the atmosphere via evaporation, albeit at a much lower rate than would be the case in the tropics, but is this a meaningful number? And even if it is, where else can that heat go?  I assume the extra longwave radiation is not that significant. 

In other words, how much heat could be retained in the cryosphere season-to-season?

The heat goes into the ocean, some of it on the surface only to be gone by winter heat loss, some of it in the deeper layers where it builds and builds until one day it is pumped upwards (wind/cyclone/whatever) and melts the ice.

Nightvid Cole

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Re: Triple Point Of Water
« Reply #3 on: May 13, 2016, 06:45:16 PM »
I've been pondering arctic phase changes and etc for a while and kept getting confused by one thing...

If you have an ice floe or similar condition of both ice and liquid existing close to the freezing point, you also have water vapor existing, right?  But as I understand the usual phase diagram, in normal conditions (e.g., ~100kpA/1ATM pressure) you should only have liquid and solid states, the triple point being much lower.

What am I missing?

It is the PARTIAL PRESSURE of the water vapor that must be at the triple point, not the total pressure.

What I ultimately want to know is the equation for the water vapor capacity of air vs temperature even well below 0C.

Google "vapor pressure of water". Again we are dealing with partial pressure.

Another thing I've  been pondering, and quite related, is where the extra heat goes as one approaches a state where the arctic is increasingly ice free (since it doesn't go into melting the ice any more). The sun shines on the water and it absorbs heat (in the summer).  Presumably it loses heat to the atmosphere via evaporation, albeit at a much lower rate than would be the case in the tropics, but is this a meaningful number? And even if it is, where else can that heat go?  I assume the extra longwave radiation is not that significant. 

In other words, how much heat could be retained in the cryosphere season-to-season?

Mostly into warming the upper Arctic Ocean water. And a portion, but not all, of that heat will be released into the atmosphere in the early freezing season following the near ice free summer.