Discussion On Water and Atmospheric Moisture

Discussion On Water and Atmospheric Moisture
John Aubert ( American River College Water and Atmospheric Moisture
Physical Geography Lecture Notes Page 3 of 7
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Water and Atmospheric Moisture
I. Introduction – (What causes precipitation?): One of the fundamental questions we will answer in the next few sections is ” What causes precipitation?” This is a complex and involved process, but involves some major, important steps. Start at the bottom…
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II. Distribution of Water on Earth: See chart in book; notice that most water (by far) is in the oceans. The main point here is that oceans have an enormous effect on Earth’s climate and weather.
III. Changes of Phase of Water: Water exists in three states, and routinely changes between these states. This is called “change of phase.” Heat energy (called latent heat) is either absorbed or released during the changes of phase of water.
Change of Phase of Water
A. Hydrogen Bonds: The hydrogen atoms in water molecules are naturally attracted to each other by a phenomenon called hydrogen bonding. Ice has incredibly strong hydrogen bonds which progressively break as melting and evaporation occur. Keep in mind that it takes energy to break these bonds and keep them broken.
B. Latent Heat (or “Hidden” Heat): Latent heat is the energy which breaks the bonds. It holds the water and vapor molecules apart.
1. Melting and Evaporation (called cooling processes):
-Hydrogen Bonds break during these processes!
-The water must absorb latent heat in order to break the bonds and keep them broken. We say that the latent heat is “hidden” in the water in this process.
-Because the heat energy must be “taken” from the air or land in order to break the hydrogen bonds, the air or land cool down.
-For this reason these processes are called “cooling processes”.
2. Condensation and Freezing (called warming processes – sometimes):
-Hydrogen Bonds formed during these processes!
-The water must release (or let go of) the latent heat in order to form the bonds.
-Since the energy is “given” to the air or land, warming occurs.
-For this reason these processes are called “warming processes”.
IV. Humidity: Defined as the water-vapor content of the atmosphere.
A. Saturation (filled to capacity w/ water vapor): Air has a finite (limited) capacity to hold water vapor. When air is filled to capacity with water vapor, it is said to be saturated.
B. Relationship Between Saturation