Basic State Energy Budget Analysis for Phases 1, 2 and 3 of GATE

Abstract

A diagnostic study of the budget of zonal and eddy components of available potential and kinetic energy is presented for the large-scale basic (time-averaged) state of the atmosphere for Phases 1, 2 and 3 of GATE. The Final Validated Data Set (FVDS) is applied to a modified set of approximate-form energy equations that were originally developed by Lorenz (1955). Geopotential height, temperature, relative humidity, and wind direction and speed were subjectively analyzed at mandatory pressure levels for an area bounded by 20°N, 10°E, 10°S and 40°W. Gridpoint values were extracted at intervals of 2° latitude and longitude. Since basic state data were used, an eddy content or an exchange involving an eddy content represents only the standing eddy component of energy. Results indicate that zonal kinetic energy (KZ) is the most abundant content and is maximum in the region of the upper tropospheric easterly jet. Both KZ and zonal available potential energy (AZ) decrease from phase-to-phase, whereas the eddy contents, AE and KE, remain nearly constant in time. The dominant energy conversion CA is front AZ to AE in all phases, indicating that the eddy transport of sensible heat is from warmer latitudes to colder latitudes. The CE conversion is from AE to KE during Phases 1 and 3 and is negligible in Phase 2. The conversion between KZ and KE (CK) is negligible in all phases, while the conversion between AZ and KZ (CZ) is small and oscillates. Boundary transports show that only the flux of KZ (BKZ) is significant. The east-west transport in the upper troposphere dominates and is responsible for an import of energy into the region. Generations of AZ and AE were not computed, but residuals imply that AZ is generated by diabatic processes during all phases while AE is destroyed. Residuals also suggest that KE and KZ are destroyed by frictional dissipation. Finally, we find that our standing eddy contents AE and KE are comparable in magnitude to the eddy energy contents given by Norquist et at. (1977) for a composite of GATE Phase 3 westward propagating wave disturbances. A comparison also is made between the present results and those for June, July, August for the global region bounded by 15°N and 15°S (Kidson et al., 1969). It appears that the stationary wave component in the GATE area makes an important contribution to certain terms in the global scale energy budget, although the global standing eddies encompass different (larger) scales than those in the present study.