•Air Pressure: The weight of the air in the atmosphere pressing down.

•At sea level the air pressure is

1013.2 mb (millibars) = 1 atmosphere

1 atmosphere = 14 lbs of air pressured per 1 square inch.

How is air pressure Measured?

• Barometer:Instrument that

measures air pressure.

Air pressure units can be in inches and millibars.

Characteristics of High and Low Pressure

• High Pressure– Cooler

–

– Dry

– Associated with clear skies and cooler temperatures.

• Low Pressure– Warm

–

– Humid/moist

– Associated with stormy, cloudy, rainy weather.

When air pressure is falling a storm is approaching.

• In a high the winds move out and clockwise

• In a low they move in and counter clockwise.

• Wind move from high pressure to low pressure

Wind Blows from areas of High Pressure to AreasOf low pressure

Wind speed: The greater the difference in air pressure the faster the wind speed. Wind moves from areas of high pressure to areas of low pressure.

This is shown with closely spaced isobars.

Isobars are lines on a map that connect points of equal air pressure

Sea Breeze: Sea Breeze:

During the day, the During the day, the land land warms up faster than the warms up faster than the waterwater..

The warm air (Low pressure) over the land The warm air (Low pressure) over the land rises, rises, while the cooler air while the cooler air (High Pressure air) over the water (High Pressure air) over the water sinks sinks down and moves in to replace down and moves in to replace the warm air. the warm air.

Land Breeze:Land Breeze:At night, dry land At night, dry land cools cools faster than water, Since the land cools faster faster than water, Since the land cools faster

than the water, the air above the water is now than the water, the air above the water is now warmer warmer and less and less dense dense than the air above the dry land. The Low pressure air over the water than the air above the dry land. The Low pressure air over the water rises and the high pressure air over the land sinks and blows from the rises and the high pressure air over the land sinks and blows from the land to the sea.land to the sea.

How is wind measured?

Anemometer: Measures wind speed

Wind Vane: Shows the direction of the wind

INSOLATION: INCOMING SOLAR RADIATIONThe sun is the main source of energy for Earth. The transfer of heat and light from the sun is called radiation.

Isotherms are lines on a map that connect points of equal Air temperature.

Evaporation

Condensation

Precipitation

Evaporation

• When water absorbs enough heat energy it will change state and become water vapor.

• Most water is evaporated for the oceans and large lakes.

Factors that increase the rate of evaporation• Increased Heat: more heat more evaporation• Increased Wind: Wind provides a steady supply of dry air• Surface area: The more surface area exposed to the heat, more water will

evaporate.• Water will evaporate faster on a warm, dry, windy day

Humidity: Refers to the amount of water vapor in the air.Relative humidity (%): compares the actual amount of water vapor in the air with the amount of water vapor the air can hold.

Saturated Air: When the air cannot hold any more water vapor. 100 % humidity.

* Warm air can hold more water vapor than cold air.

Condensation

• When water vapor rises to cooler temperatures in the atmosphere and condenses back into a liquid.

• Condensation droplets stick to tiny dust particles to form clouds.

How do clouds form?• When warm humid air

rises, expand, cool and condense (stick) onto condensation nuclei, forming clouds.

• Condensation Nuclei: Tiny particles in the atmosphere that water vapor sticks to.

As the air rises it will cool to dew point temperature

Psychrometer:This instrument measures Relative humidity and Dew point (see chart)The wet bulb’s temperature decreases when you spin it because water willevaporate and evaporation has a cooling effect.

Precipitation

• As more and more water vapor condenses the water droplets become heavier and fall back to Earth.

• Precipitation can be in the form of rain, sleet, ice or snow.

• Precipitation can help remove

pollutants from the atmosphere.

Skills you need to know1. Read and interpret a station model.2. Know how to read a wet and dry bulb thermometer to

determine dew point and relative humidity. Know how to read dew point and relative humidity chart.

3. Draw isobars/isotherms4. use the temperature and air pressure conversion chart. 5. Read and interpret the Layers of the atmosphere chart. The following pages show some of these charts or you can

find them in your workbook.

How to use a psychrometer

Step 1: Read and record the dry bulb temperature.

Step 2: Spin psychrometerStep 3: Read and record the wet bulb.Step 4: Find the difference.Step 5: Match the difference and the dry bulb

on the chart to find relative humidity and dew point.

There are four main layers of the atmosphere. These layers have been divided by temperature changes.

Facts to know: The troposphere contains most water vapor. The ozone layer is in the stratosphere. The ozone absorbs ultra violet radiation from the sun.