Atmospheric Moisture

Percentage of Earth made up of water

$$70\%$$

Percentage of total Earth water held in oceans

$97\%$ (saltwater)

Percentage of total Earth water that is freshwater

$$2.5\%$$

Percentage of freshwater frozen as ice and permafrost

$$69\%$$

Percentage of freshwater found in lakes

$$21\%$$

Percentage of freshwater found in the atmosphere

$$3\%$$

Percentage of total water that is surface freshwater

$$1.2\%$$

Most important physical property of water in Earth's atmosphere

It can exist in three physical states (solid, liquid, gas) within the temperature ranges found on Earth.

Latent heat

Heat energy involved in phase changes that cannot be measured directly with a thermometer.

Phase changes during which latent heat is stored

Melting, evaporation, and sublimation.

Phase changes during which latent heat is released

Freezing, condensation, and deposition.

Global function of atmospheric latent heat transfers

Provides a mechanism for moving large amounts of heat energy from one region of Earth to another.

Specific heat

A measure describing how much the temperature of a substance changes with a given input of heat energy.

Specific heat of water compared to land

The specific heat of water is $4$ times greater than that of land.

Hydrologic cycle

A continuous loop in which water moves from oceans to the atmosphere, to land and water bodies, and back again.

Primary source of maximum global evaporation

Tropical and subtropical oceans between $40^\circ\,\text{N}$ and $40^\circ\,\text{S}$.

Key principle governing maximum air moisture capacity

It depends on temperature: warm air can hold significantly more water vapor than cold air.

Absolute humidity

The actual mass or amount of water vapor present in a given volume of air.

Factor that changes absolute humidity without changing water vapor content

Expansion or compression of air in the atmosphere.

Vapor pressure

The portion of total atmospheric pressure exerted specifically by water vapor.

Water vapor capacity

The maximum amount of water vapor that air can hold at a given temperature.

Relative humidity

The proportion of water vapor present relative to the maximum amount of water vapor air could hold at that same temperature.

Formula for relative humidity

$$\text{Relative Humidity} = \left(\frac{\text{Vapor Pressure}}{\text{Water Vapor Capacity}}\right) \times 100\%$$

Specific humidity

The mass of water vapor in a body of air compared to the total mass of the air ($\text{g/kg}$).

Factors affecting specific humidity

It is unaffected by temperature, pressure, or volume changes; it changes only by adding or subtracting water vapor.

Dew Point Temperature

The temperature to which air must be cooled for saturation to occur.

Effects of cooling air to its dew point and beyond

Cooling to the dew point reaches saturation ($100\%$ relative humidity); cooling beyond leads to condensation.

Adiabatic cooling

The cooling of an air parcel without heat energy removal, caused by expansion as atmospheric pressure decreases.

Key principle of adiabatic temperature changes

Heating and cooling occur purely as a result of atmospheric pressure changes.

Unsaturated Adiabatic Lapse Rate (UALR)

$1^\circ\text{C}$ per $100\,\text{m}$

Saturated Adiabatic Lapse Rate (SALR)

$0.5^\circ\text{C}$ per $100\,\text{m}$

Reason why SALR is lower than UALR

Latent heat energy released during condensation slows down the rate of cooling.

Lifting Condensation Level (LCL)

The altitude at which rising air cools to its dew point and condensation occurs, forming the flat base of clouds.

Environmental Lapse Rate (ELR)

The temperature change with altitude in a stationary column of air, averaging $0.65^\circ\text{C}$ per $100\,\text{m}$.

Stable atmosphere characteristics

Gentle ELR (cools slowly with altitude, $\approx 0.5^\circ\text{C}$ per $100\,\text{m}$); air parcels resist rising.

Unstable atmosphere characteristics

Steep ELR (cools quickly with altitude, $> 1^\circ\text{C}$ per $100\,\text{m}$); rising air parcels remain warmer than surrounding air and continue to rise.

Two essential conditions required for precipitation

Atmospheric moisture and adiabatic cooling to the Dew Point Temperature.

Condensation nuclei

Tiny suspended particles (such as dust, smoke, or salt) required for water vapor to condense upon.

Bergeron Ice Crystal Process

Precipitation formation process occurring in cold clouds at temperatures of $32^\circ\text{F}$ ($0^\circ\text{C}$) or lower, common in middle and high latitudes.

Collision-Coalescence Process

Precipitation formation process occurring in warm clouds, producing most tropical rainfall.

Forms of precipitation (Rain, Snow, Sleet, Freezing Rain, Hail)

Rain: Liquid water droplets. Snow: Ice crystals. Sleet: Rain droplets freezing in mid-air. Freezing Rain: Rain freezing upon contact with Earth's surface. Hail: Concentric ice layers formed on ice crystals in updrafts.

Percentage of Earth covered by clouds at any given time

$$50\%$$

Two criteria used to classify clouds

Form (shape/structure) and altitude (elevation).

Stratus clouds

Layered clouds covering large areas, found below $10\,000\,\text{ft}$.

Cirrus clouds

High, thin, wispy clouds composed of ice crystals, found above $20\,000\,\text{ft}$.

Cumulus clouds

Tall, heaped clouds reaching $40\,000$ to $60\,000\,\text{ft}$, capable of producing violent storms.

Meaning of cloud prefix or suffix "Nimbo" / "Nimbus"

Indicates that the cloud produces precipitation (e.g., Nimbostratus, Cumulonimbus).