Cold, dry air is heavy, hot, wet air is light

A Φ-saturated wind blowing over a sea with the same T neither absorbs, nor loses, Q or Φ from it. If Φ saturated air is above a colder sea, _L.H₂O condenses out of the air onto the sea- some of the LQ usually remains in the air. The energy which binds salt to pure _L.H₂O in sea water is on the order of 1 kCal per kg _L.H₂O. A warm, dry wind must spend an extra kCal for ever kg _L.H₂O it evaporates. Air saturated with Φ condenses more easily onto salty than onto fresh water as it gets that kCal/kg back

If dry air and the sea below it both have the same T, then Φ, together with its LQ, can evaporate out of the sea into the air without changing the T of either -if the sea's T is kept constant by solar energy falling onto it. The solar heating of the sea water is then equal to the LQ in Φ evaporating off it. If dry, and saturated, air have the same P and T, the dry air is heavier. This is shown in Table 2. At 1atm (bar) and 20°C, the density of saturated wet air, r sat, is 1.188 kg/m³, r of dry air is 1.198 kg/m³. Φ evaporating off of the ocean thus tends to mix with surrounding cooler, dryer air and rise up through it in invisible bubbles and plumes. The rising moist air expands and cools as it rises to greater heights.

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