Air Mass
- In meteorology, air masses are large bodies of air characterised by nearly uniform temperatures and humidity at a given altitude.
Characteristics
- Air masses have distinct boundaries and can extend horizontally for hundreds or thousands of kilometres.
- They may also reach heights as high as the top of the troposphere, approximately 10–18 km (6–11 miles) above the Earth’s surface.
- It brings constant weather conditions.
- Air masses form when the atmosphere remains in contact with a large, relatively uniform land or sea surface for a sufficiently long period, allowing it to acquire the surface’s temperature and moisture properties.
- Source regions for air masses are the high-pressure belts in the subtropics (resulting in tropical air masses) and around the poles (producing polar air masses).
- Regions with high pressure and minimal pressure difference or gradient are considered ideal source regions.
- Mid-latitudes lack major source regions due to dominance by cyclonic and other disturbances.
Classification of Air Mass

- Continental Air Mass: Originating from a homogeneous continental surface.
- Maritime Air Mass: Originating from a homogeneous oceanic surface.
Troughs and Ridges

- A trough is an elongated area of relatively low pressure extending from the centre of a region of low pressure. A trough is roughly U-shaped.
- To the east of the trough, air usually rises, allowing precipitation to develop.
- A ridge, on the other hand, looks like an upside-down U.
- Fairweather is usually associated with ridges.
- Air under a ridge sinks, which is not conducive to the development of clouds.
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