Wind #9

ATMOSPHERIC CIRCULATION AND WIND SYSTEMS

INTRODUCTION TO ATMOSPHERIC CIRCULATION

  • Atmospheric circulation refers to the large-scale movement of air and the resulting weather patterns.

  • This chapter explores the fundamental principles that govern wind and atmospheric pressure.

AIR PRESSURE AND WIND

  • Wind Importance:

    • Essential for plant growth, moisture distribution, human comfort, and generating electricity.

  • Cause of Wind:

    • Generated by temperature variations across the Earth’s surface, which create pressure differences.

  • Instruments for Measuring Air Pressure:

    • Barometer: Measures air pressure.

    • Highest Recorded Pressure:

      • Dead Sea, Israel: 430 m (-1412 ft) at 1065 mb (31.44 in Hg).

    • Lowest Recorded Pressure:

      • Typhoon Haiyan (2013): 860 mb (25.40 in Hg).

      • Typhoon Tip (October 12, 1979): 870 mb (25.69 in Hg).

    • Historical High Pressure:

      • Agate region, Russia: 1083.8 mb (32 in Hg) on December 31, 1968.

    • Average Sea Level Pressure: 1013.25 mb (29.92 in Hg).

AIR PRESSURE VARIATIONS

  • Pressure Variations Across Geography:

    • Influenced by several factors including temperature and movement of air:

    • Thermal Air Pressure:

      • Caused by heating/cooling of air.

      • Warm Air: Low pressure; expands, decreases density, and rises (buoyancy).

      • Cold Air: High pressure; contracts, increases density, and remains stable.

    • Dynamic Air Pressure:

      • Created by air movement and can override thermal air pressure.

      • High Pressure: Air sinks and compresses (e.g., subtropical highs).

      • Low Pressure: Air rises and expands (e.g., Intertropical Convergence Zone - ITCZ, Subpolar lows).

WINDS AND THEIR CAUSES

WINDS: DIRECTION AND SPEED

  • Forces Affecting Wind Direction and Speed:

    1. Pressure-Gradient Force:

    • Resulting from horizontal differences in air pressure.

    • Steeper Gradient: Causes faster air flow between pressure areas.

    1. Coriolis Effect:

    • The perceived deflection of moving objects due to Earth’s rotation.

    • Deflection Direction:

      • Northern Hemisphere: Deflects to the right.

      • Southern Hemisphere: Deflects to the left.

    1. Friction:

    • Slows air flow near Earth's uneven surface (up to 1000 m or 3,280 ft).

    • Geostrophic Winds:

      • Occur above the friction layer, flows parallel to pressure gradients (isobars).

WINDS MEASUREMENT

  • Anemometer: A device to measure wind speed based on rotating propeller.

    • Wind Speed Units: Knots (1 knot = 1.15 mph or 1.86 km/h).

  • Wind Vane: Measures wind direction.

  • Prevailing Wind: The most frequent wind direction.

PRESSURE SYSTEMS

  • Types of Pressure Centers:

    • Cyclones: Low pressure centers; wind converges and rises, forming clouds.

    • Anticyclones: High pressure centers; wind diverges and sinks.

  • Behaviour of Winds Around Pressure Centers:

    • In cyclones, air converges and rises, while in anticyclones, air diverges and sinks.

GLOBAL ATMOSPHERIC CIRCULATION PATTERNS

  • Primary Circulations: Persistent airflows at a global scale, affecting weather patterns.

  • Secondary Circulations: Regional and local wind patterns.

  • Major Wind Belts:

    1. Trade Winds:

    • Flow from 30° latitude toward the equator, deflected by the Coriolis effect.

    1. Westerlies:

    • Flow from 30° towards 60°, also deflected by Coriolis.

    1. Polar Easterlies:

    • Flow from polar regions toward 30°.

LOCAL WIND SYSTEMS

  • Include phenomena such as:

    • Sea Breezes: Daytime winds from ocean to land due to temperature differences.

    • Land Breezes: Nighttime winds from land to sea as land cools faster than water.

    • Valley & Mountain Breezes: Local winds caused by temperature differences from daytime heating and nighttime cooling.

    • Chinook and Foehn Winds: Warm, dry winds descending from mountains.

MONSOONS AND EL NIÑO

  • Monsoon: Seasonal reversal of winds significantly affecting climates and agriculture (e.g., South Asia).

    • Onshore air brings moisture in summer (May-July), while offshore air is dry in winter.

  • El Niño Southern Oscillation (ENSO):

    • A climate pattern characterized by periodic warming (El Niño) and cooling (La Niña) of ocean temperatures in the Pacific.

    • Impact of El Niño: Affects precipitation patterns globally, leading to droughts or floods in various regions.

    • Normal Phase: Represents neutral conditions transitioning in either direction to affect global climate.

WIND FARMING

  • Wind Turbines: Convert kinetic energy of wind into electricity, representing a renewable energy source.

    • Challenges: Include geographic limitations, demand variability, environmental concerns involving wildlife (birds, bats).

  • Current and Future Wind Energy Goals:

    • Significant increase in turbine installations and capacity expected to power millions of homes.