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Lecture 8 Part 1Weather and Climate Notes

Difference Between Weather and Climate

  • Weather: Condition of the atmosphere in one area at a specific time.
  • Climate: General weather conditions prevailing in an area over a long period.

Water and Atmospheric Moisture

  • Unique Properties of Water:
    • High specific heat, cohesive properties, and unique solid-liquid-gas states.
  • Water Cycle:
    • Continuous movement of water on Earth through evaporation, condensation, precipitation, and runoff.
  • Effects of Clouds:
    • Influence local weather; reflect sunlight and trap heat.
  • Types of Fog:
    • Radiation fog, advection fog, upslope fog, and evaporation fog.

Air Mass

  • Definition: Distinct body of air reflecting characteristics of its source region.
  • Characteristics:
    • Temperature and moisture characteristics affect the overlying air.
    • Extends through the lower half of the atmosphere.

Classification of Air Masses

  • Moisture Types:
    • m: Maritime (wet)
    • c: Continental (dry)
  • Temperature Types:
    • A: Arctic
    • P: Polar
    • T: Tropical
    • E: Equatorial
    • AA: Antarctic

Specific Humidity

  • Specific Humidity: Mass of water vapor (grams) per mass of air (kilograms) at a specific temperature.
  • Maximum Specific Humidity: Maximum mass of water vapor possible in a kilogram of air at a specified temperature.

Principal Air Masses Affecting North America

Winter Air Mass Patterns
  • mP: Maritime polar - Cool, humid, unstable (avg. SH 4.4 g.kg⁻¹)
  • CA: Continental arctic - Very cold, dry, stable (avg. SH 0.1 g.kg⁻¹)
  • CP: Continental polar - Cold, dry, stable (avg. SH 1.4 g.kg⁻¹)
  • mT: Maritime tropical - Warm, humid, stable to unstable (avg. SH 10-14 g.kg⁻¹)
Summer Air Mass Patterns
  • CA: Continental arctic - (avg. SH 0.3 g.kg⁻¹)
  • mP: Maritime polar - (avg. SH 4.4 g.kg⁻¹)
  • cP: Continental polar - (avg. SH 1.4 g.kg⁻¹)
  • mT: Maritime tropical - (avg. SH 13-17 g.kg⁻¹)
  • CT: Tropical - Hot, low relative humidity, unstable at surface (avg. SH 10 g.kg⁻¹)

Stability and Instability

  • Parcel: Body of air with specific temperature and humidity characteristics.
  • Stability: The tendency for an air parcel to remain or return to its original location.
    • Stable: Tends to return to starting place.
    • Unstable: Ascends or descends when disturbed.

Adiabatic Cooling and Heating

  • Adiabatic Process: Changes in parcel temperature with expansion or compression, no heat exchanged.
  • Adiabatic Cooling: Reduces heat through air pressure changes due to volume expansion.
  • Dry Adiabatic Rate: 10 degrees Celsius per 1 km upward.

Atmospheric Lifting Mechanisms

  • Lifting: When air mass rises, it cools adiabatically, leading to condensation and potentially precipitation.
  • Four Mechanisms:
    1. Convergent Lifting: Air flows toward low pressure areas, displacing air upwards.
    2. Convectional Lifting: Local surface heating stimulates air rise (e.g., urban heat islands).
    3. Orographic Lifting: Air forced over barriers (mountains) leads to precipitation on windward sides.
    4. Frontal Lifting: Displacement of warm air over cooler, denser air along fronts.

Precipitation Types

  • Sleet, Rain, Snow, Hail
  • Winter Precipitation: Includes warm air freezing, creating ice or sleet on colder surfaces.

Thunderstorms and Violent Weather

  • Thunderstorms: Turbulent weather with lightning and thunder; rapid upward air movement.
  • Tornadoes: Violently rotating columns of air; rated by the Enhanced Fujita Scale based on damage.

Hurricane Development Stages

  1. Tropical Disturbance: Low-pressure, cloudiness, and precipitation.
  2. Tropical Depression: Pressure drop, wind speed increases.
  3. Tropical Storm: Winds reach 39 to 73 mph; names given.
  4. Hurricane: Winds exceed 74 mph, pronounced rotation.

Anatomy of a Hurricane

  • Eye: Calm center; surrounded by an eye wall with maximum winds.
  • Rainbands: Spiraling bands of clouds and thunderstorms; capable of strong precipitation and tornado formation.

The Saffir-Simpson Hurricane Wind Scale

  • Categories:
    • Category 1: 74-95 mph - Some flooding, little to no structural damage.
    • Category 2: 96-110 mph - Trees down, minor roof damage.
    • Category 3: 111-130 mph - Mobile homes destroyed, severe flooding.
    • Category 4: 131-154 mph - Major structural damage, roofs ripped off.
    • Category 5: >155 mph - Complete devastation in most wooden structures.

Flood Risks in Canada

  • Number of floods increasing; significant floods have occurred since 2010.
  • Growing need for resilience against floods due to climate change-induced extreme weather.