Atmospheric Circulation and Weather

Overview

• Discussion of atmospheric circulation and weather.
• Previous lecture: Differences in temperature in different regions of the Earth.
• Equator: surplus of heat; Poles: deficit of heat.

Heat Redistribution

• Heat circulation solves the paradox of more heat loss than received in polar regions.
• Mechanism: Air and water circulation transfers heat from equator to poles.
• Prevents overheating at equator and extreme cold at poles.

Atmospheric Pressure

• Drives wind movement; air moves from high pressure to low pressure.
• Hydrostatic pressure: weight of air above a point.
• Modified by rotation, local effects like air movement.
• Pressure measured in pascals, millimeters of mercury, or bar.

Pressure Measurement

• Barometer use: mercury-filled glass tube inverted in mercury vessel.
• Height of mercury column indicates atmospheric pressure.
  • Higher pressure = taller column.
• Standard atmospheric pressure: 101325 pascals, 760 mm of mercury, 1 bar.

Wind Dynamics

• Air movement due to pressure differences; bulk air movement = wind.
• Wind described by direction and speed (vector quantity).
• Measured by wind vanes (direction) and anemometers (speed).

Wind Speed Classification

• Beaufort scale: 0 (calm) to 12 (hurricane force).
• Classifies wind speed range and corresponding descriptions.

Atmospheric Pressure Formula

• Considers non-zero lapse rate (temperature decreases with altitude).
• Pressure formula factors: reference pressure, temperature, lapse rate, height.

Forces Affecting Wind

• Coriolis Force: deflects wind due to Earth’s rotation; maximum at poles, zero at equator.
• Gravitational Force: affects air movement, pulls air down.
• Frictional Force: reduces wind speed, significant near the ground.

Air Masses

• Large bodies of air with uniform properties: temperature and humidity.
• Source areas: large, uniform, flat surfaces, minimal surface winds.
• Classified by source region: polar, tropical, continental, marine.

Fronts

• Transition zones between air masses.
• Types: Stationary, Cold, Warm, Occluded (Cold/Warm Occlusion).

General Atmospheric Circulation

• Governed by energy surplus and deficit.
• Pressure belts emerge due to convection and subsidence.
• Migration with seasons influenced by the Earth's tilt and rotation.
• Hadley, Polar, and Ferrel cells explained.
• Influence of these cells on wind patterns and ocean currents.

Seasonal and Local Winds

• Seasonal: monsoons due to shifting heating and pressure zones.
• Local winds: small-scale, e.g., sea/land breezes, mountain/valley winds.
• Adiabatic heating and cooling effect.

Cyclones

• Tropical Cyclones: over warm oceans, powered by condensation.
• Extratropical Cyclones: formed beyond tropics, through cyclogenesis or transition.

Thunderstorms

• Local storms with intense convection, associated with cumulonimbus clouds.
• Common in pre-monsoon season in certain regions.

This lecture covered the essentials of atmospheric circulation, its impact on weather patterns, and the various factors influencing wind movement and pressure differences around the globe. Understanding these concepts is crucial for grasping how weather systems operate and interact across different climatic zones.