Rossby wave is another aspect of flows resulting from the rotation of a system. Wave motions with a constant Coriolis frequency $f$ have been considered and these waves all have frequencies larger than $f$. However, there are wave motions at lower frequencies that owe their existence to the variation of $f$ with latitude. These waves are known as Rossby waves

Their spatial scales are so large in the atmosphere that they usually have only a few wavelengths around the entire globe. This is why Rossby waves are also called planetary waves