The Temperate ClimateThe Temperate Climate

The Temperate Hadley CellThe Temperate Hadley Cell• Westerly Prevailing Winds

• Warm inputs (often from the Tropical Hadley Cell)

• Cold inputs form the Polar Hadley Cell

• Weather develops where the cold and warm inputs collide guided by the Jet Stream

• Westerly Prevailing Winds

• Warm inputs (often from the Tropical Hadley Cell)

• Cold inputs form the Polar Hadley Cell

• Weather develops where the cold and warm inputs collide guided by the Jet Stream

Weather Systems & Air Masses

• Weather System – recurring circulation pattern & associated weather

• Air mass – large bodies of air with uniform temp & moisture– Up to thousands of km across– May extend up to top of

troposphere– Measured by:

• Temperature• Humidity

Air Masses

• Develop over source

regions

• Take on characteristics of

the region

• Air masses classified by:

– Latitude (Arctic (A), polar (P),

tropical (T), equatorial (E))

• Indicate temperature

– Surface type (Maritime (m),

continental (c))

• Indicate moisture content

Source Regions

• Idealized continent & oceans show source regions for air masses

• Combined air

mass labels (no

cE, mA or mAA)

– mE, mT, cT, mP,

cP, cA, cAA

The Pineapple express

Cold dry air from Alaska

Warm moist air from Hawaii

Fronts• Surface of contact between 2 distinct air

masses– E.g. boundary between polar & tropical air → polar

front

Fronts• Cold air is heavier than warm air….the warm air

is pushed over the cold air

Fronts• Warm Front – moving front → warm air slides

over cold air– Slower than cold front– Warm front stimulates nimbostratus clouds & rain

Cyclones• Converging, inspiraling air

rises → condensation

• Cyclonic storm:– Intense convection

– Strong winds

– Heavy precipitation

• 3 types of traveling cyclones:– Midlatitude cyclone (or

extratropical cyclone)

– Tropical cyclone

– Tornado

Anticyclones• High pressure

• Fair weather system

• Descending air

warms adiabatically

• No condensation

A “Perfect Storm”

• Intense cyclonic storm

• L marks the center of rotation

• Strong wind & precip hit NE US (blue & orange)

LL

Midlatitude Cyclones

• Dominant weather systems in mid & high latitudes

• Form, intensify and dissolve along polar front

• Air converging along front can create circulation

• Cyclone may last a few days, moving west-to-east

Lifecycle of Midlatitude Cyclone

Upper-Air Disturbances• Closely related to

midlatitude cyclone development at surface

• Upper-air convergence → high surface pressure

• Upper-air divergence → low surface pressure

Cyclone Tracks & Families• Certain regions good to develop cyclones• Upper-level winds consistently steer cyclones• So, consistent cyclone tracks are well known• Sets of tracks form cyclone families

Midlatitude CycloneTracks

Cold Air Outbreaks

• Occasionally cold air from polar regions pushes far south

• This February image shows cold, clear air as far south as Florida

• White pattern E & SE of image is clouds from cold front

• White in NW of image is snow cover