Westward Propagation in the Oceans: Do Linear Rossby Waves Matter?
Thomas, Matthew1; Cipollini, Paolo2; Benveniste, Jérôme3; Tailleux, Remi4
1Ifremer, FRANCE; 2National Oceanography Centre, Southampton, UNITED KINGDOM; 3ESA, ITALY; 4University of Reading, UNITED KINGDOM
Rossby Waves (RW) are westward propagating large scale baroclinic waves that owe their existence to the latitudinal variation in the Earth's local rotation rate. In the oceans they constitute the primary mode of adjustment to large scale atmospheric disturbances and are important in maintaining the strength of western boundary currents. They are therefore a key process to study, but in practice they have been difficult to separate from westward propagating nonlinear vortex-like eddies owing to Rossby waves and eddies having similar amplitudes and propagations speeds. Distinguishing between the two is important because their horizontal redistribution of local heat and tracers differ, and because they have different impacts on the ocean's adjustment to external forcing. Here we describe a new method that provides for the first time a global decomposition of the sea surface height field into Rossby waves and eddies. The results suggest that long Rossby waves contribute approximately one third or more of the sea surface height variance in the tropics, but less than 10% in the mid-latitudes. The results confirm the idea that although eddies tend to dominate westward propagating signals throughout the ocean, long Rossby waves nevertheless appear to remain important, especially at low latitudes. In light of recent results that suggest traditional methods of isolating RW's are inaccurate, our method provides a first step towards quantifying the presence of RW's in the global ocean.