The atmosphere is the layer of gases surrounding the Earth, held in place by gravity. It consists mainly of nitrogen (78%), oxygen (21%), and other gases like argon, carbon dioxide, and water vapor.
Structure based on temperature:
Based on chemical composition, the atmosphere has two main layers:
Layers based on temperature variations:
[Diagram would show temperature profile with altitude, indicating temperature inversions at stratosphere and thermosphere]
Factors affecting atmospheric pressure:
Major global pressure belts:
[Diagram would show alternating high and low pressure belts from equator to poles]
Importance of atmosphere:
Wind is the horizontal movement of air from areas of high pressure to areas of low pressure.
Factors of origin:
The most important reason for wind origin is pressure difference (pressure gradient force) - air moves from high pressure to low pressure areas.
Factors determining wind velocity and direction:
The Coriolis Force is an apparent force caused by Earth's rotation that deflects moving objects to the right in the Northern Hemisphere and to the left in the Southern Hemisphere.
Contribution to wind direction:
[Diagram would show wind deflection patterns in both hemispheres]
Pressure Gradient Force is the force that results from pressure differences over distance. It's the primary force that initiates wind movement.
Contribution to air movement:
Earth's gravitational force contributes to air movement by:
Naming of wind refers to the system of identifying winds based on their direction of origin.
Wind naming convention:
Wind velocity determination:
Units of wind velocity:
Wind classification:
Primary circulation refers to the global-scale wind patterns that distribute heat around Earth.
Characteristics:
[Diagram would show global wind patterns with trade winds, westerlies, polar easterlies, and circulation cells]
Secondary circulation includes seasonal wind patterns like monsoons and cyclones that modify primary circulation.
Climate influence with examples:
Local winds are winds that blow over small areas due to local temperature and pressure differences.
Examples and weather influence:
A cyclone is a large-scale air mass that rotates around a strong center of low pressure.
Types of cyclones:
Climate influence: Bring heavy rainfall, strong winds, can cause flooding; redistribute heat and moisture globally.
An air mass is a large body of air with relatively uniform temperature and humidity characteristics.
Classification:
Climate contribution: Determines temperature, humidity, and weather patterns of regions they dominate.
A front is a boundary separating two different air masses.
Formation: Forms when two air masses with different temperature and humidity characteristics meet but don't mix readily.
Types and climate relationship:
Monsoon winds are seasonal wind systems that reverse direction between summer and winter.
Formation: Caused by differential heating between land and ocean, creating seasonal pressure differences.
Distinct impact areas:
(a) Why do all weather phenomena occur mainly in troposphere?
Because troposphere contains 75% of atmospheric mass, almost all water vapor, and has vertical temperature gradient causing convection and weather systems.
(b) What would be the consequence of the increase in the amount of carbon dioxide?
Enhanced greenhouse effect leading to global warming, climate change, sea level rise, and extreme weather events.
(c) What is the reason behind the prevalence of high pressure of dry air than moist air?
Dry air is denser and heavier than moist air because water vapor molecules are lighter than nitrogen and oxygen molecules they displace.
(d) How does the ozone layer help the living-beings?
Absorbs harmful ultraviolet (UV) radiation from the sun, protecting living organisms from skin cancer, cataracts, and genetic damage.
(e) Why is the air pressure highest at the sea level?
Because the weight of the entire atmosphere above exerts maximum pressure at sea level, with pressure decreasing with altitude as less air remains above.
(f) What is the reason behind variation in vertical extent of the troposphere in the polar region and equatorial region?
Due to temperature differences - warmer at equator causes more thermal expansion (higher troposphere), colder at poles causes contraction (lower troposphere).
(g) Why is horizontal movement of wind parallel to the earth's surface not felt in the equatorial low pressure belt?
Because the strong upward convection currents (vertical movement) dominate in this region of intense heating, minimizing horizontal wind flow.
(a) What is the vertical extent of the atmosphere?
About 10,000 km from Earth's surface, though 99% of mass is below 32 km.
(b) Up to what altitude from the earth's surface does chemical composition of gases remain almost same?
Up to about 80-100 km (homosphere).
(c) What is the name of the boundary-line between homosphere and heterosphere?
The homopause or turbopause.
(d) What is Ferrell's Law?
Describes the deflection of winds to the right in Northern Hemisphere and left in Southern Hemisphere due to Earth's rotation.
(e) What is Beaufort Scale? Write briefly about the utility of this scale with example.
A scale from 0-12 that estimates wind speed based on observed sea or land conditions. Useful for mariners and meteorologists when instruments aren't available. Example: Force 8 = Gale, 34-40 knots.
(f) Write in brief about Lapse Rate.
The rate at which temperature decreases with increasing altitude in the atmosphere. Normal lapse rate is about 6.5°C per kilometer in troposphere.
(a) Homosphere: Lower atmosphere (0-80 km) where gases are uniformly mixed with constant proportions.
(b) Heterosphere: Upper atmosphere (>80 km) where gases separate by molecular weight.
(c) Air temperature, earth's surface height and air pressure relationship: Temperature decreases with height; pressure decreases with height due to less overlying air.
(d) Polar High Pressure Belt: High pressure areas near poles (85-90° N&S) with cold, dense, sinking air.
(e) Wind system: Organized pattern of air movement on various scales from local to global.
(f) Pressure Gradient: Rate of pressure change over distance, determines wind strength.
(g) Trade wind: Consistent easterly winds in tropics (0-30° N&S) that historically aided trade routes.
(h) Horse latitude: Subtropical high pressure belts (25-35° N&S) with calm winds where sailing ships historically stranded.
(i) Roaring Forties: Strong westerly winds between 40-50° S with minimal land obstruction.
(j) Anticyclone: High pressure system with clockwise (NH) or counterclockwise (SH) outward winds.
(k) Jet Stream: Fast-flowing, narrow air currents in upper troposphere.
(l) Isobar: Lines on weather maps connecting points of equal atmospheric pressure.
(m) Tropical Cyclone: Intense circular storm over warm tropical oceans with low pressure center.
(a) Horizontal wind and Vertical wind:
Horizontal wind moves parallel to Earth's surface; vertical wind moves perpendicular (up/down).
(b) Wind and Air mass:
Wind is moving air; air mass is large body of air with uniform characteristics.
(c) Tropical cyclone and Extra-tropical cyclone:
Tropical: warm core, no fronts, over oceans; Extra-tropical: cold core, fronts, over land/ocean.
(d) Sea breeze and Land breeze:
Sea breeze: daytime, from sea to land; Land breeze: nighttime, from land to sea.
(e) Mountain wind and Valley wind:
Mountain wind (katabatic): nighttime, down slope; Valley wind (anabatic): daytime, up slope.
(f) Cyclone and Anticyclone:
Cyclone: low pressure, inward winds; Anticyclone: high pressure, outward winds.
(g) Cold Front and Warm Front:
Cold front: cold air replacing warm, steep slope; Warm front: warm air replacing cold, gentle slope.
(h) Cold wave and Hot Wave:
Cold wave: prolonged unusually cold weather; Hot wave: prolonged unusually hot weather.
(i) Troposphere and Stratosphere:
Troposphere: temperature decreases with height, weather occurs; Stratosphere: temperature increases, contains ozone layer.
(a) Where is Ozone layer located?
(2) Stratosphere
(b) What is amount of oxygen in the atmosphere in terms of volume?
(1) 20.94%
(c) The most important reason for air movement is
(2) Pressure difference
(d) The instrument used for determination of wind velocity is
(2) Anemometer
(e) The unit of wind velocity is
(1) Knots
(f) Monsoon wind belongs to which of the following class?
(3) Secondary circulation
(g) The name of the cyclone formed in the coastal region of the Pacific Ocean in the east is
(4) Typhoon