Physical Geography Exam 2

the measured weight of air as it exerts pressure on Earth’s surface
decreases with increasing altitude
Air density is greatest near the Earth’s surface

Warm air results in lower air pressure
Cooler air results in higher air pressure

Barometer

Air pressure changes with altitude
Average air pressure at sea level = 1013.25 mb

A circulating body of air that exerts relatively high pressure as air sinks toward the surface
Air flow diverges

A circulating body of air where relatively less pressure is created as air rises away from the surface
Air flow converges

create large-scale circulatory systems that are interconnected by airflow

the process by which air flows horizontally from high-pressure to low-pressure

Isobars indicate the geographic patterns of pressure systems
Red arrows illustrate the path of airflow relative to pressure systems

Winds are named for the direction in which they originate

causes motion in the atmosphere

The greater the difference in pressure, the steeper the gradient
The steeper the gradient, the faster the airflow

Due to Earth’s rotation
Deflects objects traveling in the atmosphere
Earth’s eastward rotation below
Northern Hemisphere, deflection is to the right
Southern Hemisphere, deflection is to the left

Occurs at ground level
Strongest at surface, diminishing at about 1500 m (5000 ft)
Causes wind to slow down and move in irregular ways

spiraling descending and rising air are linked horizontally by advection

the tropical convection loop
Air at tropics is warmed by year-round direct sunlight

Warming creates a zone of low pressure at Equator as air rises into the atmosphere
Winds converge into ITCZ by advection

Air rising from ITCZ eventually sinks at subtropics creating zones of high pressure
Dry and warm winds diverge from STH

the circulatory loop that mixes cool polar air with warm tropical air

the line of contact between contrasting air masses at about 60 N/S

formed by high-altitude winds that are formed with the temperature/pressure gradient

develop as undulations in the Polar Front and moderate significant temperature difference on either side

the circulatory loop in the polar regions

Air flowing northward from midlatitudes sinks, producing a weak high-pressure system
Consists of masses of rotating, descending dry air that flows toward the Polar Front

Trade Winds ITCZ
STH Westerlies and Trade Winds
Westerlies and Polar Easterlies Polar Front
Polar High Polar Easterlies

Seasonal shift of the ITCZ and prevailing wind direction in the subtropics

Winter: ITCZ in south
Cold air, high pressure
Summer: ITCZ in north
Warm air, low pressure

Breeze blows from high- pressure sea to low- pressure land

Breeze blows from high- pressure land to low- pressure sea

Breeze blows upslope as mountain slopes heat up

Breeze blows downslope as mountain slopes cool off

Extremely cold, dense air flows downslope under force of gravity
Flow at great speeds

Occurs when a steep pressure gradient develops in mountainous regions
high pressure on windward side
low pressure on leeward side

Surface currents are driven by winds as energy transfers by friction

form as continents block the movement of water

Slow vertical mix of water between layers of the ocean

caused by high-density water that is cooler and saltier

caused by low-density water that warms in tropical regions

Reversal of “normal” flow of currents and winds in tropical Pacific
Occurs every 3-8 years
Affects climate
Changes ocean surface temperature
Changes patterns of precipitation

Collection of turbines used to harness wind power
Conversion to clean usable energy

Attraction between the hydrogen atoms of water molecules
Explains water’s physical states

Movement of water between various storage locations
Amount of water is finite
Total amount evaporated equals the total precipitated globally
Yet, local and regional imbalances occur

refers to the concentration of water vapor in the air

Maximum amount of water vapor that a body of air can hold
Subject to air temperature
Warm air can hold more water vapor than cold air

the point where the air cannot hold any more water vapor at its current temperature

How much water vapor is actually in the air

Ratio of specific humidity to maximum humidity
How close the air is to saturation, at its current temperature

Specific humidity is low
Relative humidity is high

Specific humidity is high
Relative humidity is low

Maximum humidity increases with warming
Specific humidity is constant
Relative humidity gradually decreases

Temperature at which a mass of air is saturated
Related to changes in relative or specific humidity

results in evaporation directly from leaf pores in plants into the atmosphere

the combination of evaporation and transpiration

Net radiation which increases heating
Air temperature which influences maximum humidity
Relative humidity and moisture capacity of air

Applies to unsaturated air
Dry air cools or warms at 10C/1000 m or 5.5F/1000 ft

Applies to air that reaches the level of condensation, or the altitude of saturation
Rate varies with moisture content and temperature
Average rate is about 10C/1000 m or 5.5F/1000 ft

visible masses of suspended, minute water droplets or ice crystals

Air must be saturated
Either by cooling below the dew point or by adding water vapor to the air

There must be a substantial quantity of small airborne particles for water vapor to collect
Such particles are known as condensation nuclei

Form
Cirrus
Cumulus
Stratus

Altitude
High
Middle
Low

develops at night when air cools to the dew point and is held below a temperature inversion, or an overlying body of warmer air

develops when warm air flows over a cooler surface, cooling it to the dew point

develops when cool marine air comes in direct contact with colder ocean water

Air cools at DAR to dew point
Forms clouds that cool at WAR and precipitation follows

Air descends downslope, warming at DAR
Creates rain shadow of dry conditions

Airflow interrupted by a mountain range

Unequal heating of Earth’s surfaces

little convection and no precipitation

strong convection bubbles lift and create precipitation

a large body of the lower atmosphere with uniform conditions of temperature and moisture

any large body of land or water where air derives its characteristics

Boundaries between differing air masses
When one air mass advances in a front,
frontal uplift causes clouds and/or precipitation

Warm air advances
Warm air slowly lifted

Cold air advances
Warm air rapidly lifted

A well-organized low-pressure system that migrates across a region while it spins

500-mb upper air-pressure surface
Occurs at a specific but varying altitude over any given place on Earth
Vertically divides atmosphere in two, from surface to top
Explains pressure changes associated with temperature change

form when height of pressure surface is higher and anticyclones occur

form when height of pressure surface is lower and cyclones occur

is the process that forms midlatitude cyclones
Conditions in upper atmosphere and surface are significant
Upper-level convergence sends air to the surface, creating high pressure
Upper-level divergence allows air to rise, creating low pressure

Cumulus Stage
Begins with convection or advancing cold front into mT air
Rapid rising air forms cumulus clouds
Developing Stage
Condensation releases latent heat
Mature Stage
Very unstable air with development of strong updrafts
Intense precipitation brings cold air down to create downdrafts
Dissipation Stage

Collisions among ice crystals and rain droplets cause difference in electrical charge within clouds
Ground has positive (+) charge
Most lightning within clouds from positive (+) to negative (-)
In strong storms, leader (-) from cloud meets streamer (+) from ground, creating “spark” as cloud-to-ground lightning

Small, intense cyclone formed in supercell thunderstorms

are large rotating updrafts
Form at high altitudes with strong updrafts and wind shear
A horizontal vortex of air gets pulled vertically in updrafts

Develop in homogeneous air masses at low latitudes
Fueled by abundant water vapor and latent heat
Early Formation:
Easterly Wave slow-moving trough migrates along tropical easterlies
Upper air converges on windward side and diverges on leeward side, causing rapid uplift

Tropical storms in the Atlantic or eastern Pacific with very high winds
Rare combination of environmental variables:
Warm ocean surface
High evaporation
Favorable upper air winds
High pressure aloft

Around the eye, air flows inward and upward
In the eye, air flows toward surface and warms

Originate in West Africa driven by trade winds
Intensify over warm tropical Atlantic
Driven northeast by westerlies

the state of the atmosphere at a specific place and time on Earth’s surface

the long-term average values of weather elements, such as temperature and precipitation

Most widely used classification system
Stems from the recognized relationship between major vegetation regions and regional climate characteristics
System’s description of world climates is based on
Average monthly temperature
Average monthly precipitation
Total annual precipitation

Surrounds the Equator from 25 N/S
Consistently warm average temperatures
Subcategories based on precipitation only
Tropical rainforest (Af)
Tropical monsoon (Am)
Tropical savanna (Aw)

Poleward of A climates
Subtropical high creates precipitation patterns
Subcategories based on precipitation and temperature:
Hot low-latitude desert (BWh)
Cold midlatitude desert (BWk)
Hot low-latitude steppe (BSh)
Cold midlatitude steppe (BSk)

20 to 60 N/S
Distinct warm seasons and cold seasons
Subcategories
Humid Subtropical Hot-Summer (Cfa, Cwa)
Mediterranean Dry-Summer (Csa, Csb)
Marine West Coast (Cfb, Cfc)

35 to 60 N/S
Longer cold seasons and limited warm seasons
Subcategories:
Humid Continental Hot-Summer (Dfa, Dwa)
Humid Continental Mild-Summer (Dfb, Dwb)
Subartctic (Dfc, Dwc, Dwd)

Nonmountainous areas poleward of 70 N/S
Long, cold winters with little precipitation
Subcategories
Tundra (ET)
Ice cap (EF)