Unit 7 - Physical Geography

Latent heat transfer

Energy transferred during a change in the phase of water

Specific heat

The amount of heat required to raise the temperature of a substance

Humidity

The amount of water vapor present in the air

Specific humidity

The mass of water vapor held by a parcel of air expressed in g/kg

Relative humidity (RH)

The amount of water vapor in the air relative to the maximum amount it can hold at that temperature

Relative humidity formula

RH = (100 × specific humidity) / saturation-specific humidity

Saturated air

Air with a relative humidity of 100%

Dew point temperature

The temperature at which air holds the maximum amount of water vapor possible

What happens at the dew point

Air becomes saturated and condensation can begin

What happens to RH when air temperature decreases

Relative humidity increases if the amount of water vapor stays the same

What happens to RH when air temperature increases

Relative humidity decreases if the amount of water vapor stays the same

Two ways relative humidity can change

Water vapor can be gained or lost through phase changes or air temperature can change

Adiabatic process

Heating or cooling that occurs solely as a result of pressure change

What happens to rising air

It expands and cools

What happens to sinking air

It compresses and warms

Dry adiabatic rate (DAR)

The rate at which unsaturated air cools or warms as it changes elevation

Dry adiabatic rate in Celsius

10°C per kilometer

Dry adiabatic rate in Fahrenheit

5.5°F per 1000 feet

What does dry mean in DAR

Unsaturated air with no condensation

Lifting condensation level (LCL)

The point where rising air cools to its dew point temperature

What happens at the LCL

Air becomes saturated at 100% RH and condensation begins so clouds can form

Moist adiabatic rate (MAR)

The rate at which saturated air cools as it rises

Moist adiabatic rate in Celsius

6°C per kilometer

Moist adiabatic rate in Fahrenheit

3.3°F per 1000 feet

Why is MAR lower than DAR

Condensation releases latent heat which slows the cooling of saturated air

Four causes of upward air motion

Convergence and convection and orographic lifting and frontal lifting

Convergence

Wind moves together in one location due to pressure gradients and forces air upward

Convection

Air heated by a warm surface rises because it becomes less dense

Orographic lifting

Air moves up and over a mountain range

Windward side

The side of a mountain facing incoming air where air rises and precipitation can occur

Leeward side

The side of a mountain away from incoming air where air sinks and a dry rain shadow can form

Rain shadow

A dry area on the leeward side of a mountain

Frontal lifting

One air mass overtakes another and forces warmer air aloft

Condensation nuclei

Particles such as sea salt and dust and aerosols on which water vapor condenses

Cloud

A collection of water droplets or ice particles or both suspended in the air

Fog

A cloud layer at or close to the surface

Advection fog

Fog caused when air moves over a cooler or warmer surface and a temperature change causes condensation

Evaporation fog

Fog that occurs over water

Upslope fog

Fog that occurs because of adiabatic processes as air moves upslope

Valley fog

Fog associated with cold dense air sinking into a valley

Radiation fog

Fog formed when radiative cooling of the ground cools the air above it to its dew point

Why is radiation fog unlikely over water

Water temperature changes more slowly than land so the surface usually cools less quickly

Precipitation

Liquid or solid water falling from the sky

What must happen before precipitation falls

Water droplets or ice crystals must grow large enough to fall

Collision-coalescence process

Cloud droplets collide and combine into larger droplets

Bergeron-Findeisen process

Water vapor deposits onto ice crystals and water droplets evaporate to supply more vapor

Melting

The phase change from solid to liquid

Freezing

The phase change from liquid to solid

Evaporation

The phase change from liquid to gas

Condensation

The phase change from gas to liquid

Sublimation

The phase change from solid directly to gas

Deposition

The phase change from gas directly to solid

What happens to heat during melting and evaporation

Heat is absorbed

What happens to heat during freezing and condensation

Heat is released

Specific humidity versus relative humidity

Specific humidity measures the mass of water vapor while relative humidity compares actual water vapor with the maximum possible at that temperature

How does warm air affect moisture capacity

Warm air can hold more water vapor than cooler air

Cirrus

High thin wispy clouds

Cirrocumulus

High clouds made of small cloud patches

Cirrostratus

High thin sheet-like clouds that can produce a halo

Altocumulus

Middle-level clouds appearing in patches or rounded masses

Altostratus

Middle-level layered clouds

Nimbostratus

Thick layered clouds associated with prolonged precipitation

Stratus

Low layered clouds

Stratocumulus

Low clouds in rounded layers or groups

Cumulus

Puffy clouds often associated with fair weather

Cumulonimbus

Tall clouds associated with thunderstorms and strong vertical development

Lenticular clouds

Lens-shaped clouds often associated with airflow over mountains

Rain

Frozen precipitation melts and reaches the ground as rain

Freezing rain

Frozen precipitation melts in warm air then freezes on cold surfaces

Sleet

Frozen precipitation melts in shallow warm air then refreezes before reaching the surface

Snow

Snow falls through cold air and reaches the surface