ATM_SC 1050 Exam Study Guide: Chapters 4–7

Vocabulary flashcards covering core atmospheric science terminology from Chapters 4 through 7: atmospheric moisture, phase changes, humidity metrics, cloud classification, atmospheric stability, and precipitation processes.

Sublimation

The phase change where water transforms directly from a solid (ice) to a gas (water vapor) with energy added.

Deposition

The phase change where water transforms directly from a gas (water vapor) to a solid (ice) with energy removed.

Saturation

The balanced state where the rate of evaporating water molecules equals the rate of condensing water molecules ($\text{Evaporation} = \text{Condensation}$).

Condensation Nuclei

Tiny airborne particles of dust, smoke, and salt onto which water vapor molecules adhere and condense to begin cloud droplet formation.

Absolute Humidity

The mass of water vapor contained within a given volume of air, calculated as $\text{vapor mass} \div \text{volume}$ and expressed in $g/m^3$.

Specific Humidity

The mass of water vapor per unit mass of air, expressed in $g/kg$; it is the most reliable humidity measure because it does not change when an air parcel expands or contracts.

Relative Humidity (RH)

The ratio of water vapor actually in the air to the maximum amount needed for saturation at a given temperature and pressure, expressed as $(\text{Actual Vapor Pressure} \div \text{Saturation Vapor Pressure}) \times 100\%$.

Dewpoint

The temperature to which air must be cooled at constant pressure and water vapor content for saturation to occur.

Heat Index

The apparent or "feels like" temperature determined by combining air temperature and relative humidity.

Fog

A cloud in direct contact with the ground, formed either by cooling the air to its dewpoint or by adding water vapor through evaporation and mixing until saturation occurs.

Cirrostratus

A thin, sheet-like high-level cloud made of ice crystals that covers the sky and typically produces an optical halo around the sun or moon, predicting precipitation within $12\text{--}24\,\text{hours}$.

Cirrocumulus

A high-level cloud consisting of small, white, rounded puffs occurring individually or in rippling rows resembling fish scales ("mackerel sky").

Altocumulus

A middle-level cloud (bases between $6{,}500\text{--}23{,}000\,\text{ft}$) composed of water droplets and ice crystals forming gray, puffy masses arranged in waves or bands.

Altostratus

A gray or bluish middle-level cloud covering the sky like a thin blanket with a milky look, causing the sun to appear dimly without casting surface shadows.

Stratocumulus

A low-level cloud occurring below $6{,}500\,\text{ft}$ that appears low and lumpy in rows or patches, often with blue sky visible between elements, and is typically precipitation-free.

Nimbostratus

A dark gray, wet-looking low-level cloud that produces continuous, steady light-to-moderate precipitation (rain, drizzle, or snow) with poor visibility.

Cumulonimbus

A vertically developed thunderstorm cloud with low bases and tops extending to $60{,}000\text{--}80{,}000\,\text{ft}$, characterized by strong updrafts, heavy rain, lightning, hail, and an anvil top.

Anvil

The flat, spread-out top of a mature cumulonimbus cloud that points in the direction of storm movement under the influence of upper-level winds.

Castellanus

Vertical castle-like or tower-like extensions found on altocumulus clouds that serve as an indicator of instability aloft and possible afternoon thunderstorms.

Lenticular Cloud

A smooth, lens- or saucer-shaped cloud that hovers over a mountain, formed when moist air flows in waves over high topography while the cloud remains stationary.

Pileus

A thin cap cloud that forms over the top of a rapidly developing cumulus or cumulonimbus cloud when moist winds are deflected upward and over the cloud summit.

Mammatus

Rounded, pouch-like or udder-like sacs hanging beneath the anvil of a cumulonimbus cloud, created by sinking cold air and strong winds.

Contrail

Short for condensation trail; a high ice-and-water cloud forming in the wake of jet aircraft engines from exhaust particles and water vapor.

Wall Cloud

A low-hanging cloud that typically rotates beneath the updraft region of a cumulonimbus cloud and from which tornadoes can descend.

Shelf Cloud

A low, horizontal, wedge-shaped cloud along the leading edge of a thunderstorm formed as cold downdraft outflow cuts beneath warm moist updraft air; it is non-rotating and indicates strong straight-line winds.

Geostationary Satellite

A satellite positioned at the equator roughly $22{,}300\,\text{miles}$ above the surface that orbits at the same speed Earth rotates to continuously observe a fixed geographic area.

Polar-Orbiting Satellite

A satellite that traverses over the north and south poles while Earth rotates beneath it, capturing high-detail imagery across successive orbits.

Infrared (IR) Satellite Imagery

Satellite imagery that measures radiated temperature day and night; colder, higher cloud tops emit less radiation and appear bright white, whereas warmer, lower surfaces appear dark.

Air Parcel

An imaginary volume of air with flexible walls that does not mix with the surrounding environment, used to model vertical atmospheric motions and thermodynamic changes.

Adiabatic Process

A thermodynamic change in which an air parcel expands and cools or compresses and warms purely through pressure changes, without exchanging heat with the surrounding environment.

Dry Adiabatic Lapse Rate (DALR)

The constant rate of $10\,^\circ\text{C/km}$ at which a rising unsaturated air parcel cools by expansion (or a sinking parcel warms by compression).

Moist Adiabatic Lapse Rate (MALR)

The rate of approximately $6\,^\circ\text{C/km}$ at which a saturated rising air parcel cools; it is less than the DALR because condensing moisture releases latent heat.

Environmental Lapse Rate (ELR)

The actual rate of temperature change of the ambient surrounding air with height, directly measured by a weather balloon (radiosonde).

Absolutely Stable Atmosphere

An atmospheric state occurring when $\text{ELR} < \text{MALR}$; any lifted air parcel is colder and denser than its environment at all levels and sinks back to its origin.

Absolutely Unstable Atmosphere

An atmospheric state occurring when $\text{ELR} > \text{DALR}$; any lifted air parcel is warmer and less dense than its surroundings at all levels and continues rising freely.

Orographic Lifting

The forced ascent of an air mass over a topographic barrier like a mountain, yielding cooling, clouds, and precipitation on the windward side and a warm, dry rain shadow on the leeward side.

Collision and Coalescence

The warm-cloud precipitation process where larger cloud drops fall faster than smaller drops, colliding with and merging into them to form raindrops.

Bergeron Process

The cold-cloud precipitation process where ice crystals grow rapidly at the expense of surrounding supercooled liquid water droplets because saturation vapor pressure is lower over ice than over water.

Supercooled Droplets

Liquid water droplets that remain in a liquid state at ambient temperatures below freezing ($0\,^\circ\text{C}$).

Accretion (Riming)

The growth of an ice crystal as it collides with supercooled liquid water droplets that freeze instantly upon contact, producing graupel (snow pellets).

Virga

Precipitation that falls from a cloud base but evaporates completely in dry air before reaching the ground, appearing as wispy streaks hanging beneath clouds.

Fallstreaks

Ice crystals falling from high cirrus clouds that sublimate or evaporate into drier air below, appearing as delicate, wispy streamers.

Sleet

Clear to translucent ice pellets formed when snow melts completely in a warm layer aloft and then refreezes before reaching the ground while passing through a deep sub-freezing surface layer.

Freezing Rain

Precipitation that falls as supercooled liquid drops through a shallow surface sub-freezing layer and freezes instantly upon contact with cold objects, forming a hazardous glaze of ice.

Blizzard

A severe winter weather event characterized by sustained conditions of falling or blowing snow reducing visibility to less than $1/4\,\text{mile}$ and frequent wind gusts of $35\,\text{mph}$ or greater for at least $3\,\text{hours}$.

Hail

Layered balls or lumps of ice produced in cumulonimbus updrafts, where frozen drops are repeatedly carried into cold upper regions until they exceed the updraft's capacity and fall.

Tipping Bucket Rain Gauge

A meteorological recording device with two balanced miniature buckets that alternately tip and empty each time $0.01\,\text{inch}$ of precipitation collects, triggering an electronic measurement contact.

Cirrus

A high-level cloud formed above $20{,}000\,\text{ft}$ that is thin, wispy, and composed almost entirely of ice crystals, indicating fair weather and upper-level wind direction.

Stratus

A uniform, low-level grayish cloud layer covering the entire sky like elevated fog without contacting the ground, frequently producing light mist or drizzle.

Cumulus

A vertically developing cloud characterized by a sharp, flat, gray base and buoyant, white, cotton-ball dome tops formed by rising thermals.

Cumulus humilis

A fair-weather cumulus cloud exhibiting only slight vertical development, indicative of a stable atmospheric environment that suppresses deep convection.

Cumulus congestus

A towering cumulus cloud exhibiting substantial vertical growth and turbulent tops, capable of generating heavy rain showers and evolving into a thunderstorm.

Scud Clouds

Ragged, wind-torn cloud fragments that break away beneath nimbostratus or cumulonimbus bases in zones of high turbulence and moisture.

Undulatus Asperatus

A dramatic, wavy cloud formation characterized by visible rolling, undulating fluid waves rippling through the cloud base.

Luke Howard's Cloud Roots

The four foundational Latin terms describing cloud morphology: stratus (layer), cumulus (heap or pile), cirrus (curl of hair), and nimbus (rain-bearing).

Factors Accelerating Evaporation

Increases in water or ambient temperature, which provide molecules with kinetic escape energy, along with wind or mixing, which removes saturated air from the liquid interface.

Actual Vapor Pressure (AVP)

The partial pressure contributed exclusively by water vapor molecules within an air sample, reflecting the absolute quantity of vapor present.

Saturation Vapor Pressure (SVP)

The maximum partial pressure achievable by water vapor at a given temperature, increasing exponentially as warmer air expands its thermodynamic capacity for vapor.

Diurnal Cycle of Relative Humidity

The typical daily pattern where relative humidity reaches its highest value near sunrise during the temperature minimum and drops to its lowest value in mid-afternoon during peak heating.

Visible Satellite Imagery

Meteorological imagery operating strictly during daylight that captures reflected sunlight, wherein optically thick clouds reflect high albedo and appear brilliant white.

Water Vapor Satellite Imagery

Imagery tracking moisture content in the middle and upper troposphere across day and night, presenting dry descending air as orange or black and moist ascending air as green or white.

ASOS Cloud Detection Ceiling

The vertical detection ceiling of $12{,}000\,\text{ft}$ above which automated surface observing instruments cannot detect or report cloud cover.

Okta

The standard meteorological measurement unit representing fractional sky cloud cover in eighths, ranging from $0/8$ to $8/8$.

Sky Cover Categories

Standard meteorological sky classifications: Clear ($0/8$), Few ($1/8\text{--}2/8$), Scattered ($3/8\text{--}4/8$), Broken ($5/8\text{--}7/8$), and Overcast ($8/8$).

Conditionally Unstable Atmosphere

The atmospheric state occurring when $\text{MALR} < \text{ELR} < \text{DALR}$, where a lifted parcel remains stable and denser if unsaturated, but becomes buoyant and unstable if forced to saturation.

Neutral Atmosphere

The atmospheric equilibrium occurring when $\text{ELR} = \text{DALR}$ for unsaturated air or $\text{ELR} = \text{MALR}$ for saturated air, causing a displaced parcel to experience zero net acceleration.

Radiosonde

A sensor package transported by a weather balloon to gather vertical environmental profiles of temperature, moisture, and pressure to establish the environmental lapse rate.

Atmospheric Stabilization Mechanisms

Environmental processes that decrease the lapse rate by cooling surface air (such as nocturnal radiational cooling) or warming air aloft (such as warm air advection).

Atmospheric Destabilization Mechanisms

Environmental processes that increase the lapse rate by warming the ground through solar insolation or cooling the upper troposphere through cold air advection or cloud-top radiational cooling.

Convective Cloud Development Chain

The multi-step sequence where solar insolation heats the Earth's surface, boundary-layer air warms via conduction, buoyant thermals rise and cool adiabatically, and condensation initiates at the lifting condensation level.

Convergence

A mechanical lifting process occurring when horizontal air streams flow toward a central low-pressure area and are forced upward, generating cloud development.

Frontal Uplift

A dynamic lifting process where a warm, buoyant air mass is forced up and over a cooler, denser air mass along a sloping boundary.

Tropopause Convective Cap

The thermal boundary above which temperatures stop decreasing and begin warming into the stratosphere, establishing extreme stability that terminates vertical updrafts and causes cumulonimbus clouds to flatten into anvils.

Graupel

White, opaque, rounded snow pellets formed when falling ice crystals collide with supercooled liquid cloud droplets that freeze instantly upon impact through accretion.

Snow-to-Liquid Ratio

The volumetric measurement comparing snowfall depth to its melted liquid equivalent, commonly averaging $10:1$ ($10\,\text{inches}$ of snow yields

Sublimation

The phase change where water transforms directly from a solid (ice) to a gas (water vapor) with energy added.

Deposition

The phase change where water transforms directly from a gas (water vapor) to a solid (ice) with energy removed.

Melting

The phase change where water transforms from a solid (ice) to a liquid with energy added.

Freezing

The phase change where water transforms from a liquid to a solid (ice) with energy removed.

Saturation

The balanced state where the rate of evaporating water molecules equals the rate of condensing water molecules ($\text{Evaporation} = \text{Condensation}$).

Condensation Nuclei

Tiny airborne particles of dust, smoke, and salt onto which water vapor molecules adhere and condense to begin cloud droplet formation.

Hydrologic Cycle

The continuous circulation of water through the atmosphere, oceans, land, and living organisms via evaporation, transpiration, condensation, precipitation, and runoff.

Absolute Humidity

The mass of water vapor contained within a given volume of air, calculated as $\text{vapor mass} \div \text{volume}$ and expressed in $\text{g/m}^3$.

Specific Humidity

The mass of water vapor per unit mass of air, expressed in $\text{g/kg}$; it remains constant when an air parcel expands or contracts without mass exchange.

Relative Humidity (RH)

The ratio of water vapor actually in the air to the maximum amount needed for saturation at a given temperature and pressure, expressed as $(\text{Actual Vapor Pressure} \div \text{Saturation Vapor Pressure}) \times 100\%$.

Mechanisms to Change Relative Humidity

The two methods to alter relative humidity: changing water vapor content (adding or removing moisture) or altering air temperature (which changes water vapor capacity).

Dewpoint

The temperature to which air must be cooled at constant pressure and water vapor content for saturation to occur.

Heat Index

The apparent or "feels like" temperature determined by combining ambient air temperature with relative humidity.

Fog

A cloud in direct contact with the ground, formed either by cooling the air to its dewpoint or by adding water vapor through evaporation and mixing until saturation occurs.

Two Primary Methods of Fog Formation

Cooling the air down to its saturation point (dewpoint), or adding moisture via evaporation and mixing until saturation is achieved.

Cirrus

A high-level cloud formed above $20{,}000\,\text{ft}$ that is thin, wispy, and composed almost entirely of ice crystals, indicating fair weather and upper-level wind direction.

Cirrostratus

A thin, sheet-like high-level cloud made of ice crystals that covers the sky and typically produces an optical halo around the sun or moon, predicting precipitation within $12\text{--}24\,\text{hours}$.

Cirrocumulus

A high-level cloud consisting of small, white, rounded puffs occurring individually or in rippling rows resembling fish scales ("mackerel sky").

Altocumulus

A middle-level cloud (bases between $6{,}500\text{--}23{,}000\,\text{ft}$) composed of water droplets and ice crystals forming gray, puffy masses arranged in waves or bands.

Altostratus

A gray or bluish middle-level cloud covering the sky like a thin blanket with a milky look, causing the sun to appear dimly without casting surface shadows.

Stratocumulus

A low-level cloud occurring below $6{,}500\,\text{ft}$ that appears low and lumpy in rows or patches, often with blue sky visible between elements, and is typically precipitation-free.

Nimbostratus

A dark gray, wet-looking low-level cloud that produces continuous, steady light-to-moderate precipitation (rain, drizzle, or snow) with poor visibility.

Stratus

A uniform, low-level grayish cloud layer covering the entire sky like elevated fog without contacting the ground, frequently producing light mist or drizzle.

Cumulus

A vertically developing cloud characterized by a sharp, flat, gray base and buoyant, white, cotton-ball dome tops formed by rising thermals.

Cumulus humilis

A fair-weather cumulus cloud exhibiting only slight vertical development, indicative of a stable atmospheric environment that suppresses deep convection.