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during 1979-2002. In addition, the two reanalyses are similar for the 1958-1978
period showing warming in the Antarctic - a reversal of the 1979-2002 pattern
where the Arctic showed warming.
Three of the four panels from the ERA-40 and NCEP-NCAR reanalyses indicate
an equatorial warming over the eastern Pacific and is a region to compare during the
analysis.
4.3.2 Troposphere
The retrieved temperature from the MSU channel 2 (ch2) represents the layer
temperature with a peak at 600 hPa (Zou et al.
2009
); the mean temperature from
500 to 700 hPa is employed to represent the middle tropospheric temperature in the
NCEP/NCAR and the ERA-40 reanalyses.
Compared to the stratospheric analysis, the tropospheric temperatures tended to
increase in the two study periods. For the period of 1979-2002 (Fig.
4.2a-c
), the main
warming areas are found over the Eurasian continents, western Pacific, North Ameri-
can continents, and the southern middle latitudes. The temperature over the tropical
Indian Ocean and Pacific Ocean decreased in the two reanalyses (Fig.
4.2a, b
), but
clear evidence is found that the MSU ch2 temperature tended to increase over these
regions although its amplitude is small (Fig.
4.2c
). In addition, the temperature over
the Antarctic shows a strong cooling trend in the NCEP/NCAR reanalysis, while the
temperature over some areas appears to have a warming trend in the ERA-40
reanalysis.
The main warming areas in 1958-1978 (Fig.
4.2d, e
) appeared over most of the
southern hemisphere and the Arctic zone in the two reanalyses. The biggest
temperature trend difference between 1979-2002 and 1958-1978 occurred in the
northern middle-high latitudes, where the trend is dominated by negative values.
The largest warming is observed over the southern high latitudes, but the pattern
shows a significant difference in the NCEP and ERA-40 reanalyses. It is worth
noting that a negative trend can be found over the northern high latitudes of the
Eurasian continent, North Pacific Ocean, and west coast of the North American
continent in both periods.
Based on Table
4.1
, the global mean temperature tended to increase in the
troposphere and decrease in the stratosphere between the two periods of 1958-1978
and 1979-2002. Both the stratospheric and tropospheric temperature trends in the two
periods are similar in the two reanalysis datasets and can also be confirmed in theMSU
measurements for 1979-2002 although there is a different temperature trend between
the two reanalyses and the MSU measurements over the Antarctic zone and tropical
eastern Pacific. However, the variability and temperature trend patterns also show
significant differences between the two periods in the temperature structure observed
over the tropical and middle-high latitudes. Overall, the analyses show sufficient
similarity to proceed with the multiple linear regression analyses to ascertain the
contributions from solar forcing, aerosols, QBO, and El Ni˜o.
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