Rossby waves are planetary waves that determine basic meteorological conditions at latitudes outside of the tropics.

Rossby waves are an essential conseuqence of

• Planetary Vorticity must be conserved
• The coriolis force varies with latitude - this is known as the β effect.

Rossby waves have several important features:

• They redistribute momentum and transmit energy
• They interact in complex ways with the general circulation.
• Their natural system timescales generally produces regionally peristent weather on the scale of 3-5 days.

What is Planetary Vorticity and why must it be conserved?

Vorticity is generated in the atmospheric and ocean fluids by the rotation of the earth since these fluides can't co-rotate with the earth because of internal currents and friction and various energy losses. Vorticity is a measure of spin.

Any air parcel that is stationary relative to the Earth's surface will acquire planetary vorticity as it changes latitude due to the coriolis force. At the equator voriticy is zero and maximizes at the poles.

This means that weather is fundamentally caused by latitude migration of parcels of air. This migration is driven by pressure gradients which in turn are driven primarily by the NS horizontal temperature gradient on land+sea

We define the planet to have net positive vorticity since it is rotation in one specific direction.

Relative vorticity is produced by two main effects:

• latitude migration (curvature of earth)
• velocity shear

The sum of a parcel's planetary vorticity and its relative vorticity is called the absolute vorticity

East of the any large scale vortex there will be divergence and upward motion of the air. West there will be convergence and downward motion. This often produces clouds and precipitation.

Parcels displaced northward in latitude will achieve negative relative velocity and therefore, to conserve planetary vorticity, parcels have to then move south to increae positive relative velocity. This is why this is a planetary wave and at any given time there me be 3,5 or 7 of these Rossby Nodes:







Rossby waves of course occur in the ocean and since that is a rotating fluid and this causes "parcels of ocean" to drift with latitude and to move up and down within the ocean. Note that Rpassby Waves as of March 2017, have now been confirmed to exist in the Sun.





The increase in vorticity is because f (planetary vorticity) has increased compared to the relative vorticity ζ because the "circumference of the earth" is lower at high latitude. This is equivalent to the coriolis force being higher .





This movement is a planetary wave and the data now show that a large disturbance in the Oceans - like the Madden Julian Oscillation (MJO) which is a large scale convective feature in the summer time Indian Ocean can effectively propogate such a planetary wave.