(meandering shifts in the trajectory of high-altitude winds)
Rossby waves are curves in the wind pattern in the upper
atmosphere in the mid latitudes, the pattern's curves
resulting from the Earth's rotation.
The same mechanism creates similar curves in the
current pattern of the ocean.
The key factor in instigating and maintaining them is
the variation in Coriolis force over latitude.
Essentially, the tendencies that fix the position of
the boundary between atmospheric "cells" (such as the Hadley cell)
approximate the wave equation, in a manner analogous to a taut
string's tendencies that allow traveling waves along the string.
Understanding Rossby waves is key to Earth weather prediction
and they also serve as a useful model for wind patterns found on
other planets.
Such waves have also been considered as possible triggers for some
types of planet formation within protoplanetary disks.