Dw. Waugh, SEASONAL-VARIATION OF ISENTROPIC TRANSPORT OUT OF THE TROPICAL STRATOSPHERE, JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES, 101(D2), 1996, pp. 4007-4023
The seasonal variation of the isentropic transport out of the tropical
stratosphere is examined using contour advection calculations with wi
nds from meteorological analyses for the period July 1991 to June 1994
. Calculations using winds from three different meteorological analyse
s are compared. There is good qualitative agreement between the differ
ent calculations for extratropical structures but not for structures i
n the tropics. There is also reasonable agreement between area diagnos
tics (for transport out of the tropics) derived from these calculation
s. Transport out of the tropics occurs in Rossby wave breaking events
in which filaments of tropical air are drawn into middle latitudes. In
all years these wave breaking events occur during the fall to spring
period when there are westerlies throughout middle latitudes (late Sep
tember to early May in the northern hemisphere). This includes periods
before the formation of, and after the breakup of, the polar vortex.
In the northern hemisphere the rate of transport out of the tropics du
ring fall to spring fluctuates around a constant value, whereas in the
southern hemisphere there is a relatively quiet midwinter period, wit
h maxima in the transport in early and late winter.