Improvement of vertical and residual velocities in pressure or hybrid sigma-pressure coordinates in analysis data in the stratosphere I. Wohltmann and M. Rex Alfred Wegener Institute for Polar and Marine Research, Potsdam, Germany
Abstract. Stratospheric vertical winds from analysis data
in pressure (p) or hybrid pressure (σ-p) coordinates,
for use in e.g. chemical transport models
(CTMs) or trajectory models,
often suffer both from excessive
noise and errors in their mean magnitude, which in turn
can introduce errors in important dynamical quantities like vertical mixing
or constituent transport with the residual circulation. Since
vertical velocities cannot be measured directly, they are
inferred from other quantities, typically from horizontal wind divergence,
that is the mass continuity equation.
We propose a method to calculate the vertical wind field from the
thermodynamic energy equation in p or σ-p vertical coordinates
that substantially reduces noise and
overestimation of the residual circulation. It is completely
equivalent to the approach using potential temperature (θ) as a vertical
coordinate and diabatic heating rates as vertical velocities, which has
already been demonstrated to give superior results to the continuity equation.
It provides a quickly realizable improvement of the vertical winds,
when a change of the vertical variable would cause an inadequate effort
(e.g. in CTMs).
The method is only applicable for stably stratified regions like
Citation: Wohltmann, I. and Rex, M.: Improvement of vertical and residual velocities in pressure or hybrid sigma-pressure coordinates in analysis data in the stratosphere, Atmos. Chem. Phys., 8, 265-272, doi:10.5194/acp-8-265-2008, 2008.