Effect of Tropical Easterly Jet in India Monsoon

The Indian monsoon is one of the most complex weather systems in the world. Many atmospheric factors work together to bring rainfall to the Indian subcontinent. Among these, the Tropical Easterly Jet (TEJ) plays a crucial role during the monsoon season. Understanding the effect of tropical easterly jet in India monsoon helps explain why rainfall patterns vary across regions and why some years experience stronger or weaker monsoons.

In this article, we will explore what the Tropical Easterly Jet is, how it forms, and its direct impact on the Indian monsoon system.

What is the Tropical Easterly Jet?

The Tropical Easterly Jet (TEJ) is a fast-moving stream of air that flows from east to west in the upper troposphere, typically around 12–15 km above the Earth’s surface.

This jet stream develops mainly during the Northern Hemisphere summer, especially between June and September, which coincides with the Indian southwest monsoon season.

Key characteristics of the Tropical Easterly Jet include:

• Wind direction: East to West
• Altitude: Around 100–200 hPa pressure level
• Average speed: 40–80 km/h, sometimes even higher
• Core region: Southern India and the Indian Ocean

The TEJ is strongly linked to the intense heating of the Tibetan Plateau and the surrounding landmass during summer.

Formation of the Tropical Easterly Jet

The formation of the TEJ is closely related to large-scale atmospheric circulation over Asia and the Indian Ocean.

1. Heating of the Tibetan Plateau

During summer, the Tibetan Plateau becomes extremely hot because it lies at a very high altitude. This intense heating creates a strong upper-level high-pressure system over the region.

2. Development of Pressure Gradient

The heating over Asia and comparatively cooler temperatures over the Indian Ocean create a pressure difference in the upper atmosphere. This pressure gradient initiates strong east-to-west winds.

3. Establishment of the Jet Stream

As a result, a powerful Tropical Easterly Jet stream forms across South Asia, extending from Southeast Asia across India toward Africa.

This upper-level jet becomes one of the defining atmospheric features of the monsoon circulation.

Effect of Tropical Easterly Jet in India Monsoon

The effect of tropical easterly jet in India monsoon is significant because it directly influences rainfall intensity, monsoon stability, and regional precipitation patterns.

Let’s understand its major impacts.

1. Strengthening of the Southwest Monsoon

One of the most important effects of the Tropical Easterly Jet is that it strengthens the southwest monsoon circulation.

The TEJ enhances upper-level divergence in the atmosphere. When air diverges at higher altitudes, it allows rising moist air from the lower atmosphere to continue ascending. This vertical movement promotes the development of monsoon clouds and rainfall.

As a result:

• Moisture-laden winds from the Arabian Sea and Bay of Bengal become stronger.
• Convective activity increases.
• Rainfall over India becomes more intense.

A strong Tropical Easterly Jet is therefore usually associated with a healthy and active monsoon season.

2. Support for Deep Convection and Cloud Formation

The TEJ also plays a key role in maintaining deep convection, which is essential for heavy rainfall.

When the upper atmosphere allows air to move outward efficiently, it reduces atmospheric pressure at lower levels. This encourages warm and moist air to rise rapidly, forming large cumulonimbus clouds.

These clouds are responsible for:

• Heavy monsoon showers
• Thunderstorms
• Intense rainfall events

Without the support of upper-level jets like the TEJ, convection would weaken and rainfall could decrease.

3. Influence on Monsoon Onset and Progress

The presence of the Tropical Easterly Jet is also linked to the timely onset of the Indian monsoon.

Meteorologists observe that:

• When the TEJ forms early and becomes strong, the monsoon tends to advance smoothly across India.
• If the jet is weak or delayed, the monsoon onset may be late or irregular.

Therefore, the TEJ acts as an indicator of monsoon strength and progression.

4. Impact on Regional Rainfall Distribution

The TEJ significantly influences where rainfall occurs within India.

Its strongest core is usually located over peninsular India, particularly:

• Southern India
• Central India
• Parts of the Arabian Sea region

Regions located under the strongest part of the jet often experience:

• Enhanced convection
• Increased rainfall activity

On the other hand, if the jet shifts north or south, rainfall distribution across India may change.

5. Weak TEJ and Monsoon Failure

A weak Tropical Easterly Jet can negatively affect the monsoon system.

When the TEJ weakens:

• Upper-level divergence decreases.
• Rising motion in the atmosphere weakens.
• Cloud formation reduces.

This can result in:

• Reduced rainfall
• Breaks in the monsoon
• Increased chances of drought conditions

Several studies have found that weak TEJ years often correspond with below-normal monsoon rainfall in India.

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What is the difference Between Tropical Easterly Jet and Subtropical Westerly Jet

To fully understand the effect of tropical easterly jet in India monsoon, it is important to compare it with another major jet stream: the Subtropical Westerly Jet (STWJ).

Key differences include:

Before the monsoon begins, the Subtropical Westerly Jet shifts northward. This shift allows the Tropical Easterly Jet to develop, creating favorable conditions for monsoon circulation.

Why the Tropical Easterly Jet is Important for Monsoon Prediction

Meteorologists closely monitor the Tropical Easterly Jet because it provides valuable clues about the upcoming monsoon season.

The strength, position, and speed of the TEJ help scientists:

• Estimate monsoon rainfall intensity
• Track active and break phases of monsoon
• Predict regional rainfall variations
• Improve seasonal climate forecasts

Satellite observations and weather models now track the TEJ continuously to improve monsoon predictions.

Conclusion

The effect of tropical easterly jet in India monsoon is profound and multi-dimensional. This upper-level jet stream plays a crucial role in strengthening monsoon circulation, enhancing cloud formation, and influencing rainfall distribution across the country.

A strong Tropical Easterly Jet usually supports a vigorous and well-distributed monsoon, while a weak jet can lead to reduced rainfall and monsoon breaks. Because of its influence on atmospheric dynamics, the TEJ remains one of the most important features studied by meteorologists while analyzing the Indian monsoon system.

Understanding the Tropical Easterly Jet not only helps explain the behavior of the monsoon but also improves our ability to forecast rainfall patterns that affect agriculture, water resources, and the overall economy of India.

Frequently Asked Questions (FAQs)

What is the Tropical Easterly Jet?

The Tropical Easterly Jet (TEJ) is a strong upper-level wind current that flows from east to west across South Asia during the summer monsoon season.

At what altitude does the Tropical Easterly Jet occur?

The Tropical Easterly Jet occurs in the upper troposphere, usually between 12 and 15 km above the Earth’s surface, around the 100–200 hPa pressure level.

How does the Tropical Easterly Jet affect the Indian monsoon?

The effect of tropical easterly jet in India monsoon includes strengthening monsoon winds, enhancing rainfall through upper-level divergence, and supporting deep convection that produces heavy rain.

When does the Tropical Easterly Jet form?

The Tropical Easterly Jet forms during summer months (June to September) due to intense heating over the Tibetan Plateau and surrounding land areas.

What happens if the Tropical Easterly Jet becomes weak?

A weak Tropical Easterly Jet can lead to:

• Reduced monsoon rainfall
• Breaks in monsoon activity
• Possible drought conditions in some parts of India