Introduction
Jet streams are narrow corridors of high-velocity, geostrophic winds circulating in the upper troposphere, typically at altitudes between 9 to 14 kilometres. Driven by strong latitudinal thermal gradients and Coriolis force, these high-altitude wind belts act as critical atmospheric engines dictating temperate and tropical weather patterns globally.
Major Classifications of Jet Streams
- Polar Front Jet (PFJ): Located around 50° to 60° latitude in both hemispheres, this jet stream is formed along the polar front and plays an essential role in the formation and steering of temperate (extratropical) cyclones.
- Sub-Tropical Westerly Jet (STWJ): Flowing near 30° latitude, it steers winter mid-latitude weather systems into South Asia, directly governing the arrival of Western Disturbances over northwest India.
- Tropical Easterly Jet (TEJ): A unique, seasonal upper-tropospheric jet formed due to intense heating over the Tibetan Plateau during the Northern Hemisphere summer, serving as an important catalyst for the burst of the Indian Summer Monsoon.
Key Characteristics and Atmospheric Dynamics
- Meandering Path (Rossby Waves): Jet streams do not flow in straight lines; rather, they meander in large planetary loops termed Rossby waves. These waves expand and contract poleward and equatorward, transferring heat between latitudes.
- Seasonal Variation in Velocity: Jet velocities are markedly higher in winter (frequently exceeding 300 km/h) because the temperature contrast between the equator and the poles is at its steepest. In summer, the reduced thermal contrast weakens them.
- Upper-Level Divergence and Surface Lows: Along the troughs (equatorward dips) of jet streams, upper-air divergence occurs. This divergence induces lifting of surface air, promoting low-pressure systems, cloud cover, and stormy weather.
- Upper-Level Convergence and Surface Highs: Beneath the ridges (poleward bulges), upper-air convergence leads to subsidence, producing stable, high-pressure conditions that can stall and trigger persistent heatwaves or 'Omega blocking' patterns.
Conclusion
Jet streams remain central to maintaining global thermodynamic equilibrium and directing precipitation regimes. However, rapid warming due to Arctic Amplification is weakening the pole-to-equator thermal gradient, leading to wavier and slower jet streams that increasingly lock severe weather anomalies like prolonged heat domes and torrential rainfall in place.