Intro to Meteorology: Atmospheric Moisture, Clouds, Stability, and Precipitation

Comprehensive vocabulary flashcards covering atmospheric moisture, cloud classification, atmospheric stability, and precipitation processes from Intro to Meteorology lecture notes.

Sublimation

The phase change of water directly from a solid (ice) to a gas (water vapor) through an increase in energy.

Deposition

The phase change of water directly from a gas (water vapor) to a solid (ice).

Atmospheric Saturation

The equilibrium state occurring when the rate of evaporating water molecules equals the rate of condensing water molecules.

Condensation Nuclei

Microscopic airborne particles such as dust, smoke, and salt onto which water vapor readily adheres to condense.

Air Parcel

An imaginary volume of air defined as having flexible walls that prevent it from mixing with the surrounding environment.

Absolute Humidity

A measure of atmospheric moisture defined as the mass of water vapor in grams divided by the volume of air in cubic meters ($\text{g/m}^3$).

Specific Humidity

The weight of water vapor per unit weight of air, expressed as grams of water vapor per kilogram of air ($\text{g/kg}$).

Actual Vapor Pressure (AVP)

The pressure exerted solely by water vapor in the atmosphere, providing a measure of the total amount of water vapor molecules present.

Saturation Vapor Pressure

The pressure water vapor would exert if the atmosphere were completely saturated at a given temperature, which increases as temperature rises.

Relative Humidity (RH)

The ratio of the actual water vapor content in the air to the maximum water vapor capacity required for saturation at a given temperature and pressure, expressed as a percentage.

Dew Point

The temperature to which air must be cooled at constant pressure for saturation to occur; higher values indicate greater total moisture content.

Heat Index

The apparent temperature experienced by the human body, calculated by combining air temperature and relative humidity.

Fog

A cloud in contact with the ground, formed either by cooling the air to its dew point or by adding water vapor through evaporation.

Cirrus Clouds

High-level clouds formed above $20{,}000\text{ feet}$ that are thin, wispy, composed almost exclusively of ice crystals, and generally indicate fair weather.

Cirrocumulus Clouds

High-level clouds appearing as small, round, white puffs that occur in isolated patches or in rows producing a rippled appearance resembling the scales of a fish.

Cirrostratus Clouds

Thin, sheet-like high clouds that allow the sun and moon to shine through, frequently create halos, and predict approaching precipitation within $12\text{ to }24\text{ hours}$.

Altocumulus Clouds

Middle-level clouds with bases between $6{,}500\text{ and }23{,}000\text{ feet}$ appearing as gray, puffy masses or bands, whose castle-like vertical extensions (castellanus) can precede afternoon thunderstorms.

Altostratus Clouds

Middle-level clouds forming a grayish or bluish, milky overcast blanket where the sun is only dimly visible, shadows are absent, and widespread rain often follows.

Stratocumulus Clouds

Low-level clouds with bases below $6{,}500\text{ feet}$ that appear low and lumpy in rows or patches, often with blue sky visible between them, typically without precipitation.

Nimbostratus Clouds

Dark gray, wet-looking low clouds producing continuous light precipitation such as drizzle, rain, or snow, often accompanied by poor visibility and scud clouds.

Cumulonimbus Clouds

Vertically developed thunderstorm clouds with bases near $2{,}000\text{ feet}$ and tops reaching $40{,}000\text{ feet}$ or higher, sustained by strong updrafts and downdrafts.

Anvil

The flattened top of a tall cumulonimbus cloud pointing in the direction of the thunderstorm's motion.

Lenticular Clouds

Lens- or saucer-shaped clouds that form when moist air flows over mountainous barriers.

Pileus

A thin, scarf-like cloud capping the top of a growing cumulus or cumulonimbus cloud caused by deflected upward wind.

Mammatus Clouds

Pouch-like hanging sacs on the underside of a cumulonimbus cloud anvil, formed by sinking cool air and strong winds.

Contrail

A condensation trail composed of ice crystals formed in the wake of jet aircraft engines from exhaust particles and water vapor.

Wall Cloud

A low-hanging cloud feature that typically rotates counterclockwise beneath a cumulonimbus cloud, from which tornadoes can descend.

Shelf Cloud

A low, horizontal cloud formed when cool thunderstorm downdrafts spread out and force incoming warm, moist air to lift and condense.

Funnel Cloud

A rotating column of condensed water droplets extending downward from the base of a cloud that does not make contact with the ground.

Geostationary Orbiting Satellite

A satellite positioned at the equator at an altitude of approximately $22{,}300\text{ miles}$ that orbits at the same rate the Earth rotates to continuously observe a fixed area.

Polar Orbiting Satellite

A satellite that traverses over the North and South Poles while the Earth rotates underneath, providing detailed global imagery over multiple orbits.

Adiabatic Process

A thermodynamic process in which an air parcel expands and cools as it rises, or compresses and warms as it sinks, without exchanging heat with the surrounding environment.

Dry Adiabatic Lapse Rate (DALR)

The constant rate of temperature change for an unsaturated air parcel undergoing expansion or compression, equal to $10\,^\circ\text{C/km}$.

Moist Adiabatic Lapse Rate (MALR)

The rate of temperature change for a saturated air parcel undergoing expansion or compression, equal to approximately $6\,^\circ\text{C/km}$.

Environmental Lapse Rate (ELR)

The actual rate of temperature change with altitude in the surrounding atmosphere, measured vertically by launching a weather balloon.

Absolutely Stable Atmosphere

An atmospheric state occurring when the environmental lapse rate is less than both the moist and dry adiabatic lapse rates ($\text{ELR} < \text{MALR}$ and $\text{ELR} < \text{DALR}$), causing lifted air parcels to sink back.

Absolutely Unstable Atmosphere

An atmospheric state occurring when the environmental lapse rate is greater than both the moist and dry adiabatic lapse rates ($\text{ELR} > \text{MALR}$ and $\text{ELR} > \text{DALR}$), causing lifted air parcels to continue rising.

Orographic Lifting

Forced mechanical ascent of air up and over a topographic barrier like a mountain, yielding condensation and precipitation on the windward side.

Collision and Coalescence Process

A warm cloud precipitation process where falling droplets of different sizes and speeds collide and merge into larger raindrops.

Bergeron Process

A cold cloud precipitation process in mixed clouds where ice crystals grow by acquiring vapor at the expense of surrounding supercooled liquid water droplets.

Accretion

The process where falling ice crystals collide with supercooled liquid water droplets, causing them to freeze immediately and produce graupel.

Graupel

Snow pellets formed through the process of accretion when supercooled droplets freeze onto falling ice crystals.

Virga

Streaks of precipitation that fall from a cloud base but evaporate completely in dry air before reaching the ground.

Fallstreaks

Trails of ice crystals or snow falling from high-altitude cirrus clouds that evaporate or sublimate before reaching the surface.

Sleet

Tiny ice pellets formed when snowflakes melt into raindrops in a warm atmospheric layer aloft and subsequently refreeze while falling through a deep sub-freezing layer near the surface.

Freezing Rain

Precipitation that falls as supercooled liquid through a shallow freezing layer near the surface and freezes immediately upon contact with sub-freezing ground objects.

Blizzard

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

Hail

Precipitation consisting of layered or transparent pieces of ice produced in thunderstorms when strong updrafts repeatedly circulate frozen raindrops through sub-freezing upper cloud layers.

Tipping Bucket Rain Gauge

A precipitation-measuring instrument containing two small buckets that alternately fill with $0.01\text{ inches}$ of rain, tip over, and record electrical signals to track rainfall amounts.