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Clouds and Atmospheric Phenomena

Lecture Overview

  • Course: GEOG 1112

  • Topic: Clouds, Air Masses, and Fronts

Cloud Classification

  • Categories of Clouds:

    • Cirrus

      • Description: Thin, wispy clouds made of ice crystals.

      • Altitude: Highest in the atmosphere.

    • Altus

      • Description: Middle altitude clouds.

    • Stratus

      • Description: Layer-like gray sheets covering most or all of the sky.

      • Altitude: Lowest among cloud types.

    • Cumulus

      • Description: Individual, puffy clouds with a flat, horizontal base.

      • Altitude: Can occur at any altitude.

    • Nimbo- or -nimbus

      • Description: Associated with precipitation.

Cloud Types and Identification

  • Cloud types arranged by altitude:

    • 12 km: Cirrus / Cirrocumulus

    • 9 km: Cumulus / Altocumulus

    • 6 km: Stratus / Stratocumulus

    • 3 km: Cumulonimbus / Nimbostratus

    • 0 km: Low altitude clouds.

Cumulonimbus Development

  • Altitude and Conditions:

    • 6000 m (19,700 ft): Upper-air flow.

    • 5000 m (16,400 ft): Ice crystals present.

    • 4000 m (13,120 ft): Formation of anvil tops.

    • 3000 m (9840 ft): Mixture of ice and water droplets.

    • 2000 m (6560 ft) and below: Water droplets predominant; heavy rain and gusts.

Air Masses & Fronts

  • Air Mass:

    • Definition: Large body of lower atmosphere with uniform temperature and moisture conditions.

  • Source Regions:

    • Moisture Content:

      • c: continental - dry

      • m: maritime - moist

    • Latitude Indicators:

      • A or AA: Arctic or Antarctic

      • P: Polar (50-60º N or S)

      • T: Tropical (20-35º N or S)

      • E: Equatorial

Precipitation Processes

  • Uplift Mechanisms:

    • Precipitation driven by atmospheric uplift.

      • Types of Lifting Mechanisms:

        • Convectional: Warm air bubbles rise.

        • Orographic: Air is forced upwards over mountains.

        • Frontal: Air masses collide, driving air upwards.

        • Convergent: Occurs at low pressure centers or troughs.

Types of Uplift

  • Convectional Uplift:

    • Stable Air vs. Unstable Air:

      • Stable: Upper troposphere warmer—hinders strong convection.

      • Unstable: Cold upper troposphere drives strong convection.

    • Example Measurements:

      • 40˚C (Warm)

      • 25˚C

      • 8˚C (Cool)

      • 20˚C (Cooler)

Local Heating and Convection

  • Atmospheric Temperature Relationships:

    • Moist Adiabatic Lapse Rate: ~0.6°C/100m

    • Dry Adiabatic Lapse Rate: 1°C/100m

    • Level of Condensation: Points where air cools and condenses.

Orographic Uplift

  • Concepts:

    • Windward Side: Receives moisture-laden air.

    • Leeward Side: Characterized by dry descending air (Rain Shadow).

    • Influenced by prevailing winds and water vapor from oceans.

Convergent Lifting

  • Pressure Patterns:

    • Depicts the movement of air masses, with high and low-pressure areas.

    • The ITCZ (Intertropical Convergence Zone) plays a key role in convergent lifting.

Frontal Lifting

  • Fronts Explained:

    • Named after the incoming air mass.

    • Characteristics of Cold and Warm Fronts:

      • Cold Fronts:

        • Cold air is denser, forces warm air above it (400 km wide).

      • Warm Fronts:

        • Warm air moves up and over cooler air (1000 km wide).

Examples of Cold and Warm Fronts

  • Cold Front Formation:

    • Cirrus, Cumulonimbus clouds developing as cold air lifts warm air.

  • Warm Front Formation:

    • Cirrus, Cirrostratus, Altostratus clouds indicating gradual lifting.