CSIR NET June 2016 Q47: Physical Oceanography
Equatorial oceanic Kelvin waves are a specific class of long ocean waves that propagate eastward along the equator at characteristic speeds of only a few metres per second. Tsunamis are shallow-water (long) waves whose wavelength is very much greater than the ocean depth, which is precisely what makes them travel with a speed depending only on depth.
Equatorial oceanic Kelvin waves typically travel eastward at only about 2-3 m/s, not 20 m/s, so statement 1 is a realistic figure while statement 2 substantially overstates their speed.
Crucially, tsunamis are classified as shallow-water waves precisely because their wavelength is very much GREATER than the ocean depth (not less) — this is what allows their speed to be approximated simply as √(g × depth). Statement 3, which claims the wavelength is LESS than the ocean depth, therefore describes the situation backwards and is the false statement.
Crucially, tsunamis are classified as shallow-water waves precisely because their wavelength is very much GREATER than the ocean depth (not less) — this is what allows their speed to be approximated simply as √(g × depth). Statement 3, which claims the wavelength is LESS than the ocean depth, therefore describes the situation backwards and is the false statement.
Option 1 (Kelvin waves at 3 m/s) is a realistic, true statement about equatorial Kelvin wave speeds.
Option 2 (20 m/s) substantially overstates real Kelvin wave speeds and would itself be questionable, but per the intended answer the marked false statement is option 3.
Option 3 is correct as the FALSE statement — tsunami wavelength is much greater than, not less than, ocean depth, which is the defining property of these shallow-water waves.
Option 4 (Coriolis force changes facilitate Rossby waves) is a true statement, since the latitudinal variation of the Coriolis parameter (the beta effect) is indeed the physical basis for Rossby wave propagation.
Option 2 (20 m/s) substantially overstates real Kelvin wave speeds and would itself be questionable, but per the intended answer the marked false statement is option 3.
Option 3 is correct as the FALSE statement — tsunami wavelength is much greater than, not less than, ocean depth, which is the defining property of these shallow-water waves.
Option 4 (Coriolis force changes facilitate Rossby waves) is a true statement, since the latitudinal variation of the Coriolis parameter (the beta effect) is indeed the physical basis for Rossby wave propagation.