Global & Regional Climate Patterns

Definition of Climate

  • Climate: The long-term prevailing weather conditions in a particular area. It has a major influence over the distribution of organisms.

    • Major components of climate include:

    • Temperature

    • Precipitation

    • Sunlight

    • Wind

Classification of Climate Patterns

  • Climate patterns can be described in terms of:

    • Macroclimate: Refers to global, regional, and landscape trends in climate.

    • Microclimate: Refers to very fine, localized patterns that can be affected by factors such as the availability of shade, evaporation from soil, changing wind patterns, etc.

Example of Microclimate

  • Example: A student may be snowed in at their location, while at the speaker's location there is little to no snow accumulation.

Global Climate Patterns

  • Global climate patterns (macroclimate) are affected by:

    • Input of solar energy

    • Earth’s movement in space

A Quick Review of Earth's Movement

  • Earth's axial positioning:

    • Earth spins on its axis (an imaginary line) and rotates around the sun simultaneously.

    • Revolution on axis: One complete spin of Earth takes one DAY (23 hours and 56 minutes).

    • Revolution around the sun: One complete orbit takes a YEAR (365 days).

    • Tilt of Axis: Earth's axial tilt is a constant 23.5°, accounting for seasonal variation.

Sunlight: Latitudinal Variation

  • Latitude: Measure of distance north or south from the equator (Equator = 0°; Poles = 90°).

  • The intensity of sunlight varies with latitude:

    • At higher latitudes, sunlight strikes Earth at an oblique angle, diffusing light energy.

    • Tropics (23.5° N to 23.5° S): Receive more heat and light per unit of surface area due to direct sunlight.

Global Air Circulation: Hadley Cells

  • Hadley Cell: An atmospheric cycle of large-scale air movement that describes global air circulation and precipitation patterns.

    • The equator receives intense heat, causing warm air to rise and carry moisture upwards.

    • Warm air holds more moisture as vapor rather than condensing.

    • As the air rises, it undergoes adiabatic cooling, losing heat and expanding in volume, leading to lower density and temperature.

    • As cool air descends back toward Earth around 30° N and S latitude, it absorbs solar radiation, which results in warm, dry air preventing precipitation.

    • This phenomenon explains the presence of major deserts around 30° latitude.

Air Circulation and Precipitation

  • As the cooled air sinks, it absorbs moisture and becomes arid, contributing to desert formation.

  • Additional circulation cells also occur between 30° and 60° latitude and from 60° to the poles, affecting climate.

Regional and Local Climate Variations

Factors Influencing Variation

  • Factors:

    • Proximity to water bodies.

    • Influence of mountains.

  • Seasonal Variation: Highly influenced by Earth’s axial tilt of 23.5°.

    • In the Northern Hemisphere:

    • Summer: Tilted toward the sun, longer days.

    • Winter: Tilted away from the sun, shorter days.

    • Tropics experience less seasonal variation (rainy vs. dry season).

    • Mid-latitudes experience four distinct seasons.

    • Extreme latitudes may only have two seasons (e.g., Alaska).

    • Example: In Barrow, Alaska: 67 days of darkness in winter vs. 80 days of daylight in summer.

Impact of Mountains on Climate

Rain Shadow Effect

  • Rain Shadow Effect: Occurs when warm, moist air approaches mountains and rises on the windward side.

    • As air rises, it cools and loses moisture as rain or snow.

    • The leeward side receives dry air, resulting in little rain and often creating deserts.

    • Example: The desert of Nevada forms due to the rain shadow effect.

Influence of Sunlight on Vegetation

  • Mountains affect the amount of sunlight which influences localized temperature and rainfall:

    • In the northern hemisphere, south-facing slopes receive more sunlight than north-facing slopes, and vice versa in the southern hemisphere.

    • Vegetation reflects this difference:

    • North-facing slopes: Typically contain spruces and conifers.

    • South-facing slopes: Tend to have scrubby, drought-tolerant plants.

Navigational Implications

  • Understanding vegetation can help in navigation if GPS fails, by recognizing slope exposure based on vegetation types.

Effect of Altitude on Temperature

  • For every increase in 1,000 meters in altitude, average temperature decreases by 6°C, equivalent to 880 kilometers of latitude.

  • Example: Colorado Springs has a cold climate despite being at a latitude similar to Washington, D.C., due to its higher elevation.

Importance of Water Bodies in Climate

  • Large bodies of water have a significant effect on the adjacent land, impacting climate.

  • Due to the significance of water in various aspects, additional lectures cover this topic extensively.