On the Transport of Quasi-Geostrophic Potential Vorticity1

The meridional transport of quasi-geostrophic potential vorticity is calculated from atmospheric data from 1 yr. The calculation is based on available data for the transports of relative momentum and sensible heat from eight standard pressure levels. The results show that the transport of potential vorticity is negative (southward) in the major part of the troposphere above the lowest layer of the atmosphere. A small region of positive (northward) transport is found in connection with the subtropical jet stream in summer. The computed transports of potential vorticity are used in a calculation of the mean annual heat sources in the atmosphere from a steady state quasi-geostrophic model. The results show that the atmosphere is heated south of 50°N and cooled north of this latitude and that the major heat source and heat sink are found around 70 cb. The calculation compares favorably with the determination of the heat sources from heat budget calculation. It is shown that the transport of potential vorticity is along the gradient of the potential vorticity in the troposphere above approximately 80 cb. Exchange coefficients for the transport of potential vorticity are computed as a function of latitude and pressure for the annual mean values. In addition, exchange coefficients for the transport of sensible heat are obtained, and it is shown that these coefficients are positive in the troposphere below 20 cb.