Previous: Low-frequency Variabilities of the Tropical CPT Next: References Up: Ext. Abst.
Air entering the stratosphere across the tropical Cold Point Tropopause
(CPT) is dehydrated by cold temperature at the CPT. Thus the tropical
CPT plays an important role in determining the observed low concentration
of stratospheric water vapor. The climatology of the tropical
CPT has been investigated using sounding observations and ECMWF
reanalyses. The CPT exhibits interannual variability associated
with both the equatorial stratospheric QBO and tropospheric ENSO.
The influence of the QBO on the tropical CPT is mainly zonally
symmetric. However, the ENSO signature in the tropical CPT has
East-West dipole and North-South dumbbell features. Both the QBO
and ENSO signatures propagate upward as ``low-frequency tape recorders''.
A cooling trend in the tropical CPT temperatures has been found,
which in the absence of other changes would be expected to lead
to a negative trend in stratospheric water vapor. Thus, the observed
positive trend in stratospheric water vapor is probably caused
by dynamical changes. The cooling trend also suggests that a ``stratospheric
fountain'' was necessary in most years during the period 1973-1998
or the western Pacific is the main location to dehydrate air parcels
wherever they enter the stratosphere across the tropical CPT.
This is a part of Xue-Long Zhou's Ph.D dissertation (The tropical cold point tropopause and stratospheric water vapor, Ph.D. dissertation, State University of New York at Stony Brook,
121pp., 2000). Three manuscripts can be obtained by contacting
Xue-Long Zhou at ``xlzhou@atmos.washington.edu''
Previous: Low-frequency Variabilities of the Tropical CPT Next: References Up: Ext. Abst.