What are jet streams?
These are bands of powerful high-speed winds or currents of air that circulate in shifting flows from west to east direction at an altitude of about 8 to 15 kilometers above the earths surface. Jet streams are formed where there is a large temperature difference between two air masses.Jet streams usually take a meandering path across the atmosphere at a rapid speed covering a long distance which can be thousands of miles long and they move seasonally the same way the angle of the Sun in the sky migrates north and south.
The major jet streams are developed near the boundary between the tropopause and the stratosphere, they are westerly winds (they flow from west to east). They tend to move faster in winter where there is a huge temperature difference between the tropical,temperate, and polar air masses.
A line is often used to indicate jet stream on the weather map, this line shows the location of the strongest wind. Jet streams may appear thin as a single line but they are actually regions where the wind speed increases toward a central core of the greatest strength.
Jet streams are very powerful, cold and fast as well, they are capable of hindering aircraft operations especially when pilots try to fly against them. Apart from planet earth, other planets such as Saturn and Jupiter have jet streams running from west to east. Sometimes, jet streams can start, fade away, split into two or smaller rivers of air that merge again downstream or flow in a different direction and even in the opposite direction of the remainder of the jet.
Jet stream speed and direction
Jet streams speeds can cover up to 129 to 225 kilometers per hour (80 to 140 miles per hour), however, they can even travel more than 443 kilometers per hour (275 miles per hour), while the average speed may reach up to 110 km per hour in the summer season to more than 180 kilometers per hour in the winter season. This high speed is caused by temperature, hence, the greater the temperature, the faster the speed of the jet stream. However, they are faster in winter where there are greater temperature differences between the tropical,temperate, and polar air masses. Jet streams usually take a meandering path across the atmosphere at a rapid speed covering a long distance which can be thousands of miles long.
Causes of Jet Streams
To be specific, the jet stream is caused by the melting of polar and tropical air masses just under the tropopause where winds are the strongest. When two air masses of different densities come in contact with each other, the pressure created by the different densities causes winds to increase in speed. The wind does not flow directly from the warm to the cold direction. As these winds try to flow from the warm area in the nearby stratosphere down into the cooler troposphere they are deflected by theCoriolis Effectand move west along the boundaries of the original two air masses; when there is much meandering in the flow, the eastward movement of air tends to slow down. The results are the polar and subtropical jet streams that are formed around the world. Furthermore, the earth rotation and its uneven heating by the sun also lead to the formation of high-altitude jet streams, earths rotation divides the circulation of air into three cells, Polar, Ferrel and Hadley circulation cells. Near the boundary of the Ferrel and Hadley circulation cells is where the subtropical jet stream is formed and the polar jet stream is formed near the Polar and Ferrel circulation cells.
Discovery of Jet Streams
Wasaburo Ooishi a Japanese meteorologist in 1920 was the first to detect the jet stream. He was able to do this using pilot balloons to track upper-level winds as they move towards the Earths atmosphere close to Fuji mountain. Even though he was the first to make the observation of this wind which contributed significantly to the wind pattern, his work was strictly limited within Japan and not worldwide because it was published in Esperanto.
More was known about the jet stream in 1934 when an American pilot by name Wiley Post, embarked on flying only himself around the world. He made a pressurized suit that would enable him to fly at high altitudes(above 6,200 meters which is equivalent to 20,300ft. During this adventure, Post noticed that his ground speed was greatly higher than his airspeed measurements, which shows that he was flying in a current of air. Even with all these discoveries, the knowledge of jet stream was still very limited to many people until in1939 when Heinrich Seilkopf, a German meteorologist decided to use the jet stream in his research work.
A better knowledge of jet stream began to spread in the 1940s during the Second World War when some pilots found high-flying aircraft encountered by upper winds of very great velocity, there was however a difference in the winds when flying between Europe and North America. These are known to be centered around the bands of rapid air movement, which are known as jet streams.
Properties of jet streams
- Jet streams are slim belts at the high altitude near the top of the troposphere. Their speed varies from 129 to 225 kilometers per hour (80 to 140 miles per hour), the average speed can cover up to 110 km per hour in the summer season to more than 180 kilometers per hour in the winter season. Their shape is circular.
- Jet stream speed decreases radially outwards. For one to understand this properly, you have to imagine a river, the river current is usually the strongest at the center with decreasing strength as one moves toward the bank of the river. However, it can be said that jet streams are “rivers of air”.
- The flow of jet streams is not in the form of a straight line. Their circulation path is wavy and meandering. The meanders in the jet stream flow are slower than the rest of the air and are called Rossby waves.
- They are several hundred kilometers wide and about 2km to 5km deep.
- From time to time, the jet stream breaks through the tropopause and moves into the lower stratosphere. A specific amount of water vapor tries to reach in the lower stratosphere with jet streams and this layer exhibits occasional cirrus clouds. So also, in some other time, the jet stream effect extends down to an altitude of about 3 km from the earths surface.
- They dip and rise in altitude/latitude, splitting at times and forming eddies, and even disappearing altogether to appear somewhere else.
- Jet streams also “follow the sun” in that as the sun’s elevation increases each day in the spring, the average latitude of the jet stream shifts poleward. By Summer in the Northern Hemisphere, it is typically found near the U.S. Canadian border.) As autumn approaches and the sun’s elevation decreases, the jet stream’s average latitude moves toward the equator.
- There is a clearly identified longitudinal difference in the strength of the jet stream. In winter, the highest wind velocities of the jet stream are found near the east coast of Asia and the weakest over the eastern Atlantic and Pacific Oceans. In summer, the strongest jet is situated along the Canadian border and the Mediterranean region.
Two popular jet streams zones occur in each hemisphere (North and South hemispheres). One is the sub-tropical jet stream which is located at 30 degrees latitude and another is a polar front jet stream whose position varies with the boundary between polar and temperate air. There exist other jet streams, typically some of these are formed when wind speeds increase above 58 miles per hour (93.3 kilometers per hour) in the upper atmosphere at about 6 miles (9.6 kilometers) to 9 miles (14.5 kilometers) above the surface. Some of these move seasonally close to the equator.
Types of jet stream
- The polar front jet stream
- The subtropical jet stream
- Eastern Tropical Jet Stream
- Polar Night Jet Stream
- Local jet stream
The description of these jet streams are explainedbelow:
The polar front jet stream
Polar front jet stream originated as a result of temperature difference, it runs at a more meandering path than the Sub Tropical Jet Stream. It is found at a height between 6km and 9km in the atmosphere and is associated with the polar front zone in the north and south hemispheres. The polar front jet stream is formed above the convergence zone extending between 400 to 600 latitudes in both hemispheres (polar cold air mass and tropical warm air mass). It moves towards the poles or north direction in summers and towards the equator in the winter or south direction. When moving to the south it takes very cold air with it to the subtropical region.
Sub-tropical jet stream
The subtropical Jet stream is closer to the equator, running in both sides of the hemispheres between 200 and 300 latitudes. This jet stream blows continuously from west to east in a more regular manner than the polar front jet streams. Its speed is comparatively lower than polar jet streams. The air currents arising near the equator descend at 300 N and S latitudes. A part of these air masses takes the form of Sub Tropical Jet streams. It swings to the north of Himalayas in summer in North India.
Eastern Tropical Jet Stream
This is a seasonal Jet Stream that is located in the upper troposphere at a higher height between 14km and 16km, It blows between the equator and 200N latitude in summer at a similar time of South-West Monsoon over south-east Asia, India, and Africa, this jet stream influences the Indian monsoon. Its direction is opposite to that of the other two jet streams. It runs in eastern direction with its speed reaching 180 km per hour.
Polar Night Jet Streams
Polar night jet stream is developed in the winter season as a result of a steep temperature gradient in the stratosphere around the poles and extends at the height of 30km. This jet stream becomes very strong westerly circulation with high wind velocity during winter, however, their velocity reduces in summer with an easterly direction. Another name for Night jet stream is stratospheric sub-polar jet streams.
Local Jet Streams
The local jet stream is locally formed as a result of local thermal and dynamic conditions, very with few local importance are known with this jet stream.
How do jet streams affect weather?
Jet streams are very cold, a fast-moving wind that affects weather worldwide, and as such, they assist meteorologists in the forecasting of weather due to their position in the high atmosphere.
They play a significant role in determining the weather by separating colder air and warmer air, jet streams generally push air masses around, moving weather systems to new areas and even causing them to become enclosed if they have moved too far away. Even though they have been used as an important factors in the prediction of weather, jet streams may not always follow a straight path, they may change an areas weather patterns due to different climatic factors; the patterns are called peaks and troughs, so they can shift away, making it difficult for even skilled meteorologists to arrive at an accurate future weather forecast.
Effectsof Jet Stream
- Jet streams affect weather patterns and can push air masses around the world due to the strong and rapidly moving air currents.
- The occurrence of monsoon in India is said to be closely related to Eastern Tropical Jet streams.
- Jet streams, for the most part, contribute to the formation of cyclones, anticyclones storms and depressions and influence their characteristics.
- When there is a stable weather condition, the airplanes flying in the parallel directions of jet streams gain great speed and considerably save fuel and time. in other words, flying in or out of jet streams direction can reduce flight time and fuel consumption.
- It is difficult for airplanes to fly in the opposite direction of jet streams due to their strength and fastness as airplanes usually encounter difficulty flying against them, however, pilots will rather choose to fly with the jet stream or above them; but not in the opposite direction or against them.
- Jet streams are important because they contribute to worldwideweatherpatterns and as such, they help meteorologists forecast future weather events based on their position and strength. However, continuous research is still being carried out on these jet streams with respect to their effect on weather conditions.