Introduction

The earth receives varying amounts of insolation, and it causes differential heating of the surface and atmosphere. It will produce a density difference in the air. When heated, air will expand and compress when cooled. This will result in a variation of atmospheric pressure. It will cause the movement of air from high pressure to low pressure in three-dimensional motions across the globe.Air moving horizontally is referred to as wind.

Atmospheric Pressure

Atmospheric pressure is the force exerted by the weight of the air column above a unit area from sea level to the top of the atmosphere.It is usually measured in millibars (mb), with the average sea level pressure being 1,013.2 mb.Due to gravity, air at the surface is denser, leading to higher pressure.

• The gradual change of pressure between different areas is known as a barometric slope or pressure gradient. If the isobars are closer, then the pressure gradient will be high and vice versa.

Vertical Variation of Pressure

• Decrease with Height: Atmospheric pressure decreases rapidly with elevation, approximately 1 mb for each 10 m increase in height.
• Pressure Gradient: The vertical pressure gradient force is significant but balanced by the gravitational force, preventing strong upward winds.

Horizontal Distribution of Pressure

• Isobars:Lines that join points with equal atmospheric pressure, used to represent pressure distribution on weather maps.
• Pressure Systems:
  • Low-Pressure System: Enclosed by one or more isobars, with the lowest pressure at the center, often associated with stormy weather.
  • High-Pressure System: Enclosed by one or more isobars, with the highest pressure at the center, typically associated with calm, clear weather.