GLOBAL ATMOSPHERIC CIRCULATION
Earth is a spinning sphere.

More energy received at equator than at poles



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 earth's orbit.

N-S circulation. Hot air raises at equator, Movement poleward at tropopause, descent at 30o, movement equator-ward at Earth's surface.

WALKER CIRCULATION:

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) hemisphere
    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 transport poleward

    Meridional Flow: high amplitude waves, greater heat and moisture transport poleward

WEATHER PATTERNS ASSOCIATED WITH SEMIPERMANENT FEATURES

Teleconnections: 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
http://ggweather.com/enso/mjo.htm

MONSOON CLIMATOLOGY




    1. LAND-SEA CONTRAST
    • differential heating: land warms faster than ocean
    • warm air on land raises and is replaced by moist air over ocean

    2. PLATEAUS
    • 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

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