ESCI 1010 Weather and Climate
Chapter 8 Notes
The Concept of Scale
• Global scale
o ITCZ, Westerlies, Rossby waves
• Synoptic scale
o Cyclones, anticyclones, troughs, ridges
o Cover hundreds or thousands of square km
• Mesoscale
o Land breezes, thunderstorms
o Events on the order of tens of square km and occur on time scales from minutes to days
• Microscale
o Smallest exchanges of mass and energy that occur on time scales of seconds to minutes
o Turbulence, wind gusts
Global Circulation
• Single cell model originally proposed by George Hadley to describe the movement of
atmosphere from the warm tropics to the cooler poles
• Real world is closer to a three cell model due to the Earth’s rotation
• Equatorial Low: region of low pressure at the surface found along the equator (also known as
doldrums)
• Intertropical Convergence Zone (ITCZ): an area of general convergence between the Northern
and Southern trade winds that creates a general area of low pressure
• Hadley Cell: lower latitude convection cell with rising, moist air associated with the equatorial
low on the ascending arm and sinking, dry air associated with the subtropical high on the
descending arm
• Subtropical High: A semi-permanent area of divergence and subsidence that exists around 30°N
and 30°S latitude (also known as horse latitudes)
• Ferrel Cell: circulation cell that immediately flanks the Hadley cell in each hemisphere
• Westerlies: wind belts found in the mid-latitudes of both hemispheres that have a strong west-
to-east component
• Polar Front: boundary between polar air poleward and tropical air equatorward
• Subpolar Low: a belt of convergence and upward motion that exists around 60°N and 60°S
latitude
• Polar Cell: located at the poles where surface air moves from the polar highs to the subpolar
lows
• Polar High: an anticyclone that is assumed to occupy the inner polar regions and is believed to
be thermally induced in part
• Polar Easterlies: low-level winds originated in the polar highs but are often very weak or absent
Three Cell Model vs. Reality
• ITCZ can be observed from space, deserts exist in predicted locations, and trade winds most
persistent on Earth so Hadley cell good representation of lower latitude
• Ferrel and polar not as well represented
• Land-ocean contrasts or influence of topography not considered in the three cell model
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Chapter 8 Notes
The Concept of Scale
• Global scale
o ITCZ, Westerlies, Rossby waves
• Synoptic scale
o Cyclones, anticyclones, troughs, ridges
o Cover hundreds or thousands of square km
• Mesoscale
o Land breezes, thunderstorms
o Events on the order of tens of square km and occur on time scales from minutes to days
• Microscale
o Smallest exchanges of mass and energy that occur on time scales of seconds to minutes
o Turbulence, wind gusts
Global Circulation
• Single cell model originally proposed by George Hadley to describe the movement of
atmosphere from the warm tropics to the cooler poles
• Real world is closer to a three cell model due to the Earth’s rotation
• Equatorial Low: region of low pressure at the surface found along the equator (also known as
doldrums)
• Intertropical Convergence Zone (ITCZ): an area of general convergence between the Northern
and Southern trade winds that creates a general area of low pressure
• Hadley Cell: lower latitude convection cell with rising, moist air associated with the equatorial
low on the ascending arm and sinking, dry air associated with the subtropical high on the
descending arm
• Subtropical High: A semi-permanent area of divergence and subsidence that exists around 30°N
and 30°S latitude (also known as horse latitudes)
• Ferrel Cell: circulation cell that immediately flanks the Hadley cell in each hemisphere
• Westerlies: wind belts found in the mid-latitudes of both hemispheres that have a strong west-
to-east component
• Polar Front: boundary between polar air poleward and tropical air equatorward
• Subpolar Low: a belt of convergence and upward motion that exists around 60°N and 60°S
latitude
• Polar Cell: located at the poles where surface air moves from the polar highs to the subpolar
lows
• Polar High: an anticyclone that is assumed to occupy the inner polar regions and is believed to
be thermally induced in part
• Polar Easterlies: low-level winds originated in the polar highs but are often very weak or absent
Three Cell Model vs. Reality
• ITCZ can be observed from space, deserts exist in predicted locations, and trade winds most
persistent on Earth so Hadley cell good representation of lower latitude
• Ferrel and polar not as well represented
• Land-ocean contrasts or influence of topography not considered in the three cell model
1
