Rossby waves, also known as planetary waves, are large-scale atmospheric waves that occur in the Earth's atmosphere. They are named after the Swedish meteorologist Carl-Gustaf Rossby, who first described them in the 1930s. Rossby waves are important for understanding weather patterns and climate dynamics.
Rossby waves are caused by the rotation of the Earth and the variation in the Coriolis effect with latitude. The Coriolis effect is an apparent deflection of the path of moving objects caused by the Earth's rotation. This effect is strongest at the poles and weakens towards the equator. Rossby waves arise due to the tendency of the atmosphere to restore balance between the pressure gradients and the Coriolis force.
In the Northern Hemisphere, Rossby waves are characterized by alternating troughs (areas of low pressure) and ridges (areas of high pressure) in the atmospheric flow. These waves are typically several thousand kilometers in wavelength and extend from the troposphere (lower atmosphere) to the stratosphere (upper atmosphere).
Rossby waves propagate in a westward direction, against the eastward flow of the prevailing westerly winds. This motion is known as retrograde motion. The speed at which Rossby waves travel is much slower than the wind speed, typically only a few kilometers per hour. As a result, they can move across the globe relatively slowly, taking several days or weeks to complete a full circuit around the Earth.
The propagation of Rossby waves is influenced by various factors, including the temperature gradients in the atmosphere, the distribution of land and ocean, and interactions with other atmospheric phenomena such as jet streams and weather systems. Rossby waves play a crucial role in the formation and movement of weather systems, such as mid-latitude cyclones and anticyclones, and can have significant impacts on weather patterns, including the occurrence of prolonged heatwaves, cold spells, and storm tracks.
Understanding the behavior of Rossby waves is important for meteorologists and climatologists as they provide insights into long-term weather patterns, atmospheric circulation, and climate variability.