Earth's Atmosphere

The processes that cause air to rise, thereby generating clouds:

(1) Orographic lifting, (2) Frontal lifting, (3) Convergence, and (4) Localized convective lifting

Maritime (m) air mass

An air mass that originates over the ocean. Maritime air masses are relatively humid.

Polar high

An anticyclone that is assumed to occupy the inner polar regions and is believed to be thermally induced, at least in part.

Hygrometer

An instrument designed to measure relative humidity.

Aneroid barometer

An instrument for measuring air pressure that consists of evacuated metal chambers that are very sensitive to variations in air pressure.

Hygroscopic nuclei

Condensation nuclei that have a high affinity for water, such as salt particles.

Adiabatic temperature change

Cooling or warming of air that occurs because air is allowed to expand or is compressed, not because heat is added or subtracted.

Subtropical high

Not a continuous belt of high pressure but rather several semipermanent, anticyclonic centers characterized by subsidence and divergence located roughly between latitudes 25 and 35 degrees.

Atmospheric Convection

On an Earth that did not rotate the uneven distribution of atmospheric temperatures would lead to two large convection cells.

Continental vs. Marine

The high specific heat of water means that the oceans act as a temperature buffer in coastal areas.

Solar Radiation

The sun transmits all wavelengths to Earth. However, we only feel some of the radiation due to absorption in the atmosphere.

Temperature

A measure of the degree of hotness or coldness of a substance. Is the average kinetic energy of all atoms or molecules in a substance.

Mercury barometer

A mercury-filled glass tube in which the height of the mercury column is a measure of air pressure.

Altostratus

A middle cloud. Stratified veil of clouds that is generally thin and may produce very light precipitation. When thin, the Sun or Moon may be visible as a "bright spot," but no halos are produced.

Altocumulus

A middle cloud. White to gray clouds, often made up of separate globules; "sheepback" clouds.

Ozone

A molecule of oxygen that contains three oxygen atoms. Is generated when a free oxygen atom collides with an O2 molecule. The conditions for this reaction are very special and only occur high in the atmosphere (10-50 km). This 'ozone layer' is critical for our survival as it absorbs short wavelength UV radiation.

Doppler radar

A new generation of radar that can handle the tasks performed by conventional radar and also detect motion directly. It greatly improves tornado and severe storm warnings.

Tipping-bucket gauge

A recording rain gauge consisting of two compartments ("buckets"), each capable of holding 0.025 centimeter of water. When one compartment fills, it tips, and the other compartment takes its place.

Saffir-Simpson hurricane scale

A scale from 1 to 5 that is used to rank relative intensities of hurricanes.

Enhanced Fujita intensity scale (EF-scale)

A scale originally developed by Theodore Fujita for classifying the severity of a tornado, based on the correlation of wind speed and the degree of destruction.

Monsoon

A seasonal reversal of wind direction associated with large continents, especially Asia. In winter, the wind blows from land to sea; in summer, from sea to land.

Stationary front

A situation in which the surface position of a front does not move; the flow on either side of such a boundary is nearly parallel to the position of the front.

Tornadoes

A small, very intense cyclonic storm with exceedingly high winds, most often produced along cold fronts in conjunction with severe thunderstorms. These are also areas of low pressure (but on a much smaller scale than hurricanes). The air rushing into the area of low pressure leads to the swirling wind pattern.

Local wind

A small-scale wind produced by a locally generated pressure gradient.

Snow

A solid form of precipitation produced by sublimation of water vapor.

Thunderstorm

A storm produced by a cumulonimbus cloud and always accompanied by lightning and thunder. It is of relatively short duration and usually accompanied by strong wind gusts, heavy rain, and sometimes hail.

Polar front

A stormy frontal zone that separates air masses of polar origin from air masses of tropical origin.

Bergeron process

A theroy that relates the formation of precipitation to supercooled clouds, freezing nuclei, and the different saturation levels of ice and liquid water.

Rime

A thin coating of ice on objects that is produced when supercooled fog or cloud droplets freeze on contact.

Hurricane

A tropical cyclonic storm that has winds in excess of 119 kilometers (74 miles) per hour. Form as extreme areas of low pressure in areas with hot moist air.

Tropical (T) air mass

A warm-to-hot air mass that forms in the subtropics.

Tornado warning

A warning issued when a tornado has actually been sighted in an area or is indicated by radar.

Chinock

A wind that blows down the leeward side of a mountain and that warms by compression.

Prevailing wind

A wind that consistently blows from one direction more than from any other.

Eye

A zone of scattered clouds and calm averaging about 20 kilometers in diameter at the center of a hurricane.

Arctic (A) air mass

Air mass that originates at high polar latitudes. Generally very cold and dry.

Mist

A clouds of water droplets suspended in the atmosphere at or near Earth's surface.

Freezing rain (glaze)

A coating of ice on objects formed when supercooled rain freezes on contact.

Polar (P) air mass

A cold air mass that forms in a high-latitude source region.

Climate

A description of aggregate weather conditions; the sum of all statistical weather information that helps describe a place or region. The average state of the tropopause at any given location.

Psychrometer

A device consisting of two thermometers (wet-bulb and dry-bulb) that is rapidly whirled and, with the use of tables, yields the relative humidity and dew point.

Rainshadow desert

A dry area on the lee side of a mountain range. Many middle-latitude deserts are of this type.

Advection fog

A fog formed when warm, moist air is blown over a cool surface.

Tornado watch

A forecast issued for areas of about 65,000 square kilometers (25,000 square miles), indicating that conditions are such that tornadoes may develop; it is intended to alert people to the possibility of tornadoes.

Cloud

A form of condensation best described as a dense concentration of suspended water droplets or tiny ice crystals.

Cold Fronts

A front along which a cold air mass thrusts beneath a warmer air mass. These fronts advance more quickly than warm fronts and consequently develop a steeper slope between the warm and cold air. This promotes the rapid rise of warm air and the formation of storms.

Warm Fronts

A front along which a warm air mass overrides a retreating mass of cooler air. It is hard for less dense warm air to replace cold air. This, combined, with a slow retreat of the cold air mass due to friction, lead to a long-tapered slope with warm air rising over the cold air. This leads to the warm air adiabatically rising forming clouds and leading to the precipitation over broad areas.

Humidity

A general term referring to water vapor in the air but not to liquid droplets of fog, cloud, or rain.

Anticyclone (high)

A high-pressure center characterized by a clockwise flow of air in the Northern Hemisphere.

Air mass

A large body of air that is characterized by a sameness of temperature and humidity.

Middle-latitude (midlatitude) cyclone

A large low-pressure center with a diameter often exceeding 1000 kilometers (600 miles) that moves from west to east and may last from a few days to more than a week and usually has a cold front and a warm front extending from the central area of low pressure.

Radiosonde

A lightweight package of weather instruments fitted with a radio transmitter and carried aloft by a balloon.

Sea breeze

A local wind blowing from the sea during the afternoon in coastal areas.

Land breeze

A local wind that blows from land toward the water during the night in coastal areas.

Cyclone (low)

A low-pressure center characterized by a counterclockwise flow of air in the Northern Hemisphere.

Clouds of vertical development

Clouds having bases in the low height range but extending upward into the middle or high altitudes.

High clouds

Clouds that normally have their base above 6000 meters; the base may be lower in winter and at high-latitude locations.

Middle clouds

Clouds that occupy the height range from 2000 to 6000 meters.

The three mechanisms of heat transfer are:

Conduction, Convection, and Radiation.

Nucleating Water Vapor

Even if the air is saturated in water vapor, it will not create liquid droplets if there aren't small solids (aerosols) to nucleate on.

Precipitation

In clouds that are at very low temperatures (below the freezing temp < 0 degrees Celsius) precipitation forms from water being attracted to ice crystals, until the ice crystals reach a critical size and begin to fall. They can then remelt to form rain droplets or continue to fall as snow flakes depending on the atmospheric conditions. This can also form in clouds that are at temperatures below freezing through coalescence of droplets of water.

Upslope fog

Fog created when air moves up a slope and cools adiabatically.

Frontal (precipitation) fog

Fog formed when rain evaporates as it falls through a layer of cool air. A type of evaporation fog.

Radiation fog

Fog resulting form radiation heat loss by Earth.

Steam fog

Fog that has the appearance of steam; produced by evaporation from a warm-water surface into the cool air above. A type of evaporation fog.

Fronts on Weather Maps

Fronts are denoted by red lines with rounded teeth (warm front) and blue lines with sharp teeth (cold front) on the weather maps. The teeth point in the direction of movement.

How do fronts form?

Fronts are related to high and low pressure systems and are thus ultimately tied back into the convection of the entire atmosphere!

Sleet

Frozen or semifrozen rain that forms when raindrops freeze as they pass through a layer of cold air.

Water Vapor

H2O gas is always present in the atmosphere (0.01%-4%). It can come from a variety of sources: evapotranspiration from plants, sublimation of ice. We call the amount of water vapor in the air humidity.

Wind is controlled by the following combination of forces:

Pressure gradient force, Coriolis effect, and Friction

Westerlies

The dominant west-to-east motion of the atmosphere that characterizes the regions on the poleward side of the subtropical highs.

Eye wall

The doughnut-shaped area of intense cumulonimbus development and very strong winds that surrounds the eye of a hurricane.

Lake-effect snow

Snow showers associated with cP air mass to which moisture and heat are added from below as it traverses a large and relatively warm lake (such as one of the Great Lakes), rendering the air mass humid and unstable.

Stratocumulus

Soft, gray clouds in globular patches or rolls. Rolls may join together to make a continuous cloud.

Diffused light

Solar energy is scattered and reflected in the atmosphere and reaches Earth's surface in the form of diffuse blue light from the sky.

Lifting condensation level (condensation level)

The height at which rising air that is cooling at the dry adiabatic rate becomes saturated a condensation begins.

How does solar radiation heat the Earth?

Solar radiation can be absorbed, transmitted, or reflected/scattered.

Transmission of Solar Energy

Solar radiation striking Earth at a low angle must travel through more of the atmosphere leading to loss of energy through interaction with atmospheric gases and particles. Low angle solar radiation is also distributed over a larger area.

Solar Energy

Solar radiation transfers energy from the sun to the Earth's surface.

Freezing nuclei

Solid particles that serve as cores for the formation ice crystals.

Vertical Structure of the Atmosphere

The atmosphere can be envisioned as an envelope of gas that is gravitationally held to our planet. Thus, it follows that the pressure drops as you move higher into the atmosphere. The thermal structure of the atmosphere is complex and has to do with the absorption of energy at different levels.

Heat

The kinetic energy of random molecular motion. Is representative of the amount of thermal energy in a substance.

Front

The boundary between two adjoining air masses that have contrasting characteristics. The boundary between different packages of air. They are named after the temperature of the air that is moving most quickly. In other words, warm fronts occur when warm air advances rapidly into an area previously occupied by cold air and cold fronts occur when cold air advances into an area previously occupied by warm air.

Condensation

The change of state from a gas to a liquid.

Absolute instability

The condition of air that has an environmental lapse rate that is greater than the dry adiabatic rate (1 degree Celsius per 100 meters).

Absolute stability

The condition of air that has an environmental lapse rate that is less than the wet adiabatic rate.

Conditional instability

The condition of moist air with an environmental lapse rate between the dry and wet adiabatic rates.

Supercooled

The condition of water droplets that remain in the liquid state at temperatures well below 0 degrees Celsius.

Convergence

The condition that exists when the distribution of winds within a given area results in a net horizontal inflow of air into the area. Since convergence at lower levels is associated with an upward movement of air, areas of convergent winds are regions favorable to cloud formation and precipitation.

Divergence

The condition that exists when the distribution of winds within a given area results in a net horizontal outflow of air from the region. In divergence at lower levels, the resulting deficit is compensated for by a downward movement of air from aloft; hence, areas of divergent winds are unfavorable t cloud formation and precipitation.

Air-mass weather

The conditions experienced in an area as an air mass passes over it. Because air masses are large and fairly homogeneous, air-mass weather will be fairly constant and may last for several days.

Sublimation

The conversion of a solid directly to a gas, without passing through the liquid state.

Valley breeze

The daily upslope winds commonly encountered in a mountain valley.

Coriolis effect

The deflective force of Earth's rotation on all free-moving objects, including the atmosphere and oceans. Deflection is to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. Also called Coriolis force. This will "bend" a current moving across a surface that is rotating at a different speed. The Earth rotates to the east, and by necessity, this rotation occurs faster at the equator than the poles. Thus, if you were to throw something from the equator to the north or south it would deflect to the East. Likewise, if you threw something towards the equator it will be deflected to the west.

Jet stream

A strong eastward air current that mark the boundaries between convection cells.

Weather radar

Instruments that utilize transmitters to send out radio waves at wavelengths that can penetrate clouds, to produce a reflected signal called an echo that can be displayed on a monitor to show the location and intensity of precipitation.

Frontal lifting (wedging)

Lifting of air that results when cool air acts as a barrier over which warmer, lighter air will rise.

Subpolar low

Low pressure located at about the latitudes of the Arctic and Antarctic Circles. In the Northern Hemisphere, the low takes the form of individual oceanic cells; in the Southern Hemisphere, there is a deep and continuous trough of low pressure.

Absorption

Materials can absorb solar radiation. For example, the ozone layer utilizes short wavelength UV radiation to breakdown O2 and turn it into O3. Atmospheric gases can also absorb long wavelength radiation (infrared). Visible light is not effectively absorbed by the atmosphere. Objects with a low albedo solar radiation and can re-emit that energy as long wavelength infrared radiation.

Two processes are responsible for the formation of precipitation:

The Bergeron process and the Collision-coalescence process

Three cloud types that make up the low clouds:

stratus, stratocumulus, and nimbostratus

There are a variety of factors that lead to the temperature distribution on Earth:

(1) The amount of incoming solar radiation to an area, (2) An area's altitude, (3) An area's albedo, and (4) An area's specific heath (how much energy needs to be absorbed to increase the temperature).

Equatorial low

A belt of low pressure that lies near the equator and between the subtropical highs.

Fog

A cloud with its base at or very near Earth's surface.

Nimbus

A clouds that is a major producer of precipitation.

Occluded front

A front formed when a cold front overtakes a warm front.

Standard rain gauge

A gauge that has a diameter of about 20 centimeters and funnels rain into a cylinder that magnifies precipitation amounts by a factor of 10, allowing for accurate measurement of small amounts.

Collision-coalescence process

A theory of raindrop formation in warm clouds (above 0 degrees Celsius) in which large cloud droplets (giants) collide and join together with smaller droplets to form rain drops. Opposite electrical charges may bind the cloud droplets together.

Cumulus

As one of the three basic cloud forms, refers to clouds that consist of globular masses that are often described as cottonlike in appearance. As one of the two types of clouds of vertical development, refers to dense, billowy clouds often characterized by flat bases, which may occur as isolated clouds or may be closely packed.

Cirrus

As one of the three basic cloud forms, refers to high, thin ice-crystal clouds. As one of the three high cloud types, refers to thin, delicate fibrous, ice-crystal clouds, which sometimes take the form of hooked filaments called "mares' tails."

Low clouds

Clouds that form below a height of about 2000 meters.

Air pressure

Force exerted by the weight of the air above. Is a measure of the force exerted on an object by air. It is closely related to air density and temperature.

How is air forced to rise?

Forced uplift over topographic barriers. Forced uplift over a moving mass of cold air.

Hurricane Destruction

Hurricanes can have powerful winds and 'push' water onto the shore in a process known as a storm surge. These processes can act together to be desctructive.

Orographic lifting

Mountains acting as barriers to the flow of air and forcing the air to ascend. The air cools adiabatically, and clouds and precipitation may result.

Hail

Nearly spherical ice pellets having concentric layers and formed by the successive freezing of layers of water.

Differential Heating of the Earth

Recall that Earth's rotational axis is tilted relative to it's orbital plane and that this configuration leads to an uneven distribution of solar radiation throughout the year.

Latent heat

The energy absorbed or released during a change in state.

Mixing ratio

The mass of water vapor in a unit mass of dry air; commonly expressed as grams of water vapor per kilogram of dry air.

Inclination of the axis

The tilt of Earth's axis from the perpendicular to the plane of Earth's orbit.

Conduction

The transfer of heat through matter by molecular activity. Energy is transferred through collisions form one molecule to another.

Condensation nuclei

Tiny bits of particulate matter that serve as surfaces on which water vapor condenses.

Aerosols

Tiny solid and liquid particles suspended in the atmosphere. Are small (microscopic) particles of solids or liquids that are suspended in the atmosphere. They play an outsized role in weather an climate in that they can reflect sunlight and serve as a location for water condensation.

Cumulonimbus

Towering clouds, sometimes spreading out on top to form an "anvil head". Associated with heavy rainfall, thunder, lightning, hail, and tornadoes.

Trace Components of the Atmosphere

Trace gases include Carbon Dioxide (CO2), Methane (CH4), and Water Vapor (H2O) which are all greenhouse gases. Aerosols and Ozone are these as well.

Electromagnetic radiation

Transfer of energy in the form of light and related types of radiation, including gamma rays, x rays, ultraviolet light, infrared light, microwaves, and radio waves.

Trade winds

Two belts of winds that blow almost constantly from easterly directions and are located on the equatorward sides of the subtropical highs. The bottom part of each convection cell also experiences the Coriolis effect, leading to consistent wind directions as air flows back into the area where air convectively rises and away from areas where air convectively sinks.

Mesosphere

The layer of the atmosphere immediately above the stratosphere and characterized by decreasing temperatures with height. Above the stratosphere lies this, where temperatures again fall with elevation.

Stratosphere

The layer of the atmosphere immediately above the troposphere, characterized by increasing temperatures with height due to the concentration of ozone. Above the troposphere lies this, where ozone (O3) is produced. Production of ozone releases thermal energy. This thermal energy heats the upper part of this. The transition from decreasing temperature with height to increasing temperature marks the boundary between the troposphere and this. This thermal inversion also make it difficult for weather to pierce the stratosphere, because there is no driving force for convection.

Relative humidity

The ration of the air's actual water-vapor content to the amount of water vapor required for saturation at that temperature (and pressure). The measure of how much water a parcel of air holds relative to its saturation point. High relative humidity means that the air is close to saturation. Low relative humidity means that it is very far from saturation.

Albedo

The reflectivity of a substance, usually expressed as a percentage of the incident radiation reflected.

Thermosphere

The region of the atmosphere immediately above the mesosphere, which is characterized by increasing temperatures due to absorption of very shortwave solar energy by oxygen. Temperature increases with elevation again in this but gases are so dilute that you would not feel hot if you could experience this layer. This is where most of us would consider outer space to begin.

Relative Humidity and Temperature

The saturation point is highly dependent on temperature, such that colder air can hold less water than hot air.

Rotation

The spinning of a body, such as Earth, about its axis.

Weather

The state of the atmosphere at any given time. The sum of the physical conditions that we feel in the tropopause at any given moment (i.e., rain, temperature, wind, storms). It can change rapidly.

Dew-point temperature (dew point)

The temperature to which air has to be cooled in order to reach saturation. Often shortened to dew point.

Nor'easter

The weather associated with an incursion of mP air into the Northeast from the North Atlantic; strong northeast winds, freezing or near-freezing temperatures, and possible precipitation make this an unwelcome weather event.

Intertropical convergence zone (ITCZ)

The zone of general convergence between the Northern and Southern Hemisphere trade winds.

Cirrostratus

Thin sheet of white, ice-crystal clouds that may give the sky a milky look. Sometimes produce halos around the Sun and Moon.

Cirrocumulus

Thin, white, ice-crystal clouds that take the form of ripples, waves, or globular masses all in a row. May produce a "mackerel sky". Least common of high clouds.

Environmental Lapse Rate

This is just a measure of what the atmospheric temperature is relative to elevation.

Effects of Land

Water and land have different specific heat capacities. Thus, they heat and cool at different rates. The uneven distribution of these surfaces changes the atmospheric circulation pattern relative to the idealized model, which had a constant surface composition.

Water vs. Land

Water has a much higher specific heat than the solids that make up the land surface. So, it must absorb more solar radiation to increase temperature. This means that it heats and cools more slowly than land.

Wind flows from areas with _________ air pressure to those with ________ pressure.

high, low

Tropical storm

By international agreement, a tropical cyclone with maximum winds between 61 and 119 kilometers (38 and 74 miles) per hour.

Tropical depression

By international agreement, a tropical cyclone with maximum winds that do not exceed 61 kilometers (38 miles) per hour.

The basic cloud forms:

(1) Cirrus, (2)Stratus, and (3) Cumulus (They are named according to their form and altitude.)

The 'lapse rate' is the change in air's temperature relative to elevation. There are two lapse rates:

(1) The environmental lapse rate and (2) The adiabatic lapse rate

In terms of the same 6 basic elements weather and climate are expressed in:

(1) air temperature, (2) humidity, (3) type and amount of cloudiness, (4) type and amount of precipitation, (5) air pressure, and (6) speed and direction of the wind.

Hurricanes diminish in intensity whenever they:

(1) move over ocean waters that cannot supply warm, moist tropical air; (2) move onto land; or (3) reach a location where the large-scale flow aloft is unfavorable

Composition of Earth's Atmosphere

Nitrogen (N2) and oxygen (O2) compose most of Earth's atmosphere. However, trace components play the biggest role in moderating climate.

Pressure (barometric) tendency

The nature of the change in atmospheric pressure over a period of several hours. It can be a useful aid in short-range weather prediction.

Consequences of Uneven Heating

The uneven distribution of solar radiation on Earth, Combined with the bottom-up mechanism of heating creates a convective instability near the equator. In other words, we now have large areas with hot, low density air near the Earth's surface at the equator underlying cold, high density air higher in the troposphere.

Seasons

The uneven distribution of solar radiation throughout the year is why we have this.

Overrunning

Warm air gliding up a retreating cold air mass.

Laws of Radiation

1. All objects, at whatever temperature, emit radiant energy. 2. Hotter objects radiate more total energy per unit area than do colder objects. 3. Hotter objects radiate more energy in the form of short-wavelength radiation than do cooler objects. 4. Objects that are good absorbers of radiation are good emitters as well. Gasses are selective absorbers and radiators.

Atmospheric Heating

About 50% of all solar radiation is absorbed by the Earth's surface and reradiated skyward. This energy is then absorbed by gases in the atmosphere. Thus, the atmosphere is heated from the bottom up.

Wind

Air flowing horizontally with respect to Earth's surface. Air flows from areas of higher pressure to areas of lower pressure.

Stratus

As one of the three basic cloud forms, refers to sheets or layers (strata) of cloud that cover much or all of the sky. As one of the three low cloud types, refers to a low, uniform cloud layer that resembles fog but does not rest on the ground and that may produce drizzle.

Unstable air

Air that does not resist vertical displacement. If it is lifted, its temperature will not cool as rapidly as the surrounding environment, and so it will continue to rise on its own.

Stable air

Air that resists vertical displacement. If it is lifted, adiabatic cooling will cause its temperature to be lower than the surrounding environment; if it is allowed to do so, it will sink to its original position.

Nimbostratus

Amorphous layer of dark gray clouds. One of the primary precipitation-producing clouds.

Continental (c) air masses

An air mass that forms over land; it is normally relatively dry.

Rain

Drops of water that fall from a cloud and have a diameter of at least 0.5 millimeter.

Earth's Rotation

Earth's rotational axis is tilted relative to it's orbital plane around the sun. this leads to an uneven distribution of solar radiation throughout the year.

Tornado Destruction

Extremely high wind speeds can lead to total destruction. However, the size of these is typically 500-2000 feet. So, the path of destruction is quite narrow.

Four levels of cloud heights are recognized:

High, Middle, Low, and Clouds of vertical development

Atmospheric Stability

Hot air will want to rise until it has cooled to the same temperature as the surrounding air. At that point, the densities will be the same and the air will have reached an equilibrium state. The critical point here is that if you take air from lower in the atmosphere and let it rise, it will rise according to the adiabatic lapse rate until it is the same temperature as the surrounding air. This leads to several potential outcomes.

Polar easterlies

In the global pattern of prevailing winds, winds that blow from the polar high towards the subpolar low. Unlike the trade winds, however, these winds should not be thought of as persistent winds.

Drizzle

Precipitation from stratus clouds consisting of tiny droplets.

Coriolis and Atmospheric Circulation

On a rotating Earth the convection cells cannot reach the poles before being turned completely to the east or west due to the Coriolis effect. Thus, we have three convection cells on either side of the equator.

Cloud Formation

Relative humidities in excess of 100% would be needed to begin to nucleate water droplets and form clouds if it were not for aerosols (small solids suspended in the atmosphere). These particles serve as nucleation points and allow many tiny droplets to form. Clouds can be thought as collections of these tiny droplets that are so small they can be held aloft in the atmosphere.

Coriolis Effect and Wind

The Coriolis effect will work to turn the wind toward the East if it is moving away from the equator or to the west of it is moving away from the equator.

Storm surge

The abnormal rise of the sea along a shore as a result of strong winds.

Source region

The area where an air mass acquires its characteristic properties of temperature and moisture.

Pressure gradient force

The force that results from a difference in atmospheric pressure between two locations. Horizontal pressure gradient forces are what cause winds to blow.

Circle of illumination

The great circle that separates daylight from darkness.

Troposphere

The lowermost layer of the atmosphere. It is generally characterized by a decrease in temperature with height. This occupies the lowest 11 km of the atmosphere. It is where weather occurs and is the part of the atmosphere that we are most familiar with. The temperature here decreases with height. this makes sense if you remember the ideal gas law PV=nRT. The reduction in temperature with elevation in this is called the environmental lapse rate. The upper atmosphere plays an important role in blocking UV radiation (stratosphere).

Saturation

The maximum possible quantity of water vapor that the air can hold at any given temperature and pressure. The atmosphere can only hold so much water depending on it temperature. If it is fully saturated with water, then some will condense. This is what is happening when you observe fog or clouds.

Air

The mixture of gases and particles that make up Earth's atmosphere. Nitrogen and oxygen are most abundant.

Mountain breeze

The nightly downslope winds commonly encountered in mountain valleys.

Tropic of Cancer

The parallel of latitude, 23 1/2 degrees north latitude, marking the northern limit of the Sun's vertical rays.

Tropic of Capricorn

The parallel of latitude, 23 1/2 degrees south latitude, marking the southern limit of the Sun's vertical rays.

Vapor pressure

The part of the total atmospheric pressure that is attributable to water-vapor content.

Reflection

The process by which light, sound, or energy is returned without being absorbed or scattered. About 30% of the solar radiation that reaches Earth is reflected back into outer space. The fraction of solar radiation reflected by a given substance is known as albedo. Typically darker materials absorb radiation and lighter materials reflect.

Deposition

The process by which water vapor is changed directly to a solid, without passing through the liquid state.

Scattering

The process in which electromagnetic radiation or particles are deflected or diffused.

Evaporation

The process of converting a liquid to a gas.

Dry adiabatic rate

The rate of adiabatic cooling or warming in unsaturated air. The rate of temperature change is 1 degrees Celsius per 100 meters.

Wet adiabatic rate

The rate of adiabatic temperature change in saturated air. The rate of temperature change is variable, but it is always less than the dry adiabatic rate.

Environmental lapse rate

The rate of temperature decrease with increasing height in the troposphere.

Radiation

The transfer of energy (heat) through space by electromagnetic waves. The transmission of energy in the form of waves. you know UV radiation (think sunburn), visible light, and infrared (think heat).

Convection

The transfer of heat by the movement of a mass or substance. It can take place only in fluids. The movement of thermal energy through the bulk movement of molecules. It is driven by density differences between a mobile substance that is hot vs. cold.

Greenhouse effect

The transmission of short-wave solar radiation by the atmosphere coupled with the selective absorption of longer-wavelength terrestrial radiation, especially by water vapor and carbon dioxide. Transmission of short wavelength radiation and absorption of long-wavelength radiation by gases is how greenhouses are kept warm, and this relationship is why the absorption of gas in the atmosphere is called this.

Tornado Formation

They form in severe storms when rising air is able to tilt swirling masses of air near the Earth's surface into a vertical configuration. They most commonly form in storms moving along cold fronts where there is a dramatic difference in air temperature across the front. The middle of the US is perfect for this scenario.

Adiabatic Lapse Rate

This is the rate of temperature change for a package of air as pressure increases or decreases.

Localized convective lifting (convective lifting)

Unequal surface heating that causes localized pockets of air (thermals) to rise because of their buoyancy.

Three cloud types make up high clouds:

cirrus, cirrostratus, and cirrocumulus