Moisture in the Atmosphere and Precipitation

Vocabulary terms and concepts covering atmospheric moisture, vertical circulation, adiabatic processes, lapse rates, cloud formation, and precipitation physics.

The Sun

The primary source of energy that drives weather and the water cycle.

Vapor Transport

The movement of water vapor through the atmosphere between the ocean, land, and atmosphere.

Conduction

The process where heat energy from the Earth's surface is transferred to the air directly in contact with that surface.

Convection

The upward transfer of heat by warmer, less dense air rising through the atmosphere.

Isothermal

A state where temperature remains constant; the transcript notes that the atmosphere is not isothermal.

Adiabatic change

A process where no energy from the surrounding atmosphere is exchanged across the boundaries of a defined volume or parcel of air.

Adiabatic cooling

The cooling of a gas as it expands under adiabatic conditions without the gain or loss of heat, identified as the main cause of cloud formation.

Sensible heat

Heat added or removed from a system that results in a change in temperature.

Latent heat

Heat added or removed from a system to cause a phase change (e.g., melting, evaporation) without changing the temperature.

Moist air

A mixture of dry-air constituents (nitrogen, oxygen, etc.) and a variable amount of water vapor.

Humidity

A description of the atmosphere's capacity to contain water vapor, varying due to evaporation and condensation.

Partial pressure

The pressure exerted by a single gas within a mixture of gases.

Vapor pressure

The partial pressure exerted specifically by water vapor in the atmosphere.

Saturation vapor pressure

A function of temperature where evaporation equals condensation; it increases as temperature increases.

Lifting condensation level (LCL)

The altitude in the atmosphere where a rising air parcel reaches saturation and a cloud base forms.

Lapse Rate

A quantification of how temperature changes with height, specified in units of $\text{}^ ext{o} ext{C/km}$.

Environmental temperature lapse rate (ELR)

The actual rate of temperature decrease with altitude in the vertical troposphere, averaging approximately $6.5^ ext{o} ext{C/km}$.

Temperature inversion

A condition, often occurring at night close to the ground, where the ELR is negative and air temperature increases with height.

Dry adiabatic temperature lapse rate (DALR)

The rate at which a parcel of air containing no liquid water cools as it ascends (or warms as it descends), estimated at $1.00^ ext{o} ext{C} / 100 ext{\,m}$ or $10^ ext{o} ext{C/km}$.

Wet adiabatic temperature lapse rate (WALR)

The rate at which a parcel of saturated air containing liquid water changes temperature, estimated at $0.50^ ext{o} ext{C} / 100 ext{\,m}$ or $5^ ext{o} ext{C/km}$.

Condensation nuclei

Microscopic aerosol particles (dust, sea spray, or pollution) that provide surfaces for water vapor to condense upon at the point of saturation.

Aitken nucleus

A class of condensation nucleus with a diameter strictly less than $0.2\,\mu ext{m}$.

Normal nucleus

A condensation nucleus with a diameter ranging from $0.2\,\mu ext{m}$ to $2\,\mu ext{m}$.

Giant nucleus

A condensation nucleus with a diameter greater than $2\,\mu ext{m}$.

Homogeneous nucleation of condensation

The formation of pure water droplets from supersaturated vapor without the aid of aerosols; this does not occur in nature.

Heterogeneous nucleation on aerosols

The formation of droplets in nature using atmospheric aerosols as nuclei, determined by the number, type, and size of the aerosols.

Hydrophytic (wettable)

A property of aerosols that allows condensed water to flow over the surface, making them favorable for droplet formation.

Collision-Coalescence

The process by which cloud droplets grow into raindrops by bumping into and merging with one another.

Cloud physics

The study of physical processes leading to the formation, growth, and precipitation of clouds.

Hygroscopic seeding

A cloud modification application for warm clouds intended to increase precipitation.

Glaciogenic seeding

A cloud modification application specifically for cold clouds.