Western Disturbances (WD) are Low-pressure, non-monsoonal systems originating in the mid-latitude region bringing Winter Rainfall (locally called Mahawat) in India.
- The word ‘disturbance’ is used because air within low pressure systems (fronts, depressions and cyclones) tends to be unstable.
About Western Disturbances (WD)
- Origin: WD forms over Mediterranean Sea region due to interactions between contrasting air masses.
- Formation: A high-pressure area over Ukraine forces cold polar air to intrude into warmer zones, creating instability and triggering cyclogenesis, which leads to the formation of WD.
- Subtropical Westerly Jet: WD are embedded within the mid-latitude (Above 20° latitude) Subtropical Westerly Jet (SWJ), which guides their eastward movement.
- The SWJ: It is a massive ribbon of fast-moving, high-altitude wind current flowing from west to east between 20° and 40° latitude in the upper atmosphere.
- Moisture Sources: As these systems travel across West Asia, Iran, Afghanistan, and Pakistan, they pick up additional moisture from the Caspian Sea (north) and Persian Gulf (south) before reaching India.
- Himalayan Obstruction: Upon reaching the Himalayas, the disturbances are obstructed, causing rainfall in the plains (Orographic rainfall) and snowfall in the western Himalayas.
