National Meteorological Center wind data from December 1970 to February 1971 were used to compute the 90-day winter mean eddy kinetic energy, and the energy exchange between waves and between waves and zonal mean flows at 200 mb, over mid-latitude (33.0–48.1°N), subtropical (10.0–28.7°N) and tropical (5.0°N–14.8°S) belts. In the mid-latitude (subtropical) belt, waves of wavenumbers 1–10 lose (gain) energy to (from) zonal mean flows with large contributions from wavenumbers 2–3 and 5–7. Energy exchanges over the tropical belt are quite different from those in the mid-latitude and subtropical belts with conspicuously small wave-zonal flow interaction and somewhat larger wave-wave nonlinear interactions. Wavenumber 8 receives substantial energy via wave-wave interaction with other waves in both the sub-tropical and tropical belts.
Sometimes the 200 mb eddy kinetic energy was well above its 90-day winter mean at all latitudinal belts. Such occasions were characterized by an extremely strong jet stream near Japan and a stronger than usual local Hadley cell over eastern Asia. Above-normal cloudiness and 700 mb transient eddy kinetic energy over the East and South China Seas possibly indicated enhanced low-level monsoon surges from the Siberian high. The tropical belt appeared to be more barotropically unstable than normal, with many wavenumbers receiving large amounts of energy from zonal mean flows via wave-zonal flow interaction. Similarly, periods of below normal 200 mb eddy kinetic energy exhibited some definite synoptic and energetic characteristics.