Earth's Climatic Regions

Topic 9: Earth's Climatic Regions

Weather vs. Climate

  • Weather

    • Refers to short-term atmospheric conditions including:

    • Temperature

    • Humidity

    • Cloudiness

    • Precipitation

    • Pressure

    • Winds

  • Climate

    • Refers to average weather conditions over a long period, often termed as climate "normals".

    • Still based on temperature, precipitation, etc., but helps establish long-term patterns.

    • Influences the global distribution of ecosystems, also known as biomes.

Earth’s Climatic Classification

  • Classification is based on various climate components:

    • Insolation/Latitude

    • Temperature

    • Pressure

    • Air masses

    • Precipitation

Principal Temperature Controls

  1. Latitude: Affects the angle of solar insolation; regions near the equator receive more direct sunlight year-round.

  2. Altitude: Higher altitudes generally experience cooler temperatures.

  3. Cloud Cover: Affects the amount of solar radiation that reaches the ground, influencing temperature.

  4. Land/Water Distribution: Land heats and cools more rapidly than water, affecting local climates.

Precipitation Mechanisms

  • There are four primary mechanisms for precipitation:

    1. Convergent Lifting

    2. Convectional Lifting

    3. Orographic Lifting

    4. Frontal Lifting

Precipitation Insights

  • Equatorial Regions:

    • Characterized by wet climates due to:

    • Convergence of trade winds

    • High levels of convection (heating)

    • Ample moisture availability

  • Subtropics:

    • Generally dry climates attributed to:

    • Sinking air associated with Hadley cells that create high pressure.

  • Mountain Areas:

    • Climate varies significantly:

    • Wet on the windward side

    • Dry on the leeward side

  • Continental Interiors:

    • Typically dry, as they are located far from moisture sources.

Types of Temporal Precipitation Patterns

  1. Uniform: All months receive approximately the same precipitation.

  2. Summer Maximum: More precipitation occurs in summer months.

  3. Winter Maximum: Precipitation peaks in winter months.

  4. Double Maxima: Peaks of precipitation occur in two distinct seasons, e.g., spring and fall.

Guess the Region: Climate Characteristics

  • Tropical Rainforest:

    • Mean precipitation = 2971 mm (115 in.)

    • Mean Annual Temperature = 25°C (77°F)

  • Low-Latitude Hot Steppe:

    • Mean precipitation = 450 mm (18 in.)

    • Mean Annual Temperature = 20°C (68°F)

Global Climate Classifications

  • Five Climate Regions of the World:

    1. Tropical (3 types)

    2. Mesothermal (mild winter, 3 types)

    3. Microthermal (cold winter, 4 types)

    4. Polar and Highland (2 types)

    5. Desert (2 types)

Tropical Climates

  • Located between the Tropic of Cancer and Tropic of Capricorn.

    • Characterized by consistent insolation and daylength leading to warm temperatures throughout the year; no winters.

    • Rainfall is heavily influenced by the Intertropical Convergence Zone (ITCZ), resulting in year-round moisture surpluses.

    • Warm oceans lead to an unstable atmosphere conducive to precipitation.

Subtypes of Tropical Climates

  1. Tropical Rainforest:

    • Characterized by constant wet conditions and large water surpluses.

  2. Tropical Monsoon:

    • Defined by seasonal wind reversals with a brief dry season lasting at least a month.

  3. Tropical Savanna:

    • Exhibits distinct wet and dry seasons of approximately equal length.

Mesothermal Climates

  • Primarily found in midlatitude regions with mild winters, characterized by warm and temperate conditions with true seasonality.

    • Key Influences:

    • Changing air masses (maritime Tropical, continental Polar)

    • Midlatitude wave cyclones

    • Differences between west and east coastal regions

    • Temperature decreases progressively poleward

Types of Mesothermal Climates

  1. Humid Subtropical:

    • Moist conditions throughout the year, commonly found in regions like Texas.

  2. Marine West Coast:

    • Maintains year-round moisture, typically influenced by maritime Polar air masses, leading to mild winters.

  3. Mediterranean:

    • Characterized by dry summers, often due to subtropical high-pressure systems and cold ocean currents.

Microthermal Climates

  • Found in middle to high latitudes with distinct seasonal temperature variations.

    • Key Characteristics:

    • Winters are typically cold and long

    • Summers vary from hot in southern microthermal regions to cool in northern zones

    • Generally year-round moisture; however, certain regions in Asia exhibit dry winters

    • Notably, there are no microthermal climates located in the Southern Hemisphere.

Types of Microthermal Climates

  1. Humid Continental:

    • Subdivided into hot-summer (e.g., U.S. Midwest & Northeast) and mild summer types.

  2. Subarctic:

    • Divided into cool summer and very cold winter (e.g., Siberia).

Polar and Highland Climates

  • Polar climates are characterized by a lack of true summer, with temperatures remaining below 10°C (50°F) even during the longest days.

  • Key moisture characteristics include extremely dry conditions resembling “frozen deserts”.

Subtypes of Polar Climates

  1. Tundra:

    • Characterized by summer temperatures barely exceeding freezing with underlying permafrost.

  2. Ice Cap:

    • Temperatures remain below freezing year-round, specifically in Greenland and Antarctica.

Desert (Arid and Semiarid) Climates

  • The most extensive climate region, primarily characterized by the moisture demand (Potential Evapotranspiration, POTET) exceeding moisture supply (Precipitation, PRECIP), leading to a constant deficit.

    • Causes include:

    • Subtropical high-pressure systems

    • Cold ocean currents

    • Rain shadow effects

    • Great distances from water sources

Subtypes of Desert Climates

  1. Arid Desert:

    • Example: Riyadh, Saudi Arabia.

  2. Semi-Arid Steppe:

    • Example: Walgett, Australia.

World Climate Classification

  • Tropical climates:

    • Tropical Rainforest: Rainy all year

    • Tropical Monsoon: 6 to 12 months of rain

    • Tropical Savanna: Less than 6 months of rain

  • Desert climates:

    • Arid Deserts: Found in tropical and midlatitude regions

    • Semiarid Steppes: Found in both tropical and midlatitude areas

  • Mesothermal climates:

    • Humid Subtropical: Moist all year

    • Winter Dry: Hot to warm summers

    • Marine West Coast: Moist all year with warm to cool summers

    • Mediterranean: Dry summers, typically hot and warm.

  • Microthermal climates:

    • Humid Continental: Hot summers, moist all year

    • Asian Winter Dry: Mild summers, moist all year

    • Subarctic regions: Cool summer to very cold winters

  • Polar climates:

    • Tundra: Defined by temperature and plant life

    • Ice Caps and Ice Sheets: Classified as permanent freeze zones, example includes areas in Antarctica.