Lecture 7 Part 1 Atmospheric and Ocean Circulation: In-Depth Notes

Atmospheric and Ocean Circulation

Major Global Circulation Patterns

• Surface Wind Bands:
  • Low pressure produces rising air.
  • High pressure results in descending air.

Air Pressure

• Defined as the weight of the atmosphere per unit area.
• Influenced by the motion, size, and number of air molecules.
• Variation with Altitude:
  • Air pressure and density decrease as altitude increases.
• Heating Effects:
  • Heated air increases molecular activity, spacing, and decreases density and pressure.
  • Warm air is less dense than cold air.

Water Vapor

• Moist air is lighter than dry air due to molecular weight differences.
• Humid air contributes to low pressure; cold, dry air results in high pressure.

Barometer

• Measures atmospheric pressure.
• Types:
  • Mercury barometer (invented by Torricelli).
  • Aneroid barometer (no liquid).

Isobar

• A line representing constant pressure on a map.

Wind

• Defined as the horizontal movement of air, driven by pressure and temperature variances.
• Measurement Methods:
  • Beaufort Scale, anemometer, wind sock, weather vane.

The Beaufort Scale

• Developed by Francis Beaufort in 1805.
• Measures wind speed from 0 (calm) to 12 (hurricane).
  • Examples of Scale:
  • 0: Calm, under 1 mph.
  • 12: Hurricane, 73+ mph.

Wind Direction and Naming

• Winds are named for their origin (e.g., westerlies from the west).

Forces Influencing Wind Patterns

• Three Main Forces:
  • Pressure Gradient Force, Coriolis Force, Friction Force.

Pressure Gradient Force

• Results from pressure differences across surfaces.
• The pressure gradient is the change in pressure over distance.

Coriolis Force

• Caused by Earth's rotation; it deflects moving air.
• In the Northern Hemisphere: deflected right; in the Southern Hemisphere: deflected left.

Friction Force

• Acts against wind, decreasing with height.
• Extends approx. 500 m above the surface.

High and Low Pressure Systems

• Low Pressure Systems:
  • Center pressure < surrounding areas; air rises, forming clouds and possibly precipitation.
  • Winds swirl counterclockwise (NH) and clockwise (SH).
• High Pressure Systems:
  • Center pressure > surrounding areas; air sinks; winds blow outward creating anticyclonic flow.

Upper Atmosphere Circulation and Jet Streams

• Geostrophic Winds: Flow parallel to isobars in the upper troposphere.
• Jet Streams: Fast winds in the tropopause, blowing from west to east, stronger in winter.

Global Atmospheric Circulation

• Transfers thermal energy from the equator to poles, influencing precipitation and wind patterns.
• Hadley Cells: Large-scale convection cells causing rising at the equator and sinking at ~30°.
• Trade Winds: Encircle Earth, blowing from the tropics to the equator.

Precipitation Patterns

• Latitudinal Variations: Vary across different atmospheric circulation zones (e.g., Doldrums near the equator).

Monsoonal Winds

• Seasonal wind shifts affecting weather, especially notable in the Asian monsoon.

Local Winds

• Types:
  • Sea Breezes: Cool air moves from water to land.
  • Land Breezes: Cool air moves from land to water at night.
  • Anabatic: Winds rise up slopes; Katabatic: Winds descend slopes.
  • Foehn: Warm, dry winds descending from mountain ranges (e.g., Chinook winds).

Ocean Surface Currents

• Driven by wind, influenced by the Coriolis Effect, forming gyres.

Thermohaline Circulation

• Driven by temperature and salinity differences in seawater.
• Heat sources at the ocean bottom play minor roles.

El Niño and La Niña

• El Niño: Characterized by warm ocean currents, leading to increased winter precipitation and varied global conditions.
• La Niña: Marked by cooler ocean temperatures and influences on hurricane activity in the Western Atlantic.

Wind Power and Tidal Power

• Wind Power: Canada ranks 7th globally; issues include noise and wildlife impacts.
• Tidal Power: E.g., Bay of Fundy; renewable energy with potential ecological impacts.