Atmosphere and Weather Notes

Temperature and Radiation Balance

Temperature Fluctuations

  • Temperature varies throughout the day due to incoming solar radiation and outgoing terrestrial radiation. Figure 2.10 illustrates this relationship in mid-latitudes, showing temperature rising after dawn, peaking, and then decreasing after sunset.
  • Dew Formation: When water vapor contacts a cold surface below the dew point, it condenses into dew, releasing latent heat and warming the nearby air.

Influence of Clouds on Night-time Energy Budgets

  • Thick cloud cover acts as a 'blanket' by absorbing and re-radiating long-wave radiation, which minimizes temperature differences between day and night.
  • Warmer clouds re-radiate more long-wave radiation, while high-level clouds radiate less due to their cold upper surfaces.
  • A balance is typically achieved between incoming solar radiation and outgoing long-wave radiation.

Global Energy Budget

  • Variations occur in the energy budget based on location and time.
  • Globally, incoming solar radiation is balanced by outgoing terrestrial radiation.
  • Absorption Rates: 71% of incoming solar radiation is absorbed (48% by the Earth, 23% by greenhouse gases). These amounts are radiated back to maintain balance.
  • Imbalance in these processes may indicate global warming.

Surface Energy Budget (Table 2.3)

  • Gains:
    • Absorbed solar radiation: 48%
    • Absorbed long-wave radiation: 6%
  • Losses:
    • Latent heat transfer (evaporation): 25%
    • Sensible heat transfer (convection): 5%
    • Long-wave radiation direct to space: 12%
  • Total gains equal total losses to maintain balance.

Atmospheric Energy Budget (Table 2.4)

  • Gains:
    • Absorbed solar radiation: 23%
  • Losses:
    • Latent heat transfer (evaporation): 25%
    • Sensible heat transfer (convection): 5%
    • Radiation from atmosphere to space: 59%

Albedo and Global Energy Distribution

Albedo

  • Albedo refers to the reflectivity of a surface.
  • Components of Reflected Solar Energy:
    • Reflected by Earth's surface: 5%
    • Reflected by clouds: 18%
    • Scattered by atmospheric particles: 6%

Global Energy Budget (Figure 2.11)

  • Incoming Solar Energy: 100 units of short-wave radiation.
  • Distribution:
    • 59 units radiated by the atmosphere to space.
    • 12 units of long-wave radiation lost directly to space.
    • 5 units scattered to the atmosphere.
    • 14 units absorbed by atmosphere.
    • 4 units absorbed by clouds
    • 25 units latent heat transfer, evaporation
    • 4 units sensible heat transfer.
    • 48 units absorbed by the surface.
  • The atmosphere cools primarily through radiation, while the Earth's surface heats through radiative absorption.
  • Without atmospheric absorption of long-wave radiation, Earth's surface temperature would be up to 40°C lower.

Albedo Patterns (Figure 2.12)

  • Key Areas of Albedo:
    • (a) ITCZ (Inter-tropical Convergence Zone): Heavy cloud cover.
    • (b) Sub-tropics: Little cloud due to subsidence of air in anticyclones.
    • (c) Polar Front: Heavy cloud cover.
    • (d) Polar Regions: High albedo due to ice and snow cover.

Atmospheric and Oceanic Transfers

Air Mass Source Regions (Figure 2.16)

  • Air Mass Types:
    • A: Arctic
    • AA: Antarctic
    • cP: Polar Continental
    • cT: Tropical Continental
    • mE: Equatorial Maritime
    • mP: Polar Maritime
    • mT: Tropical Maritime
  • Winds move from these source regions, influencing temperature and moisture.
  • ITCZ (Intertropical Convergence Zone) and Polar Front are key boundaries.

Ocean Currents and Heat Distribution

  • Ocean currents, driven by prevailing surface winds, distribute surplus heat energy from tropics to higher latitudes.
  • Warm currents transfer 20% of the energy compared to 80% transferred by winds.
  • Examples of warm and cold ocean currents and their impact on regional temperatures (Figure 2.17).

January Temperature and Ocean Currents (Figure 2.17)

  • Warm currents: North Atlantic Drift, Gulf Stream, North Equatorial Current, Guinea Current, Brazil Current, Agulhas Current, Kuro Siwo, Equatorial Counter-Current, East Australian Current
  • Cold Currents: Past Greenland Current, Norwegian Current, North Pacific Current, Humboldt (Peru) Current, Falkland Current, West Wind Drift, South Equatorial Current

Solar Radiation Distribution (Figure 2.14)

  • Isoline map showing average annual distribution of solar radiation in Watts per square meter (W/m^2).
  • Regions with high solar radiation (more than 225 W/m^2) and low solar radiation (less than 150 W/m^2) are detailed.

Net Radiation Balance (Figure 2.15)

  • Illustrates surplus and deficits of heat energy across different latitudes.
  • Surplus: Areas between 40° and the Equator.
  • Deficit: Areas between 40° and the poles.
  • Heat is transferred from surplus to deficit areas by winds and ocean currents.

Atmospheric Transfers by Wind Belts

  • Winds move air masses, which are large bodies of air with uniform temperature and moisture.
  • Frontal zones separate different air masses, creating temperature and humidity gradients.
  • Air masses gain characteristics from their source regions via prolonged contact with ground or sea.
    • Subtropical high-pressure belts are source regions for warm tropical air masses.
    • Polar air masses form over continents, becoming very cold in winter and relatively cool in summer.

Air Masses Classification

  • Air masses are classified as continental or maritime based on their formation location.
    • Maritime air masses are moist.
    • Continental air masses are dry.
  • Winds from the sea transfer moisture.

Characteristics of Air Masses (Table 2.6)

  • Equatorial maritime (mE): warm, very moist
  • Tropical maritime (mT): mild in winter, moist
  • Tropical continental (cT): warm in summer, very warm, dry
  • Polar maritime (mP): cool, moist
  • Polar continental (cP): cold, dry
  • Continental Arctic/Antarctic (cA/cAA): very cold, very dry

Latitudinal Radiation Patterns

  • Variations in average annual solar radiation are measured at the Earth's surface, with highest radiation exceeding 225 W/m^2 and lowest below 150 W/m^2.
  • Total insolation in the southern hemisphere is generally lower than in the northern hemisphere.

Case Study: Energy Budgets in Equatorial Regions and Hot Deserts (Table 2.5)

Equatorial Regions

  • Incoming Solar Radiation: High (about 440 Watts/m^2 per year).
  • Radiation at Earth's Surface: 150-200 W/m^2
  • Absorption and Scattering: Very high due to convective cloud cover.
  • Surface Albedo: Low (about 10% for tropical rainforest).
  • Energy Absorption: Wet soils conduct energy down.
  • Sensible Heat Transfer: Strong uplift, especially in daytime.
  • Latent Heat Transfer: Very high due to moisture from water bodies and transpiration.
  • Radiation Balance: Positive, with large gains over losses.
  • Temperature: Hot temperatures year-round, with daytime highs around 30°C and nighttime lows around 23°C (daily range of 7°C).

Hot Deserts (Latitude 15-30°)

  • Incoming Solar Radiation: Less (about 340 Watts/m^2 per year).
  • Radiation at Earth's Surface: 250-300 W/m^2
  • Absorption and Scattering: Low due to cloudless skies.
  • Surface Albedo: High (28%, rising to 40% with sand cover).
  • Energy Absorption: Little energy transferred down into the rock or dry sand.
  • Sensible Heat Transfer: Strong uplift by day, strong conduction cooling at night, sinking of cold air.
  • Latent Heat Transfer: Very low due to dry air.
  • Radiation Balance: Positive, but with a smaller surplus.
  • Temperature: Extreme diurnal temperatures; daytime averages around 38°C, reaching 50°C in summer, dropping to 15°C at night and 5°C in winter nights.