ESS227
Prof. Jin-Yi Yu
Which Direction does Winter Storm Move?
•For a typical midlatitude
synoptic-scale disturbance, with similar meridional and zonal scales
(l ≈ k) and zonalwavelength of order 6000 km, the Rossby wave speed
relative to the zonal flow is approximately −8 m/s.
•Because
the mean zonal wind is generally westerly and greater than 8 m/s, synoptic-scale Rossby waves usually move eastward, but at a phase
speed relative to the ground that is somewhat less than the mean zonal
wind speed.