What is Jet Stream?
In Geography, jet streams are defined as the fast-flowing air currents characterized by their narrow and meandering type current. The jet stream is prevalent in some planets including our planet Earth.
On Earth, main jet streams are located near the altitude of the tropopause region and are located in the western winds which are flowing west to east. The path of this wind has a typical meandering shape. Jet streams can start, stop, split into two, or can have more parts. While, at last, they combine into one single stream.
On the same subject matter, we will present our discussion in an elaborate fashion.
Subtropical Jet Stream
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The Subtropical jet stream is a belt of strong upper-level winds that lie above the regions of the subtropical high-pressure region. Unlike the polar front jet streams, this wind travels in the lower latitude regions and at a slightly higher elevated region, this is because of the increase in height of the tropopause layer at the lower latitudes. The temperature gradients of this jet stream do not extend to the surface area, for this reason, the surface front is not evident. While in the tropical region an easterly jet is at times found at upper levels. Mainly this wind is found when a landmass is located poleward of an ocean, for this reason, the temperature increases with the latitude.
Subtropical Westerly Jet Stream
The name ‘Subtropical Westerly Jet stream’ is located over 27-degree to 30-degree north latitude. In our country, the jet streams blow south of the Himalayas. This wind blows in India all through the year except in the summertime. The north and the north-western parts of the country experience western cyclonic disturbances, this happens for the westerly flow in the wintertime. While in summertime the subtropical westerly jet streams move northwards towards the Himalayas with the movement of the sun.
The Western disturbances abbreviated as WDS are the mid-tropospheric to upper‐tropospheric mesoscale vortices. They typically propagate along with the subtropical westerly jet stream. This brings heavy rainfall in the country, Pakistan, and in northern India during the boreal winter.
They act similarly to the Tibetan Plateau vortices (TPVs). This wind also affects southwest China during the springtime and in the summer season. This wind originates from the Tibetan Plateau.
The similarity implies the existence of a general group of upper‐tropospheric vortices that features interactions with the orography of the Hindu Kush‐Himalaya‐Tibetan Plateau region.
Equatorial Jet Stream
The Jet streams are the narrow bands of strong and gusty winds blowing in the upper levels of the atmosphere. Normally the jet streams blow from east to west, but at times it often shifts to north and south as well. Like any other winds, the jet streams follow the boundaries between the hot and cold air. The cold and hot boundaries are characterized in the wintertime. The jet streams are the strongest in both the northern and the southern hemisphere.
The Daunting Question is, why does the Wind Blow from West to East?
To recollect from our previous study, if the earth did not rotate, the global winds, the warm air at the equator would drift towards both the polar regions. Hence, we see that the earth’s rotation has divided the wind circulation into three cells. The rotation of the planet is also responsible for the cause of jet streams.
When the wind moves away from the equatorial region, the motion of the air is not directed towards north and south but it is affected by the momentum as it drifts away from the equator. This is reasoned out for the momentum of how fast a location present on or above the earth moves relative to the earth’s axis.
Your location will determine the speed relative to the earth’s axis. If you stand on the equator, and your friend is standing on a 45-degree latitude line, you will find miraculously that you move faster than your friend. While another friend, suppose standing on the pole will not move at all. While he or she will only spin standing on the pole. This speed of rotation is great enough to lower the weight up to one pound if standing on the pole than on the equator.
What Causes Jet Stream?
We need to understand this fact, that the Sun doesn’t heat the entire earth evenly, at some places it heats more like in the equator, the sun is unbearable. While, at some places, the sun rays may not reach properly, like in the polar regions. For this very reason, the areas near the equator are quite hot and the areas near the poles are very cold.
So, when the Earth’s warmer air masses meet or collide with the cooler air masses, the warmer air rises higher in the atmosphere while the cooler air sinks to replace the warm air which rose above. This movement creates an air current, or wind to gush down. This forms the jet stream.
On Our Planet, There are Four Jet Streams.
Two Polar Jet streams.
Two Subtropical Jet streams.
The Jet streams are formed in the atmosphere when the warm air masses meet the cool air masses.
On average, jet streams blow at about 110 miles per hour, calculated approximately. The temperature difference between warm and cold air masses is quite dramatic then it will cause the jet streams to move speedier, which can be 250 miles per hour.
FAQs on Subtropical Jet Stream
1. What exactly is the Subtropical Jet Stream (STJ)?
The Subtropical Jet Stream (STJ) is a high-altitude, fast-flowing current of air located where the tropical Hadley Cell and the mid-latitude Ferrel Cell meet. It is formed primarily due to the Earth's rotation (the Coriolis effect) and the significant temperature difference between the warm tropical air and the cooler subtropical air. It exists in both the Northern and Southern Hemispheres.
2. In which direction does the Subtropical Jet Stream flow and why?
The Subtropical Jet Stream consistently flows from west to east. This direction is a direct result of the conservation of angular momentum on a rotating Earth. As air from the equator moves poleward, it travels over a part of the Earth that is rotating more slowly, causing the air current to be deflected eastward, creating a powerful westerly wind.
3. At what altitude and latitude is the Subtropical Jet Stream typically found?
The STJ is typically found at a high altitude of about 10 to 16 kilometres above the Earth's surface, near the tropopause. Latitudinally, it is located around 20° to 35° in both the Northern and Southern Hemispheres, often corresponding with the horse latitudes, which are known for high surface pressure.
4. What is the main difference between the Subtropical Jet Stream and the Polar Front Jet Stream?
The primary differences between the Subtropical Jet Stream (STJ) and the Polar Front Jet Stream (PFJ) are:
- Location: The STJ is found at lower latitudes (20°-35°), while the PFJ is located at higher latitudes (45°-65°).
- Formation: The STJ is a result of the conservation of angular momentum within the Hadley Cell, whereas the PFJ forms due to the strong temperature and pressure gradient where cold polar air meets warm tropical air.
- Consistency: The STJ is more consistent in its position and strength throughout the year, while the PFJ is more variable and meanders significantly, directly influencing daily weather changes in the mid-latitudes.
5. How does the Subtropical Jet Stream influence India's climate?
The STJ plays a crucial role in India's climate, especially during winter. In the winter months, the southern branch of the STJ flows over the northern Indian plains and is responsible for steering Western Disturbances. These disturbances are extratropical storms that bring essential rainfall and snowfall to northern India. During the summer, the STJ shifts north of the Himalayas, allowing the Tropical Easterly Jet to establish, which is a key factor for the onset of the southwest monsoon.
6. Why is the Subtropical Jet Stream generally stronger in winter?
The strength of the Subtropical Jet Stream is directly related to the temperature gradient between the equatorial and subtropical regions. In winter, this temperature difference is much more pronounced, with very warm air in the tropics and significantly cooler air in the subtropics. This stronger temperature contrast creates a steeper pressure gradient, which in turn drives higher wind speeds, making the jet stream more powerful.
7. What does it mean for the jet stream to meander, and what is the effect?
A meandering jet stream follows a wavy, snake-like path instead of a straight line. These large-scale waves are known as Rossby waves. The 'troughs' (dips towards the equator) in the meander allow cold air to move to lower latitudes, often causing cold spells. The 'ridges' (bulges towards the poles) allow warm air to move to higher latitudes, leading to warmer and more stable weather conditions on the surface below.
8. How does the Tibetan Plateau affect the Subtropical Jet Stream?
The massive and high-altitude Tibetan Plateau acts as a significant physical barrier to the STJ. During the winter, it bifurcates (splits) the jet stream into two branches: one that flows north of the plateau and another that flows south of it over the Indian subcontinent. In the summer, the intense heating of the plateau helps reverse the pressure systems and plays a key role in the northward shift of the STJ, which is essential for the Indian monsoon.
9. What are the typical wind speeds within the Subtropical Jet Stream?
Wind speeds within the Subtropical Jet Stream are consistently high but can vary. They typically average around 120 to 150 kilometres per hour. However, within the core of the jet stream, speeds can often exceed 250 kilometres per hour, especially during the winter when the temperature gradients are at their strongest.
