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The project's main emphasis has been on the
long-term trends in geopotential height and temperature
in the tropopause and lower stratosphere
regions over the warm pool region of the
tropical western Pacific. The region has several
well maintained and continuously operated
radiosonde stations with daily reports of winds
and temperatures as far back as the late 1950s,
and with data usually extending at least up to the
10 hPa (~30 km) level. The data used so far were
obtained from the mass storage facility at NCAR
and more recently from the CARDS () data
archive. The latter data extends through the year
2002.
The warm pool region has been identified
as one of the most critical regions of the Pacific
Ocean from the point of view of global climate,
and the stratosphere has been expected to show
cooling as a result of both increases in greenhouse
gases and decreases in ozone content. The results
obtained so far have been surprising. The long-term
trend in stratospheric temperatures was
small and not even of consistent sign from 1960
until about 1990, but thereafter a strong cooling
set in at all the stations examined. For most stations
only data prior to 1999 has been studied,
but the CARDS file has recently been used to
look at temperatures from the island station of
Yap at the typical pressure level of 70 hPa. The
cooling there has continued through 2002 at a
rate of about 0.4 degrees per year, and temperatures
are now about 7°C below the long term
1960-1990 average. Examination of the seasonal
dependence of the strong cooling suggests that it
is not radiative in origin, but instead results
from intensification of the upwelling in the tropical
stratosphere caused by wave-mean flow
interaction at midlatitudes. This work is continuing,
and the implications for climate change in
the tropical Pacific will be explored.
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Stratospheric indications of global change
CIRES Research Theme
Climate System Variability
Project Personnel
G.C. Reid
Funding Source(s)
NOAA
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