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 10 o N and 10 o S 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 30 o N and 30 o S

End Result Band of low pressure near the equator, bands of higher pressure 30 o N and 30 o S 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 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