Atmospheric Dynamics and Climate Classification

Posted on Aug 24, 2024 in Geology

DYNAMIC AIR

The temperature difference between the poles and the Equator, along with Earth’s rotation, drives atmospheric circulation. This circulation involves horizontal air movement parallel to the surface and vertical movement that can reach the top of the troposphere.

LATITUDINAL DISTRIBUTION OF SOLAR ENERGY

The amount of solar energy a location receives depends on:

  • The Angle of the Sun: Energy received is greater at smaller, more direct angles.
  • Exposure Time: Earth’s axial tilt affects the hours of daylight a location receives based on its orbital position.

Therefore, the tropics receive more solar energy with minimal seasonal variation. As you move towards the poles, energy decreases annually, leading to greater seasonal differences.

VERTICAL MOVEMENTS IN THE ATMOSPHERE

These movements are caused by temperature differences with altitude and lead to changes in surface air pressure:

  • Ascending Air Masses: Create low-pressure areas (depressions). Rising air cools, causing water vapor to condense into clouds and potentially precipitation. This is associated with unstable, rainy weather.
  • Descending Air Masses: Create high-pressure areas (anticyclones). Descending air warms, causing water vapor to evaporate, leading to fewer clouds. This is associated with dry, sunny weather.

HORIZONTAL MOVEMENTS IN THE ATMOSPHERE

Pressure variations cause air to move from high-pressure (anticyclones) to low-pressure (cyclones) areas.

  • Wind: Air movement compensating for pressure differences. Isobars connect locations with the same atmospheric pressure.
  • Divergence: Air descending from an anticyclone causes outward surface winds, leading to good weather due to the lack of contact between diverging air masses.
  • Convergence: Air rising in cyclones causes inward, spiraling surface winds (due to the Coriolis force), leading to potentially bad weather due to the contact between converging air masses.
  • Coriolis Force: Causes fluids moving horizontally on Earth to drift right in the Northern Hemisphere and left in the Southern Hemisphere.

ATMOSPHERIC DYNAMICS

Studied on different scales:

  • Global: Climate changes over centuries, including periods like the Little Ice Age.
  • Hemispheric: Seasonal changes with regular temperature and precipitation oscillations.
  • Regional: Severe weather events like storms, cyclones, and hurricanes lasting days or weeks.
  • Local: Phenomena like coastal breezes (lasting hours) and dust devils (lasting minutes).

STUDYING CLIMATE

A region’s climate is defined by its rainfall and temperature values. Longer periods of data provide more reliable and representative climate information. Data spanning centuries can reveal patterns and trends in climate fluctuations.

TRENDS

Changes in one or more climate variables sustained over decades or centuries. For example, Spain has a trend towards drier conditions.

PATTERNS

Deviations from average temperature or rainfall values over several years. For example, El Niño can bring torrential rains to South America’s Pacific coast every 3 to 7 years.

FLUCTUATIONS

Short, local anomalies in average temperature or rainfall, often unpredictable. For example, snow in Kenya is uncommon.

FACTORS DETERMINING WEATHER AND CLIMATE

  • Latitude: Determines temperature and air mass dynamics, influencing climate zones.
  • Altitude: Influences air temperature.
  • Continentality: Affects air moisture and temperature differences between summer and winter.
  • Prevailing Winds: Influence temperature and rainfall based on whether they are warm or cold.

CONVERGENCE ZONES AND CLIMATE ZONATION

Warm equatorial air and cold polar air converge, creating mixing zones. The Coriolis force deflects these air masses, creating three convective cells in each hemisphere:

  • Polar Air Masses
  • Warm Air Masses (30-40 degrees latitude)
  • Tropical Air Masses (between 30 degrees latitude and the Equator)

These air masses interact in convergence zones, leading to abundant rainfall (if the movement is upward) or clear skies (if the movement is downward).

STUDYING CLIMATE (CONTINUED)

Climate zones are distributed in bands parallel to the Equator, influenced by convergence zones and topography. The Köppen-Geiger climate classification system categorizes climates based on precipitation and temperature, distinguishing five main types:

  • Tropical: Average annual temperature above 18°C, precipitation exceeding evaporation.
  • Dry: Average annual rainfall less than evaporation.
  • Temperate Humid: Mild temperatures, precipitation exceeding evaporation.
  • Continental: Cold temperate climate, precipitation exceeding evaporation.
  • Polar: Warmest month’s average temperature below 10°C.

ZONAL AND AZONAL CLIMATES

  • Zonal Climates: Correspond to their latitudinal climate zones.
  • Azonal Climates: Do not correspond to their latitudinal climate zones, influenced by factors like altitude.

CLIMOGRAMS

Graphs representing a location’s monthly rainfall and temperature over a year.

FEATURES

The rainfall scale should be double the temperature scale to accurately represent dry seasons.

INTERPRETING CLIMOGRAMS

  • Rainfall: Total rainfall, distribution throughout the year, months of maximum and minimum rainfall.
  • Temperature: Average annual temperature, annual temperature range (difference between the warmest and coldest month’s average temperatures).
  • Aridity: Periods where rainfall is below the temperature curve, indicating dry seasons.

Climograms can help identify climate types based on characteristic features:

  • The temperature curve’s shape (bell-shaped in the Northern Hemisphere, inverted bell-shaped in the Southern Hemisphere).
  • Annual temperature range (higher range indicates greater distance from the Equator and continentality).
  • Presence and timing of dry seasons (summer for Mediterranean climates, winter for some tropical climates, year-round for arid climates).