Weather is.... • The current state of the atmosphere...what is happening right now
Main points to remember as we learn about weather: • The sun warms the earth’s surface and therefore all the air above the surface • The earth is warmed most at the equator and least at the poles---why? • The air above land is warmed more quickly than air above water. • Warm air expands and rises, creating an area of low pressure • Cold air is dense and sinks, creating an area of high pressure
Weather Factors • Weather: The state of the atmosphere at a specific time and place TEMPERATURE= the average motion of molecules ↑TEMP= ↑movement of molecules= feels hot ↓TEMP= ↓movement of molecules= feels cold
Air Pressure • Warm air • expands and rises • leaves behind Low pressure • Cold Air • contracts and sinks • leaves an area of High pressure
Wind Movement • Uneven heating of the earth’s surface causes some areas to be warmer than others. • Warm always follows cold to share it’s warmth- when this happens in the atmosphere, wind happens!
What causes winds? • Wind is movement of air from an area of high pressure to an area of low pressure • It is this difference in pressure that makes the air move = wind
What causes winds? • Winds are measured by direction and speed • An anemometer is the tool we use to measure wind speed • Wind chill= ↑ cooling the wind causes
Local Winds • Land cools and heats faster than the ocean. • Water holds heat longer than land, and takes longer to heat or cool.
Sea Breeze • During the day, the land gets hotter faster than the water. • The heated air rises, leaving behind an area of low pressure. • Wind from the cooler sea blows in to take the place of that warmer air. • These happen during the day!
Land Breezes • At night, lands cools off faster than the sea. • Cool air sinks creating an area of high pressure. • Wind blows from the land to the sea.
Global Circulation and Wind Systems • Solar energy is at its greatest around the equator---Why?
Global Winds: • Wind belts: Horse Latitudes= 30°N and S of equator =calm winds= worlds desert areas Jet Streams= 10km above the surface blow from the west to the east
Intense heat = Powerful CONVECTION • Warm, moist air rises and leaves behind an area of low pressure. This is why most rain forests are found along the equator. • That air rises until it reaches the top of the troposphere, where it can’t rise any further. • It spreads out towards the polar regions HOT follows COLD wanting to share its warmth. • As it spreads it begins to cool and sink-usually 30°N and S of the equator- sinking air produces an area of H pressure with dry conditions= desert regions on earth
Some or the air moves back towards the equator as it sinks... • Tradewinds: Where do you think they got their name? Who were these winds particularly important to?
There was an area that sailors avoided with their lives... • THE DOLDRUMS... is the area around the equator where the wind completely dies out... which meant death as soon as the fresh water ran out.
Water in the Atmosphere: Humidity • Humidity: measure of the amount of water vapor stuck between molecules in the air. The air’s ability to hold water depends on the air temp • The hotter the air, the more water the air can hold • Cold air: molecules move slower so droplets of water can start to stick together=condensation • Relative humidity: the amount of water vapor(%) compared to the amount the air can hold- tool used is a psychrometer. • 100%=air is saturated
Cloud Formation • Clouds form when water vapor condenses on dust, salt particles in the air • The temperature in which condensation begins is called the dew point
TYPES OF CLOUDS • Cirrus Clouds: wispy, feathery clouds Form only at high levels, therefore are made of ice crystals
Types of Clouds • Cumulus Clouds: are puffy white cotton ball looking clouds
Cumulonimbus Clouds • These are thunderstorm clouds
Types of Clouds • Stratus Clouds: clouds that form in flat layers- cover all or most of the sky and are low level clouds
Air Masses • Air masses are masses of air that have the same characteristics of the surface over which it develops • Pressure Systems descending (going down)=H pressure ascending (going up)=L pressure
Fronts: the boundary between 2 air masses • Warm Front • warm air slides over cold air • large bands of precipitation form This is the symbol on a map for a warm front
Cold Fronts • Cold air pushes under a warm air mass. • Warm air rises quickly • Narrow bands of violent storms form This is the symbol for a cold front
Occluded Front • 2 air masses merge and force warm air between them to rise quickly. • Strong winds and heavy precipitation will occur This is the weather map symbol for an occluded front
Stationary Front • Warm or cold front stops moving • Light wind and precipitation may occur across the front boundary This is the weather map symbol for a stationary front
Reading a weather map • ISOBAR= connects areas of equal pressure BAR comes from BARometric pressure
Reading a weather map... • Isotherm: Connects areas of equal temperature; therm means temperature