Rossby Waves: Types and Significance

Rossby waves are an important phenomenon observed in the atmosphere and oceans of planets. These waves greatly influence the weather system of the earth. Read here to know in detail about the Rossby waves.

Carl-Gustaf Arvid Rossby, an American meteorologist of Swedish descent, made the initial discovery of Rossby waves in 1939.

According to scientists, Rossby waves are a naturally occurring phenomenon like La Niña and El Niño. These waves have been responsible for some extreme weather events in recent times.

In recent years, many changes and extreme weather events have been observed all over the globe-

• Extreme floods are devastating Pakistan, caused by a combination of heavy monsoon rains and melting glaciers.
• Western Europe and central and eastern China have experienced record-breaking heatwaves and droughts leading to water restrictions.
• Severe downpours have caused floods in places ranging from Dallas in the United States to Seoul in South Korea, which experienced its heaviest torrential rain in a century.
• Record-breaking heat extremes have also been recorded in Japan, the central US, and the UK, where temperatures exceeded 40℃ for the first time.

What are Rossby waves?

Rossby waves are a type of inertial wave and are also referred to as a planetary waves. They can be seen in the atmospheres and oceans of planets. It develops in rotating fluids spontaneously, due to the planet’s rotation.

These waves in the Earth’s atmosphere are enormous meanders in winds at high altitudes that have a significant impact on the weather. These waves are related to the jet stream and pressure systems.

Oceanic Rossby waves travel along the thermocline, which separates the warm surface layer from the colder, deeper ocean.

When air from the polar area moves towards the Equator while air from the tropics moves towards the poles, these waves are created.

• Heat tends to flow from high low to high latitudes due to variations in the solar radiation received.

The operation of high-pressure cells and low-pressure cells like cyclones, which are crucial in generating the weather of middle and higher latitudes is explained by the existence of waves.

A true Rossby wave needs to meet some specific criteria. For one thing, these waves only occur inside barotropic fluids, a category of fluids whose densities are a function of pressure alone

Types:

1. Oceanic Rossby waves
2. Atmospheric Rossby waves
3. Poleward propagating atmospheric/ Topographic Rossby waves

Oceanic waves

Unlike waves that break along the shore, Rossby waves are huge, surging movements of the ocean that stretch horizontally across the planet for hundreds of kilometers in a westward direction.

They are so large and massive that they can change Earth’s climate conditions.

• Along with rising sea levels, King Tides, and the effects of El Niño, oceanic Rossby waves contribute to high tides and coastal flooding in some regions of the world.

Atmospheric waves

Atmospheric Rossby waves form primarily as a result of the Earth’s geography.

Rossby waves help transfer heat from the tropics toward the poles and cold air toward the tropics in an attempt to return the atmosphere to balance.

They also help locate the jet stream and mark out the track of surface low-pressure systems.

The slow motion of these waves often results in long, persistent weather patterns.

They are influenced by Coriolis force and pressure gradient.

The rotation causes fluids to turn to the right as they move in the northern hemisphere and to the left in the southern hemisphere.

Poleward propagating atmospheric/ Topographic waves

Over extremely warm sea surfaces in the tropics, such as during El Nio episodes, deep convection (heat transfer to the troposphere) is intensified.

Rossby waves in the atmosphere are produced as a result of this tropical force, and they migrate both eastward and poleward.

The waves explain the statistical connections between low and high-latitude climates.

Difference between jet streams and Rossby waves:

The major difference between these is their circulation or movement pattern-

• A jet stream is a circulation of fast-moving air that is thousands of miles away and is not very dense.
• While Rossby is the name given to the swirling or meandering motion of the jet stream.

Significance of Rossby waves

Rossby waves are a dominant component of Ferrel circulation.

The tropical air carries heat poleward, and the polar air absorbs heat as it moves toward the Equator.

The existence of these waves explains the low-pressure cells (cyclones) and high-pressure cells (anticyclones) that are important in producing the weather of the middle and higher latitudes.

Sun and other planets like Venus and Jupiter have these waves in their atmosphere as well.

• Solar Rossby waves were first observed in the movement of magnetic structures in the solar corona.
• By studying the sun’s Rossby waves, scientists hope to gain a better understanding of environmental changes known as “space weather,” which affects everything from TV broadcasts and power grids to GPS systems and military satellites.

These waves have been suggested as an important mechanism responsible for the heating of the ocean on Europa, a moon of Jupiter.

Rossby wave instabilities are also thought to be found in astrophysical discs, for example, around newly forming stars.

The twin cyclones:

The interplay of the wind and the monsoon system combined with the Earth system produces these synchronous cyclones which are caused by equatorial Rossby waves.

• This system has a vortex in the northern hemisphere and another in the southern hemisphere, and each of these is a mirror image of the other.
• The vortex in the north spins counterclockwise and has a positive spin, while the one in the southern hemisphere spins in the clockwise direction and therefore has a negative spin.
• Both have a positive value of the vorticity which is a measure of the rotation.
• Very often twin cyclones are formed from these Rossby waves.

-Article written by Swathi Satish