An Observational Study of the Spatial and Temporal Scales of Transient Eddy Sensible Heat Fluxes

Abstract

The preferred spatial and temporal scales of transient baroclinic waves that are responsible for the transport of sensible heat in midlatitudes are evaluated as a function of pressure, season, and hemisphere. The 7-level initialized ECMWF operational global analyses for the years 1980?88 are used in this study. A clear seasonal cycle in the spatial scales of the baroclinic waves is seen in the Southern Hemisphere lower troposphere. The scale selection and phase relationships of the baroclinic waves are observed to be similar in the Southern and Northern Hemispheres, indicating that the same mechanism may be responsible for the transport of heat in both hemispheres even though there are very large differences in the magnitude of the heat transported by stationary waves and in the structure of baroclinic zones. The secondary heat flux maximum at 200 hPa is dominated by large-scale wavenumbers 2?3 in the winter and spring in both hemispheres. This may be an indication that there is a mechanism that is responsible for the heat transport at 200 hPa that is different from the mechanism at the primary heat flux maximum, at 850 hPa where intermediate-scale waves dominate.