Atmospheric Circulations: Planetary Winds, Pressure Belts, Shifting of Pressure Belts.
Atmospheric circulations is the large-scale movement of air through the Earth’s atmosphere, distributing heat and moisture around the globe. This process is driven by the uneven heating of the Earth’s surface, leading to differences in air pressure and creating various wind and pressure patterns.
Planetary Winds
1. Trade Winds:
- Location: Occur between 0° and 30° latitude in both hemispheres.
- Direction: Blow from the northeast in the Northern Hemisphere and from the southeast in the Southern Hemisphere towards the equator.
- Characteristics: These are steady and persistent winds that facilitate the movement of weather systems and ocean currents.
2. Westerlies:
- Location: Found between 30° and 60° latitude in both hemispheres.
- Direction: Blow from the southwest in the Northern Hemisphere and from the northwest in the Southern Hemisphere towards the poles.
- Characteristics: These winds are more variable and can bring weather changes, influencing temperate climates.
3. Polar Easterlies:
- Location: Occur between 60° latitude and the poles in both hemispheres.
- Direction: Blow from the east towards the west.
- Characteristics: These cold, dry winds are less consistent and influence polar climates.
Pressure Belts
1. Equatorial Low (Intertropical Convergence Zone – ITCZ):
- Location: Near the equator, approximately between 5°N and 5°S.
- Characteristics: Characterized by low pressure, high temperatures, and high humidity, leading to frequent thunderstorms and heavy rainfall.
2. Subtropical High:
- Location: Around 30°N and 30°S.
- Characteristics: Characterized by high pressure, clear skies, and low precipitation, creating desert conditions in many regions.
3. Subpolar Low:
- Location: Around 60°N and 60°S.
- Characteristics: Characterized by low pressure and frequent cyclonic activity, leading to variable weather and precipitation.
4. Polar High:
- Location: Near the poles.
- Characteristics: Characterized by high pressure and cold, dry air.
Shifting of Pressure Belts
1. Seasonal Shifts:
- Causes: The tilt of the Earth’s axis causes the sun’s direct rays to shift between the Tropic of Cancer (23.5°N) and the Tropic of Capricorn (23.5°S) throughout the year, leading to the seasonal movement of pressure belts.
- Impact on Weather: This shift causes changes in wind patterns and weather systems, influencing monsoons, trade winds, and westerlies.
2. Monsoons:
- Summer Monsoon: During the Northern Hemisphere summer, the ITCZ moves northward, drawing moist air from the oceans over land, leading to heavy rainfall in regions like South Asia.
- Winter Monsoon: During the Northern Hemisphere winter, the ITCZ moves southward, causing dry, cooler air to flow from the continent towards the ocean, leading to dry conditions.
3. Impact on Climate:
- Tropical Regions: Experience wet and dry seasons due to the shifting ITCZ.
- Temperate Regions: Experience variations in precipitation and temperature as westerlies shift.
Practice Questions
- Planetary Winds:
- Explain the formation and characteristics of trade winds.
- How do westerlies influence the climate of temperate regions?
- Pressure Belts:
- Describe the main characteristics of the equatorial low-pressure belt.
- What are the climatic implications of the subtropical high-pressure belt?
- Shifting of Pressure Belts:
- How does the seasonal shift of the ITCZ affect weather patterns in tropical regions?
- Discuss the role of shifting pressure belts in the formation of monsoons.
UPSC-Style Question
Discuss the global atmospheric circulation system, focusing on planetary winds and pressure belts. How does the shifting of pressure belts influence climatic patterns around the world? (250 words)
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