GLOBAL ATMOSPHERIC CIRCULATION
More energy received at equator than at poles
Earth is a spinning sphere.
Poleward of 40° more energy lost to space than received from the sun
Moving energy poleward produces the world's climate patterns
1. HADLEY CIRCULATION
At equator, warm raising air produces a belt of low pressure and
easterly winds. Known as the ITCZ, shifts north and south with
N-S circulation. Hot air raises at equator, Movement poleward at tropopause,
descent at 30o, movement equator-ward at Earth's surface.
E-W circulation, air raising in Indonesia, descending in Galapagos
Major Semi-Permanent Features of Atmospheric Circulation:
Earth is a spinning sphere.
2. THE WESTERLIES a belt of strong westerly winds at ca. 40°. Between the
sub-tropical highs and sub-polar lows
3. THE ITCZ inter-tropical convergence zone (Hadley Cells)
a. Coriolis Effect:: deflection toward right (left) in northern (southern)
b. Flux density of energy is greatest at equator (2 cal cm-2 yr-1) top of atm.
Equatorward of 4Oo, more energy received than emitted.
Poleward of 4Oo, more energy radiated back into space than received.
Redistribution of this energy is the driving force for climate.
Global Geography (Ocean Basins) produce more Semi-Permanent Features of Atmospheric Circulation
4. SUB-TROPICAL HIGHS: Descending air at 30o produces clockwise circulating
cells, strongest in summer; e.g., Pacific & Bermuda - Azores High,.
5. SUB-POLAR LOWS at 60o circulate counterclockwise, and are strongest in
winter. e.g., Aleutian Low, Greenland Low.
USE OF SEMI-PERMANENT FEATURES TO EXPLAIN CLIMATE CHANGE
Circulation of the westerlies is in the form of waves
Rossby Waves long-period, planetary-scale waves that are the major
source of meridional transport of energy.
Zonal Flow: (e.g., winter - greater temperature
gradient) low amplitude waves,
stronger winds, less heat and moisture
Meridional Flow: high amplitude waves,
greater heat and moisture transport poleward
WEATHER PATTERNS ASSOCIATED WITH SEMIPERMANENT FEATURES
precipitation and temperature anomalies associated with atmospheric circulation patterns.
ENSO: El Niño - Southern Oscillation
SOI Southern Oscillation Index
Atmospheric Pressure of Tahiti - Darwin (for example)
|PNA - Pacific North American Pattern
(Leathers et al., 1991, 1992; Cyan, 1996)
High PNA strong meridional transport by westerlies, strong Aleutian Low
Low PNA zonal transport by jet stream
PDO - Pacific Decadal Oscillation 20-30 year period
(Mantua et al., 1997)
High PDO (warm) strong Aleutian Low, weak transport of moisture by westerlies into Northwest
Low PDO cooler wetter Pacific Northwest
Other weather-pattern acronyms
1. LAND-SEA CONTRAST
- differential heating: land warms faster than ocean
- warm air on land raises and is replaced by moist air over ocean
- land at high elevation (thinner atmosphere) absorbs more insolation
- land (and air) heat faster, creating greater land-sea contrast
3. CROSS-EQUATORIAL FLOW
- air moving from winter to summer hemisphere strenghthensflow
- picks up moisture crossing ocean
4. TOPOGRAPHIC BARRIERS
- Coriolis effect deflects moving air right (left) in northern (southern) hemisphere
- African (Tethyan) mountains deflect air and enhance cross-equitorial flow
5. GEOLOGIC HISTORY
- Monsoon Maxima coincide with coincidence of perihelion and summer solstice
- Pleiatocene Pluvials
- Cretaceous (coincidence of perihelion and equinox)
Global Climate Readings