About the Jet Stream Simulator
This simulation visualises the polar and subtropical jet streams as fast ribbons of upper-atmosphere wind, together with the large meanders known as Rossby waves. The flow is built from idealised Gaussian zonal jets centred at fixed latitudes, with a sinusoidal meridional displacement whose phase advances with time. Tracer streamlines are advected through this synthetic wind field, illustrating how warm air is carried poleward in ridges and cold air equatorward in troughs.
The controls let you switch between Winter and Summer, set the Rossby wavenumber (2–7 meanders), scale the equator-to-pole temperature gradient and the jet speed, and adjust simulation speed. A blocking high (Omega block) adds a stationary anticyclonic vortex that splits the flow. This matters because the jet stream steers the mid-latitude weather we experience, and persistent blocking patterns drive prolonged heatwaves, cold snaps and floods.
Frequently Asked Questions
What is the jet stream?
The jet stream is a narrow band of very fast wind near the tropopause, roughly 10 km up, flowing broadly west to east. It forms where there is a sharp horizontal temperature contrast, chiefly between the cold poles and warmer mid-latitudes. This page shows two: the stronger polar jet and the weaker subtropical jet.
What are Rossby waves?
Rossby waves are the large north-south meanders of the jet stream, caused by the variation of the Coriolis effect with latitude. The simulator models them as a sine wave displacing the jet, with the wavenumber slider setting how many ridges and troughs wrap around. Ridges carry warm air poleward and troughs draw cold air equatorward.
What does the temperature gradient control do?
The temperature gradient slider scales the equator-to-pole temperature contrast from 0.3x to 2.0x. A stronger gradient increases the modelled jet core speed and wave amplitude, and is reported as a stronger polar vortex in the diagnostics. This reflects the real link between baroclinicity and jet intensity.
Why is the winter jet faster than the summer jet?
In winter the pole cools far more than the tropics, so the temperature gradient is steep and the simulator sets the base polar jet to about 75 m/s. In summer that contrast shrinks, the base drops to roughly 38 m/s, and the subtropical jet shifts poleward. Switching season here changes the base speed and jet latitudes accordingly.
What is a blocking high or Omega block?
A blocking high is a large, near-stationary region of high pressure that diverts the jet stream around it, often tracing an Omega shape. Enabling the checkbox adds a slow-moving anticyclonic vortex that deflects the flow and tracers. In reality such blocks can persist for 5 to 30 days, locking in heatwaves, cold spells or flooding.
What is the polar vortex shown in the diagnostics?
The polar vortex is a band of strong upper-level winds encircling cold polar air. In this model it is a qualitative readout tied to the temperature gradient: above 1.2x it reads Strong, between 0.8x and 1.2x Moderate, and below that Weak. A weaker vortex in reality allows cold air to spill into mid-latitudes.
How are the moving particles calculated?
Each tracer samples the local wind from the combined Gaussian jets, the Rossby wave displacement and any blocking vortex, then steps along the normalised direction by a fixed amount per frame. Particles fade in and out over a limited lifetime and respawn at random positions, producing the flowing streamline effect rather than tracking real air parcels.
Is this simulation physically accurate?
It is a qualitative, educational model rather than a numerical weather prediction. The jet positions, the winter speed near 75 m/s and the wave behaviour are realistic in character, but the wind field is a hand-built idealisation. It does not solve the primitive equations, so use it to build intuition, not to forecast.
Why do ridges and troughs change the weather below?
Where the jet bulges poleward in a ridge, warm air is drawn up beneath it, often bringing settled, mild conditions. Where it dips equatorward in a trough, cold air plunges south and storms develop. The red and cyan shading in the simulation marks these warm intrusions and cold outbreaks along the polar jet.
What does the Rossby wavenumber slider represent?
The wavenumber sets how many full meanders fit around the hemisphere, from 2 to 7. Low wavenumbers give a few large, slow-moving waves typical of amplified, blocky patterns. Higher wavenumbers produce many smaller waves and a more progressive flow. Changing it resets the tracer field to the new pattern.
How does the jet stream affect everyday weather and flights?
The jet stream steers cyclones and fronts across the mid-latitudes, so its position governs whether a region sees storms or calm. Aviation exploits it too: eastbound flights ride tailwinds within the jet to save time and fuel, while westbound flights detour to avoid the headwind, which is why crossing times differ by direction.