Evaluation of the Temperature Trend and Climate Forcing in the Pre- and Post Periods of Satellite Data Assimilation - Satellite-based Applications on Climate Change - page 53

Fig. 4.1 Trend of December-February temperature (K/decade) in the lower stratosphere
(70-100 hPa) in the three datasets. Shaded areas indicate a positive trend of temperature.
For 1979-2002: ( a ) NCEP/NCAR reanalysis, ( b ) ERA-40 reanalysis, and ( c ) MSU Ch4 measure-
ment; For 1958-1978: ( d ) NCEP/NCAR reanalysis and ( e ) ERA-40 reanalysis in 1958-1978
(Adapted from Powell and Xu ( 2011 ), Figure 2)

4.3.1 Stratosphere

Because the measurement from MSU channel 4 represents the lower stratosphere
layer temperature with peak at 87 hPa (Zou et al. 2009 ), the layer mean temperature
between 70 and 100 hPa was chosen to represent the lower stratospheric tempera-
ture in the NCEP/NCAR and the ERA-40 reanalyses.
In 1979-2002, the temperature tended to decrease over most of the global areas
except for the area north of 60 N latitude where warming consistently occurred
(Fig. 4.1a-c ) in the three datasets. The basic pattern can be confirmed by visually
comparing the analyses with each other. The largest warming with a rate of
2.1-2.7 K/decade was identified over the high latitudes of the North American
continent. However, it is worth noting that the temperatures tended to increase over
the tropical eastern Pacific in the ERA-40 reanalysis, which is different from the
other two datasets.
The temperature trend in the 1958-1978 period (Fig. 4.1d, e ) differs from its
counterparts in the 1979-2002 period in the two reanalyses. The largest warming is
observed south of 60 S, and the maximum rate was 1.5 K/decade. For the NCEP
reanalysis (Fig. 4.1d ), the largest cooling rate of 1.8 K/decade was observed over

the high latitudes of the Eurasian continents. In contrast, the cooling rate is only

0.9 K/decade over the same location in the ERA-40 reanalysis (Fig. 4.1e ). Note
that a similar warming can be found over the tropical eastern Pacific in both
reanalyses. The basic temperature patterns are confirmed in the polar regions of
all three datasets and indicate the greatest positive change in the Arctic occurred