Structure & Characteristics

Atmosphere: A thick blanket of gases surrounding a planet *composed of AIR (a mixture of gases)

* Levels of oxygen and other gases decrease with elevation until there are too few gas molecules to detect. * Temperatures may also fluctuate with changes in elevation

Thermosphere * Named the thermosphere because of changes in temperature that rise with altitude and interaction with the Sun * During the day temperatures in this layer of the atmosphere can increase by degrees Celsius * This is also the layer where the auroras may occur because of high energy photons from the Sun exciting molecules in the atmosphere

* Aurora Borealis VideoAurora Borealis Video * Aurora video from the International Space Station Aurora video from the International Space Station

Mesosphere * Meso- means “middle” * Temperatures decrease with height in this layer and reach the coldest temperatures in the atmosphere at the top of the Mesosphere (-90 o Celsius!) * Most meteors burn up in this layer

Stratosphere * Second layer of the atmosphere. * This layer contains the ozone layer- a concentration of O 3 molecules that absorb UV rays from the Sun and warm the Earth. * Because of the ozone layer the temperatures in the Stratosphere increase with height. * This is also a layer where airplanes may sometimes fly on long distance flights.

Troposphere * The lowest layer of the atmosphere that starts at the surface of the Earth. * This is where most of the weather occurs because most of the clouds are formed in this layer. * Temperatures in the troposphere decrease with height as well as density of air particles making it harder to breathe the higher you climb.

Most of the changes we experience in the atmosphere come from differences in temperature or differences in air pressure. Differences in temperature come from different amounts of solar radiation absorbed by the atmosphere and the surface of the Earth.

* Radiant energy: energy that comes from the sun 50% of the Sun’s energy is reflected or absorbed by the atmosphere. This can vary according to latitude.

* Solar energy is transferred through the atmosphere through radiation. Radiation: the transfer of energy in the form of waves

* When solar radiation is absorbed by the atmosphere or by the surface then it can be measured in terms of heat or temperature. Heat: the form of energy that flows between two samples of matter due to their difference in temperature Temperature: average kinetic energy of the atoms or molecules in a particular substance

Conduction: direct transfer of energy from one substance to another Convection: transfer of energy in a fluid (warm air rises, cool air sinks)

* Global convection is responsible for transferring heat from different areas of the Earth through masses of air or convection cells.

* Temperature can vary according to 3 things: 1) Geographic Position 2) Altitude

* Temperature can vary according to 3 things: 3) Surface Material

Thermometer: instrument used for measuring temperature Isotherms: lines on a weather map that connect places with the same temperature

* Water vapor is the most important ingredient in cloud formation and changes in the weather. Water in the atmosphere relies on changes in temperature and heat energy

Humidity: amount of water vapor in the atmosphere Maximum saturation = as much water vapor as the air can hold

* As temperature increases so does the amount of water the air can hold. Relative humidity: (present water vapor/ water vapor when saturated) x 100 Specific humidity: actual moisture in the air

* A number of factors affect the humidity of the air. Pressure and temperature can change the amount of moisture the air can hold and have an effect on dew point. Basic Trends 1) As temperature increases, maximum saturation increases  Maximum saturation = 100% relative humidity  100% relative humidity = dew point

Dew Point: the temperature at which the air becomes cool enough for water vapor to condense into liquid water.  high relative humidity indicates that the dew point is closer to the current air temperature. Relative humidity of 100% indicates the dew point is equal to the current temperature.

Psychrometer: instrument used for measuring relative humidity Hygrometer: instrument used for measuring the specific humidity or moisture in the air

* The result of the air reaching its dew point is the condensation of water vapor into clouds. Cloud: visible masses of tiny water and ice particles suspended in the atmosphere For a cloud to form you must have: -Water or moisture in the air -Dust particles -A change in temperature and/or pressure

* Clouds are characterized by their size, shape and altitude. * The 3 main groups of clouds are: 1) Cumulus 2) Stratus 3) Cirrus

Fog: condensation that forms clouds near the Earth’s surface

Cirrus Clouds - thin, feathery, made of ice crystals - form at high altitudes - seen when weather is fair, but can mean rain or snow - “a curl of hair”

Stratus Clouds -Low sheets or layers; gray and smooth -Block out the sun -Associated with rain and drizzle -“a layer”

Cumulus Clouds -Piled in thick, puffy masses -Usually mean fair weather -“a pile”

Cumulonimbus Clouds large cloud that produces LIGHTNING, THUNDER, HEAVY SHOWERS = Thunderstorms

Nimbostratus Rain Clouds Stratocumulus

Cirrostratus Cirrocumulus

Contrails Mammatus

* Precipitation: any moisture that falls from the atmosphere * Occurs when condensation in the clouds becomes too heavy and falls to the surface * Starts when water vapor attaches to condensation nuclei then becomes visible

Types of Precipitation Drizzle: fine drops….less than 0.5mm diameter Rain drops: larger… 0.5mm to 5mm diameter Snow: falls in clumps of six-sided crystals Sleet: pellets of ice that fall to the ground when raindrops fall through freezing air

Types of Precipitation Hail: lumps of ice - comes from cumulonimbus clouds - made of layers of ice

Formation of Hail

Extreme Weather Lightning: a discharge of electricity from a thundercloud to the ground, or cloud to cloud, or ground to cloud

Extreme Weather Lightning characteristics temperature inside lightning flash can reach 28,000°C at this temperature, air expands explosively and sudden expansion makes thunder!

Extreme Weather Tornado: a narrow, funnel-shaped column of spiral winds that extends downward from the cloud base and touches the ground strongest winds between 360 and 500 km/hr funnel less than 500 m across always travel with a parent thunderstorm at speeds ranging from 40 to 65 km/hr

Extreme Weather Tornados usually occur during spring and summer and most likely occur in late afternoon

Extreme Weather Fujita Scale: scale used for categorizing tornadoes by strength and damage

Extreme Weather Hurricane: an intense tropical low-pressure area with sustained winds starting at 75 mph Hurricanes only form in warmer water temperatures and in other parts of the world they can be called cyclones or typhoons

Extreme Weather Parts of a Hurricane Eye: central area of sinking air; 15 to 20 km wide Eye wall: area of the hurricane surrounding the eye with the most violent winds in the storm

Extreme Weather Parts of a Hurricane Storm surge: currents formed when hurricanes pile water up along the shore and blow it inland

Extreme Weather Movement of Air in a Hurricane Hurricane winds and strength depend on the updraft of warm air and water along with downward pressure of colder air

Extreme Weather Leading up to the storm Tropical depression: wind speeds up to 38 mph; some circular rotation at surface Tropical Storm: wind speeds from mph; can be named, shows drop in pressure, distinct rotation

Extreme Weather Leading up to the storm Hurricane watch: threat of storm conditions within hours Hurricane warning: due to strike within 24 hours

Extreme Weather Hurricane Ratings Use the Saffir-Simpson scale that rates hurricanes based upon their wind speed, storm surge, and damage.