Weather Unit Study Guide

Weather: the condition of the atmosphere at a particular place and time
Climate: the average, year-after-year conditions of temperature, precipitation, winds, and clouds in an area
•	Primarily determined by temperature and precipitation
Climate Region: a large area with similar climate conditions all throughout
Microclimate: a much smaller area where the climate may be different than its general climate region due to factors such as presence of mountains, coastal regions, open space, etc.
Temperature: 
•	Mainly affected by latitude, altitude, distance from large bodies of water, and ocean currents
Precipitation: 
•	Mainly affected by prevailing winds and presence of mountains
•	Precipitation falls on the windward side of the mountains, the side the oncoming wind hits. By the time the air reached the other side of the mountains, it has lost much of its water vapor, so it is cool and dry. The land on the leeward side of the mountains-downwind- is in a rain shadow.
Polar Zone: 66.5 to 90 north, 66.5 to 90 south
Temperate Zone: 23.5 to 66.5 north, 23.5 to 66.5 south
Tropical Zone: 23.5 north to 23.5 south
Ocean Current: A certain direction that seawater flows in a particular area
Diagram of Ocean Currents:

Main Layers of the Atmosphere:
•	Troposphere: 
•	The lowest layer (surface of the Earth)
•	For every 1 km. increase in altitude, the air gets 6.5 degrees C cooler
•	Stratosphere
•	Extends from the end of the troposphere (the tropopause) to about 50 km. above the earth’s surface
•	The upper stratosphere is warmer than lower stratosphere due to the presence of ozone, which helps maintain more heat energy
•	The lower stratosphere is about -60 degrees C
•	Mesosphere
•	The middle layer of the atmosphere
•	Extends from 50km. above the earth’s surface to 80 km.
•	Protects the earth from objects from out of space
•	Shooting stars are meteoroids that burn up as they reach the mesosphere
•	Thermosphere
•	Two layers- ionosphere and exosphere
~ Ionosphere starts at 80km. and ends at 550 km.
~ The Aurora Borealis, or ‘Northern Lights’ occur in the ionosphere
~Exosphere starts at 550km. and extends outwards into space (no defined limit)
•	Very hot, close to 1,800 degrees C
High Pressure Systems: Air moving downward creates high pressure and rotates clockwise. 
•	Clouds don’t form in high pressure (fair weather)
Low Pressure Systems: Air moving upward creates low pressure and rotates counterclockwise
•	Clouds form (contributing to rainy or stormy weather)
Wind: Horizontal movement of air across the earth’s surfaces 
•	Named based on the direction it comes from
•	Ex. Westerlies travel from west to east
Air Mass: A body of air that has certain characteristics all throughout
•	Humidity and temperature are the two main characteristics used for classification
•	Its first name is based on humidity
•	Maritime: Humid (wet) air masses that form over oceans
•	Continental: Drier air masses that form over land
•	Its last name is based on temperature
•	Polar: Cold air masses from the north
•	Tropical: Warmer air masses from the south
•	Ex. A maritime tropical air mass forms over warm ocean water and is moist and warm.
Weather Front: The area where two or more air masses meet and don’t mix; a boundary between two or more air masses
•	There are four types of fronts
•	Cold Front: Fast moving cold air runs into a slow moving warmer air mass; the cooler air slides under the warmer air and pushes the warmer air upward
•	Warm Front: Warm air mass collides with a slow moving cold air mass; warm air is less dense and so moves over the cooler air 
•	Stationary Front: Cold and warm air masses meet, without either air mass being moved by the other
•	Occluded Front: A warm air mass is caught between two cooler air masses and is lifted above them
Air Pressure: the force air exerts on everything else
•	It creates wind
•	It creates clouds
•	It gives clues about what will happen next
•	Air is mostly made up of nitrogen (78%) and oxygen (21%)
•	Air pressure depends on the number of air molecules and how fast they are moving
•	Pressure is greater at lower levels because the air’s molecules are squeezed under the weight of the air above 
•	Millibars are a direct pressure measurement
•	Air pressure decreases as altitude increases
•	Winds are stronger where the high and low pressure systems are close together
How strong winds will be and where they will blow is determined by 3 factors:
•	Pressure Gradient Force (PGF): To forecast winds, meteorologists note the size of the pressure difference and the distance between the high and low pressure areas
•	Friction: As winds blow near the surface of the earth, it rubs against trees, hills, buildings, and other objects that slow it down. There is less friction over water than over land. 
•	Coriolis Effect: If the earth was not spinning, then the wind would blow straight from high pressure to low pressure and die down when the pressures equalize. But the earth is spinning, which is why winds curve as they blow. This curving motion is called the Coriolis Effect. 
Cloud: a visible mass of condensed water vapor floating in the atmosphere, typically high above the ground
•	Fog is a type of cloud!
Clouds are categorized by:
•	Shape 
•	Height
•	What they do
Shape:
•	Cirrus: Thin, wispy
•	Cumulus: Puffy, Billowy
•	Stratus: Flat, sheet-like
Height:
•	Cirro-: High clouds above 20,000 feet above sea level
•	Alto-: Middle level- 6,000 to 20,000 feet above sea level
What They Do
•	Nimbo-, -nimbus: Clouds that bring precipitation