Weather and Climate

Evaporation from the ocean

Transport through the atmosphere

Condensation and precipitation

Return to the ocean

Many smaller sub cycles

Clouds form when air masses are cooled to their dew point

Generally cooled by upward movement

Cloud formation depends on atmospheric stability

Stable atmosphere

lifted parcel of air to cooler (and denser) than surrounding air

lifted parcel returns to the original level

Unstable atmosphere

lifted parcel of air is warmer (and less dense) than surrounding air

Moved to a higher level, it will continue to rise

“thermals”

Rising moist air cools and eventually reaches the dew point

Droplets condense around condensation nuclei in saturated air

no condensation nuclei: supersaturated air

In a state of atmospheric instability, a parcel of air will always be warmer, and therefore less dense, than the surrounding air at any altitude. The parcel will, therefore, continue on in the direction pushed when the upward force is removed.

In a state of atmospheric stability, the parcel of air will always be cooler, and therefore more dense, that he surrounding air at any altitude. It will, therefore, return to the original level when the upward force is removed.

Cooling of rising air slowed by release of latent heat of vaporization

Huge numbers of droplets appear as clouds

Precipitation

Water returning to Earth’s surface

Dew and frost are surface processes, not precipitation

Precipitation forms in two ways

Coalescence of cloud droplets

Growth of ice crystals

Coalescence process

takes place in warm cumulus clouds, near the tropic oceans

clouds contain giant salt condensation nuclei

Ice-crystal process

Takes place in clouds of middle latitudes

Ice crystals capture nearby water molecules and grow

Fall as snow in the winter; melt and turn to rain in summer

Idealized model

Region 10oN and 10oS of equator receives more direct solar energy

Air heats up, rises and spreads toward poles

Air cools and becomes more dense as it rises sinking back to the surface at latitudes 30oN and 30oS

End Result

Band of low pressure near the equator, bands of higher pressure 30oN and 30oS of the equator

Large convective cells form to equalize pressure

Large, horizontally uniform bodies of air

Moisture and temperature conditions nearly the same

Four main types

Continental polar

Maritime polar

Continental tropical

Maritime tropical

Dictate air mass weather

weather conditions remain the same over several days

weather changes when a new mass moves in or when the air mass acquires local conditions

Boundaries between air masses at different temperatures

Cold front

cold air mass moves into and displaces warmer air upward

moist rising air cooled

Warm front

Warm air mass advances over a cooler air mass

Long, gently sloping front

Clouds and rain may form in advance of the front

Stationary front

Forces influencing warm and cold air masses become balanced

Mechanisms

Bulges or waves often form between air masses

Overriding, uplifted cold air produces a low pressure area

Further cold front motion leads to an occluded front and a cyclone storm

Cyclone

Low pressure area with inflowing, upward force winds

Circulation pattern caused by the Coriolis effect

Anti-cyclone

High pressure area

Air sinks, is warmed, relative humidity is lowered

Rapid, violent weather changes

Often associated with frontal passage

Three major types

thunderstorms

tornadoes

hurricanes

Usually develops in warm, very moist, and unstable air

Three stages

Cumulus – associated with convection, mountain barriers, or a cold front

Mature

Updraft can no longer support growing ice crystals and snow flakes

Falling frozen water melts and becomes rain

Hail formed through ice accumulation cycles

Final

All updrafts are exhausted

Updrafts, downdrafts and circulating precipitation separate electrical charges

Charges accumulate in different parts of the thunderhead

Lightning

Discharge between charge centers

Can be cloud to ground, ground to cloud, or cloud to cloud

Expanding pressure wave from heated air produces crack of thunder

Smallest, most violent weather disturbance

Rapidly whirling column of air

diameter of 100-400 meters

wind speeds up to 480 km/h

Damage produced

high winds

drop in pressure at center

flying debris

Associated with intense thunderstorms

Tropical depression

Tropical Storm

Hurricane

Tropical depression

area of low pressure

winds generally moving at 55 mph or less

Tropical storm

more intense low pressure areas

Winds between 56 and 120 mph

Hurricanes

Very intense low pressure

Winds in excess of 120 km/h

Fully developed hurricane has a calm eye surrounded by intense rain and thunderstorms

Based upon mathematical models of the atmosphere

Billions of calculations necessitate use of supercomputers

Fairly accurate forecasts up to three days possible

Major uncertainty:insufficient technology to connect small and large scale events

Ultimately oceanic influences need to be better understood

Composite, larger weather patterns occurring over a number of years.

Determining factor in

types of plants and animals in a given location

types of houses built

lifestyles

Influences

shape of the landscape

types of soil

agricultural type and productivity

Two primary factors

1.Intensity of incoming solar radiation

2.Number of daylight hours

Low altitudes

High solar radiation

Yearly variation small

Temperature uniformly high

Middle latitudes

Higher solar radiation during one part of the year; lower during the other

Overall temperatures lower with greater variation than low latitudes

High latitudes

Maximum amount of radiation during one part of the year; none in the other

Overall temperatures are lowest with violent variation

Defined in terms of yearly temperature averages

Tropical climate zone

near equator

receives most solar radiation

hot

Polar climate zone

least solar radiation

cold

constant daylight part of summer; constant darkness part of winter

Temperate climate zone

intermediate between others

Four

Major

Factors

Altitude

Higher altitude air radiates more energy into space

Mountains

Cooler air at higher altitudes

Upwind slopes receive more precipitation; downwind slopes receive less

Large bodies of water

high specific heat of water moderates temperature changes

Ocean currents

can bring water nearby that has a different temperature that the land

Problems

No sharp boundaries

No two places have exactly the same climate

Marine climate

Near ocean

Influenced mostly by air masses from the ocean

Can be polar or tropical

Continental climate

far from ocean

influenced mostly by air masses from large land areas

can be polar or tropical

Other classifications:

arid

semiarid

humid

Microclimate: a local pattern in climate

Can be associated with large cities