An observational study of the upward sensible heat flux by synoptic-scale transients

For eight 30-day periods, two in each season, vertical transient eddy fluxes of sensible heat were computed at the 850, 500 and 200 mb levels. Use was made of NMC analyses and 6-h forecasts of the ω-field available twice a day.

Vertical heat fluxes are strong in the Atlantic and Pacific storm track, and over Scandinavia and Canada. The conversion of potential to kinetic energy (which is directly related to the upward sensible heat flux) by the synoptic scale transients, averaged over the whole atmosphere north of 20° N, shows maxima in spring (2.6 W m^-2) and fall (2.2 W m^-2). Summer and winter show lower conversion rates (1.2 and 2.1 W m^-2, respectively). The yearly conversion amounts to 2.0 W m^-2 which is in good agreement with the value of 2.2 W m^-2 obtained by Oort and Peixoto (1974). Their estimate includes standing eddies, however.

We find that the zonal mean vertical and northward sensible heat fluxes are strongly coupled. The parameterization inline image ω'T' = μv'T' is tested both with regard to latitude and season. It appears to perform quite well with μ = -1.5 x 10^-4 to -2 x 10^-4 m mb^-1.