Further Evidence of Traveling Planetary Waves

Abstract

Evidence of regularly propagating, large-scale waves is found in a 73-year record of Northern Hemisphere sea-level pressure data and in a nine-year record of upper air data. Cross-spectrum analyses indicate that south of 50°N, in all seasons, a zonal wavenumber 1 disturbance moves westward around the world in 5 days. In addition, north of 50°N a zonal wavenumber 1 disturbance moves westward around the world in one to three weeks with an average period near 16 days. This disturbance appears to be strongest in winter and spring. The structure of the 16-day wave during winter is studied in detail, and it is shown to be consistent, in many respects, with that of a theoretically predicted free planetary wave, or wave of the second class. A similar conclusion can be made concerning the 5-day wave.