Download NSTA Meteorology Reading 8 • Weather`s Central Actor: Water

NSTA Meteorology Reading 8
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Weather’s Central Actor: Water
‣ Water is the only substance on Earth that naturally occurs in all three states (solid,
liquid, and gas)
‣ Liquid water covers nearly ⅔ of Earth’s surface
‣ Water, in one form or another, affects almost all living and nonliving things
‣ The total quantity of water in all forms in Earth’s hydrosphere is constant
- Hydrologic Change aka The Water Cycle
‣ Water evaporates or transpires into the atmosphere
‣ In the atmosphere, it condenses and returns to Earth’s surface as precipitation
‣ May be temporarily stored in glaciers, lakes, underground reservoirs, or living things
before returning to bodies of water or transpiring or evaporating back to the
atmosphere
‣ Earth’s water: 97% in oceans, 2.2% frozen in ice caps, 0.001% in the atmosphere
‣ The water in the atmosphere is essential for creating Earth’s weather systems and
climate
‣ Relative humidity = measure of moisture content; the amount of water vapor present
relative to the maximum amount of water vapor that can exist at that temperature;
expressed as a percentage of the maximum amount that can exist
‣ Dew point = temperature reached when warm, unsaturated air is cooled and the
amount of water vapor already present will equal the total amount that can exist
- Water’s Chemistry
‣ Behavior of water is attributable to its molecular structure
‣ Water molecule = one oxygen atom and two hydrogen atoms held together by covalent
bonds
‣ Arrangement of atoms within water molecule results in polarity = molecules have
slightly positive and negative charges on opposite sides
‣ Hydrogen bonding results from the attraction between the positively charged side of
one molecule and the negatively charged side of another
‣ Hydrogen bonds largely responsible for properties of liquid water
‣ Hydrogen bonds allow water to absorb or release a significantly greater amount of
thermal energy to change its temperature a certain amount
‣ Specific hear indicates the amount of energy required to change the temperature of the
material
‣ Water absorbs and retains so much thermal energy, that the ocean tends to moderate
Earth’s air temperature and climate
‣ Water has a large latent heat = the amount of energy associated with changes of state;
results from hydrogen bonding
- Water, Precipitation, and Clouds
‣ Condensation nuclei are necessary to decrease the rate of evaporation from the drop
and allow water droplets to grow
‣ When condensation continues, water molecules coalesce into cloud droplets, the
precursors of raindrops and other forms of precipitation
‣ If air mass below the freezing point of water and ice nuclei are present, ice crystals form
and result in hexagonal shapes which may develop in snowflakes
‣ Cloud droplets, supercooled cloud droplets, or ice crystals become visible as clouds
when they form in sufficient numbers
NSTA Meteorology Reading 8
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Type, size, and shape of cloud depends on nature of cloud droplets or ice crystals and
existing atmospheric conditions
Cloud classifications:
* Cirrus (hairlike): high, feathery clouds made of ice crystals
* Stratus (layered): clouds made of water droplets that form in layers
* Cumulus (pile or heap): detached clouds made of water droplets having appearance
of a mound, dome, or tower
* Other prefixes and suffixes added to describe particular cloud formation (ex. Suffix
“nimbus” added when cloud is producing rain or snow)
Precipitation develops within clouds where sufficient numbers of cloud droplets, ice
crystals, or supercooled cloud droplets have formed
Weather phenomena are all directly related to the unique properties of water