The Atmosphere and Weather

The Air Around You What is weather? The condition of Earth’s atmosphere at a particular time and place. What is the atmosphere? The envelope or blanket of gases that surround the Earth. Made of nitrogen, oxygen, carbon dioxide, water vapor and more making the conditions on Earth suitable for living things.

Air Pressure Air has mass, density, and pressure Density- amount of mass in a given volume of air (density= mass/volume) Pressure- the force pushing on an area or surface Air pressure is the result of the weight of a column of air pushing down on an area.

Air pressure is measured by a barometer Altitude affects air pressure- the higher you go, less air pressure. Altitude affects density- the higher you go, less oxygen molecules.

Layers of the Atmosphere Troposphere, stratosphere, Mesosphere, Thermosphere. Troposphere- first layer, lowest, where we live. Weather occurs here. Contains almost all the mass of the atmosphere. Stratosphere- second layer, where the ozone layer is. Temperature warms up as it reaches the top. Mesosphere- drop in temperature (meso-middle) protects Earth’s surface from being hit by meteoroids.

Thermosphere- outermost layer of Earth’s atmosphere. Extends to space Thermosphere- outermost layer of Earth’s atmosphere. Extends to space. Extremely high temperature though feels very cold. Ionosphere and exosphere are part of the thermosphere. Ionosphere causes aurora borealis, exosphere extends to space.

Energy in the Earth’s Atmosphere Energy comes from the sun as electromagnetic waves. Most of the energy from the sun travels to the Earth in the form of visible light and infrared radiation. A small amount arrives as ultraviolet light. Visible light: all the colors of the rainbow Infrared radiation: wavelengths are longer than red light, is not visible and felt as heat. Ultraviolet radiation- invisible energy shorter than violet light.

What is Infrared Radiation? The light we see with our eyes is really a very small portion of what is called the "Electromagnetic Spectrum." The Electromagnetic Spectrum includes all types of radiation - from the X-rays used at hospitals, to radio waves used for communication, and even the microwaves you cook food with. Radiation in the Electromagnetic Spectrum is often categorized by wavelength. Short wavelength radiation is of the highest energy and can be very dangerous - Gamma, X- rays and ultraviolet are examples of short wavelength radiation. Longer wavelength radiation is of lower energy and is usually less harmful - examples include radio, microwaves and infrared. A rainbow shows the optical (visible) part of the Electromagnetic Spectrum and infrared (if you could see it) would be located just beyond the red side of the rainbow. Although infrared radiation is not visible, humans can sense it - as heat. Put your hand next to a hot oven if you want to experience infrared radiation "first-hand! https://www.youtube.com/watch?v=P_PVz8HrrCI

Some sunlight is absorbed or reflected by the atmosphere before it can reach the surface. The rest passes through to the surface. Some light is scattered (reflected light). Gases scatter short wavelengths of visible light (blue and violet) more than long wavelengths (red and orange) making the sky look blue.

When the Earth’s surface is heated, it radiates most of the energy back into the atmosphere as infrared radiation. It is absorbed by water vapor, carbon dioxide, methane, and other gases. Greenhouse effect- process by which gases hold heat in the air.

Wind! Wind: a horizontal movement of air from an area of high pressure to an area of low pressure. Winds are caused by differences in air pressure. Convection currents move areas of warm air to cool air. Global winds: blow steadily from specific directions over long distances.

The Coriolis Effect: Earth’s rotation causes winds to curve The Coriolis Effect: Earth’s rotation causes winds to curve. Ex: Global winds in the N. Hemisphere turn to the right.

Global Wind Belts Major global wind belts are the trade winds, the polar easterlies, and the prevailing westerlies. Trade Winds- when cold air sinks, it produces high pressure. Due to the Coriolis effect, winds blow toward the equator and turn west away from it. Located in the N.H. between 30° N latitude and equator and in S.H. 30° S latitude and the equator.

Prevailing Westerlies- Located between 30° and 60° N and S latitudes and blow towards the poles and east due to the Coriolis effect. Play an important role in weather in the US. Polar Easterlies- cold air near poles sinks and flows back towards the lower latitudes. Coriolis effect sends winds west and meets the Prevailing Westerlies at 60° N and S latitudes. This mixes warm and cold air and creates a major effect on weather in the US.

Jet stream- bands of high speed winds Jet stream- bands of high speed winds. Blow from west to east at 200-400 km per hr. Wander north and south in a wavy pattern which brings change in temperature and weather.

Humidity and Cloud Formation Humidity: the amount of water vapor in the air. The amount of water vapor the air can hold depends on the temperature. Warmer air holds more water. Clouds form when water vapor in the air condenses to form liquid water or ice crystals. (condensation)

The temperature where condensation starts is called dew point The temperature where condensation starts is called dew point. (temp above freezing=water droplets; temp below=ice crystals) Particles in the air (dust, smoke) allows for condensation to occur for cloud formation. (on the ground=dew or frost)

Types of Clouds 3 main types based on shape, then classified by altitude. Cirrus Clouds- wispy/feathery, form at high levels Cirrocumulus- rows of cotton balls or scales of a fish-a storm is coming Cumulus Clouds- fluffy round piles of cotton- indicate fair weather Cumulonimbus- towering clouds with flat tops- T-storms

Fog- clouds that form at or near the ground. Stratus clouds- form in layers, cover all or most of the sky in a dull gray color, Nimbostratus- thickened stratus clouds produce drizzle, rain, or snow Altocumulus and Altostratus- based on how high in the sky they are. Middle level clouds are higher than regular stratus and cumulus clouds but lower than cirrus and other high clouds. Fog- clouds that form at or near the ground.

Types of Precipitation Depending on the size of water vapor, will depend on if a cloud will produce precipitation. Rain-drops of water, smaller drops called mist. Sleet-when rain falls through a layer of air that is freezing, frozen particles fall as ice. Freezing rain-rain that freezes on a cold surface Snow-ice crystals Hail-round pellets of ice produced by t-storms of rain freezing being updrafted and forming new ice around it like layers of an onion. Can be the size of golf balls.

Air Masses and Fronts Air mass-a huge body of air with similar temperature, humidity, and air pressure at any given height. 4 major types in N. America: maritime tropical, continental tropical, maritime polar, and continental polar. maritime (oceans) tropical (warm)- brings warm humid air, t-storms in summer or snow in winter (Cali or S.E. USA)

Maritime (oceans) Polar (cold)- cool humid air (cold N. Pacific and N Maritime (oceans) Polar (cold)- cool humid air (cold N.Pacific and N. Atlantic oceans) Continental(land) Tropical (warm)- hot dry air (SW and Great Plains) Continental (land) Polar(cold)-masses that move from the Artic circle -clear cold, dry air in winter, storms in summer when clashes with maritime tropical.

In the continental US, air masses are commonly moved by the prevailing westerlies and jet streams. Front- boundary where air masses meet. Storms and changeable weather develop along fronts.

Thunderstorms A t-storm is a small storm with heavy precipitation, thunder and lightening. T-storms form in large cumulonimbus clouds called thunderheads. Form on hot humid afternoons when warm air is forced along a cold front. Air rises rapidly and cools rapidly. Lightning-sudden spark of an electrical discharge of positive and negative electrical charges in clouds.

Tornadoes Tornado- rapidly whirling, funnel-shaped cloud that reaches down from a storm cloud to the Earth’s surface. Brief but wind speeds can reach 500 km per hr. Develop in thick cumulonimbus clouds that bring t- storms, typically in the spring and summer. Tornado alley- middle of the US in the Great Plains due to cold dry air from north clashing with warm moist air from the south.

Hurricanes Hurricanes-tropical cyclones w/winds of 119 km per hr or higher and about 600 km across. Begins over warm ocean waters as low-pressure area or a tropical disturbance. Draws energy from warm humid air above ocean surface. Bands of high winds and heavy rains Winds spiral inward towards area of low pressure inside Storm surges create a dome of water that is pushed in from the ocean and floods costal areas.