Jet stream

the jet stream determines the global climate

In the global wind circulation there are numerous currents that transport cold and heat and distribute it to all corners of the planet. Many currents are fed by differences in pressure changes, others in air densities, some from the rise of water vapor from the oceans, etc.

Today we come to talk about the famous jet stream. These are air flows that circulate high up at high speed and around the planet, from west to east, taking advantage of the discontinuities that exist between convective cells. Do you want to know how the jet stream works and what effects the jet stream has on the weather?

Jet streams

the jet stream occurs in the northern and southern hemispheres

It is often referred to as a singular jet stream, but there are four large jet streams circling the planet, two in each hemisphere.

First we have the polar jet stream, which is found at 60 ° latitude, both in the northern and southern hemispheres, and is responsible for the general dynamics of the atmosphere at mid-latitudes.

We also have the subtropical jet stream that circulates around 30 ° and is less important in the meteorology of the area. Because this has less influence on the climate, the polar jet stream is less named and only considered as important and conditioning.

These currents are almost reaching the limit of the troposphere, about 10 kilometers high in mid-latitudes, where they can reach extraordinary speeds of about 250 km / h, even getting to find winds of up to 350 km / h. To save on fuel and decrease travel time, many commercial aircraft fly in these currents to take advantage of the boost from wind speed.

The jets have a typical width of about 200 kilometers and a thickness that varies between 5.000 and 7.000 meters, although the maximum winds are only reached in their central part, which is known as the core of the jet. The jet that affects the Iberian Peninsula is the polar one.

When was this current discovered?

jet stream oscillations

These air currents began to be studied during the Second World War and the first studies were made public at the end, since during the war, this study was a military secret. The Japanese were the first to discover that a great air current circulated through the northern and southern hemispheres that had extraordinary speeds and took advantage of it to launch balloon bombs at the Americans.

At first, the United States was not afraid that Japan could plan an air attack being located about 7.000 km from each other and separated by ocean. That distance for the planes that existed was almost unattainable. However, the discovery of the jet stream allowed the Japanese to make reconnaissance flights to the west coast of the United States, and they also devised an ingenious method of attack. From Japan they were releasing gigantic paper balloons from which were hanging abundant explosives. When the balloons managed to reach the jet they crossed the Pacific in record time and with the help of a timer they dropped the load on their target. They managed to detonate more than 1000 explosives sparking wildfires throughout the western United States.

Jet Stream Characteristics

jet stream summer and winter

The polar jet is formed right in the areas where the warm air masses coming from the Equator converge with the cold currents coming from the North Pole. These currents surround the Earth and oscillate, forming waves that look similar to the meanders of a river.

Depending on the time of year in which we are, the jet is not always at the same latituderather, there is a seasonal sway. During the summer and spring months it is situated at about 50 ° North latitude and in winter it is about 35-40 ° N latitude. In winter the power of the jet is much greater than in summer and reaches more extreme speeds. During the summer months the tropical warm air mass is more powerful, displacing the jet stream further north. On the other hand, in winter, the polar air masses are more strengthened, so they are able to expand more at lower latitudes.

The Polar Jet corresponds on the surface to the Polar Front and its undulations, called Rossby waves, give rise to high pressures to the right of the stream and low pressures to the left, which on the surface are reflected as anticyclones (subtropical anticyclones, such as the anticyclone of the Azores, which has an enormous influence on the Iberian Peninsula) and storms (the Atlantic storms of the Polar Front), respectively.

Therefore, the path of the current determines the path of the Atlantic storms associated with the Polar Front. The trajectory of the jet stream depends entirely on its speed. When the speed is higher, the air stream follows a path from west to east and oscillates gently. When this type of circulation takes place it is called zonal or parallel.

On the other hand, when the speed of the current decreases, the waves are accentuated and deep troughs are generated to the south and ridges to the north, which originate areas with low and high pressure on the surface. When this type of circulation takes place, it is called azonal or meridian.

Gutters and dorsal

jet stream produces troughs and ridges

The troughs that are formed by the slower circulation of the polar jet stream are penetrations of cold air to the south of the zonal path of the current. These troughs have cyclonic dynamics so they appear on the surface as storms.

The numbers are the opposite. They allow the penetration of tropical air to the north, anticyclonic in nature, and leaves traces of higher temperatures and good weather. When the troughs and the ridges are mixed and alternated they grant great variability to the time of the middle latitudes.

At times, these air masses displaced from their usual latitudes can detach from the main jet, being isolated from it. If that air mass detached from the rest of the jet comes from a trough, it is called an isolated depression at high levels or more colloquially known as a cold drop.

Azores anticyclone

the Azores anticyclone affects the Iberian Peninsula

As mentioned above, the Azores anticyclone has a huge influence on our climate on the Iberian Peninsula. Therefore, it is important to know what happens throughout the year with it.

They originate in the intertropical zones near the equator. Due to the great insolation there is an intertropical convergence zone characterized by the presence of storms. Around this area there is a large area of ​​anticyclones that produce, for example, the Sahara desert.

One of the anticyclones is that of the Azores. When summer arrives and the amount of incident solar radiation is greater, the anticyclone swells. The anticyclone acts as a shield and does not allow the fronts to reach most of Spain, therefore, there will be no rains. The only area that is more unprotected is the north, so it is possible to sneak in the fronts that run through central Europe. For this reason, our summer registers very little rain and many sunny days, and only in the north can we find more abundant rainfall.

In winter, this anticyclone becomes smaller and retreats to the south. This situation will allow the entry of fronts from the Atlantic and only something from the south and the Canary Islands will be protected. Will also leave free passage at the entrance of cold winds from the north.

Whether some springs or autumns are rainier or less depends on the oscillations of the Azores anticyclone, which does not usually move smoothly, but bounces up and down. When the boat turns down, it allows the fronts to enter the Iberian Peninsula, and when it turns up, it prevents the fronts from approaching our peninsula, granting us sunny days and good weather.

Jet stream and global warming

major snowfall floods and droughts

It is continually mentioned in the media that global warming and climate change increase the frequency and intensity of droughts and floods. However, why is not mentioned. It is related to changes it produces in the jet stream.

In the past 15 years alone, the devastating drought in California, the heat waves in the United States and Western Europe, the deadly floods in Pakistan, were exacerbated when man-made climate change disrupted these huge air currents.

It must be taken into account that if we modify these patterns and mechanisms of movements in the warm and cold air masses we will be triggering more heat waves, droughts, and additional humidity in the air leading to more flooding. Small changes in these currents can generate impacts on the global climate, such as slowdowns in air masses. But what can cause the cold and warm air masses circulating in the jet stream to slow down? Well basically a smaller temperature difference between tropical air and polar air. This smaller difference is occurring due to global warming, since all the air on the planet is warming.

After several studies, it has been concluded that the human being, after the industrial revolution, has caused the reduction of 70% of the speed of the jet stream. This can lead to an increase in extreme events such as drought and floods.

As you can see, the planet's climate is adjusted to these currents and they are a mechanism that must remain stable if we want the meteorological phenomena to continue to occur correctly.


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  1.   Laura Fernández said

    Hello, the whole article is very good, except the final blurb, I would like to know when this article was written, thank you.