Consider an eddy of 200 km diameter that is located at 20 degree S and reaches f
ID: 665 • Letter: C
Question
Consider an eddy of 200 km diameter that is located at 20 degree S and reaches from the sea surface to the sea floor (1). It is slowly rotating in clockwise direction with a vorticity of xi=-1 x10'4 1/s. The eddy is drifting to 18 degree S (2) and from there back to 20 degree S (3) and to 22 degree S (4). The water depth is everywhere H=4000 m. Describe in key words what happens to the eddy at locations (1), (2), (3), and (4). [ ignore friction].(2P) Assume now that the water depth at location (1) and (3) is H=4000m, while it is H=3000m at location (2) and H=5000m at location (4). Describe in key words what happens to the eddy at locations (1), (2), (3), and (4). [ use calculations if needed; for formulas see lecture 8, slides 19+21; Ohm = 7.3 x10'5 1/s; positive velocity=counter-clockwise rotation; ignore friction]. (4P)Explanation / Answer
A] as the eddy moves toward the equator, it will slow down because planetory vorticity at the equator is zero. planetary vorticity increases the closer you get to the poles, where it is at its max. so if the eddy moves toward the equator, planetary vorticity in that area will cause the eddy's relative vorticity to decrease and the eddy will slow. As the eddy moves away from the equator, it will speed up. So you can figure out what its doing from 1 to 2 and 2 to 3 and so forth [either slowing or speeding up]
B] again, an eddy's relative vorticity i conserved as it adapts to different conditions. in this case, because relative vorticity/H is constant, the changing water depth will cause the eddy to either speed up or slow down. Decreased depth will squish the water column and will stretch the eddy horizontally. the eddy will move faster in order to conserve its vorticity. increased depth will allow for more room for the column to be stretched and it will retract horizontally. the eddy will move slower to conserve total vorticity.