Topic VI “Meteorology”Weather Studies

I. Moisture in the Atmosphere: the primary source of energy for the water cycle is the Sun. It unevenly heats Earth’s surface.

A. Phases of the Water Cycle:

1. Evaporation: liquid to gas. Requires energy making it a cooling process.

2. Condensation: gas (water vapor) to a liquid. Releases energy into the air.

3. Transpiration: the releasing of water in the air by plants.

4. Precipitation: the falling of liquid or solid water from clouds.

Ex. Rain, sleet, snow and hail.

B. Factors Affecting Evaporation Rate:

1. Temp.: as temp. inc. evap. rate inc.

2. Humidity: as humidity inc. evap. rate decreases.

3. Wind: as wind inc. evap. rate inc.

4. Surface Area: as surface area inc. evap. rate increases.

C. Relative Humidity: a comparison between the amount of moisture in the air with the amount that the air can hold at that temp.

1. Dewpoint Temp.: the temp. at which condensation occurs.

* dew: drops of water forming on a cool surface.

* frost: water vapor freezes (sublimates) on a frozen surface.

2. Sling Psychrometer: instrument used to determine the dewpoint temp. and relative humidity.

3. Steps to determine Dewpoint:

a. Find dry bulb temp.

b. Find the diff. Between the wet and dry bulb temps.

c. Use the chart on page 12 of the ref. Table.

D. Clouds: collection of tiny water droplets or ice crystals suspended in the atmosphere.

1. Cloud Formation:

a. Warm moist air rises.

b. Air cools below dewpoint temp. and droplets form around condensation nuclei (dust/salts).

2. Cloud Types:

a. Cumulus: big puffy white clouds.

b. Cirrus: whispy ice crystals high in the atmosphere.

c. Stratus: low clouds that blanket the sky.

II. Air Pressure: the force/weight of air pushing on a surface. Air pressure pushes in all directions equally. Pg. 13 ref. Table.

A. Barometer: instrument used to measure air pressure.

* As air pressure increases, the barometer rises.

B. Factors Affecting Air Pressure:

1. Temperature: as temp. increases, air pressure decreases.

2. Altitude: as altitude increases, air pressure decreases.

3. Humidity: as humidity increases, air pressure decreases.

C. Winds: caused by differences in air pressure. The greater the difference (gradient) the stronger the winds.

1. Isobars: connect points of equal air pressure.

*the closer the isobars the stronger the winds.

D. Local Breezes: smaller horizontal movement of air .

1. Sea breeze: air flows from the sea to the land.

*cooler air (high pressure) over the sea, flows towards warmer air (low pressure) over the land.

2. Land breeze: air flows from the land to the sea.

* Air over the land cools at night and flows towards the warmer air over the water.

E. Wind Direction: flow from regions of high to low pressure and named for the direction they come from.

1. Cyclone: (low pressure) winds blow counterclockwise towards the middle.

2. Anticyclone: (high pressure) winds blow clockwise and out.

F. Global Winds: caused by the unequal heating of earth’s surface. Page 14 ref. Table.

1. Diverging zones: cool, dry high pressure air sinks at the poles and 300 lat.

2. Converging zones: warm, moist low pressure air rises at the equator and 600 lat.

III. Air Masses: large masses of air that have a characteristic temp. and moisture of their source region. Page 13 ref. table.

A. Source Regions:

1. Maritime: formed over water. (moist)

2. Continental: formed over land. (dry)

3. Polar: cool air from high latitudes

4. Tropical: warm air from low latitudes.

IV. Front: the boundary that separates two different air masses. Pg. 13 ref.

A. Types of Fronts:

1. Cold Front: dense cold air forces warm moist air upward creating heavy precipitation for short periods of time at the frontal boundary.

2. Warm Front: warm air slowly rises over cold air producing long periods of light precipitation ahead of the frontal boundary.

3. Occluded Front: a fast moving cold front over takes a slower warm front causing clouds and precipitation.

4. Stationary Front: cold and warm air masses near each other with neither advancing causing long periods of light precipitation.

B. Synoptic Weather Maps: show weather conditions on a national or global basis.

1. Storm Tracks: most storm systems move from west to east across the U.S.

V. Severe Weather:

A. Hurricanes: a large rotating storm of tropical origin.

*they get their energy from warm water. Once they hit land they lose energy.

Hurricane Eye

B Tornadoes: caused by the collision of warm, moist air with cold, dry air. Winds can exceed 370 mph.

C. Storm Safety:

1. Stay indoors

2. Store food/water

3. Have batteries/flashlights

4. Have a radio