Section 9.1 Global wind patterns
Subsection 9.1.1 Circulation scales
microscale (<1 km in size): PGF, CEN, friction (cumulus clouds, parcels)
mesoscale (1-1000 km): PGF, CEN, friction, Cor (thunderstorms, fronts)
synoptic scale (>1000 km): geostrophic balance (mid-latitude cyclones)
planetary scale (10,000 km): geostrophic balance (atmospheric circulation cells; prevail over longer timescales)
Subsection 9.1.2 Circulation models
model: simplified description of a complex system
used to explain and predict observations using cause-and-effect relationships
Any circulation model for the Earth should be able to explain:
steady and calm winds observed by mariners
Regions that lack winds
Global patterns of cloudiness
Midlatitude cloud patterns
Global patterns of precipitation
Global Circulation on Non-Rotating Earth
single cell circulation (Hadley model)
contrast in temperatures between the poles and the equator creates a large convection cell in both hemispheres.
Global Circulation on Rotating Earth
three-cell circulation: Hadley, Ferrel, and Polar cells
Coriolis effect deflects flow, poleward flows cool and sink
Not all cells are meridional (N-S motion), there are also zonal cells (E-W motion)
For example, Walker circulation is the zonal component of a Hadley cell
this behavior is observed in El Nino Southern Oscillaiton
Subsection 9.1.3 Observed circulation patterns
Global Circulation Model: Observation
tropical trade winds converging in Intertropical convergence zone (ICTZ) (region of the doldrums)
midlatitude westerlies encounter the polar easterlies along the polar front
Idealized zonal pressure belts:
The equatorial low is an intertropical convergence zone (ITCZ).
Subtropical highs (STH) are high-pressure zones in the belts about 20°–35° latitude on either side of the equator.
Polar highs near the Earth’s poles are where the polar easterlies originate.
seasonal reversal of winds; generally driven by pressure differences.
The Asian monsoon, which affects India and its surrounding areas, China, Korea, and Japan.
The North American monsoon occurs in the southwestern U.S. and northwestern Mexico: this monsoon is driven by the extreme temperatures, which generate a low-pressure center over Arizona and results in a circulation pattern that brings moist air from the Gulf of California and from the Gulf of Mexico, to a lesser degree.
Cloud and Precipitation patterns also show clear trends related to planetary circulation