The Asian Subtropical Jet Summer-Winter Weather

A typical feature of asian weather is the Sub Tropical Jet Stream we will help to explain this in this article. When we mention the Asian regions weather we usually find three items of interest whilst on this topic for summer. The Subtropical Jet is a diverted band of the Westerly Jet that moves north and south dynamically according to winter or summer weather in Asia, in this section we discuss the Summer STJ in Asia. The three summer Asian weather factors that affect the STJ in summer are:

  • The Intertropical Convergence Zone (ITCZ): Located near the equator is a band of rising air (ascending) that brings semi frequent areas of tall clouds and rain/thunderstorms.
  • The Sub Tropical Highs: Located near the 30 degrees latitude region is a continual band of weather that heats up parts of Asia in summertime over land especially and cools the surface of seas in the Asian maritime area as High Pressure air currents move towards the surface from above (descending).
  • The Sub Tropical Jet:The Subtropical Jet, a component of the Jet Stream that is formed when there is redistribution of the Jet due to a influence outside the normal flow. The Himalayas in Asia for example.

This is explained in our below image.

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Sub Tropical Jet 101.

It is important to know that the STJ has two phases a weak phase and strong phase controlled by the position of the STJ in the Asian Summer/Winter. In the above image the effects of the STJ during summer are weakened due to the fact that parts of the Asian Continent over land are heated. This then leads to a temperature gradient inversion from what is normal being that instead of a south (Hot ) to north (Cool) gradient in Asia in Summer there is a south (Cool) to hot (North) gradient with heating at the Sub Tropical High Band. Why is this important? This Asian Temperature gradient is what will weaken the STJ in the Northern Hemisphere summer and then the STJ Sub Tropical Jet affects weather by reinforcing the Sub Tropical High System over areas of Asia. Rain-wise the STJ has lessened effects in the Asian Summer as the wind energy is weaker with the STJ locating closer to the ITCZ where the spin of the earth on a axis is weaker (also affects coriolis effect).

In our above image we see the Temperature Gradient explained (Top Right inset), The Location of two weather features (Bottom Right inset), and the main summer STJ image explaining in a helpful way the concept of the summer STJ.

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Sub Tropical Jet 101 Winter.

In the Asian Winter the effects of the Sub Tropical Jet then strengthen (Higher Upper Winds) with the East Asia section of the STJ moving position north and in areas of Nth East Asia weather becomes a lot colder on this one example. This movement of the STJ is caused by the weather change from summer to winter that triggers a different temperature gradient and the STJ locating closer to the Poles where the axis spin is faster creating stronger STJ winds. This process is also linked to a stronger coriolis effect from the STJ Mid-Latitude location at Nth East Asia.

In the Top Right Inset of the above image we see that the temperature gradient now changes profile to the Asian Winter profile. In our helpful example we see that in Winter the STJ has a more profound effect on Winter Weather due to increased wind strength in the Upper Air Column.

Lastly at our bottom right inset we see in the north of the inset the hidden winter factor that affects the STJ the polar vortex that enlarges in the northern hemisphere winter.

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Sub Tropical Jet Autumn 2024 Scenario.

Image 1 above Sat Upper for 10-10-2024 showing the examples we have spoken of for the near winter STJ in Asia and is a Satellite Global composite infrared image showing these tremendous wind highways in the upper air column (30,00 ft to 32,00ft Westerly/Polar jet). The STJ sits within a 21,120 feet to 42,240 feet region.

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Sub Tropical Jet Autumn 2024 Scenario two.

Image 2 above Sat Contours for 10-10-2024 showing the examples we have spoken of for the near winter STJ in Asia and is a geopotential height example at 29,000ft in Asia. The STJ sits within a 21,120 feet to 42,240 feet region. The north section of the map is lopped off due to a geographic constraint on the map from the GFS 0.25p chart set. The STJ position is clearly defined.

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Sub Tropical Jet Autumn 2024 cooling.

Image 3 above shows the correspondence with the STJ and Polar Jet for 10-10-2024 giving examples we taught in this article on how the STJ influences weather. This is exemplified in the cooling of the Asian regions at surface (GFS 2.0 m Temps) according to the upper wind river profiles and near winter positioning of the STJ and Polar Jet. At the Himalayas exists the western normal area of the STJ that also cools the region on its path eastwards. Lastly at North Asia is beginning to get Cold as Winter nears arrival in mid Oct.

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