Lesson 9 - Measuring Atmospheric Moisture

Water in The Atmosphere

It's a liquid! It's a solid! It's a gas! It's water, the only substance which naturally appears in the atmosphere as any one of the three phases of matter. And what makes these three phases possible is water's molecular polarity.

 

The Structure of H2O

Polar molecules interact with each other via hydrogen bonding, and, as shown on the picture below, water contains enough hydrogen bonds to make it one of the most polar molecules known. Rising and falling temperatures directly influence the exchange of energy between the hydrogen bonds, and this energy plays an important part in local weather, as well as in the general circulation of the atmosphere.

During atmospheric transformations, whether from rain to snow or vapor to fog, a water molecule's hydrogen bonds are assembled, dismantled, and reassembled. In order to make these changes, the molecule must either absorb or release energy. While in most cases, molecules that absorb energy increase their molecular motion and generate heat, most of the initial energy water absorbs is spent breaking up hydrogen bonds in order to regroup them. Temperature, or more specifically, the energy temperature measures, greatly determines whether a water molecule will be able to release enough energy to freeze, or absorb enough energy to melt.

Temperature and Air Moisture

Although it would be easy to assume that ice is water's heaviest, most compact state, in actuality, a water molecule reaches maximum density while still in liquid form, at 39°F (3.98°C). Any change in temperature from 39°F will cause water to lose this maximum density: water increases in volume at either warmer or cooler temperatures. Therefore, since water is present in all the air surrounding the earth, even small changes in air temperatures influence the density of the existing air moisture.

 
Next Page Home