Rossby wave westward propagation (mean wind is zero)

• If Coriolis param. f were const., a low pressure region could be stationary; winds circulating in balance with PGF
• b-effect: Increasing f northward (N. Hem.) implies imbalance in mass transport, yields progagation
• At “short”* wavelengths, energy of a wave packet can propagate eastward & have north/southward components due to transport of vorticity=spin of flow
  *for deep waves in atm, “short”~1000s of km

Rossby wave westward propagation (mean wind is zero)

• Example of a Rossby wave packet in ocean upper layer (from the Regional Ocean Modeling System).
• Properties depend on wavelength so adjustment from the initial conditions leaves a longer wavelength packet propagating slowly westward.
• Short wavelengths or mean flow yield more complex propagation.

Rossby wave propagation - short wavelengths (mean current zero)

• Another Rossby wave packet in ocean upper layer but at smaller scale (100 vs 1000 km).
• [Properties depend on wavelength so adjustment from the initial conditions gives wave packets whose energy propagates north and south as well as eastward.
• Individual highs and lows still propagate westward.

Rossby wave pattern excited by stationary source

• Convective heating or flow over mountain can maintain wave packets against dissipation (friction etc.).
• Stationary Rossby wave remains after adjustment—has balance of westward propagation tendency vs. winds carrying it eastward
• Bottom line: Rossby waves create long-distance connections in the climate system with complex flow patterns!