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.