The Atmosphere Weather and Climate 2.5.1Summarize information from charts and graphs regarding layers of the atmosphere, temperature, chemical composition, and interaction with radiant energy.

Weather and Climate… what’s the difference? Weather is always changing and refers to the state of the atmosphere at a given time and place Climate is based on the observations of weather conditions over many years and helps us describe a region To understand weather and climate, we first need to understand what our atmosphere is made of

The Composition of the Atmosphere How old is the earth? _______ Over this period of time the composition of the atmosphere has changed dramatically “Air” is not a single gas, it is a mixture of gases

The Composition of the Atmosphere The most abundant gas in the atmosphere is nitrogen The second most abundant is oxygen Together make up 99% of clean, dry air Carbon dioxide is important for absorbing energy in the atmosphere Water vapor is the source of all clouds and precipitation and absorbs heat given off by Earth

Composition of the Atmosphere Ozone: a form of oxygen with three oxygen atoms bonded together instead of just two (that’s the O2 we breathe) Results from oxygen absorbing radiation (energy) from the sun The ozone layer is crucial for life on Earth because it absorbs potentially harmful radiation The ozone layer allows life on Earth to exist

The Composition of the Atmosphere We just finished talking about the oceans, which contain water. Liquids are one type of fluid Gases are also fluids Most of the properties of our atmosphere that influence weather, climate, and life as we know it, come from the fluid nature of the atmosphere Check it out!

The Structure of the Atmosphere The atmosphere thins very quickly as you travel away from Earth’s surface The atmosphere is divided vertically into 4 layers based on temperature

The Structure of the Atmosphere Layers of the atmosphere The lowest = troposphere Temperature decreases as altitude increases Most important weather phenomena occur here 2nd = stratosphere 3rd = mesosphere Top = thermosphere

Atmospheric Basics Solar Fundamentals The Sun is the source of all energy in the atmosphere. This energy is transferred to Earth and throughout the atmosphere through conduction, convection & radiation.

Atmospheric Basics Solar Fundamentals Conduction is the transfer of energy that occurs when molecules collide. Through conduction, energy is transferred from the particles of air near Earth’s surface to the particles of air in the lowest layer of the atmosphere. For conduction to occur, substances must be in contact with one another. Conduction affects only a very thin atmospheric layer near Earth’s surface.

Atmospheric Basics Solar Fundamentals Convection is the transfer of energy by the flow of a heated substance. Pockets of air near Earth’s surface are heated, become less dense than the surrounding air, and rise. As the warm air rises, it expands and starts to cool. When it cools below the temperature of the surrounding air, it increases in density and sinks. Convection currents are among the main mechanisms responsible for the vertical motions of air, which in turn cause different types of weather.

Atmospheric Basics Solar Fundamentals Radiation is the transfer of energy through space by visible light, ultraviolet radiation, and other forms of electromagnetic waves. The Sun is shining on, and therefore warming, some portion of Earth’s surface at all times. While Earth is absorbing solar radiation, it is also continuously sending energy back into space.

Heating of the Atmosphere Heat vs. temperature Heat is the energy transferred from one object to another due to differences in temperatures. Bottom line: heat is transferred between objects because of differences in temperature

Heating of the Atmosphere The heating of the atmosphere comes from solar energy The solar energy is transferred to Earth through radiation When radiation hits an object, three things happen 1. some radiant energy is absorbed 2. some radiant energy is transmitted through substances like water and air 3. some radiant energy bounces off the object without being absorbed or transmitted

Heating of the Atmosphere If we did not have gases to absorb solar radiation, Earth would not be a place where we could live This heating of the lower layer of the atmosphere from radiation absorbed by heat absorbing gases is called the greenhouse effect … so just like plants grow better in a greenhouse, all life on Earth is able to flourish because of the greenhouse effect

Heating of the Atmosphere The temperatures we experience are due to the amount of heating of the atmosphere above us and the ground and water around us. Land heats and cools more rapidly than water Land also reaches higher and lower temperatures than water The temperature of the land and water influences the temperature of the air above it This explains why inland areas experience greater temperature variations than cities near large bodies of water

Think about it! City A is located on the Outer Banks of NC and City B is located inland. Which city would experience greater variations in temperature and why?

Air Masses and Weather Weather patterns result from the movement of large bodies of air called air masses Air masses are characterized by similar temperatures and amounts of moisture at certain altitudes. When air masses move, the characteristics of the air mass change and the weather in the areas over which they move changes

Starts off at -460C Ends up at 700C

Air Masses and Weather Example of air mass/weather interaction: A cold, dry air mass moves over warm, tropical waters The air mass becomes warmer and wetter The weather over those waters becomes colder and drier You try… A warm, dry air mass moves over a cold, wet area The air mass becomes ______________ and _______ The weather over that area becomes ____________ and ____________

When air masses meet… Fronts When two air masses meet, they form a front- the boundary that separates the two There are 4 types of fronts Warm fronts Cold fronts Stationary fronts Occluded fronts

Fronts Warm fronts Form when warm air moves into an area formerly covered by cold air Shown on a weather map by a red line with semi-circles pointing toward the colder air Warmer air Colder air

Fronts Warm front

Fronts Warm fronts As the warmer, less dense air rises, it cools This produces clouds and frequent precipitation Warm fronts move slowly, so the precipitation is light-to-moderate over a large area for a long period of time

Fronts Cold fronts Form when cold, dense air moves into an area formerly occupied by warmer air Shown on a weather map by a blue line with triangles pointing toward the warmer air Colder air Warmer air

Fronts Cold Front

Cold Fronts Fronts Move much more quickly than warm fronts Associated with heavy precipitation that is short-lived

Stationary Fronts Fronts Form when the flow of air is neither toward the cold air mass, nor toward the warm air mass The front does not move Shown by blue triangles on one side and red semicircles on the other Gentle to moderate precipitation

Occluded Front Fronts Forms when a cold front overtakes a warm front Complex weather patterns

Thunderstorms Severe Storms Develop when warm, humid air rises in an unstable environment Warm air Heavy rain Cooler air

Tornadoes Severe Storms Violent windstorms Form as a vortex extends down from a cumulonimbus cloud A vortex is a rotating column of air Most tornadoes form along with severe thunderstorms

Tornadoes Severe Storms Tornado Watches: there is the possibility of a tornado in the area Tornado Warning: a tornado has been spotted in the area or is indicated by radar

Damage Caused by Tornadoes Extremely high winds can tear buildings apart, slip cars, and even suck the water out of a riverbed

Hurricanes Severe Storms A hurricane is a large, rotating tropical weather system with wind speeds of at least 74 mph Hurricanes are the most powerful storms on Earth In other countries they are also known as typhoons and cyclones

How Do Hurricanes Form? A hurricane begins as a group of thunderstorms moving over tropical ocean waters Winds traveling in two different directions collide causing the storm to spin Warm water gives the storm energy and causes it to grow

Structure of a Hurricane The eye is a zone of scattered clouds and calm averaging about 20 kilometers in diameter at the center of a hurricane. The eye has the warmest temperatures. The eye wall is a doughnut-shaped area of intense cumulonimbus development and very strong winds that surrounds the eye of a hurricane.

Damage Caused by Hurricanes Hurricane winds can knock down trees and telephone poles However, the most damage during a hurricane comes from flooding due to heavy rain and storm surges A storm surge is a wall of water that builds up over the ocean and can be up to 20 feet before it crashes onto the shore

2.5.4c Moisture, Precipitation, and Clouds

Water in the Atmosphere Water exists in three different forms. What are they? SOLID Examples: Snow, ice LIQUID Examples: Rain, water GAS Examples: Clouds, water vapor How do each of these forms of water influence weather?

Water in the Atmosphere When it comes to understanding atmospheric processes, water vapor is the most important gas in the atmosphere. Why do you think water vapor is so important?

Water in the Atmosphere Even though water vapor is important, it only makes up from 0 – 4% of the atmospheric gases. When have you felt water vapor at close to 4%? What about 0%? How do you know? Water vapor is the HUMIDITY that you feel in the air!

Water in the Atmosphere What do you think the word “SATURATED” means? What do you think it would mean if air is Saturated? Air that has reached its water vapor capacity is said to be saturated.

Water in the Atmosphere Warm, saturated air contains more water vapor than cold air Dew point is the temperature to which air is cooled to reach saturation. The point at which condensation can occur When have you noticed the humidity more, in the summer or in the winter? That’s because warm air can hold more water vapor!

Water in the Atmosphere Relative humidity is the ratio of air’s water-vapor content to its capacity to hold water vapor at that same temperature. Relative humidity indicates how near the air is to saturation, not the actual quantity of water vapor in the air. Relative Humidity varies with temperature. Cooling air increases its relative humidity. Warming air decreases its relative humidity.

Water in the Atmosphere Why does lowering the air temperature cause Relative humidity to increase? Because colder air cannot hold as much water vapor! Why does increasing air temperature cause relative humidity to decrease? Because warm air can hold more water vapor and it will take more water vapor for it to become saturated.

Lifting Air When air is compressed the air molecules move faster and the temperature rises. Air compression causes changes in temperature even though heat isn’t added or subtracted. When air is allowed to expand, it cools. When air is compressed, it heats up.

Lifting Air Orographic Lifting Orographic lifting occurs when mountains act as barriers to the flow of air, forcing the air to ascend.

Lifting Air Frontal Wedging How does the relatively flat areas form clouds? Frontal Wedging A front is the boundary between two adjoining air masses having contrasting characteristics.

Lifting Air Convergence Convergence occurs when two air masses converge. The air flows together and rises.

Lifting Air Localized Convective Lifting Localized convective lifting occurs where unequal heating on earth’s surface causes pockets of air to rise.

Lifting Air Clouds form because as you go up in elevation, it gets colder. Cold air cannot hold as much water vapor so it transforms into clouds. Cool, expanded air Using the info from yesterday, discuss how clouds form because as you go up, it gets colder. Cold air cannot hold as much water vapor so it transforms into clouds. Warm, compressed air

Lifting Air – Creating Clouds When air expands to form clouds, the water vapor is transformed to clouds by condensation. Generally, there must be a surface for water vapor to condense on. Condensation nuclei are tiny bits of matter that serve as surfaces on which water vapor condenses when condensation occurs in the air. Examples of condensation nuclei include dust, smoke and salt particles.