J. Eluszkiewicz et al., DYNAMICS OF WINTERTIME STRATOSPHERIC TRANSPORT IN THE GEOPHYSICAL FLUID-DYNAMICS LABORATORY SKYHI GENERAL-CIRCULATION MODEL, JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES, 100(D10), 1995, pp. 20883-20900
The kinematics of air motions in and around the polar vortices in the
Geophysical Fluid Dynamics Laboratory SKYHI general circulation model
are investigated by means of a Lagrangian particle analysis. Particles
initialized in the mesosphere and upper stratosphere rapidly descend
to the middle stratosphere. This descent is unmixed in the sense that
the isentropic mass transport into the vortex is less than 5% of the v
ortex mass per month. Transport out of the vortex is less than 10% of
the vortex mass per month. The reversible component of the Lagrangian
mean downward velocity (in isentropic coordinates) is approximated to
better than 20% by the diabatic heating rate at the time mean location
of the center of mass. The interplay between diabatic descent and hor
izontal mixing in causing the steepness of tracer contours (e.g., N2O)
around the vortex edge is vividly illustrated in our trajectory exper
iments. These experiments also illustrate the limitations of the conce
pt of ''air parcel'' within the midlatitude surf zone. The dynamics of
polar descent are investigated by diagnosing the forcing of the resid
ual circulation. In the upper stratosphere, diabatic descent inside po
lar vortices is driven by Eliassen-Palm flux divergences associated wi
th motions of-period shorter than 2 days (presumably gravity waves) in
the Antarctic, but, of period greater than 3 days (presumably planeta
ry waves) in the Arctic. In the lower stratosphere, long period proces
ses, mainly from the 10 to 1 hPa region, produce descent near the vort
ex edge in both hemispheres.